PROGRESS TOWARDS TOTAL SYNTHESIS OF OPTICALLY ACTIVE PHOMACTINS E AND F By Dmytro Berbasov A DISSERTATION Submitted to Michigan State University In partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chemistry 2013 ABSTRACT' PROGRESS TOWARDS TOTAL SYNTHESIS OF OPTICALLY ACTIVE PHOMACTINS E AND F By Dmytro Berbasov Phomactins are well-known platelet-activating factor antagonists containing a unique bridged-heterocyclic skeleton. Inspired by the interest from the pharmaceutical industry and challenged by the skeleton complexity of the phomactins, several research groups devised a target-oriented synthesis of the phomactin family members. In this thesis, I developed a second generation approach to the syntheses of all members of the phomactin family through one intermediate. The key transformations like the intermolecular cyclohexadienone annulations reaction and the ring closing metathesis were extensively investigated and optimized. In addition, the main intermediate was either synthesized in an optically pure form via the Corey-Bakshi-Shibata reduction with ee more than 96% or resolved with the Sharpless epoxidation up to 99% ee. The syntheses of the main intermediates require the Horner-Wadsworth-Emmons olefination, Weinreb amide preparation, Wulff-Dotz cyclohexadienone annulation reaction, and the Grubbs ring closing metathesis. ACKNOWLEGMENTS I would like to express my sincere gratitude to my advisor, Dr. William Wulff, who taught me to have patience to search for the truth and an open mind to see it. Without his knowledge and his guidance this dissertation would not have been possible. I could not have imagined having a better advisor and mentor for my graduate work. I would like to thank my committee members: Babak Borhan, Robert Maleczka, and Milton Smith, for their valuable comments, stimulating questions and helpful suggestions. I am also thankful to other faculty members of the Chemistry Department at Michigan State University for support during my graduate studies. I thank my current and former labmates: Chunrui Wu, Mikhail Barabanov, Alex Predeus, Victor Prutyanov, Anil Gupta, Munmun Mukherjee, Wynter Gilson, Nilanjana Majumder, Li Huang, Maria Pascual, Aman Desai, Hong Ren, Yong Guan, Zhensheng Ding, Mathew Vetticatt, Xin Zhang, WenJun Zhao, Yubai Zhou, Xiaopeng Yin, and Roberto Moran, for the stimulating discussions and all fun we have had. I also thank my friends from the Chemistry Department at Michigan State University: Roozbeh Yousefi, Kumar Ashtekar, Mercy Anyika, Aman Kulshrestha, Luis Sanchez, Wenjin Wang, Atefeh Garzan, Hovig Kouyoumdjian, Moe Eldakd, Carmin Burrell, Luis Mori Quiros, Chrysoula Vasileiou, Marina Tanasova, Arvind Jaganathan, Damith Perera, Ramin Vismeh, Gina Comiskey, Rosario Amado-Sierra, and Calvin Grant. Finally, I would like to thank my wife Irina, my sister Tetyana, my parents, Oleg and Tamara, for their support, my friends Konstantin Mihalchuk, Oleg Harchenko, Sergey Korolev, Hisanory Ueki, Trevor Ellis, and Rohit Tiwari, for their friendship. ! iii TABLE OF CONTENTS LIST OF TABLES…………………………………………..…………………………………..vii LIST OF SCHEMES………………………………………..…………………………………viii KEY TO ABBREVIATIONS………………………………..………………………………….xii CHAPTER 1 INTRODUCTION TO PHOMACTIN CHEMISTRY………………………………………….1 1.1 Structure and biological activity of phomactins………………………………………....1 1.1.1 Isolation and characterization of the family of phomactins………………………..1 1.1.2 The role of phomactins in nature……………………………………………………..6 1.1.2.1 Relationship of phomactins and taxol……………………………………………6 1.1.2.2 Synthetic analogs from the Sato and Leff/Rawal group…………………….....8 1.1.2.3 Synthetic analogs from Pattenden…………………………………………….....9 1.1.2.4 Platelet activating factor (PAF)………………………………………………….10 1.2 Synthetic approaches towards phomactins…………………………………………....11 1.2.1 Development of total synthesis…………………………………………………...…11 1.2.1.1 Yamada’s total synthesis of phomactin D……………………………………...11 1.2.1.2 Pattenden’s total synthesis of phomactin A……………………………………12 1.2.1.2.1 Studies towards furanochroman core of phomactin A……………………12 1.2.1.2.2 Pattenden’s total synthesis of phomactin G………………………...……..15 1.2.1.3 Halcomb’s total synthesis of phomactin A……………………………………..16 1.2.1.4 Wulff’s total synthesis of phomactin B2………………………………………...19 1.2.1.5 Hsung’s total synthesis of (±)-phomactin A…………………………………….19 vii ! 1.2.2 Partial synthesis of phomactins……………………………………………………...23 1.2.2.1 Cho’s intermediate for Halcomb’s total synthesis…………………………..…23 1.2.2.2 Contributions from Danishefsky’s group…………………………………….….24 1.2.2.3 Lee’s cascade sequence toward 1-oxadecalin………………………………..25 1.2.2.4 Macrocyclization through the Nozaki-Hiyama-Kishi reaction by Maleczka’s group…………………………………………..……………………………………….…..26 1.2.2.5 Rawal’s preparation of phomactin analogs…………………………………….26 1.2.2.6 Diels-Alder cycloaddition for the construction of the oxadecalin core by Totah……………………………………………………………………………………….28 1.2.2.7 Thoma’s [2,3]-Wittig rearrangement as a key step for the preparation of phomactins………………………………………………………………………………...29 1.3 Retrosynthesis…………….………………………..……………………………………..30 1.4 Conclusion…………………………………………………………………………………31 1.5 BIBLIOGRAPHY…………………………………………………………………………..35 CHAPTER 2 SYNTHESIS OF PRECURSORS OF CHIRAL ALCOHOL 133…………………………..39 2.1 Introduction ..................................................................................................………..39 2.2 Preparation of the aldehyde 135 .................................................................………..40 2.2.1 Horner-Wadsworth-Emmons olefination in the preparation of 135 ........………..41 2.2.2 Coates protocol in the preparation of 135..............................................………..42 2.2.3 Preparation of 135 from acetyl protected geraniol 148 ..........................………..43 2.2.4 Synthesis of aldehyde 135 through unprotected geraniol 148...............………..47 2.3 Preparation of alcohol 138 ..........................................................................………..52 2.3.1 Approach from vinyl iodide 139 .............................................................………..52 2.3.2 Preparation of alcohol 138 from aldehyde 135 ......................................………..53 viii ! 2.4 Preparation of ketone 137 ...........................................................................………..54 2.4.1 Oxidation of alcohol 138 ........................................................................………..54 2.4.2 Preparation of Weinreb amide 141 ........................................................………..55 2.4.2.1 Improving the E-selectivity of the Horner-Wadworth-Emmons (HWE) olefination .....................................................................................................………..57 2.4.2.2 Separation of E and Z isomers of 141 .............................................………..58 2.4.2.3 Isomerization of Z-isomers ...............................................................………..59 2.4.2.4 Conversion to ketone 137 ................................................................………..60 2.5 Conclusion ...................................................................................................………..61 2.6 BIBLIOGRAPHY ..........................................................................................………..62 CHAPTER 3 PREPARATION OF CHIRAL ALCOHOL 138 ...................................................………..64 3.1 Introduction ..................................................................................................………..64 3.2 Enantioselective nucleophilic addition of an alkyne to aldehyde 135 ..........………..65 3.3 Corey-Bakshi-Shibata (CBS) reduction .......................................................………..67 3.4 Resolution via Sharpless epoxidation .........................................................………..72 3.5 Conclusion ...................................................................................................………..74 3.6 BIBLIOGRAPHY ..........................................................................................………..75 CHAPTER 4 PREPARATION OF FISCHER CARBENE COMPLEX 134 AND ITS PRECURSORS..78 4.1 Introduction ..................................................................................................………..78 4.2 Preparation of enyne 194 trough Csp3-Csp3 coupling ...................................………..79 4.3 Catalytic versions of Csp3-Csp3 coupling .......................................................………..82 ix ! 4.4 The preparation of enyne 194 through a Wittig olefination ..........................………..85 4.5 Preparation of enyne 194 through the Corey-Fuchs and Seyfert-Gilbert homologation .....................................................................................................………..86 4.6 Preparation of enyne 194 through Csp3-Csp coupling and alkyne deprotection ...........................................................................................................................………..88 4.7 Preparation of the Fischer carbene complex 134 ........................................………..91 4.8 Conclusion ...................................................................................................………..93 4.9 BIBLIOGRAPHY ..........................................................................................………..94 CHAPTER 5 CYCLOHEXADIENONE ANNULATION AND RING CLOSING METATHESIS REACTIONS......................................................................................................………..97 5.1 Introduction ..................................................................................................………..97 5.2 Preparation of protected alcohol .................................................................………..98 5.3 Cyclohexadienone annulation reaction of complex 134 ..............................……….99 5.4 Ring closing metathesis ..............................................................................………103 5.5 Alternative route to phomactin E .................................................................………106 5.6 Diastereoselective 1,3-directed addition of methyl group ............................………109 5.7 One-pot cyclohexadienone annulation and ring closing metathesis ...........………112 5.8 Conclusion ...................................................................................................……....115 5.9 BIBLIOGRAPHY ..........................................................................................………116 EXPERIMENTAL SECTION ..............................................................................……....118 BIBLIOGRAPHY ................................................................................................………192 x ! LIST OF TABLES Table 1.1 Biological activities of phomactins……………………………………….………..4 Table 1.2 Summary of all synthetic approaches towards phomactins……………...……32 Table 2.1 Wittig olefination of 149a under different conditions……………………...……44 Table 2.2 Effect of protecting group on Wittig olefination……………………………..…..46 Table 2.3 Sharpless dihydroxylation of geraniol derivatives………………………………49 Table 2.4 Preparation of alcohol 138 from aldehyde 135………………………………....53 Table 2.5 Horner-Wadsworth-Emmons olefination of ketone 144………………………..58 Table 2.6 Preparation of ketone 137 from Weinreb amide 141………………………..…60 Table 3.1 CBS reduction of enynone 137……………………………………………….….71 Table 4.1 Solvent influence on Grignard preparation………………………………….…..80 3 3 Table 4.2 Catalytic Csp -Csp coupling………………………………………………….….82 3 Table 4.3 Csp -Csp coupling………………………………………………………………....89 Table 4.4 TMS deprotection……………………………………………………………….…90 Table 5.1 Diastereoselective cyclohexadienone annulations with propargyl alcohol 216……………………………………………………………………………………………..100 Table 5.2 Diastereolectivity of the cyclohexadienone annulations under different conditions………………………………………………………………………………….….102 Table 5.3 Ring closing metathesis……………………………………………………..…..104 . Table 5.4 Ring closing metathesis optimization in toluene…………………………..….105 Table 5.5 Diastereoselective 1,3-nucleophilic addition of methyl group...……….…….109 Table 5.6 One pot benzannulation and ring closing metathesis………………………...113 vii ! LIST OF SCHEMES Scheme 1.1 Phomactin A………………………………………………………………………1 Scheme 1.2 Phomactins B, B1, B2, C, D………………………………………………….…1 Scheme 1.3 Chemical correlation of phomactins B, B1, B2……………………………..…2 Scheme 1.4 Chemical correlation of phomactins C and D…………………………………3 Scheme 1.5 Phomactins E and F……………………………………………………………..4 Scheme 1.6 Phomactins H, I, J and 13-epi-phomactin I……………………………………5 Scheme 1.7 Biosynthetic relationship of phomactatriene and taxadiene ………………..7 Scheme 1.8 Synthetic analogs of phomactins………………………………………………8 Scheme 1.9 Pattenden’s unnatural phomactins…………………………………………….9 Scheme 1.10 Platelet activating factor………………………………………………………10 Scheme 1.11 Yamada’s total synthesis of phomactin D…………………………………..11 Scheme 1.12 Pattenden’s first approach to the furanochroman core……………………12 Scheme 1.13 Pattenden’s successful synthesis of the furanochroman core......……….13 Scheme 1.14 Pattenden’s macrocyclization approach…………………………………….14 Scheme 1.15 Pattenden’s synthesis of phomactin A………………………………………14 Scheme 1.16 Pattenden’s total synthesis of phomactin G………………………………..15 Scheme 1.17 Macrocyclization by Halcomb………………………………………………..16 Scheme 1.18 Halcomb’s synthesis of the tricyclic core of phomactin A………………...17 Scheme 1.19 Halcomb’s total synthesis of (+)-phomactin A……………………………...18 Scheme 1.20 Wulff’s first generation approach to phomactins…………………………...19 Scheme 1.21 Intramolecular [3+3] cycloaddition towards oxadecalin…………………...20 Scheme 1.22 Unique reactivities of tricycle 87……………………………………….........21 viii ! ! Scheme 1.23 Modified synthesis of annulation precursor………………………………...21 Scheme 1.24 Hsung’s total synthesis of (±)-phomactin A………………………………...22 Scheme 1.25 Regioselective synthesis of 100 and a short synthesis of 104…………...23 Scheme 1.26 Danishefsky’s transannular Suzuki macrocyclization…………….............24 Scheme 1.27 Danishefsky’s highly stereoselective Diels-Alder reaction towards oxadecalin core…………………………………………………………………….…………..25 Scheme 1.28 Lee’s cascade cyclization approach………………………………………...25 Scheme 1.29 Maleczka’s NHK coupling towards phomactins……………………………26 Scheme 1.30 Rawal’s approach to synthetic analogs of phomactins……………………27 Scheme 1.31 Totah’s strategy for the synthesis of phomactin A…………………………28 Scheme 1.32 Thomas’s approach to phomactins………………………………………….29 Scheme 1.33 Retrosynthetic analysis of intermolecular benzannulation reaction……...30 Scheme 2.1 Approaches towards chiral alcohol 133………………………………………39 Scheme 2.2 Interrelations between intermediates for alcohol 133……………………….40 Scheme 2.3 Preparation of aldehyde through HWE olefination………………………….42 Scheme 2.4 Preparation of ester 140 based on Coates protocol………………………...43 Scheme 2.5 Preparation of aldehyde 135 from protected geraniol 148…………………45 Scheme 2.6 The literature example of terpene TBS deprotection……………………….47 Scheme 2.7 Final modifications of the synthesis of allyl alcohol 145.…………………...51 Scheme 2.8 Preparation of alcohol 138 from vinyl iodide 139……………………………52 Scheme 2.9 Oxidation of alcohol 138 with MnO2………………………………………….55 Scheme 2.10 Preparation of ketone 137 through the Weinreb amide 141……………...55 Scheme 2.11 Isomerization of Weinreb amide with PhSLi………………………………..60! Scheme 3.1 Carreira’s protocol for the enantioselective addition of trimethyl silylacetylene to aldehyde 135……..………………………………………………………...65 ix! ! Scheme 3.2 Trost’s protocol for enantioselective nucleophilic addition…………………66 Scheme 3.3 A proposed model for the CBS reduction…………………………………….68 Scheme 3.4 Corey’s preparation of CBS catalyst………………………………………….69 Scheme 3.5 Mathre’s procedure for diphenylprolinol 179 preparation…………………..70 Scheme 3.6 Optimized procedure for a large scale CBS catalyst preparation…………70 Scheme 3.7 Sharpless model for resolution of allylic alcohols…………………………...73 Scheme 3.8 Sharpless resolution of alcohol 138…………………………………………..73 Scheme 4.1 Different routes tested for the preparation of enyne 194 and vinyl iodide 195………………………………………………………………………………………………78 3 3 Scheme 4.2 Preparation of enyne 194 through Csp -Csp coupling…...……………….79 Scheme 4.3 The equilibrium of Grignard reagent………………………….………………80 Scheme 4.4 Normant reaction as a side reaction…………………………………….……83 Scheme 4.5 Oxidative addition and rearrangement leading to side products……….….84 Scheme 4.6 Preparation of enyne 194 through Wittig olefination………………………..85 Scheme 4.7 Preparation of aldehyde 193…………………………………………………..86 Scheme 4.8 Alkynylation of aldehyde 193………………………………………………….87 Scheme 4.9 Substitution of alcohol with good leaving groups…………………………...88 Scheme 4.10 Negishi’s synthesis for enyne 194…………………………………………..91 Scheme 4.11 Preparation of vinyl iodide 195 and Fischer carbene complex 134……..92 Scheme 5.1 Preparation of protected propargyl alcohol…………………………………..98 Scheme 5.2 Benzannulation vs cyclohexadienone annulation reactions……………….99 Scheme 5.3 Original sequence for phomactin E and F………………………………….106 Scheme 5.4 Alternate sequence for phomactin E………………………………………..108 x! ! Scheme 5.5 Deprotection-protection of alcohol 247……………………………………..110 Scheme 5.6 Alkylation and deprotection steps with TIPS protecting groups………….111 Scheme 5.7 Alkylation and deprotection with DMT protecting group…………………..112 xi! ! KEY TO ABBREVIATIONS (DHQD)2PHAL 13 1 C NMR H NMR Hydroquinidine 1,4-phthalazinediyl diether Carbon nuclear magnetic resonance Proton nuclear magnetic resonance BINOL 1,1'-Bi-2-naphthol CBS Corey-Bakshi-Shibata Cbz Carboxybenzyl CD Circular dichroism COSY Correlation spectroscopy DDQ 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone DIBAL-H Diisobutylaluminium hydride DMA Dimethylacetamide DMDO Dimethyloxirane DMT Dimethoxytrityl DQF-COSY Double quantum filtered correlation spectroscopy GC Gas chromatography HMBC Heteronuclear multiple-bond correlation spectroscopy HMQC Heteronuclear multiple-quantum correlation spectroscopy HREI-MS High resolution Electron Ionization mass spectroscopy HWE Horner-Wadsworth-Emmons reaction IC50 Half maximal inhibitory concentration KHMDS Potassium bis(trimethylsilyl)amide xii ! LDA Lithium di-isopropyl amide m-CPBA meta-Chloroperoxybenzoic acid MMT Monomethoxytrityl MOM Methoxymethyl NHK Nozaki-Hiyama-Kishi NOE the Nuclear Overhauser Effect NOESY Nuclear Overhauser effect spectroscopy PAF Platelet-activating factor PDC Pyridinium dichromate pIC50 -log IC50 PMB p-Methoxybenzyl RCM Ring closing metathesis SAR Structure activity relationship TBAF tetra-n-butylammonium fluoride TBS tert-butyldimethylsilyl THF Tetrahydrofuran TIPS Triisopropylsilyl TMS Trimethylsilyl Tr Trityl UV Ultraviolet UV-vis Ultraviolet–visible spectroscopy ! xiii ! CHAPTER 1 INTRODUCTION TO PHOMACTIN CHEMISTRY 1.1. Structure and biological activity of Phomactins 1.1.1. Isolation and characterization of the family of phomactins !!In the beginning of the 90’s the search of marine fungal isolates for the inhibition of platelet activating factor (PAF) induced platelet aggregation and of the binding PAF to Scheme 1.1 Phomactin A its O H OH OH receptors was conducted by the Japanese pharmaceutical company Sankyo Co., Ltd (now Daiichi Sankyo). Their search resulted in the discovery of the O first member of the phomactin family, phomactin A 1 (Scheme 1.1) by Sato in 1991. It was isolated from a 1 marine fungus Phoma sp. which lives on the shell of the snow crab Chionoecetes opilio. The structure of phomactin A has ben confirmed by 1 H NMR and 13 C NMR spectroscopy and X-ray analysis. The last analysis was performed on a mono-p- Scheme 1.2 Phomactins B, B1, B2, C, D HO O O O R 2 R1 Phomactin B (2) OHC O O H O O HO H Phomactin B2 (4) R1 = H, R 2=OH Phomactin B1 (3) R1 =OH, R 2=H 1 ! OHC O Phomactin C (5) Phomactin D (6) bromobenzoyl derivative. No affect on adenosine diphosphate, arachidonic acid and collagen induced platelet aggregation was reported for this phomactin. The next five members of the phomactin family were reported by the same group 2 in 1994 (Scheme 1.2). Interestingly, Phomactin C was reported earlier as compound 3,4 Sch 47918 by Chu from Schering Plough Research Institute. In each case they were isolated from Phoma sp. For the elucidation of its structure, in addition to standard characterization techiques, phomactin B was also characterized by DQF-COSY and relayed COSY experiments. The X-ray structure of oxidized Phomactin B revealed an unusual dihedral angle of 94° for the double bond and carbonyl groups giving a distinct UV wavelength and 13 C NMR assignments. The relative stereochemistry was assigned based on NOE experiments. Scheme 1.3 Chemical correlation of phomactins B, B1 and B2 O HO O MnO 2 Phomactin B 1. Ac2O/pyr 2. I 2 O 7 O O OAc 8 2 ! PCC Phomactin B1 CH2Cl2 Ac2O pyr Phomactin B2 Phomactin B1 was converted to compound 7 which was found to be identical to the product resulting from oxidation of phomactin B setting the chemical relationship 2 between phomactins B and B1 (Scheme 1.3). The acetylation of phomactin B2 8 gives compound, which is the same product obtained by iodine induced dehydration of the 2 diacetylated version of phomactin B. The absolute configuration of phomactin B was determined using Mosher-ester analysis and CD methods. DQF-COSY and HMBC 2 experiments with phomactin D showed that it has the same skeleton as phomactin C. The chemical relationship between phomactin C and D was established by DIBAL-H reduction of phomactin C followed by oxidation with PDC (Scheme 1.4). Scheme 1.4 Chemical correlation of phomactins C and D OHC HO O H O DIBALH Phomactin C (5) O HOC O 9 H O PDC O Phomactin D (6) The results of studies on the inhibition of PAF-induced platelet aggregation and 1,2,5 binding of PAF to its receptors are summarized in the Table 1.1. Taking into account the close structural relationship of phomactins C and D and the significant difference in biological activities, it has been suggested that the conformation of the bicyclic ring system and the substitution pattern of hydroxyl groups have a significant 6 influence on specific binding. As can be seen from the data in Table 1.1, the highest activity was observed for phomactin D and phomactin B appeared to be the least active. 3 ! ! Table 1.1 Biological activities of phomactins Platelet Aggregation PAF binding IC50 (µM) IC50 (µM) A 1.0 23 B 17.0 >47.9 B1 9.8 20.0 B2 1.6 22.1 C 6.4 63.0 D 0.8 0.12 E 2.3 5.19 F 3.9 35.9 G 3.2 0.38 Phomactin ! The isolation of phomactins E (10), F (11) and G (12) from Phoma sp. were 5 reported in 1995 (Scheme 1.5). They were characterized by 1 H NMR, 13 C NMR spectroscopy, HREI-MS, UV-vis. The X-ray structure of phomactin E revealed that the dihedral angle between the carbonyl and the double bond for unsaturated ketone is not planar with an angle of 119°. Scheme 1.5 Phomactins E, F and G HO O O HO O OH O O Phomactin F(11) Phomactin G(12) O O Phomactin E(10) 4 ! The remaining four members of phomactin family were isolated and 7 characterized in 2004 (phomactin H, 13) and 2010 (phomactins I (14), J (16) and 13epi-phomactin I (15)) 8 by the Koyama research group from Meiji Pharmaceutical University (Scheme 1.6). These four compounds were isolated from the fungus MPUC 046 which was discovered on the surface of the marine brown alga Ishige okamurae which is a source different from that previously reported for the other phomactins. 1 Characterization was performed by H NMR and 13 C NMR spectroscopy and X-ray diffraction (except 15). A consideration of HMQC, DQF-COSY and HMBC with NOESY correlations were used to assign structural relationship for all compounds except phomactin H (13). All compounds are crystalline with high melting points. Scheme 1.6 Phomactins H, I, J and 13-epi-Phomactin I O OH O HO Phomactin H (13) R1 R 2 O Phomactin I (14) R1 = H, R 2=OH 13-epi-Phomactin I (15) R1 = OH, R 2=H 5 ! O O O O HO O OH O Phomactin J (16) 1.1.2. The role of phomactins in nature 1.1.2.1. Relationship of phomactins and taxol All phomactins bear the unique bicyclo[9.3.1]pentadecane ring system with a briedgehead quaternary carbon with a specific configuration and a methyl group on an adjacent carbon of unchanged configuration. This unique skeleton is found in several 9 10 naturally occurring compounds like cleomeolide, verticillol (19), 11 triene, 12 cesupitularin A verticilla-4(20),7,11- in addition to the phomactins. Several groups have suggested that the synthesis of the phomactins and the taxoids are related beginning with the cyclization of geranyldiphosphate 17 to the verticillen-1-yl cation intermediate 20 which is the branch point between the phomactins and the taxoids leading to the described skeleton and also towards paclitaxel through intermediate 24 catalyzed by 13-15 taxadiene synthase. Oikawa and co-workers performed detailed experimental and computational 16 studies on the biosynthetic pathway and suggested the plausible enzymatic routes towards paclitaxel and phomactin from intermediate 20 (Scheme 1.7). The results show the facile formation of phomacta-1(15),3,7-triene 28 upon treating verticillol 19 with BF3·OEt at -78 °C. Compound 28 has the main skeleton of phomactin with corresponding bridgehead quaternary chiral center and chiral tertirary center with a methyl goup next to it. This pathway is possible without enzymatic assitance due to the small barrier involved as revealed by ab initio calculations. The 1,5-proton transfer from 6 ! 20 to 23 does appear to be an enzyme-assisted process due to a required conformational change. Scheme 1.7 Biosynthetic relationship of phomactatriene and taxadiene H H PPO 17 taxadiene synthase PPO 18 H 8 H HO 12 H 19 11 H H 8 23 2.34 kcal/mol 4 20 -0.06 kcal/mol H H H taxadiene (24) H H 4 25 3.31 kcal/mol 26 11 H 21 0 kcal/mol H H H H 11 phomactatriene (28) H 27 H 22 -3.17 kcal/mol H H 30 7 ! 29 H H 31 1.1.2.2. Synthetic analogs from the Sato and Leff/Rawal groups The structure-activity relationships (SAR) of phomactin derivatives were investigated by the Sato group for the generic structure represented by 32 17 and by the 6 Leff/Rawal groups for the generic structure represented by 33. !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! ! The lipophilicity of fragment A is essential for activity based on bioassay comparisons of this fragment for phomactins E, F and several other epoxide and diol derivatives (Scheme 1.8). The observed inhibition of platelet aggregation IC50 for phomactin D is 0.12 µM, 17.0 µM for the epoxide of phomactin D and >280 µM for 17 diols. The fragment B in 32 showed better activity when this alcohol is protected with carbonyl derivatives like methoxycarbonyl (IC50 is 0.026 µM) or dimethyl carbamoyl (IC50 is 0.18 µM) as opposed to a free alcohol (IC50 is 1.3 µM). These IC50 values are for the case when fragment C is a ketone group. The free hydroxyl group in fragment C enhances the activity of 32 by 2-4 times for the same substituents in fragment B. 8 ! Leff/Rawal research group performed structure-activity relationship studies on 6 phomactin-like molecules focusing on the zones indicated in 33. The fragment D was a ketone group for most of the instances except for one which was a racemic alcohol. The modifications for fragment E include a triple bond, an isomeric trisubstituted olefin and the product of thiophenyl addition to the double bond. The fragment F was either single or double bond. These studies concluded that the presence of the ketone moiety (fragment D), the triple bond (fragment E) and the double bond (fragment F) are necessary for optimal PAF antagonism. 1.1.2.3. Synthetic analogs from Pattenden Pattenden developed the synthesis of phomactins A and G. During these 18-21 synthetic studies compounds 34-38 were prepared (Scheme 1.9) and later their 22 PAF inhibition activity was determined. !!!!!!!!!!!!!!!!!!!!!!! ! 9 ! Compound 34 was synthesized from compound 58 (Scheme 1.15) by VO(acac)2 oxidation, Dess-Martin oxidation and then 22 oxidative removal of protecting groups. Compounds 35 and 36 are epoxy and hydroxyl diastereomers of the possible biogenetic intermediate in the enzymatic conversion of phomactin G into A. Pattenden and co-workers also synthesized the compounds 37 and 38 as regioisomeric and epimeric epoxides of phomactin G. The afore-mentioned structural changes do not play a vital role in the activity of phomactin analogs based on the narrow range of the pIC50 values observed compared to those of the natural phomactins. The range of PAF potency pIC50 (-log of IC50) is in the range of 5.6-6.2 with the following order 11=37>36=35>1>34>33. 1.1.2.4. Platelet activating factor (PAF) Platelet activating factor is a phospholipid 38 consisting of phosphocholine, acetylated glycerol and ether with long straight alkyl chain (12-18 carbons) (Scheme 1.9). It is synthesized in a number of cells including platelets, injured tissue, neutrophils, basophils, monocytes/macrophages and endothelial cells. It is an activator and mediator of a number of biological processes. To name aggregation, just a few: platelet inflammation, smooth muscle contraction and hypotension. !!!! 10 ! ! 1.2. Synthetic approaches towards phomactins Several research groups havecontributed to the synthesis of phomactins. The development of total synthesis strategies will be reviewed first and then the additional synthetic strategies that lead to the phomacatriene core will be summarized. 1.2.1. Development of total syntheses 1.2.1.1. Yamada’s total synthesis of phomactin D The first member of the phomactin family that was obtained synthetically was the most active phomactin D which was synthesized by Yamada in optically active form in 23 1996. This synthesis is highlighted in brief in Scheme 1.11. Starting from the ascorbic acid derivative 41 the whole sequence was achieved in 0.5% yield and 31 linear steps. Scheme 1.11 Yamada's total synthesis of phomactin D O O BnO O H LDA, THF, -78 °C, then 40 74%, single diastereomer 40 O O O 41 OHC H CO2Et 22 steps, PhO 2S 19% overall 43 42 CO 2Et OTBS O BnO O 7 steps 16% overall H OH PhO 2S TBSO Phomactin D (6) 45 11 ! CHO I 44 t-BuLi, THF, -78 °C, then 43 72% The crucial quaternary chiral center was set at the very beginning through the two sequential Michael additions. Several high yielding transformations led to the key aldehyde 43. The bulk of the larger ring was added via an alkenyl-lithium reagent derived from vinyl iodide 44 which gave alcohol 45 as a single diastereomer. The key macrocyclization of sulfone 43 preceded in a modest yield by slow addition to a solution KHMDS to provide the target skeleton. A series of protections and deprotections and a directed epoxidation and double oxidation followed to give the natural product phomactin D 6. 1.2.1.2. Pattenden’s total synthesis of phomactin A 1.2.1.2.1. Studies toward the furanochroman core of phomactin A Preliminary studies by Pattenden’s group in constructing 24 furanochroman core of phomactin A were reported in 1996. the tricyclic The initial approach (Scheme 1.12) appeared to be problematic due to difficulties in converting the lactone 49 into a dihydrofuran. The oxadecalin skeleton was obtained by iodoetherification of 47. Scheme 1.12 Pattenden's first approach to the furanochroman core O CO2Me O H CO2Me CO2Me I OH I 2, NaHCO 3, 1. NaBH 4 Br 2. Stille MeCN, 0 °C O O coupling O OH H H 46 47 48 49 12 ! The Pattenden group did find that they could reach the furanochroman core from the 1,3-cyclohexanedione derivative 50 but with very low efficiency (0.7% yield in 11 steps). After deprotection of the MOM protected ether in 51 with camphorsulfonic acid reaction with DIBAL-H lead to cyclization to the dihydrofuran 52 (Scheme 1.13). Only then could furanochroman 53 can be obtained after treating alcohol 52 with phenylselenyl bromide, then m-CPBA and finally with dimethyloxirane DMDO. Scheme 1.13 Pattenden's successful synthesis of the furanochroman core 1.PhSeBr, HO TEA, DCM O OH O OMOM OH OH -78 °C 1. CSA 2. mCPBA, 2. iBu 2 AlH, OEt OH O OH 0 °C, DCM -78 °C H H 50 51 52 53 3. DMDO, Me 2CO, H 2O The next step was to develop the strategy for the macrocyclization. In order to 25 achieve this end Pattenden’s group examined several approaches 26 summarized in the Scheme 1.14. All methods except NHK coupling which are did not lead to the desired cylcized material. Later this approach with NHK coupling as a key step 18,20 culminated in the total synthesis of phomactin A. . Eventually this approach 27 involving an NHK coupling in the key step is similar to the phomactin D synthesis by Yamada (Scheme 1.11) in that a 12-membered cycle is closed on an existing cyclohexane framework followed by a series of deprotections and oxidations to finish the synthesis. 13 ! Scheme 1.14 Pattenden's macrocyclization approaches radical macrocyclization NHK: Nozaki-Hiyama-Kishi RO aldehyde-vinyl iodide coupling OR NHK RCM: ring closing metathesis RCM Ni 0: sp3-sp3 coupling OR Ti0: reductive carbonyl coupling Ni 0 RCM or Ti0 54 16 The overall synthesis is summarized in Scheme 1.15. The key intermediate 57 was efficiently synthesized to setup the NHK coupling which gave alcohol 58 in 36% Scheme 1.15 Pattenden's synthesis of phomactin A O O O O LDA, DMPU, THF, -78 °C, O 55 O I I I 56 76% yield R R CHO 4 steps OH CrCl2, NiCl 2 R R R = OPMB I 57 27% yield R R OH VO(acac)2 TBHP R O 1. Dess-Martin 2. DDQ O OH OH O phomactin A (1) 83% yield The desired epoxidation from β-face was achieved after inversion of the 59 99% yield yield.! R OH 2 steps 58 36% yield 60 85% yield configuration of the alcohol function in 58 to give 59. Catalytic epoxidation of 59 with 14 ! VO(acac)2 gave the bisepoxidation product (not shown) and monoepoxidation product 60 with a 5:1 ratio respectively. The total synthesis was finished by oxidation of the free alcohol in 60 and removal of both PMB ethers which induced spontaneous cyclization to racemic phomactin A. 1.2.1.2.2. Pattenden’s total synthesis of phomactin G Pattenden’s group also completed the total synthesis of phomactin G which is 21 summarized in Scheme 1.16. The strategy is quite similar to that for the synthesis of phomactin A and involves similar key transformations such as the NHK coupling, Scheme 1.16 Pattenden's synthesis of phomactin G PMBO OPNB I 5 steps I OH I 61 62 40% yield PMBO R 1. MsCl, DIPEA, DCM 2. LiBH 4, THF, CHO Dess - 1. Martin R = OPMB I 3. Dess-Martin R OH CrCl2, NiCl 2 63 84% yield OH 64 47% yield R O O OH 2. NaBH 4, 1. DessO Martin 2. DDQ O OH O CeCl3 phomactin G (12) 72% yield inversion of an alcohol, epoxidation by dimethyldioxirane and dihydrofuran ring 65 80% 66 31% formation (Scheme 1.16). The only change from the synthesis of phomactin A is a 15 ! removal of the hydroxyl group in compound 62 through a hydride attack on a mesylate 25 group. The preparation of the compound 62 was described in Pattenden prior efforts. 1.2.1.3. Halcomb’s total synthesis of (+)-phomactin A Initially Halcomb and co-workers investigated an approach to the phomacatriene 28 core using the Suzuki coupling in the key macrocyclization step. The major transformations were 1) alkylation of an enolate to install the quaternary center in 68, 2) conjugate addition of cyanide via Nagata reaction, 3) coupling of a dienyl Grignard reagent with Weinreb’s amide (not shown), 4) intramolecular Suzuki coupling of 69 in one step (Scheme 1.17). After completion of macrocycle 70 the investigations of furanochromane formation were performed. Scheme 1.17 Macrocyclization by Halcomb H steps 67 CN OTBS O O I I 69 68 9-BBN, then Pd toluene, CN OTBS 70 16% yield The tricyclic core of phomactin A, present in intermediate 76, was synthesized via following key steps (Scheme 1.18): 1. Addition of a cyclohexenyllithium reagent derived from alkyl halide 72 to the epoxyaldehyde 73. 2. An intramolecular epoxide opening in compound 74. 16 ! 3. Final tetrahydrofuran ring formation through the deprotection of 75 by DDQ (an approach used by both the Halcomb and Pattenden groups). Scheme 1.18 Halcomb's synthesis of the tricyclic core of phomactin A DMBO DMBO O O 1. t-BuLi, Br 6 steps then 73 O 2. Dess-Martin OBn OTBS OTBS 71 72 27% yield 74 54% yield DMBO O 1. TBAF 2. HCl H O OH CH3 DDQ OBn 75 69% yield O OH OH CH3 O H OBn 76 60% yield O H O OBn 73 After development of successful methods for several key transformations in the general strategy Halcomb reported a 26-step total synthesis of optically pure phomactin A (Scheme 1.19). The enantioselective route started with commercially available and affordable (R)-(+)-pulegone 77 that was transformed to bromide 78 in 4.8% yield in 18 steps. Metal halogen exchange with t-butyllithium and subsequent addition of aldehyde 79 yielded alcohol 80 in 51% yield as an inconsequential mixture of epimers. The key macrocylization involved the intramolecular Suzuki coupling of an alkyl borane with iodide 81. The coupling efficiency was not as high as expected and this may be because the macrocyclization led to the strained product 82. There were several sucessful attempts from other groups to form the macrocycle by Suzuki coupling and they will be discussed latter. The synthesis was completed by simple TBAF deprotection of 82 which gave phomactin A. 17 ! ! 18 ! 1.2.1.4. Wulff’s total synthesis of phomactin B2 Our group set the target to access all members of the phomactin family through one intermediate, the cyclohexadiene 85. This six-membered ring in 85 can be synthesized through intramolecular cychexadienone reaction of Fischer carbene 29 complex 84 developed in our group. In the first generation strategy, the intramolecular cyclohexadienone annulation of the carbene complex 84 which is accessible from 30 geraniol 83 served in the total synthesis of phomactin B2 (Scheme 1.20). A second generation strategy involving an intermolecular cyclohexadienone annulations and that will be the subject of this thesis. Scheme 1.20 Wulff's first generation approach to phomactins OH Cr(CO)5 10 steps 14% OMe O OMOM THF, 80 °C 26% 84 83 1.2.1.5. OMOM O 85 OH 14 steps 21% O OH Phomactin B2 (4) Hsung’s total synthesis of (±)-phomactin A In contrast to previous synthesis of phomactin A where macrocyclization was followed by oxadecalin ring formation, Hsung and coworkers developed a methodology 31,32 which combines these two steps via an intramolecular oxa-[3+3]-cycloaddition. 33 Initial studies revealed that the annulation precursor 86, prepared in 22 steps, upon 19 ! treatment with piperidinium acetate can provide oxadecalin 87 with moderate yield and modest regioselectivity (87:88 = 1:2.5) (Scheme 1.21). The reaction proceeds through a Knoevenagel condensation followed by a 6π-electron electrocyclic ring closure of the corresponding oxatrienes. This was first report of an intramolecular oxa-[3+3]cycloaddition reaction. Scheme 1.21 Intramolecular [3+3] cycloaddition towards oxadecalin O O N H H OAc THF, rt 76% O 86 O O O 87 34 Further studies + O 87 : 88 = 1 : 2.5 88 revealed unique features of tricycle 87 (Scheme 1.22). First the undesired compound 88 can be equilibrated to give the target compound 87. This was possible through a perycyclic ring opening followed by peryciclic ring closure catalyzed by piperidinium acetate to achieve thermodynamic equilibrium in a ratio of [4:1]:1.7. Unexpected reactivity was also encountered in oxidation process. Oxidation with mCPBA and osmium tetroxide did not give oxidation products at the desired disubstituted olefin in the oxadecalin ring. Instead the macrocyclic trisubstituted olefin was more reactive in all cases. A solution was found through a [4+2] cycloaddition of singlet oxygen which gave intermediate 89. Interestingly treatment of 89 with hydrogen gas and Lindlar catalyst reduced the peroxide bridge but the product 90 was not stable and a hetero[4+2]cycloaddition product 91 was isolated. Eventually, it was found that the 20 ! endoperoxide bridge in 89 could be opened by potassium acetate and crown ether (not shown). Scheme 1.22 Unique reactivities of tricycle 87 a. Thermodynamic equilibrium O N H OAc pericyclic ring closure b. Oxidations of 87 less reactive O O Rose Bengal, air, hυ THF, -78 °C H O O O 87 88 [4 : 1 ] atropisomer ratio O O O more reactive 87 88 : 87 [4 : 1 ] : 1.7 c. Transannular hetero-Diels-Alder cycloaddition O O H 2, OH [4+2] Lindlar O OH O O O 89 O 90 89 H O OH H OH O 91 35 Hsung also revised and shortened the synthesis of the annulation precursor 86. The key steps feature a Diels-Alder cycloaddition of Rawal’s diene 92 and a one pot borylation and Suzuki-Miyaura coupling which leads to compound 86 (Scheme 1.23). Rawal’s diene 92 was found appeared to be more reactive and selective compared to Scheme 1.23 Modified synthesis of annulation precursor OTBS Br R2 N R1 TBSO Rawal's diene 92 O O 95 93 O Diels-Alder O O Suzuki-Miyaura 94 86 21 ! O Danishefsky diene (rt vs 160 °C). Also an enantioselective version of phomactin A synthesis developed through this approach is thus theoretically possible. It requires 12 steps and provides 86 in 12% yield from diene 92. In his final optimized total synthesis of (±)-phomactin A, Hsung reported that he 31 could reach the target in 37 steps and 0.05% overall yield (Scheme 1.24). Several details concerning some of the challenging steps were highlighted in following 32,36 publications. Scheme 1.24 Hsung's total synthesis of (±)-phomactin A O Bn CO2Me O O N Piperidine, Ac2O 12 step +O O AcOEt, rt 12% 93 O TBSO 30% 96 87 86 O 4 steps 45% overall yield OMe OH O O 11 steps 23% overall yield O 98 97 22 ! OTES 9 steps 14% overall yield O OH OH O (±)-phomactin A 1.2.2. Partial synthesis of phomactins Seven groups made significant contributions to the synthesis of the phomactin framework. They are summarized below. 1.2.2.1. Cho’s intermediate for Halcomb’s total synthesis The major contribution from Cho’s group is the synthesis of compound 104 (Scheme 1.25) which can be used in place of compound 78 in Halcomb’s synthesis 37 (Scheme 1.19). This substitution should result in a shorter synthesis of keto-analogs of phomactin A (18 steps required for compound 78). The precursor 104 can be synthesized in eight steps and 30% overall yield from the pyrone 99. The synthesis features a regioselective one step synthesis of 3-methyl-5-bromo-2-pyrone 100. Previous synthesis of compound 100 required five steps in 12% overall yield. Scheme 1.25 Regioselective synthesis of 100 and a short synthesis of 104 Br O Br 99 O O O Me 3 Al PdCl 2(PPh3) 2 85% CH3 CH3 O + O Br 100 100 : CH3 0 101 2 steps 92% O O Me Br 103 102 23 ! Br 1. TBSOTf 2. Wittig OH 60% 3 steps OHC OH 61% Br OTBS 104 1.2.2.2. Contributions from Danishefsky’s group Danishefsky and co-workers have made two major contributions. One is a 38 transannular intramolecular alkyl-borane Suzuki macrocyclization. This method is good for constructing macrocycles of rings larger than six. The main advantage is higher control of the selectivity for olefin geometry in 106 compared to the widely used ring closing metathesis reaction. This methodology was developed by Danishefsky for the synthesis of natural products, containing macrocycles and in particular for phomactin A (Scheme 1.26). Halcomb used a very closely related reaction in his synthesis of phomactin A. Scheme 1.26 Danishefsky's transannular Suzuki macrocyclization Me MeO Me OTBS MeO 1. 9-BBN 2. TlOEt, Pd(0) 105 I OTBS 106 40% yield Another contribution from his group is the construction of the oxadecalin core in 39 the form of 109 through a stereoselective Diels-Alder reaction. In one step four stereocenters can be installed in a highly stereoselective manner. For pyran-based alkoxydienes like 107, endo addition of maleic anhydrides 108 is highly favored. In this particular example no other isomer was detected. The two key transformations discussed could be applied to a general strategy summarized by the highlighted disconnections for phomactin A indicated in Scheme 1.27. 24 ! Scheme 1.27 Danishefsky's higly stereoselective Diels-Alder reaction towards oxadecalin core Diels-Alder O O O OTBS OTBDPS O OH OTBS OTBDPS O OH 108 Si(iPr)2 O Si(iPr)2 O CH3CN, O O O O H O 23 °C, O O 107 109 65% intramolecular Suzuki reaction phomactin A 1.2.2.3. Lee’s cascade sequence towards 1-oxadecalin The contribution from Lee’s group is a facile construction of the tricyclic furanochroman skeleton via a Prins/Conia-ene cascade cyclization and subsequent epoxidation-dealkoxycarbonylation. In the first key transformation the one pot cyclization of β-ketoester 110 and alkynyl substrate 111 to form the 1-oxadecalin core 112 was developed with InCl3 (latter In(OTf)3) as the catalyst with high efficiency and selectivity 40 under mild reaction conditions. Three additional steps (Scheme 1.28) converted compound 112 into the tricyclic core 113 through epoxidation of the olefin, then decarboxylation of the β-ketoester with simultaneous cyclization to yield dihydrofuran 41 ring in 113. O TMS O Scheme 1.28 Lee's cascade cyclization approach In(OTf) 3, O O O CH3CN TMS O 0 to 70 °C 110 HO O 66% yield, one-pot H 112 111 25 ! O 52%, 3 steps O O H 113 OH 1.2.2.4. Macrocyclization through the Nozaki-Hiyama-Kishi reaction by Maleczka’s group 42 Findings from Maleczka’s group on macrocycle formation using the NHK reaction were reported simultaneously with similar findings from Pattenden’s 18,20,21 group. Maleczka’s approach is to construct the [9.3.1]-bicycle 115 through the Nozaki-Hiyama Kishi reaction and required 8 equiv of CrCl2 with 0.5-1% of NiCl2 as the optimal condition for cyclization (Scheme 1.29). Pattenden used the NHK reaction to construct the macrocycle in phomactins A and G. Scheme 1.29 Malezcka's NHK coupling towards phomactin CHO CrCl2, NiCl 2 OTBS I 114 OH OH DMSO/THF 60% O OTBS 115 1.2.2.5. OH 4 steps 62% 116 Rawal’s preparation of phomactin’s analogs As discussed before, Leff’s group used synthetic analogs of phomactin to find structure-activity relationship. Various modifications of structure 33 (scheme 1.8) were used for these studies. The synthesis which leads to these analogs was developed by 43 Rawal’s group. The key cyclization of 119 was developed with two alternative 26 ! methods. One is a carbonylation under CO pressure in Fischer-Porter bottle in the presence of Pd catalyst. The other one (higher yielding) required intitial conversion of triflate 119 to an aldehyde and then intramolecular nucleophilic addition of the alkynyl chain (Scheme 1.30). Scheme 1.30 Rawal's approach to synthetic analogs of phomactin O TMS I 2 ways 4 seps 66% + O OTf Y 117 118 119 27 ! 120 1.2.2.6. Diels-Alder cycloaddition for the construction of the oxadecalin core by Totah The approach that involves a Diels-Alder cycloaddition on a dihydropyrone for construction of the oxadecalin core was developed by Totah group (Scheme 1.31). Her 44-46 initial studies showed that it is very easy to construct the oxadecalin core in one step by reacting substituted diene 121 and dihydropyrone 122. Then the possibility to access the tricyclic furanochroman ring was demonstrated by preparing compound 124 and then, after treatment with TBAF, a retro aldol reaction and epoxide opening to afford furanochroman 53. Also, a borylation and Suzuki reaction was employed as a method to install the macrocycle in 126 in modest yield in a manner similar to Danishefsky’s and Pattenden’s strategies. Scheme 1.31 Totah's strategy for the synthesis of phomactin A OTBS O O OH O OTMS TBAF OH OMe furano 95% chroman OMe 25 °C, CO2Et O O 124 53 neat, MeO O TBSO pTsOH 121 9-BBN, TlOEt, O O O 85% O O O O EtO 2C O O R Pd(dppf)Cl 2, macro 123 AsPh3, cyclization O R O O THF, 122 I R=Me, H 2O 125 126 CH2CH2OBn 48% 28 ! 1.2.2.7. Thomas’s [2,3]-Wittig rearrangement as a key step for the preparation of phomactins Another promising approach has been investigated by Thomas’s group. He suggested that a [2,3]-Wittig rearrangement can be utilized to prepare intermediates for 47 the synthesis of several members of the phomactins family (Scheme 1.32). Allylic 48 ether 127, after deprotonation with BuLi, rearranges into homoallylalcohol 128. The side chain was elongated in four steps to give compound 129 which was subjected to macrocyclization conditions very similar to Yamada’s to yield macrocycle 130. In addition the preparation and rearrangement of functionalized ether derivatives of 127 49 were investigated. Scheme 1.32 Thomas's approach to phomactins O R n-BuLi, OH -50 °C, Ph(O 2)S Ph(O 2)S OTBS THF OTBS 127 128 H OBOM 4 steps PhO 2S OTBS NaHMDS, PhO 2S 0 °C 85% Br 129 OBOM steps 130 29 ! H 1.3. Retrosynthesis The total synthesis of phomactins A, G, D and B2 have been reported up until the time of this writing. Many groups are targeting only the synthesis of phomactin A, which does not make such approaches universal. We suggested a common intermediate 131 which can lead to all members of phomactins and have demonstrated that it can be used to synthesize racemic phomactin B2 (Scheme 1.33). The second generation approach is to synthesize of optically active phomactins through an intermolecular benzannulation of chiral propargyl alcohols 133 and Fischer carbene complex 134 combined with a ring-closing metathesis of diene 132. We chose phomactin E and F as the next target based on the ranking of PAF antagonist active compounds not yet synthesized and the challenge of finding an efficient access to the optically active core of the common intermediate 131. Scheme 1.33 Retrosynthetic analysis of intermolecular benzannulation reaction HO O O OPG O OPG OMe O + O Phomactin E (10) O 131 132 30 ! Cr(CO)5 OPG 133 134 1.4. Conclusion The syntheses of phomactins are of great interest for the scientific community. The interest derives from both the synthetic challenges and and pharmacological properties of these compounds. A summary of the different methods from various groups is presented in Table 1.2. Entries 1-5 are completed total syntheses by the indicated groups. Entries 6-12 are synthetic approaches supported by partial syntheses. 31 ! Table 1.2 Summary of all synthetic approaches towards phomactins Entry Research Key transformations Group Total Synthesis of phomactins Disconnection OHC 1 27 Yamada H O O Nucleophilic addition to sulfone phomactin D O OH OH 2 50 Halcomb Intramolecular Suzuki coupling O (+)-phomactin A O OH OH 3 20,21 Pattenden NHK coupling O (±)-phomactin A, G OH O 4 Wulff 30 Intramolecular benzannulation OH Phomactin B2 ! 32 ! Table 1.2 Summary of all synthetic approaches towards phomactins (cont’d) O OH OH 5 Hsung 31 Intramolecular [3+3] cycloaddition O (±)-phomactin A Partial synthesis of phomactins 6 Cho Regioselective methylation for a precursor for Halcomb synthesis 37 7 Danishefsky 8 Lee 9 10 40,48 Maleczka Rawal Diels Alder, intramolecular Suzuki coupling 38,39 Prins-Conia cascade cyclization 42 43 NHK coupling Intramolecular nucleophilic addition of alkynyl chain ! 33 ! ! Table 1.2 Summary of all synthetic approaches towards phomactins (cont’d) 11 12 Totah 44-46,51,52 Thomas Diels Alder [2,3]-Wittig rearrangment 47,49 34 ! BIBLIOGRAPHY 35 ! BIBLIOGRAPHY (1) Sugano, M.; Sato, A.; Iijima, Y.; Oshima, T.; Furuya, K.; Kuwano, H.; Hata, T.; Hanzawa, H. J. Am. Chem. Soc. 1991, 113, 5463. (2) Sugano, M.; Sato, A.; Iijima, Y.; Furuya, K.; Haruyama, H.; Yoda, K.; Hata, T. J. Org. Chem. 1994, 59, 564. (3) Chu, M.; Patel, M. G.; Gullo, V. P.; Truumees, I.; Puar, M. S.; McPhail, A. T. J. Org. Chem. 1992, 57, 5817. (4) Chu, M. T., I.; Gunnarsson, I.; Bishop, W.R.; Kruetner, W.; Horan, A. C.; Mahesh, G. P.; Gullo, V. P.; Puar, M.S. J. Antibiot. 1993, 46, 554. (5) Sugano, M.; Sato, A.; Iijima, Y.; Furuya, K.; Kuwano, H.; Hata, T. J. Antibiot. 1995, 48, 1188. (6) Zhu, X. D.; Lambertino, A. T.; Houghton, T. J.; McGilvra, J. D.; Xu, C.; Rawal, V. H.; Leff, A. R. Life Sci. 2003, 73, 3005. (7) Koyama, K.; Ishino, M.; Takatori, K.; Sugita, T.; Kinoshita, K.; Takahashi, K. 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CHAPTER 2 SYNTHESIS OF PRECURSORS OF CHIRAL ALCOHOL 133 2.1 Introduction In the previous chapter the retrosynthetic analysis for the synthesis of the phomactin family of natural products all through common intermediate which is to be accessed through a Wulff cyclohexadienone annulation of the protected chiral alcohol 133 and Fischer carbene complex 134 (Scheme 1.33) was proposed. This chapter will focus on the preparation of precursors for alcohol 133 which are not commercially available. Three major routes are considered for the preparation of chiral alcohol 133 (Scheme 2.1). Route one is the preparation of alcohol 133 through the enantioselective nucleophilic addition of acetylene derivative 136 to aldehyde 135. The second route is envisaged through an enantioselective reduction of conjugated ketone 137. The third route is the resolution of a racemic mixture of alcohols 138. Scheme 2.1 Approaches towards chiral alcohol 133 OPG 133 Route 2 Route 1 O O + M 136 OH TMS TMS 135 Route 3 137 39 TMS 138 Scheme 2.2 Interrelations between intermediates for alcohol 133 I 139 O OH O TMS 138 135 O TMS 137 OEt 140 O N OMe 141 Notwithstanding the different routes, the precursor 135 is also used to prepare racemic alcohol 138 which in turn is oxidized to ketone 137 (Scheme 2.2). The preparation of alcohol 138 was also examined from vinyl iodide 139 and from the unsaturated ester 140 through different pathways. After several approaches to make ketone 137 using various methods, the route starting from Weinreb’s amide 141 became established as very reproducible on large scale with convenient conditions and affordable commercial starting reagents. 2.2 Preparation of the aldehyde 135 The origin of the idea to involve aldehyde 135 in the synthesis of 133 was to explore the development of an enantioselective nucleophilic addition to aldehyde 135 by an appropriate acetylene derivative. The three major sequences considered for access 40 to aldehyde 135 are a Horner-Wadsworth-Emmons olefination, the Coates protocol for 1 the preparation of E-selective trisubstitueted olefins and a synthesis starting from geraniol 148b which already has the trisubstituted double-bond with the proper stereochemestry. 2.2.1 Horner-Wadsworth-Emmons (HWE) olefination in the preparation of 135 A stereochemistry of the trisubstituted double bond in aldehyde 135 is conserved in all of the phomactins targets in this work either as a double bond, an epoxide or diol. That is why the optimal method should yield the E-trisubstituted alkene in aldehyde 135 with high selectivity. With this in mind, the Horner-Wadsworth-Emmons olefination was examined first since it is well known for its good E-selectivity in the preparation of 2 certain trisubstituted alkenes. Considering the availability of the commercial compounds 142 and 143, the preparation of aldehyde 135 utilizing the HWE reaction should be practical on a large scale as well (Scheme 2.3). 41 The preparation of ester 140 was performed with a protocol that is conventional for 3 the HWE olefination. Unfortunately the a,b-unsaturated ester 140 was produced with only a modest selectivity (7:1) for the desired E-olefin. The E:Z ratio can be improved to 9:1 by fractional distillation but complete resolution could not be achieved. The reduction of ester 140 with lithium aluminum hydride to the corresponding alcohol 145 combined with a mild manganese dioxide oxidation, or a one step reduction with diisobutylaluminum hydride are two alternatives for converting ester 140 to aldehyde 135, but neither were pursued due to the less than desired olefin purity in ester 140. Scheme 2.3 Preparation of aldehyde through HWE olefination O O 142 OEt + O EtONa, then NaOH, Br 60 °C 56% 143 (EtO) 2PCH 2CO2Et, NaH, O OEt DME 43% 144 OH 140 7:1 E: Z O H 140 MnO 2 LiAlH 4 145 135 DIBAL-H 2.2.2 Coates protocol in the preparation of 135 1 The recently reported modification developed by Coates for isoprenoid chain extension was also examined (Scheme 2.4). The key steps involved the selective addition of an allyl chain to ethyl acetoacetate 142 after double deprotonation with 42 strong bases. Trapping of the Z-enolate of β-keto-ester 146 with diethyl chlorophosphate (EtO)2POCl provides 147 which after treatment with the methyl Gilman reagent results in allylic ester 140 with up to a 19:1 ratio for the desired E-olefin as reported for geranylgeraniol. Unfortunately such selectivity was not achieved for compound 140. The E-selectivity for the shorter chain terpene in 140 is not very reproducible with E/Z selectivities ranging from 7:1 to 1:1. Scheme 2.4 Preparation of ester 140 based on Coates protocol O O OEt 1. NaH 142 2. BuLi, + 0 °C, Br THF 88% 143 O O NaH, (EtO) 2PCl, OEt 0 °C, Et 2O 90% 146 EtO OEt P O O O O Me 2CuLi, OEt -78 °C OEt 60% 147 140 Taking into account the problems with olefin selectivity encountered while constructing the key double bond, attention was turned to the use of geraniol 148b as the starting material for the preparation of the aldehyde 135, since it would have the advantages of being commercially available and inexpensive and that it contains the desired E-trisubstituted double-bond as a single diastereomer. 2.2.3 Preparation of 135 from acetyl protected geraniol 148a Aldehyde 135 was utilized in the racemic synthesis of phomactin A by Pattenden in 4 2003. His synthesis of 135 starts with geranyl acetate 148 according to the sequence in Scheme 2.5 which seems promising and practical. The transformations involve a regioselective epoxidation of more electron-rich double bond followed by epoxide opening with aqueous acid and subsequent diol cleavage with a conventional protocol (Scheme 2.5). The resulting aldehyde 150 is reported to undergo Wittig olefination in 43 ten minutes on large scale. To deliver the desired aldehyde 135 the protected allylic alcohol 145a has to be deprotected and oxidized. This procedure was reported to provide the desired compound 135 in 45% overall yield if all steps work as described. Unfortunately, when the synthesis of 135 shown on Scheme 2.5, was repeated the only step, which was not reproducible as reported, was the Wittig olefination. The yields of dienyl acetate 145a were consistently in the range of 20-25% and were far off from the reported yield 93% for this step (see Table 2.1). The failure of the olefination to work as reported means that the synthesis of 135 from geraniol 148b can only be achieved in 13% overall yield. Table 2.1 Wittig olefination of 149a under different conditions Entry I t-BuOK Time, min 90 I t-BuOK 10 I (recryst.) t-BuOK(fresh) 10 I NaH 10 Br NaH 60 Br NaH 10 X 1 2 3 4 5 6 Base a) Isolated yield 44 145a, a Yield % 20-22 20 26 22 20 25 Even though the overall yield is lower than reported this route this route to aldehyde 135 nonetheless has multiple advantages. The whole sequence can be characterized as a series of operationally convenient reactions and the benefits over previous methods include: cheap and readily available reagents, aqueous and room temperature conditions, fast reaction time (all transformations could be completed in two days), the combination of one pot transformations and no purification by column chromatography or distillation. Thus, time spent in the optimization for the olefination of 150a to give 145a would be well spent since it could result in an acceptable synthesis of aldehyde 135 from commercially available geranyl acetate 148. Scheme 2.5 Preparation of aldehyde 135 from protected geraniol 148 OAc OAc 1. HClO 4, THF/H2O NBS, THF/H2O, then KOH >99% 148 Ph 3PCH 3Br, 2. NaIO 4 O 149 OAc MeOH 82% yield (80-89%)* 151a 65% yield O in 2 steps 150a (60-66%)* OH K 2CO3, t-Bu-OK 93% yield (20-24%)* OAc O MnO 2, DCM 73% yield (65-95%)* 145 *-yields from present work 135 Several potential problems which could have resulted in the very low yield of 145a were studied systematically. These possible problems include the purity of the aldehyde, the nature of the base or phosphine salt, the strength of the base, the stability of the protecting group to base and the reaction time. As summarized in Table 2.1, 45 prolonged time does not affect the yield, while recrystalization of the phosphonium salt and purification of the base (entry 3) slightly improved the yield. A change in the counterion of the phosphonium salt and a change in the base (entry 4-6) does not improve the yield either. A promising yield of 40% was observed once (entry 6) but several attempts to reproduce this result failed. The reaction was also monitored by GC revealing that no aldehyde is left after ten minutes and there is a significant quantity of desired product in the reaction mixture. After the unsuccessful attempts to improve the reaction outcomes that are discussed above, the stability of the protecting group became the next question to be addressed. Table 2.2 Effect of protecting group on Wittig olefination a Entry Compound PG Yield,% 1 149a Ac 25-40 2 149b TMS - 3 149c TBS 48 4 149d Bn 80 5 149e Tr 80 a) Isolated yield 46 The results of the screening several different protecting groups support the idea that the proper choice of the masking group is significant (Table 2.2). Compound 145c with a trimethylsilyl group cannot be prepared due to its instability during the epoxide ring opening step (148a to 149a in Scheme 2.5). The tert-butyldimethylsilyl (TBS) protected alcohol 145d is stable during the preparation of the aldehyde 149 and moderately stable during the Wittig olefination (entry 3). But the deprotection of 145c with TBAF reagent was moderate (about 65-68% yield) and similar yield was reported 5,6 for a different terpene synthesis (from 150 to 151, Scheme 2.6). Scheme 2.6 The literature example of terpene TBS deprotection5 OTBS O O OH TBAF 72% yield 152 O O 153 The robust benzyl-protected alcohol strongly points to the importance of the masking group (entry 4). Unfortunately, the deprotection of the benzyl group requires the conditions incompatible with the olefin functions. The more stable trityl protecting group seems to be the best choice for this Wittig olefination. The deprotection of the compound 145e under acidic conditions afforded the corresponding alcohol 145b in 90% yield. 2.2.4 Synthesis of aldehyde 135 through unprotected geraniol 148b Considering the previously described advantages of the overall strategy for the synthesis of the aldehyde 135 (Scheme 2.5) and the successful optimization of Wittig 47 reaction in the conversion of 149d to 145d, a reexamination of other steps was considered worthwhile. Particular focus was directed to control of the epoxide ring opening of 149 by acid since this occurs with incomplete transformation. Prolonged reaction time (24 hours versus 2 hours) does not change the ratio of epoxide 149a and diol 154a and gives a 70% yield for the diol. An alternative would be to prepare diol 154 directly from geraniol 148b. The regioselective oxidation of geraniol 148 assisted by a 7 catalytic amount of osmium tetroxide OsO4 was reported by Sharpless in 1994 (Table 2.3). Sharpless and co-workers were able to show that the unprotected hydroxyl group in geraniol shifts the regioselectivity slightly towards the allylic position (giving 80:20 mixture of 154:155 regioisomers). When geraniol 148 is protected they found that it exclusively gives the desired diol 154. However, and the non-protected geraniol 148b could be selectively dihydroxylated in the presence of the chiral additive (DHQD)2Phal providing the diol 154b in 89% yield and 94% ee. 48 Table 2.3 Sharpless dihydroxylation of geraniol derivatives PG Ratio 154 : 155 a Ac 99 1 b H 80 20 c Me 98 2 b H* >98 2 *5% mol (DHQD)2Phal, 0 °C 49 Thus, using Sharpless’s protocol it should be possible to obtain the diol 152b in high yield and with high regioselectivity (Table 2.3). Shing and co-workers have recently reporteted a simplified procedure for the cleavage of diol with activated sodium periodate NaIO4 on silica gel which gives aldehydes in high yield with a workup that 8 consist of simple filtration and vacuum removal of solvent. This protocol was also applied to the cleavage of diol 154a by Sorensen and the resulting aldehyde 149a was 9 used in the synthesis of WS9885B. The olefin 145 has not been previously prepared directly from hydroxyaldehyde 150b by a Wittig olefination. However, Wittig olefination of other hydroxyaldehydes and hydroxyketones have been successful without protection 10-12 of hydroxyl function. When methylenetriphenylphosphorane is prepared by treating the corresponding phosphonium salt with an organolithium compound in an aprotic solvent, the betaine–lithium ion pair produced upon reaction with aldehydes and 13 ketones undergo decomposition to alkenes extremely slow. The addition of at least 1.1 equiv of the t-BuOK/t-BuOH complex noticeably accelerates the betaine decomposition rate and improves the yield of the product. For this reaction base without solvent is less efficient than the complex of this base and solvent. The role of the additive is probably to exchange the lithium cation for the potassium cation, which allows more of the free betaine to be present in equilibrium with the ion pair. The tertbutyl alcohol t-BuOH as proton donor may play an important role as well. The preparation of the complex is completed according to the procedure described in literature 13,14 by dissolving the potassium in tert-butyl alcohol and evaporating the 50 alcohol under the reduced pressure to the constant weight. Then the preparation of the ylide usually requires one hour with this complex. Keeping in mind the quantitative yield of dihydroxylation and ease of isolation of 150b these two processes can be done in very efficient manner. Wittig olefination needs no more than ten minutes of stirring in the ice bath to be completed. The preparation of dienyl alcohol 145 through such sequence has been achieved for the first time (Scheme 2.7). The conversion of the allylic alcohol 145b to unsaturated aldehyde 135 with freshly prepared manganese dioxide MnO2 as described in Scheme 2.5 completes the synthesis of desired aldehyde 135. Thus the synthesis of aldehyde 135 was developed in efficient way and is summarized in Scheme 2.7. The optimized synthesis of the aldehyde 135 from geraniol 148b takes two days and was accomplished in 45-66% overall yield in four steps. All steps except the olefination do not require dry solvents and protocols avoid high temperatures. The isolation of products 154b, 150b, 145 and 135 does not require purification like chromatography, distillation and crystallization but extraction for 154b, filtration and solvent removal for 150b, 145 and 135 along with inexpensive reagents and catalytic processes makes this protocol attractive for 5-10 g 51 scale of aldehyde 135. 2.3 Preparation of alcohol 138 The preparation of alcohol 138 was accomplished in two ways: one through the vinyl iodide 139 and the other from aldehyde 135. 2.3.1 Approach from vinyl iodide 139 The initial approach taken to prepare alcohol 138 involves the vinyl iodide 139 very similar to the preparation of the vinyl iodide precursor for the synthesis of Fischer carbene complex 134 (Scheme 4.2 and 4.11). The route to 138 is depicted in Scheme 2.8 and it is a four step process. Unfortunately, the low yields and the sensitive reaction conditions do not allow scaling up the synthesis of 138. The first step is the preparation of enyne 159 from the reaction of allyl chloride 156 and propargyl chloride 158 which gives very low yield while the coupling of 158 with 155 has not been previously 15 reported, a related coupling with methallyl Grignard is known. It is not possible to increase this yield due to volatility of the product and sensitive conditions during the preparation of Grignard reagent 157. The Negishi conditions for the preparation of the E- Scheme 2.8 Preparation of alcohol 138 from vinyl iodide 139 Cl Cl 156 Mg Et 2O MgCl 158 159 20% 157 Cl2ZrCp2 Me 3 Al I2 OH I TMS 139 24% BuLi TMS O 163 H 52 138 65% trisubstituted vinyl iodide 139 16,17 makes this route low yielded and other synthesis are preferred due to more convenient conditions and higher yields. 2.3.2 Preparation of alcohol 138 from aldehyde 135 Aldehyde 135 was prepared from geraniol 148b as described in Section 2.2.4 and can be converted to alcohol 138 in one step by nucleophilic addition of trimethylsilylacetylide anion. This facile transformation was performed with lithium and Grignard reagents and the latter appeared to be the most convenient due to the fact that it can be performed at room temperature. In either case the yields are comparable (Table 2.4). Table 2.4 Preparation of alcohol 138 from aldehyde 135 O M 136 a OH TMS TMS 135 138 Entry Metal Yield, % 1 THF, -78 °C Li THF, rt MgCl b 69 2 a) Conditions 75-80 C=0.3±0.05M-reaction concentration; 135:136 ratio is 1:1.4. b) Isolated yield. 53 2.4 Preparation of ketone 137 As will be shown in the next chapter enantioselective nucleophilic addition does not provide sufficient quantities and optical purities of the required alcohol of the type 138. One of the methods that will be examined for the synthesis of the optically active alcohol 138 is the Corey-Bakshi-Shibata (CBS) reduction of the corresponding ketone 137. Two strategies for the preparation of ketone 137 will be evaluated: one is the oxidation of 138 with active manganese dioxide and the other is the direct preparation from a Weinreb amide. 2.4.1 Oxidation of alcohol 138 The choice of manganese dioxide MnO2 follows the reported stability of the olefin 18 configuration during the oxidation of allylic alcohol. Also not all forms of manganese dioxide MnO2 are suited for this oxidation. The best results are obtained with the material prepared by mixing warm solutions of manganese sulfate MnSO4 and 19 potassium permanganate KMnO4. Unfortunately, while this method was found to be useful for 1-5 gram quantities of ketone 137, preparations on larger scales resulted in significantly decreased yields, probably due to the increased surface area of the manganese dioxide MnO2, and therefore in the difficulty to completely remove the 54 product 137 by washing. The standard conditions are stirring overnight with at least five eqiv. of oxidizer in dichloromethane at room temperature (Scheme 2.9). Scheme 2.9 Oxidation of alcohol 138 with MnO 2 OH O 5 eqiv. MnO 2, TMS rt, DCM TMS 50-85% 138 137 2.4.2 Preparation of the Weinreb amide 141 The preparation of ketone 137 via the preparation of alcohol 138 (Scheme 2.2) is a longer synthesis than desired since appears to be very arduous and does not provide significant quantities to complete total synthesis of phomactin E and F. With these considereations an alternative pathway was considered. In order to facilitate large scale production, ketone 137 is considered as the target molecule rather than corresponding alcohol 138. In one of the approaches to aldehyde 135, the ethyl ester 140 was prepared with an HWE olefination of ketone 144 but this gave a mixture of E/Z isomers Scheme 2.10 Preparation of ketone 137 through the Weinreb amide 141 O Cl Cl + 161 H OMe N HCl Me 162 O O O Et 3N Cl OCH3 P(OEt) 3 (EtO) 2P OCH3 N N 70% CH2Cl2 CH3 CH3 163 164 75% O NaH, then 144 71% O O N OMe 141 E/Z= 70/30 E isomer then separated TMS BuLi 84% 55 144 TMS 137 in a 7:1 ratio (Scheme 2.3). It was only possible to partially resolve this mixture up to a 9:1 ratio of E and Z olefins. The formation of the more polar Weinreb amide 141 from HWE reaction with ketone 144 is expected to increase the electrostatic interaction between molecules and thereby amplify the efficiency of separation by distillation and/or chromatography. In addition, the ketone 137 could be obtained in one step from the amide 141. The preparation of the necessary intermediates is expected to be operationally convenient, and no stability issues are expected. For instance, amide 164 was reported to be stable 20 at room temperature for at least eight months and it is commercially available, although quite expensive. It was found the unsaturated olefins 137 and 141 are configurationally stable at high temperatures, allowing the distillation process to be a convenient method for their purification on large scales. Even though it is a four-step process as depicted in Scheme 2.10 it can be minimized to a two-step process as intermediates 163 and 164 are available from Sigma-Aldrich and other suppliers. The desired Weinreb amide 141 21 has been reported in the literature but its preparation was not described. The synthesis of a similar substrate directly derived from geraniol with two methyl groups on 22 terminal double bond has also been reported and its preparation has been desribed. 56 2.4.2.1 Improving the E-selectivity of the Horner-Wadsworth-Emmons (HWE) olefination The Horner-Wadsworth-Emmons olefination of ketone 144 was performed on a 2.5 g, 26 mmol scale giving a 72:28 mixture of E:Z isomers in 44% yield (Table 2.5, entry 1). Good selectivities are usually reported for 1,2-disubstituted olefins (it is common to observe ≥95:5 for the mixture of E:Z isomers). The E:Z selectivity with ketones is significantly lower compared to aldehydes, and the reaction requires longer reaction times. In order to increase the amount of the E isomer of 141, the literature suggests that isopropyl substitients on the phosphate 162 should be used instead of 23 ethyl substituents. Unfortunately, the reaction with 162b is significantly slower due to the increased bulkiness of phosphate group. The starting phosphate 162b is isolated from the reaction mixture with 89% recovery under this condition (entry 2). Increased temperature and reaction times eventually allows the reaction to go to completion and gives a slightly higher selectivity towards the E product 141 than 162a (entry 3). The best selectivity of the reaction with the ethyl phosphate 162a is observed at lower temperatures and proceeds with a reasonable reaction time (28 h for entry 6 and 4 days for entry 7) 57 Table 2.5 Horner-Wadsworth-Emmons olefination of ketone 144 a Yield, E:Z c Entry Compound R Solvent Base T, °C 1 162a Et THF BuLi -78 44 72:28 2 162b i-Pr DME BuLi -78 - - 3 162b i-Pr Toluene NaH 22 67 80:20 4 162b i-Pr THF NaH 22 41 66:33 5 162b i-Pr Toluene NaH 75 61 72:28 6 162a Et THF NaH -15 64 80:20 7 162a Et THF NaH -35 66 80:20 8 162a Et THF NaH 22 67 66:33 b % d a) C=0.5±0.03 M-reaction concentration; molar ratio of 144:162:base is 1:1.1:1.1. 1 b) Isolated yield. c) Determined by GC. d) Determined by H NMR and GC. 2.4.2.2 Separation of the E and Z Isomers of 141 Considering the previous success of the enrichment of the E-isomer of the ethyl ester 140 (Scheme 2.3) by simple vacuum distillation this was attempted with Weinreb amide 141, as well. The distillation of 3 g of product 141 from entry 1 (Table 2.5) with 72% E-isomer is done under high vacuum (0.2 torr) in the temperature range of 79-90 °C. The distillate was collected in two fractions: the first fraction of 1.6 g with a boiling 58 point range from 79 to 81 °C (0.2 torr) and 54% of E-isomer and the second fraction of 1.4 g with a boiling point range of 81 to 90 °C (0.2 torr) and 92% of the E-isomer. This result demonstrated that fractional distillation can be used to partially resolve the isomers of 141. In addition, it should be possible to isolate large quantities of the pure product 141 using this method. After distillation, the second fraction was subjected to further isomer enrichment by silica gel chromatography with a 10:1 mixture of hexane/EtOAc. With this eluent the amide 141 moves as a long tail instead of a sharp spot. Fifteen fractions were collected from the silica gel column. The last nine fractions gave 0.8 g of amide 141 as the pure E-isomer (more than 99% E-isomer) after evaporation of solvent. The fractional distillation becomes very efficient on large scales (10-30 g scale). Depending on apparatus setup and heat adjustments it was possible to get fractions of 5-10 grams with 85-95% E-isomer from 20 g 66-75% E-isomers of 141. 2.4.2.3 Isomerization of Z-isomers After collecting significant quantities of Weinreb amide 141 enriched with Z-isomer (>90%) resulting after several separations of isomers (around 30 g) the questions about its isomerization into useful E-isomer is investigated. For similar isomerizations 24,25 acidic 26,27 and basic conditions were suggested for α,β-unsaturated carbonyl compounds. In this particular case nucleophilic thiophenolate undergoes Michael type addition thus breaking conjugation of double bond with carbonyl group. Then intermediate 168 undergoes bond rotation and after reaching thermodynamic equilibrium and quenching with water a mixture of isomers with 66% E-olefin can be obtained and then used for separation again. 59 Scheme 2.11 Isomerization of Weinreb amide with PhSLi O MeO Li O PhSLi MeO N -78 °C Me N Me 141-Z 90% Z-isomer 2.4.1.4 SPh O Li OMe H 2O N 3 h, Me 0 °C PhS 166 O OMe N Me 141-E 66% E-isomer 167 Conversion to ketone. Conversion of Weireb amide 141 to desired ketone 137 is a straightforward 28 process. The results are presented in the Table 2.6. Table 2.6 Preparation of ketone from Weinreb amide 141 O O OMe M N Me 141 Entry a TMS 136 THF M TMS 137 Conditions Yield, % 136 1 Li 1.5 eq. 136, -78 °C 84 2 MgCl 1.5 eq. 136, rt, 2 h 83-85 3 MgCl 2 eq. 136, rt, 2h 95 b) C=0.3±0.1M-reaction concentration. b) Isolated yield. 60 b 2.5 Conclusion It is appeared to be a big problem to prepare precursors of alcohol 133. The main challenge is to control the double bond configuration. The other challenge is the scaling up the already developed procedures. The finally developed synthesis through Weinreb amide 141 meets all the requirements and allows the preparation of ketone 137 on very large scale with high selectivity. 61 BIBLIOGRAPHY 62 BIBLIOGRAPHY (1) Yinghua Jin, F. G. R., and Robert M. Coates Org. Synth. 2007, 84, 43. (2) Wolff, S.; Barany, F.; Agosta, W. C. J. Am. Chem. Soc. 1980, 102, 2378. (3) Wadsworth, W. S. In Organic Reactions; John Wiley & Sons, Inc.: 2004. (4) Foote, K. M.; Hayes, C. J.; John, M. P.; Pattenden, G. Org. Biomol. Chem. 2003, 1, 3917. (5) Völkert, M.; Uwai, K.; Tebbe, A.; Popkirova, B.; Wagner, M.; Kuhlmann, J.; Waldmann, H. J. Am. Chem. Soc. 2003, 125, 12749. (6) Song, F.; Fidanze, S.; Benowitz, A. B.; Kishi, Y. Tetrahedron 2007, 63, 5739. (7) Xu, D.; Park, C. Y.; Sharpless, K. B. Tetrahedron Lett. 1994, 35, 2495. (8) Zhong, Y.-L.; Shing, T. K. M. J. Org. Chem. 1997, 62, 2622. (9) 645. Vanderwal, C. D.; Vosburg, D. A.; Weiler, S.; Sorensen, E. J. Org. Lett. 1999, 1, (10) Danishefsky, S.; Schuda, P. F.; Kitahara, T.; Etheredge, S. J. J. Am. Chem. Soc. 1977, 99, 6066. (11) Wijnberg, J. B. P. A.; Jenniskens, L. H. D.; Brunekreef, G. A.; De Groot, A. J. Org. Chem. 1990, 55, 941. (12) Chu, M., Truumees, I.; Gunnarsson, I.; Bishop, W. R.; Kruetner, W.; Horan, A. C.; Mahesh, G. P.; Gullo, V. P.; Puar, M.S. J. Antibiot. 1993, 46, 554. (13) Schlosser, M.; Christmann, K. F. Angew. Chem. Int. Ed. 1964, 3, 636. (14) Pritchard, J. G.; Nelson, H. M. J. Phys. Chem. 1960, 64, 795. (15) Abrams, G. D.; Bartlett, W. R.; Fung, V. A.; Johnson, W. S. Bioorg. Chem. 1971, 1, 243. (16) Negishi, E.; Van Horn, D. E.; Yoshida, T. J. Am. Chem. Soc. 1985, 107, 6639. (17) Negishi, E.-i.; Zhang, Y.; Bagheri, V. Tetrahedron Lett. 1987, 28, 5793. (18) Corey, E. J.; Gilman, N. W.; Ganem, B. E. J. Am. Chem. Soc. 1968, 90, 5616. 63 (19) Fatiadi, A. J. Synthesis 1976, 1976, 65. (20) Netz, D. F.; Seidel, J. L. Tetrahedron Lett. 1992, 33, 1957. (21) Winssinger, N.; Barluenga, S.; Karplus, M. In Pct Intl 2009; Vol. WO2009/91921 A1, 158. (22) Nuzillard, J.-M.; Boumendjel, A.; Massiot, G. Tetrahedron Lett. 1989, 30, 3779. (23) Nagaoka, H.; Kishi, Y. Tetrahedron 1981, 37, 3873. (24) Price, C. C.; Meister, M. J. Am. Chem. Soc. 1939, 61, 1595. (25) Burkhard, C. A.; Brown, J. F. J. Org. Chem. 1964, 29, 2235. (26) Rainer C., Hinz, W., Hunter, R. Synlett 1997, 1, 57. (27) Roth, P.; Metternich, R. Tetrahedron Lett. 1992, 33, 3993. (28) Nahm, S.; Weinreb, S. M. Tetrahedron Lett. 1981, 22, 3815. 64 CHAPTER 3 PREPARATION OF CHIRAL ALCOHOL 138 3.1 Introduction The key intermediate for our synthesis of phomactins (Scheme 1.33) is the preparation of alcohol 133 in optically active pure form. It was a challenging task to develop scalable and reproducible conditions for the synthesis of this compound with high optical purity. Three major routes were considered for the asymmetric delivery of alcohol 133 (Scheme 2.1): an enantioselective nucleophilic addition of an alkyne to α,βunsaturated ketone 135, enantioselective reduction of ketone 137 and a resolution of racemic alcohol 138. The first route could potentially include several methods that have been developed for the catalytic enantioselective nucleophilic addition of trimethylsilylacetylene to 1 aldehydes. These methods are based on N-methylephedrine-Zn-complex by Carreira, 2,3 proline-derived dinuclear Zn catalyst by Trost, 5 4 bisoxazolidine-Zn complex by Wolf, 6 BINOL-Ti complex by Pu, sulfonamide alcohol-Ti catalyst by Wang, bis(oxazolinyl)7 8 phenyl-Ru complex by Nishiyama and an amino-alcohol-Zn complex by Guo. Several other preparations of chiral propargylic alcohols via nucleophilic addition were also 9,10 considered. The second route involving the enantioselective reduction of a ketone could be considered via either the ruthenium catalyst developed by Noyori 64 11,12 or the 13-21 Corey-Bakshi-Shibata catalyst. The third route could be envisioned via a kinetic 22 resolution of an allylic alcohol 138 using Sharpless conditions. 3.2 Enantioselective nucleophilic addition of an alkyne to aldehyde 135 The first method that was reported for the asymmetric addition of an acetylene to 1 an aldehyde was by Carreira. His zinc triflate/N-methylephedrine system gave high enantioselectivity for a number of substrates including aryl and aliphatic aldehydes. For example, he reported that an addition of trimethylsilyl acetylene 165 to cyclohexane aldehyde resulted in an optical purity of 98% ee and 93% yield for the alcohol product. Carreira reported only one example of addition to an α,β-unsaturated aldehyde, and in this case, addition to trans-cinnamyl aldehyde occurred with 80% ee and 39% yield. Thus, it was not clear whether an α,β-unsaturated aldehyde with two β-substituents such as 135 would give higher or lower asymmetric inductions than trans-cinnamyl aldehyde. In fact, reaction of 135 with trimethylsilylacetylene following Carreira’s protocol for S-enantiomer gave the alcohol S-138 in low yield (12%) as racemic product in two independent runs (Scheme 3.1). Scheme 3.1 Carreira's protocol for the enantioselective addition of trimethylsilylacetylene to 135 O OH Zn(OTf)2, Et 3N TMS (+)-N-methylephedrine TMS 23 °C, toluene 135 165 S-138 0% ee 12% yield Trost developed a procedure for the asymmetric addition of alkynes to aldehydes a 2,3 few years after Carreira’s report appeared. 65 His catalyst was generated from the bis- prolinol ligand 168 and two equivalents of dimethyl zinc and gave high enantioselectivities (77-99% ee) and high yields (≈80%). Trost’s substrate scope includes a number of α,β-unsaturated aromactic aldehydes which were successfully reacted with trimethylsilyl acetylene 165. However, almost all of Trost’s cases produced E-disubstituted alkenes and only one of his examples involved a β,β-disubstituted enal and that had two phenyl groups in the β-position. In that example Trost reported that the enantiomeric purity significantly dropped (76% ee) in comparison to trans-cinnamyl aldehyde (91% ee) suggesting that the position of substituents plays a vital role in the selectivity of attack. When the Trost catalyst was applied to our substrate 135 only moderate asymmetric induction (65% for the first run and 70% for the second one) was observed (Scheme 3.2). By replacing the trimethylsilyl group on the alkyne with a methyl ester, higher selectivity was expected based on Trost’s observations. However, the reaction of 166 with 135 was carried out according to Trost’s protocol and gave Scheme 3.2 Trost's protocol for enantioselective nucleophilic addition O 10 mol% 168 Me 2Zn (3 eq) TMS 3 eq, 1. 135 165 CO2Me 3 eq, 135 166 TMS toluene, 4 °C O 2. OH 10 mol% 168 Me 2Zn (3 eq) toluene, 4 °C Ph OH Ph N Ph HO Ph OH N 168 66 S-138 ee 65-70% OH CO2Me 167 racemic 20 adduct 167 in 62% yield with an optical rotation of [α]D = 0° (c 0.6, CHCl3). Even though the formation of S-138 in 65-70% ee with Trost’s protocol was encouraging, efforts at optimization were abandoned due to success in obtaining optically enriched alcohol 138 via CBS reduction of the corresponding ketone 137. 3.3 Corey-Bakshi-Shibata (CBS) reduction Since its introduction for promoting enantioselective hydride addition to ketones in 23,24 1987, oxazaborolidines have been applied as catalysts in other reactions including 25,26 the enantioselective Diels-Alder cycloaddition. The ultimate feature of this catalyst is that during reduction of a ketone it can discriminate between two different carbon groups as long as the two groups are not that similar in size. Several research groups showed the applicability of the CBS reagent for the 13-21 asymmetric reduction of unsaturated ketones with alkenyl and alkynyl substituents. In the case of an enynone where a ketone has both an alkenyl and alkynyl substituents, the discrimination between Re- and Si- faces of the ketone would be expected to be a challenging task. However, examples with high asymmetric induction are known. Garcia obtained a highly enantioenriched 4-alken-1-yn-3-ol moiety by the reduction of 1trimethylsilyl-4-octen-1-yn-3-one in less than 15 minutes with 95% ee and 90% yield 20,21 with two equivalents of the CBS catalyst. In another example from the synthesis of panaxytriol, Danishefsky synthesized a fragment for the target in high yield with a highly enantioselective reduction of 1trimethylsilyl-4-pentene-1-yn-3-one (>99% ee) using 2 equivalents of the same 67 18 catalyst. Other examples of reductions in similar systems also required more than 13-19 equimolar quantities of this expensive catalyst for the best enantioselectivity. Scheme 3.3. A proposed model for the CBS reduction O TMS B H H 3C B H H 169 O N H H B (S) Ph O H B N H 3C Ph (S) H O (S) Ph H TMS Ph 170 Danishefsky proposed a model to predict the configuration of the catalyst needed 18 in order to obtain the desired configuration of the product. According to his model, the required S-configuration of the alcohol 138 required for the present study can be provided by utilizing the S-configuration of the diphenylprolinol-derived catalyst. The predictive model requires that, the double bond has to be placed further from the Bmethyl group than the less bulky acetylene, which should align with the B-methyl group (Scheme 3.3). In this alignment as depicted in model 169 the delivery of the hydride will preferentially be from the Re face of the ketone to yield alcohol coordinated to the catalyst as in 170. Due to its significant cost, the catalyst was prepared according to Corey’s original 23 procedure represented in Scheme 3.4 rather than purchased. L-Prolinol 171 was protected with the benzyl carbamate Cbz-group and converted to methyl ester 172 in very high yield. The diphenylprolinol 173 was prepared by the addition of two 68 equivalents of the phenylmagnesium chloride and the acidic work-up and crystallization from aqueous methanol (Scheme 3.4). Scheme 3.4 Corey's preparation of CBS catalyst O OH NH O 1. CbzCl, NaOH 2. MeOH, BF 3⋅Et 2O OMe PhMgCl NH N Cbz 172 96% 171 Ph Ph OH 173 56% HO B(OH) 3 + MeLi 174 175 B OH toluene, Dean-Stark Ph N B Ph O 177 176 The CBS catalyst 177 was prepared by mixing methylboronic acid 176 and prolinol 173 with the subsequent removal of water. For final purification, the catalyst was distilled at 175 °C under high vacuum. The catalyst so obtained contained some unreacted prolinol 173 and was used in this form. The catalyst loses its activity with time. Specifically, unsatisfactory results were observed six months after the preparation of the catalyst (Scheme 3.4). A more convenient way to prepare large quantities of diphenylprolinol 173 has 27,28 been reported by Mathre. Even though it requires phosgene, aminoalcohol 173 can be prepared faster, with better yield and with convenient conditions (Scheme 3.5). The purity of both catalyst 177 and borane used for the reduction plays a significant role in the outcome of the selectivity in the reduction. Thus, a method to prepare large quantities of the CBS catalyst was developed. As it was noted above with Coreys’s procedure, some quantities of unreacted diphenylprolinol 173 were detected after the preparation of the catalyst. The residue of aminoalcohol 173 in the catalyst 69 prepared by Corey procedure reacted with trimethylboroxine 179 to yield the catalyst in large quantities and a very pure form after the distillation (Scheme 3.6). Having the catalyst in hand, the primary goal was to develop a highly selective and catalytic version of the ketone reduction because the final product was needed in large quantities to complete the synthesis of phomactins E and F. The purification of borane dimethylsulfide complex BH3·S(CH3)2 was done 29 according to Shiner’s procedure. His method allows to purify BH3·S(CH3)2 by removing to remove the excess of boric acid B(OH)3 and free dimethylsulfide through the vacuum distillation. Boric acid can potentially interfere with the reduction and better selectivities were observed with borane purified in this way. 70 Starting with equimolar ratio of catalyst 177, borane dimethylsulfide complex and ketone 137, the activity of the catalyst was tested in tetrahydrofuran at -30 °C and gave the optically active alcohol S-138 with 90% ee (Table 3.1, entry 1). Decreasing the catalyst loading to 10% did not change the selectivity but increased the reaction time (Entry 2). Increasing the temperature to -20 °C did not affect the reaction (Entry 3). 30 Switching to a noncoordinating solvent (Entry 4 and 5) as suggested by Mathre did not improve the outcome and in fact lead to slightly lower asymmetric inductions. As it Table 3.1 CBS reduction of enynone 137 a b Entry Cat, % Solvent Time, h Temp, °C Yield, % ee, % 1 100 THF 1 -30 60 90 2 10 THF 5 -30 60 89 3 10 THF 4 -20 63 88 4 10 DCM 4 -20 65 77 5 10 DCM 5 -45 65 78 6 200 THF 1 -20 59 96 7 200 THF 1 -35 91 c 96 a) Ratio of BH3·S(CH3)2 : 177 is 1:1 for entries 1,6,7 and 10:1 for entries 2-5. b) Isolated yield. c) Determined by HPLC 71 can be seen from Table 3.1 the yield is not very dependent on the conditions and gives a modest value for most reductions. The catalyst loading appeared to be an important factor for preparing alcohol S-138 with very high selectivity (96% ee) (Entry 6). At lower temperature the yield significantly increased (Entry 7). Similar observations (assorted 13-21 with the catalyst loadings) have been reported by different research groups. It was possible to recover up to 85% of the diphenylprolinol 173 by treating the reaction mixture with methanol, removal of solvent and then acidifying the remaining solution with sulfuric acid and filtering the resultant salt. After treating this salt with sodium hydroxide the aminoalcohol 173 was recovered. Notwithstanding the significant loading of the catalyst, the ability to recover the chiral aminoalcohol 173 makes the synthesis of S-138 very practical. 3.4 Resolution via the Sharpless epoxidation Previous enantioselective approaches led to the accumulation of several samples of alcohol S-138 with modest enantiomeric purities (80-90% ee). Also, one of the syntheses described in Chapter 2 provided racemic alcohol 138. Thus, the question of whether optically pure alcohol S-138 could be obtained by resolution techniques arose. 22 In his original paper, Sharpless provided the guidelines for choosing the stereoisomer of tartaric acid to use in order to get the desired resolution (Scheme 3.7). According to his model the undesired R-isomer of alcohol 138 was predicted to react faster with the L-isomer of tartaric acid leaving the desired S-enantiomer of S-138. 72 Scheme 3.7 Sharpless model for resolution of allylic alcohols OH L-DIPT H Fast O 98 S-180 OH H R-180 L-DIPT Slow O OH + H O : OH H OH H 2 O + OH H TMS R-138 OH H OH 38 UndeL-DIPT sired enantiFast omer reacts faster : 62 H L-DIPT Slow TMS S-138 When the Sharpless conditions were applied to our system excellent results were obtained, providing the enantiomer S-138 with more than 99% ee even when the racemic mixture was used. The drawback of this method is the difficulty in separation from epoxide 181 resulting in the low isolated yield of alcohol S-138 (Scheme 3.8). For racemic samples the purification became an issue due to the incomplete separation of the desired alcohol S-138 and undesired epoxide 181. Nevertheless this method can be used to deliver alcohol S-138 with optical purity of more than 99%. Also this is an additional proof that we obtained the desired alcohol with the right stereochemistry. 73 3.5 Conclusion It appeared to be a challenging task to find selective conditions for the enantioselective nucleophilic addition of acetylides to aldehyde 135 in the preparation of the optically active alcohol S-138. Although Trost’s protocol provided promising results, optimized conditions could not be found. Considering the ease, reproducibility and the ability to recover diphenylprolinol, the CBS reduction provided very high enantioselectivity, and was the best method that was found. The preparation of ketone 137 through Weinreb amide and subsequent reduction with CBS to give alcohol 171 provided fewer steps and more convenient operating conditions on large scale. Sharpless resolution can also be used to deliver alcohol 138 with enantiomeric purity of more than 99% ee. 74 BIBLIOGRAPHY 75 BIBLIOGRAPHY (1) Frantz, D. E.; Fässler, R.; Carreira, E. M. J. Am. Chem. Soc. 2000, 122, 1806. (2) Trost, B. M.; Weiss, A. H. Org. Lett. 2006, 8, 4461. (3) Trost, B. M.; Weiss, A. H.; Jacobi von Wangelin, A. J. Am. Chem. Soc. 2005, 128, 8. (4) Wolf, C.; Liu, S. J. Am. Chem. Soc. 2006, 128, 10996. (5) Yue, Y.; Turlington, M.; Yu, X.-Q.; Pu, L. J. Org. Chem. 2009, 74, 8681. (6) Qiu, L.; Wang, Q.; Lin, L.; Liu, X.; Jiang, X.; Zhao, Q.; Hu, G.; Wang, R. Chirality 2009, 21, 316. (7) Ito, J.-i.; Asai, R.; Nishiyama, H. Org. Lett. 2010, 12, 3860. (8) Li, Z.-Y.; Wang, M.; Bian, Q.-H.; Zheng, B.; Mao, J.-Y.; Li, S.-N.; Liu, S.-Z.; Wang, M.-A.; Zhong, J.-C.; Guo, H.-C. Chem. Eur. J. 2011, 17, 5782. (9) Johnson, W. S.; Elliott, R.; Elliott, J. D. J. Am. Chem. Soc. 1983, 105, 2904. (10) Wu, P. Y.; Wu, H. L.; Shen, Y. Y.; Uang, B. J. Tetrahedron-Asymmetry 2009, 20, 1837. (11) Noyori, R.; Ohkuma, T. Angew. Chem. Int. Ed. 2001, 40, 40. (12) Bogliotti, N.; Dalko, P. I.; Cossy, J. Tetrahedron Lett. 2005, 46, 6915. (13) Tamura, S.; Tonokawa, M.; Murakami, N. Tetrahedron Lett. 2010, 51, 3134. (14) Tamura, S.; Ohno, T.; Hattori, Y.; Murakami, N. Tetrahedron Lett. 2010, 51, 1523. (15) Laemmerhold, K. M.; Breit, B. Angew. Chem. Int. Ed. 2010, 49, 2367. (16) Trost, B. M.; Dong, G. Nature 2008, 456, 485. (17) Sabitha, G.; Bhaskar, V.; Reddy, C. S.; Yadav, J. S. Synthesis 2008, 115. (18) Yun, H.; Danishefsky, S. J. J. Org. Chem. 2003, 68, 4519. (19) McDonald, F. E.; Reddy, K. S.; Díaz, Y. J. Am. Chem. Soc. 2000, 122, 4304. (20) Garcia, J.; López, M.; Romeu, J. Synlett 1999, 429. 76 (21) Garcia, J.; López, M.; Romeu, J. Tetrahedron: Asymmetry 1999, 10, 2617. (22) Martin, V. S.; Woodard, S. S.; Katsuki, T.; Yamada, Y.; Ikeda, M.; Sharpless, K. B. J. Am. Chem. Soc. 1981, 103, 6237. (23) Corey, E. J.; Shibata, S.; Bakshi, R. K. J. Org. Chem. 1988, 53, 2861. (24) Corey, E. J.; Bakshi, R. K.; Shibata, S. J. Am. Chem. Soc. 1987, 109, 5551. (25) Corey, E. J.; Shibata, T.; Lee, T. W. J. Am. Chem. Soc. 2002, 124, 3808. (26) Balskus, E. P.; Jacobsen, E. N. Science 2007, 317, 1736. (27) Mathre, D. J.; Jones, T. K.; Xavier, L. C.; Blacklock, T. J.; Reamer, R. A.; Mohan, J. J.; Jones, E. T. T.; Hoogsteen, K.; Baum, M. W.; Grabowski, E. J. J. J. Org. Chem. 1991, 56, 751. (28) Xavier, L. C., Mohan, J. J., Mathre, D. J., Thompson, A. S., Carroll, J. D., Corley, E. G.; Desmond, R. Org. Synth. 1997, 74. (29) Shiner, C. S.; Garner, C. M.; Haltiwanger, R. C. J. Am. Chem. Soc. 1985, 107, 7167. (30) Mathre, D. J.; Thompson, A. S.; Douglas, A. W.; Hoogsteen, K.; Carroll, J. D.; Corley, E. G.; Grabowski, E. J. J. J. Org. Chem. 1993, 58, 2880. 77 CHAPTER 4 PREPARATION OF FISCHER CARBENE COMPLEX 134 AND ITS PRECURSORS 4.1 Introduction Fischer carbene complex 134 is needed to obtain the common intermediate 132 to all phomactins through the benzannulation reaction (Scheme 1.33). The key 1 intermediate enyne 194 and the E-vinyl iodide 195 both play a central role in the strategies depicted below (Scheme 4.1). Several alternative routes (routes 1-6) were considered. They included but were not limited to utilizing Li2CuCl4 as a catalyst for the coupling a Grignard reagent (route 1), different approaches for C-C coupling (routes 1Scheme 4.1 Different routes tested for the preparation of enyne 194 and vinyl iodide 195 Cr(CO)5 MgCl Cl 1 OMe 187 188 X X=I, OTs 189 190 2 TMS 134 3 I OH 194 4 8 191 I 5 MgCl O 192 O OTs 196 6 193 ! 78 ! 195 2 2), employing different alkyne protecting groups (routes 3-4), using a Wittig olefination 3 (routes 5), as well as the Seyferth-Gilbert homologation and the Corey-Fuchs transformation (route 6) (Scheme 4.1). 3 3 4.2 Preparation of enyne 194 through Csp -Csp coupling 3 The preparation of enyne 194 through Csp -Csp 3 coupling seemed to be very promising due to the fact that it can be prepared in one step from the commercially available propargyl chloride 188 and methallyl chloride 197 (Scheme 4.2). Initial attempts without any catalyst provided enyne 194 in low yield (around 20%) and satisfactory purity. In the preparation of the Grignard reagent 187, by product 2,5dimethyl-1,5-hexadiene 198 resulting from the coupling of methallyl chloride 197 and Grignard reagent 187, became the major product. Compound 198 has a boiling point very close to 194 making it difficult for separation from the target molecule. Though not ideal for obtaining enyne 194 due to its low yield and moderate purity, the procedure was typically used in advancing material for the synthesis of phomactins E and F. The reason is that the alternative methods considered were rather labor-intensive. It took a Scheme 4.2 Prepration of enyne 194 through Csp3-C sp3 coupling Cl 197 Mg Et 2O rt Cl MgCl 188 187 194 20% ! 79 ! H 198 long time to discover a superior approach, which will be discussed later and is shown in Scheme 4.12. Our attempts to increase the yield of 194 started by studying the preparation of the Grignard reagent 187. Several observations were made that deserved attention. The amount of by-product 198 produced during the preparation of methallyl magnesium chloride 187 depends on the types of activated magnesium, the solvent, the rate of alkyl halide addition, the temperature and the concentration. Scheme 4.3 The equilibrium of Grignard reagent R Mg X Mg R X 199 R 2 RMgX 200 Mg R + MgX 2 201 202 Second, the Grignard reagents in solution are known to exists in several different forms and usually as a mixture of species with different reactivities. The equilibrium Table 4.1. Solvent influence on Grignard preparation Cl Cl 197 Mg 188 MgCl H 187 194 198 Entry Solvent 194, % 198, % 1 THF 0 Up to 50% 2 Ether 20-25 5 ! 80 ! describing this nature of Grignard reagents is known as the Schlenk equilibrium 4 (Scheme 4.3). The R group in the Schlenk equilibrium can be viewed as nucleophilic, and it replaces the X group. The resulting alkyl magnesium halide 200, dialkyl magnesium 201 and magnesium halide 202 can be stabilized by coordinating solvents. For instance, diethyl ether shifts the equilibrium towards the dimer 199 and aggregated alkyl magnesium halides while tetrahydrofuran, as a better coordinating solvent, results in higher quantities of species 201 and 202. This characteristic of tetrahydrofuran explains why it was not a good solvent for the preparation of methallylmagnesium chloride 187. When using tetrahydrofuran in the preparation of 194, the only product, which was observed in the reaction, was the biscoupling by-product 198 in up to 50% yield and none of the enyne 194 could be detected (Table 4.1). Perhaps, the dialkyl magnesium 201 reacts with methallyl chloride 197 faster than the rate of the formation of methallylmagnesium chloride 187. Or perhaps the species 201 undergoes reductive elimination to give 198 directly. Eventually, the best approach for preparing methallylmagnesium chloride 187 was 5 adopted using the Tius procedure where the methallyl chloride 197 was added very slowly (over 3 hours) at 0 °C to a mixture of ether and magnesium. It is this latter strategy that was used to prepare the Grignard reagent 187 for the subsequent coupling sequences discussed below. The alternative for propargyl chloride 188 is 2,3-dichloro-1-propene (Scheme 4.10), 2 3 3 which was used by Negishi for the preparation of enyne 194. The Csp -Csp coupling ! 81 ! gave the desired compound 194 in moderate yields, but subsequent transformations were not satisfactory. 3 3 4.3 Catalytic versions of Csp -Csp coupling Notwithstanding the popularity of C-C coupling chemistry in last few decades, 3 3 Table 4.2 Catalytic Csp -Csp coupling Temp, °C Entry Catalyst Reaction Product, a By-product, time, h 194 % 198 % 1 3% Li2CuCl4 0 18 0 41 2 5% Li2CuCl4 0 18 0 29 3 NiCl2, DMA Complex 0 18 0 mixture Pd(OAc)2, 4 0 18 9 PCy3 a) Isolated yield; Reaction concentration C=0.3 M ! 82 ! 5 a 3 robust and universal methods for Csp -Csp 3 coupling for allylic and especially propargylic substrates are still not well developed. Thus, in order to improve the preparation of enyne 194 for the synthesis of phomactins E and F a number of catalysts were examined for the coupling of Grignard reagent 187 with propargyl chloride 188 were tested including Li2CuCl4, CuCl and Pd(OAc)2. Dilithium tetrachlorocuprate Li2CuCl4 is usually used to enhance the halide displacement by nucleophilic Grignard 6 reagents. Kochi and Tamura were the first to describe this reagent in 1971. Several 3 applications of Li2CuCl4 for Csp -Csp 10 including allylic Grignard reagents. 3 7-9 coupling have been previously described 3 Palladium acetate was also used for Csp -Csp 3 3 11 coupling. Recent examples of the Kumada Csp -Csp coupling 3 also suggest some promising that maybe useful conditions for obtaining compound 194. As indicated in Table 4.2, a number of different catalysts were examined for the coupling of Grignard reagent 187 with propargyl chloride 188 but none gave results that were improved over the non catalyzed reaction. The explanation for the Scheme 4.4 Normant reaction as a side reaction failure of the copper catalysed system is the presence of two possible undesired Cu⋅MgCl Cu pathways. the Normant reaction where a Cl 188 ! 83 ! Cl 203 The first pathway (Scheme 4.4) is 204 compound similar to the Gillman reagent 203 adds to the terminal alkyne to provide intermediate 204 which can lead to several side products. The second pathway (Scheme 4.5) is the oxidative addition of propargyl chloride 188 to the Gillman-like reagent 203 leading to intermediate 205. The reductive coupling migration of the allylic component (route 1) leading to bis-coupling product 198 may be faster than migration of the propargylic moiety (route 2) leading to product 194. This can potentially explain why significant quantities of by-product 198 were observed while no desired product 194 was detected. Scheme 4.5 Oxidative addition and rearrangment leading to side products CuxMgCl 203 Cl 188 Oxidative addition 1 1 Cu 2 205 ! 84 ! 198 2 194 4.4 The preparation of enyne 194 through a Wittig olefination When all the attempts to develop a scalable and reliable method for the 3 3 preparation of enyne 194 through Csp -Csp coupling failed, a preparation involving the final introduction of the double bond in the molecule was investigated. The double bond can be installed through an olefination of the corresponding ketone 192 (Scheme 4.6). The preparation through the well-known Wittig reaction seemed to be an obvious strategy to explore first. The requisite ketone 192 was prepared from propargyl chloride 188 and 12,13 acetoacetone 206 according to previously reported procedures in 47% yield. Unfortunately, when the ketone 192 was reacted with methylene triphenyl phosphorane, 3 only a very low yield of 194 was obtained (3%) (Scheme 4.6). The conversion of 192 to 193 has been previously reported by the same procedure and also was in very low yield (5 %). The optimization of conditions for the Wittig step failed to give better yields and thus the investigation of this sequence was terminated. At least two explanations can be provided for such low yields. One is that the significant quantities of triphenylphosphine oxide, that are formed could have trapped the product. Another is the strong base, which can remove the proton from the Scheme 4.6 Preparation of enyne 194 through Wittig olefination O O Cl 188 206 KOH EtOH Ph 3PCH 2Br O 192 47% ! 85 ! BuLi 194 3% propargylic position, thus, leading to reactive ketene, which in turn leads to undesired rearangments of the target product 194. 4.5 Preparation of enyne 194 through the Corey-Fuchs and Seyferth-Gilbert homologation An alternative way for the preparation of enyne 194 is to employ the installation of the alkyne moiety through transformation of the aldehyde function 193 with either the commonly used Corey-Fuchs or Seyferth-Gilbert protocols. For the preparation of aldehyde 193, the Clarke procedure was used (Scheme 14 4.7). The ester 207 was first obtained from a diethyl malonate synthesis with methallyl chloride with subsequent decarboxylation. Then, ester 207 was reduced with lithium aluminum hydride to the alcohol 208. This alcohol 208 was oxidized through the Swern oxidation to obtain aldehyde 193. Once aldehyde 193 was in hand, the efficiency with which it could serve as a precursor to 194 was examined. Scheme 4.7 Preparation of aldehyde 193 Cl 197 O O O OEt EtO 206 OEt 207 OH 208 O 193 Two approaches were explored for the preparation of enyne 194 from aldehyde 193. The first approach involved the Corey-Fuchs protocol (Scheme 4.8). Upon treatment of aldehyde 193 with two equivalents of tetrabromomethane and four ! 86 ! equivalents of triphenylphosphine, gem-dibromo derivative 209 was obtained in an excellent yield. Unfortunately, after subsequent treatment of 209 with two equivalents of butyllithium the desired product 194 could not be isolated from the reaction mixture The same problem was encountered with the second alternative approach where a much milder Bestmann-Ohira reagent 210 was used with potassium carbonate in methanol. The desired product 194 could not be isolated from this reaction mixture. Scheme 4.8 Alkynylation of aldehyde 193 Br CBr 4, Ph 3P 209 99% Br n-BuLi THF 194 0% O 193 O K 2CO3 O OEt P OEt N2 210 194 0% A possible explanation for the failure to isolate compound 194 is that this compound has a boiling point (95-99 °C) very close to the boiling point of solvents used in these transformations. Significant quantities of solvent was used in these reactors (the solvent-product ratio was >20:1) and the close proximity in boiling points between the solvent and compound 194 (within 15-20 degrees) may have lead to the loss of the desired product 194. The second approach to obtaining enyne 194 from aldehyde 193, via Bestmann-Ohira protocol involved the separation of organic and aqueous layers, resulted in a similar outcome which again may be due to the large quantities of solvents required for the procedure. ! 87 ! 3 4.6 Preparation of enyne 194 through Csp -Csp coupling and alkyne deprotection Since there were problems with the previously described methods for the 3 3 preparation of enyne 194 through Csp -Csp coupling reactions, the Wittig olefination, and alkynylation reactions with the Corey-Fuchs and Seyferth-Gilbert homologations, 3 the Csp -Csp coupling was next tested for the preparation of enyne 194. 3 The electrophiles 211 and 212 to be used in the Csp -Csp coupling reactions were prepared from the commercially available 3-methyl-3-butene-1-ol 210 (Scheme 4.9). By 15,16 the facile replacement of the hydroxyl group with iodide or tosylate. Tosylate 212 did not show good reactivity, and, thus, is omitted from the discussions that follow. Scheme 4.9 Substituition of alcohol with good leaving groups Ph 3P, Imidazole OH 66% 210 OH 210 I 2, 4 h, DCM TsCl, KOH 99% I 211 OTs 212 While screening for effective coupling reactions, several different conditions were tested with the following orgranometalic compounds. The alkynylzinc (Entry 1), Grignard 3 (Entry 2-4) and alkynyllithium (Entry 5) compounds were tested in the Csp -Csp coupling as nucleophilic trimethylsilylacetylene synthons. The results are summarized in ! 88 ! Table 4.3. The best results were obtained with the very nucleophilic lithium acetylide which gave an excellent yield and easy purification of the product by simple distillation. This method appeared to be easy to scale up and the large quantities of the TMS protected enyne 190 were synthesized with the alkynyl lithium coupling. The only step left to complete the synthesis of enyne 194 is the removal of the trimethylsilyl group from the alkyne in compound 190. Conventional methods involving 3 Table 4.3 Csp -Csp coupling TMS I TMS XM 211 190 Product, Entry MX Conditions % 1 ZnCl Iodide, Ni(PPh3)Cl2, recovered, % 7 70 THF, rt, 12 h 2 MgCl THF 0 >90 3 MgCl THF, reflux 0 >90 4 HCCMgCl THF, 0C, 24h 0 >90 5 Li THF, reflux 69 Reaction Concentration C= 0.05 M, 2 equivalents of RMX ! 89 ! tetrabutylammonium fluoride in THF and potassium carbonate/methanol were not satisfactory in the present case for the preparation of enyne 194. The outcome of the conventional methods and other procedures examined are summarized in Table 4.4. Table 4.4 TMS deprotection TMS 190 194 Product Entry Conditions a 194, % Recovered a 190, % 1 equiv. TBAF, THF, 1 0 100 -20 °C, 15 h 2 1 equiv. TBAF, THF, rt 0 0 3 K2CO3, MeOH, rt 0 0 0 0 1 equiv. AgNO3, 4 2,6-lutidine, 3 h, rt 0.33 eq TBAFx3H2O, 89 5 Et2O, rt ! 90 ! a 0 The trick to a convenient large scale preparation was to apply a very low boiling solvent like diethyl ether, TBAF hydrate in crystalline form, and after workup, removal of the solvent in a rotory evaporator with a water bath that is not higher than 15 °C (Entry 5). Another route to enyne 194 that was previously reported by Negishi involved the intermediate 214 which was synthesized from the reaction of methallylmagnesium chloride 187 with allyl chloride 213. Compound 214 was converted into the protected alkyne 191 in 15% yield by treatment of 214 with two equivalents of LDA and then acetone (Scheme 4.10). Deprotection of the alkyne with potassium hydroxide in toluene delivered the desired enyne 194 with 20% yield. Overall the yield for this sequence was 2 1.4% which is significantly lower than that reported in the literature is significantly higher. Scheme 4.10 Negishi's synthesis for enyne 194 Cl MgCl + Cl 187 Cl 214 75% (47%)* 213 2 eq. LDA then acetone OH 3% KOH toluene 194 96% (20%)* *yield in this work 191 90% (15%)* 4.7 Preparation of the Fischer carbene complex 134 Enyne 194 is needed for the preparation of the Fischer carbene complex 134 through the vinyl iodide 195. The only way to exclusively prepare E-trisubstituted vinyl ! 91 ! iodides is to use the Negishi procedure where alkyne reacts with the Tebbe-type zirconacene-trimethylaluminum complex, to give a carboaluminated product in which 17,18 aluminum is then exchanged with iodine. The preparation of vinyl iodide 195 gave variable low yields in the range of 2041%. A potential explanation for such low yields of the desired vinyl iodide 195 is that the double bond may also react with trimethylaluminum in the presence of catalytic 19 zirconocene. After the preparation of vinyl iodide 195 it was used to obtain the Fischer carbene complex 134 utilizing standard procedures of metal halogen exchange of vinyl iodide 195 with n-butyllithium and then adding the resultant nucleophile to chromium hexacarbonyl. The final carbene complex 134 was isolated by treating the chromium ate complex with methyl triflate. This conversion of 195 to 134 was quite efficient and always gave a high yield (up to 80%). Product 134 can be stored in dry benzene at least for a year in a freezer. Scheme 4.11 Preparation of vinyl iodide 195 and Fischer carbene complex 134 1. nBuLi Cr(CO)5 1. Cp2ZrCl2, I 2. Cr(CO)6 OMe AlMe3, DCM 3. MeOTf 194 2. I 2 195 20-41% ! 92 ! 134 80% 4.8 Conclusion Initially, route 1 in Scheme 4.1 seemed to be preferred to all the other alternatives although the yield for enyne 194 was a mere 20% with a limit to the possibility for scaling up. However, after solving the problem of the TMS-protecting group removal and isolation of enyne 194, route 3 (Scheme 4.1) turned out to be the best with 57% overall yield of 194 starting from the commercially available 3-methyl-3-buten-1-ol 210. An additional advantage of route 3 is that it delivers very pure enyne 194. Route 3 was also easier to scale up compared to all other routes. In addition, it allowed for a much more concentrated reaction resulting in significant solvent economy and very 3 operationally convenient conditions in comparison with route 1. Route 3 involved Csp Csp coupling of the lithium trimethylsilyl acetylide with alkyl iodide 211. The deprotection had to be done with crystalline TBAF trihydrate in diethyl ether due to high volatility of the target molecule 194. Following deprotection, the Negishi protocol was utilized to exclusively prepare the E-vinyl iodide 195 (Scheme 4.12), which was used to obtain 3 carbene complex 134. An attempt to prepare vinyl iodide 195 through a Csp -Csp coupling as indicated in route 8 in scheme 4.1 but this was not met with success. ! 93 ! 3 BIBLIOGRAPHY ! 94 ! BIBLIOGRAPHY (1) Bellina, F.; Carpita, A.; Adorni Fontana, E.; Rossi, R. Tetrahedron 1994, 50, 5189. (2) Negishi, E.-i.; Zhang, Y.; Bagheri, V. Tetrahedron Lett. 1987, 28, 5793. (3) Huntsman, W. D.; De Boer, J. A.; Woosley, M. H. J. Am. Chem. Soc. 1966, 88, 5846. (4) Schlenk, W.; Schlenk, W. Ber. Dtsch. Chem. Ges (A and B Series) 1929, 62, 920. (5) Tius, M. A.; Kannangara, G. S. K. Org. Synth. 1993, 71, 158. (6) Tamura, M.; Kochi, J. Synthesis 1971, 303. (7) Herz, J. E.; Vázquez, E. Steroids 1976, 27, 133. (8) Bullpitt, M.; Kitching, W. Synthesis 1977, 316. (9) Bringmann, G.; Jansen, J. R. Tetrahedron Lett. 1984, 25, 2537. (10) Tanis, S. P. Tetrahedron Lett. 1982, 23, 3115. (11) Ren, P.; Vechorkin, O.; Allmen, K. V.; Scopelliti, R.; Hu, X. J. Am. Chem. Soc. 2011, 133, 7084. (12) Flahaut, J.; Miginiac, P. Helv. Chim. Acta 1978, 61, 2275. (13) Görl, C.; Alt, H. G. J. Organomet. Chem. 2007, 692, 5727. (14) 353. Clarke, P. A.; Grist, M.; Ebden, M.; Wilson, C.; Blake, A. J. Tetrahedron 2005, 61, (15) Yong, K. H.; Lotoski, J. A.; Chong, J. M. J. Org. Chem. 2001, 66, 8248. (16) Helmboldt, H.; Köhler, D.; Hiersemann, M. Org. Lett. 2006, 8, 1573. (17) Negishi, E.; Van Horn, D. E.; Yoshida, T. J. Am. Chem. Soc. 1985, 107, 6639. (18) Negishi, E. Pure Appl. Chem. 1981, 53. ! 95 ! (19) Takahashi, T.; Seki, T.; Nitto, Y.; Saburi, M.; Rousset, C. J.; Negishi, E. J. Am. Chem. Soc. 1991, 113, 6266. ! 96 ! ! CHAPTER 5 CYCLOHEXADIENONE ANNULATION AND RING CLOSING METATHESIS REACTIONS 5.1 Introduction The preparation of the main components for the cyclohexadienone annulation reaction has been described in the previous chapters. The main focus of this chapter is on the development of suitable reaction conditions for the cyclohexadienone annulation reaction and the ring closing metathesis reaction. The results for the cyclohexadienone annulation reaction, ring closing metathesis reaction, 1,3-directed nucleophilic addition and one-pot cyclohexadienone annulation reaction-ring closing metathesis are summarized below. The outcomes of deprotection of the common intermediate and subsequent transformations are also reported in this chapter. While developing this part of the project two main approaches for obtaining the common intermediate 131 (Scheme 1.33) were considered. The first approach involved cyclohexadienone annulation immediately followed by ring closing metathesis. An alternative and more challenging approach involved 1,3-directed nucleophilic addition placed between the same two reactions. While the potential benefit of the latter approach was that it had fewer steps, this approach as will be discussed was not ultimately successful. Thus, the one pot procedure for cyclohexadienone annulation reaction and ring closing metathesis was the approach that was pursued in the end. By combining the two reactions in one step the most attractive approach was realized. ! ! 97 ! 5.2 Preparation of protected alcohol Having prepared the chiral alcohol S-138 through the Corey-Bakshi-Shibata reduction, the trimethylsilyl group on the alkyne was removed by the standard protocol with TBAF tetrahydrofuran solution in very high yield (Scheme 5.1). Several trityl substituted protecting groups were utilized in protection of alcohol 215. The trityl group plays a crucial role for the best diastereoselectivity in the cyclohexadienone annulation reaction (Table 5.1) and also for the construction of the macrocyclic ring in the ring closing metathesis reaction (Table 5.3). Other protecting groups that were tested cannot lead to such cyclization. The protection with substituted trityl chlorides usually proceeded in good yields. Different types of trityl groups were examined to find the right match between the conditions for deprotection of the common intermediate 131 and functionality present in 131. Scheme 5.1 Preparation on protected propargyl alcohol OH OH TBAF, THF TMS S-138 215 95% Ph Cl Ph Ph TrCl PGCl DBU, DCM 2 days Ph 4-MeOPh Cl Cl 4-MeOPh Ph Ph 4-MeOPh MTrCl DMTrCl PGCl ! OPG ! 98 216a-c 60-93% ! 5.3 Cyclohexadienone annulation reaction of complex 134 The reaction between the vinyl Fischer carbene complex 217 and terminal alkyne 218 gives rise to the substituted phenol 219 and is known as the Wulff-Dötz reaction or simply as the benzannulation reaction (Scheme 5.2). When the carbene complex is trisubstituted (R1, R2≠H) the product of this reaction is a cyclohexadienone of the type 220. If the configuration of the quaternary center in the α-position of compound 220 can be introduced selectively this method becomes even more attractive for applications in organic synthesis and especially, for the total synthesis of natural products. In our strategy, the cyclohexadienone annulation becomes the key transformation for constructing the skeleton of phomactins since it assembles the six-membered ring with the proper chiral quaternary center.! Scheme 5.2 Benzannulation vs cyclohexadienone annulation reaction Cr(CO)5 + OMe R1 ! R2 217 OH R1 R3 R3 OMe If R 2=H 219 218 ! 99 R1 or R 2 O R3 OMe If R 2H 220 ! The preparation of the carbene complex 134 was described in Chapter 4 and that of the optically active enyne 216 was described in Chapter 3. The cyclohexadienone annnulation of complex 134 was investigated with enyne 216 bearing a variety of different protecting groups and the results are presented in Table 5.1. The reaction is sensitive to the nature of the solvent, temperature and the nature of the protecting group used on chiral alcohol 216. The best diastereoselectivities and yields were obtained in acetonitrile at 60 °C with a substituted trityl on the enyne. The desired diastereomer was obtained with selectivities close to 96% (Table 5.1) with trityl and 4-methoxytrityl Table 5.1 Diastereoselective cyclohexadienone annulation with propargyl alcohol 216 b c Entry PG 221 yield, % Dr 221:222 1 DMT 75 96:4 2 Tr 83 96:4 3 TIPS 78 75:25 SiEt3 64 67:33 SiPh3 63 67:33 MOM 63 75:25 4 5 6 a a a a)-Entries performed by Chunrui Wu, b)-isolated yield, c) determined by NMR ! ! 100 ! protecting groups (Entry 1 and 2). Other protecting groups did favor the desired diastereomer but to a lesser extent (up to 3:1) (Entry 4-6). After finding that trityl is the best protecting group then optimization of the reaction conditions were next investigated. The screening of reaction conditions for the trityl protected alcohol 223 is summarized in Table 5.2. The table shows that the best solvents for these transformations were acetonitrile and toluene under slightly moderate temperatures of 50 °C. At lower temperatures the reaction was rather slow (Entry 1). At temperatures above 60 °C the diastereoselectivities went down. (Entries 1 vs 2 vs 3, 4 vs 5 and 6 vs 7 vs 8). ! ! 101 ! Table 5.2 Diastereoselectivity of the cyclohexadienone annulation under different conditions a Entry Solvent T, °C Time, h 224:225 Yield, % 1 MeCN 50 132 98:2 58 2 MeCN 60 20 93:7 74 MeCN 75 48 85:15 77 THF 60 16 94:6 75 THF 75 48 89:11 73 Toluene 75 168 85:15 81 Toluene 100 4 75:25 44 Toluene 60 90 91:9 56 3 b 4 5 6 7 b b b 8 a) Isolated yield, b) Entries performed by Michail Barabanov In conclusion, the trityl and trityl-type protecting groups (Tr, MMT, DMT) are the protecting groups of choice for these cyclohexadienone annulations of the Fischer carbene complex 134 and alkyne 223. Acetonitrile and toluene under temperature’s of less than 60 °C lead to diastereoselectivities of more than 9:1 in most of the cases with good yields. ! ! 102 ! 5.4 Ring closing metathesis Ring closing metathesis (RCM) is one of the major categories of the olefin metathesis reaction. It is a very powerful tool in forming macrocyclic rings in natural 1 product synthesis. Intermediate 224 has two terminal double bonds making it a potentially important intermediate in the synthesis of the common intermediate 226 for all phomactins via a Grubbs II catalyst mediated ring closing metathesis. The ring closing metathesis reaction with Grubbs II catalyst was examined under a number of different conditions and the results are presented in Table 5.3. At room temperature the reactions were only half completed even after two days (Entry 1-2). Increasing the temperature forced the ring closing metathesis to go to completion and gave the product 226 in 60% yield (Entry 4). Having discovered that toluene was the best solvent for the ring closing metathesis step, the optimization of reaction conditions in terms of reaction concentrations and catalyst loadings was performed. The results are summarized in Table 5.4. The ring closing metathesis reaction is usually performed under very dilute conditions to prevent dimerization of the starting compound. With concentrations higher than 10 mM the dimerization product was observed and a prolonged reaction time led to the deprotection of the DMT group (Entry 1). To force the reaction to completion, higher catalyst loadings were required (Entry 2-4). ! ! 103 ! Table 5.3 Ring closing metathesis Crude mixture Entry Solvent Cat., % Time ratio T, °C Yield, b c % 226:224 1 a 224 CH2Cl2 9.8 2d rt 50:50 50 - CH2Cl2 10 2d rt 50:50 50 48 CH2Cl2 10 1d 75 83:17 17 48 CH2Cl2 10.8 2d 80 >99:1 Trace 60 Toluene 5.1 30 min 110 90:10 10 89 6 Toluene 5.1 3h 110 95:5 5 89 7 Toluene 2.2 1h 110 70:30 30 62 Toluene 2.2 12 h 110 95:5 5 62 Toluene 0.6 12 h 110 - - 36 2 3 4 5 8 9 a a a a a a)-Entries performed by Michail Barabanov, b)- determined by NMR, c)-isolated yield ! ! 104 ! In summary, the most successful reaction conditions for the ring closing metathesis step include dilute reaction conditions (less than 10 mM), and high reaction temperatures. Given that toluene is of a paramount importance for the RCM step and good diastereoselectivities are observed in this solvent for cyclohexadienone annulations, the development of one pot procedure for these two steps will be described in Chapter 5.6. Table 5.4 Ring closing metathesis optimization in toluene O O Ph Ph O Grubbs II toluene, reflux OMe O O O OMe +Dimer +DMT deprotection OMe OMe 227 228 a Yield, % Entry C, mM Cat., % Dimer, % Time, h 1 10 2 9 10.5 20 2 3 5 3 64 0 3 5 5 3 57 0 4 10 5 2 45 2 a) Isolated yield ! ! 105 ! 5.5 Alternative route to phomactin E The original plan we wanted to follow, which is depicted in Scheme 5.3, was as follows. According to plan, the ring closing metathesis of compound 227 should lead to the main framework for all phomactins in the form of compound 228. Subsequent functional group interconversions should lead to phomactin E. The exchange of the DMT protecting group in compound 228 to the methoxymethyl ether (MOM) in 230 protecting group in compound 230 was deemed necessary since it had been found in ! ! ! 106 ! 2 our synthesis of (±)-phomactin B2 that the presence of the MOM group is essential for the Peterson olefination reaction and this synthesis included the transformation of 230 to 231. After the olefination of compound 230, the next step is the α-methylation of compound 231 to give the ketone 232 and this same conversion was also achieved in the synthesis of (±)-phomactin B2. The departure from the phomactin B2 synthesis begins with the removal of the ketone function to give 233 that is to be followed by MOM-deprotection of 233 and a sequence of epoxidations to yield 235, oxidation to obtain 236, and finally selective epoxide-ring opening to get phomactin E 9. A revision of the original sequence (Scheme 5.3) is based on reconsidering the idea of removal of oxygen during the Peterson olefination and then reinstalling it in the same position in the epoxidation of 234. The sequence, which retains this oxygen throughout and results in a reduction in the number of steps as shown in Scheme 5.4. This sequence incorporates a 1,3-directed nucleophile addition of a methyl group after cyclohexadienone annulations step but before the ring closing metathesis step. Then, protection of the diol as a cyclic acetal delivers compound 239, which is suitable for the ring closing metathesis reaction which should result in 240. The rest of the transformations are similar to the original sequence involving the conventional functional group interconversions including α-methylation (from 240 to 241), ketone reduction (from 241 to 242), epoxidation to 244 and oxidation to phomactins E 9. Therefore, the alternative sequence emphasizes deprotection after the cyclohexadienone annulation, diastereoselective 1,3-directed nucleophilic addition of the methyl group and finally protection. ! ! 107 ! ! ! ! 108 ! 5.6 Diastereoselective 1,3-directed addition of methyl group It is typically a challenge to properly control position a chiral center in a molecule. It requires a sophisticated mix of skills, as well as some art and luck. Introducing carbonoxygen bonds with the correct configuration is a synthetic challenge for the synthesis of phomactins. Previous work by others has shown that a hydroxyl group can direct the 3-6 1,3-addition of an organometallic ragent to a ketone in β-hydroxy ketones. Although this has not been reported for an enone that has a β-hydroxy group as in intermediate 237 (Scheme 5.4) this appeared to offer an attractive application to the synthesis of phomactins. However, macrocycle 228 obtained after cyclohexadienone annulations (as shown by Chunrui Wu by Peterson olefinion with Tr and MOM protecting groups) will interfere with the installation of chiral tertiary alcohol later on in total synthesis. That is Table 5.5 Diastereoselective 1,3 nucleophilic addition of methyl group Entry Conditions Dr (syn:anti) 1 H MeLi 1:1 2 H AlMe3, MeLi 3:1 3 H MeMgCl 1:1 4 ! PG TIPS MeMgCl >50:1 ! 109 ! why the 1,3-directed nucleophilic methylation of the 1,3-hydroxyketone 237 was performed right after the cyclohexadienone annulation reaction. The directed nucleophilic methylation of 1,3-hydroxyketone was planned for the preparation of chiral tertiary alcohol 238 (Scheme 5.4). The intrinsic chiral secondary alcohol in compound 221 was expected to direct the nucleophilic attack towards the desired face of the carbonyl via steric and/or coordinating interactions. Initial attempts with a free hydroxygroup in compound 221 turned out to be less promising (entry 1-3) (Table 5.5). The ratio of diastereomers (syn:anti) was determined by NMR in each case, but the diols appeared not to be stable during purification. However if the TIPS protected alcohol 221 obtained directly from the cyclohexadienone 4 annulations is directly reacted with MeMgCl, the desired diastereomer was obtained exclusively (entry 4) and it was found to be stable during purification as well. Considering the successful installation of the chiral quaternary center with oxygen, further transformations required RCM, α-methylation and epoxidation for the completion of total synthesis towards Phomactins E and F. Unfortunately, even though the success in preparing compound 247 was promising, the deprotection of the TIPS group resulted in an unstable product 248. Combining two steps (where the second step was trapping intermediate 248 with Scheme 5.5 Deprotection-protection of alcohol 247 OH OTIPS OH OH OMe 247 ! O O Cl3CO TBAF O O OCCl3 60% OMe OMe 248 249 ! 110 ! triphosgene) did not lead to product 249 and left a complex mixture (Scheme 5.5). Schemes 5.6 and 5.7 describe the successful and attempted transformations of the TIPS and DMT protected groups. It is easy to install diastereoselectively the methyl group in the presence of the TIPS protecting group but the removal of the TIPS group led to a mixture of unidentified products. Switching the sequence (deprotection first and Scheme 5.6 Alkylation and deprotection steps with TIPS protecting groups OH OTIPS O MeMgBr OTIPS 60% O OMe 250 TBAF OMe 251 OH OH OH OMe 238 TBAF 90% MeMgBr unclear results OMe 237 then alkylation) led to the isolation of alcohol 237 but 1,3-directed alkylation was not successful in both terms of selectivity and stability of the product 238. Directed alkylation did not occur in the presence of the DMT protecting group. The starting compound 252 was isolated even after a prolonged reaction time and thus compound 238 could not be obtained through this sequence. The deprotection of the DMT group from compound 252 lead to unidentified mixture. ! ! 111 ! Scheme 5.7 Alkylation and deprotection with DMT protecting group OH ODMTr O MeMgBr ODMT no reaction O OMe 252 CAN OMe 253 OH OH OH OMe 238 CAN OMe 237 MeMgBr 5.7 One pot cyclohexadienone annulations and ring closing metathesis Even though the diastereoselective 1.3-directed nucleophilic addition of the methyl group demonstrated promising results, the problems with removal of the protecting groups did not allow developing the sequence shown in Scheme 5.4 any further. In order to decrease the number of steps both the cyclohexadienone annulation and the ring closing metathesis reaction were combined to develop a one-pot protocol. At first, following the completion of cyclohexadienone annulations, the acetonitrile solution (0.02 M) containing the crude reaction mixture was transferred to toluene to make the optimal concentration of 0.001 M for the metathesis reaction (entry 1). Then, the Grubbs II catalyst was added during reflux (Table 5.6). Surprisingly, after three hours the product was isolated in only 10% yield. In an attempt to improve the process the same solvent (toluene) was used in both the reactions so that the first reaction mixture was not transferred but rather simply diluted to give a proper concentration that would avoid dimerization during the RCM reaction (entry 2). Finally, both reactions were performed ! ! 112 ! at the same concentration (entry 3). A different protecting group such as MMT was also used to make it easier to remove it for subsequent steps (entry 4). As seen from Table 5.6 the best conditions for one pot synthesis are the 0.01 M concentration in toluene. ! ! 113 ! Table 5.6 One pot benzannulation and ring closing metathesis O Cr(CO)5 OMe OPG + 134 OPG O Me Solv. A Temp, Conc. A OPG Me Solv. B Conc. B OMe 215 OMe 221 a Yield, Entry PG Solvent A Conc. A Solvent B Conc. B % 1 MMT CH3CN 0.02 Toluene 0.001 10 2 Tr Toluene 0.01 Toluene 0.005 44 3 Tr Toluene 0.01 Toluene 0.01 42 4 MMT Toluene 0.01 Toluene 0.01 16 a) Isolated yield ! ! 114 ! 5.8 Conclusion During the cyclohexadienone annulation and ring closing metathesis reactions the complexity of the system increases significantly. In the first step we set 1) a chiral quaternary carbon with very high selectivity and 2) a highly functionalized six-membered ring. The directed nucleophilic diastereoselective 1,3-addition gives good stereocontrol but it did not provide a useful approach due to the instability of unprotected alcohol 238. Also, a one pot synthesis combining the cyclohexadienone annulation and the ring closing metathesis reaction was developed. ! ! 115 ! BIBLIOGRAPHY ! ! 116 ! BIBLIOGRAPHY (1) Nicolaou, K. C.; Bulger, P. G.; Sarlah, D. Angew. Chem. Int. Ed. 2005, 44, 4490. (2) Huang, J.; Wu, C.; Wulff, W. D. J. Am. Chem. Soc. 2007, 129, 13366. (3) Ruano, G. J. L.; Tito, A.; Culebras, R. Tetrahedron 1996, 52, 2177. (4) McGrath, N. A.; Lee, C. A.; Araki, H.; Brichacek, M.; Njardarson, J. T. Angew. Chem. Int. Ed. 2008, 47, 9450. (5) Inoue, A.; Kanematsu, M.; Yoshida, M.; Shishido, K. Tetrahedron Lett. 2010, 51, 3966. (6) Bartoli, G.; Bosco, M.; Di Martino, E.; Marcantoni, E.; Sambri, L. Eur. J. Org. Chem. 2001, 2001, 2901. ! ! 117 EXPERIMENTAL SECTION All common solvents and reagents were used without purification unless otherwise noted. Oven-dried glassware was used for all reactions except flame-dried glassware, which was used for sensitive reactions and non-dry glassware, which was used when reactions were performed in aqueous solvent mixtures. An inert atmosphere of nitrogen was used when indicated. Solvents were purified by the following drying agents: dichloromethane (CaH2), acetonitrile (CaH2), ether (Na, benzophenone), tetrahydrofuran (Na, benzophenone), toluene (Na), benzene (Na). The Sorbent technologies 230x400 mesh Standard Grade silica gel was used for chromatographic purification. TLC analysis was performed on Merck Silica gel 60 coated aluminum TLC plates. Potassium permanganate KMnO4 stain solution and UV light (λ = 256 nm) was used to visualize compounds on TLC plate. Melting points were measured on a Thomas Hoover capillary melting point apparatus. Optical rotation was recorded on Perkin Elmer polarimeter 341. GC spectra were obtained on a Varian Star 3600 instrument with capillary column Alltech ECONO-CAP SE-54 (30 m X 0.53 X 1.2 µm), helium as carrier gas and indicated oven temperature. The values for chemical shifts are reported in part-per-million (ppm) and are relative to tetramethylsilane (TMS). Proton NMR data and carbon NMR data were recorded on Varian Inova-300, Varian Gemini-300, Varian Unity-plus Varian VXR-500 (300, 500 MHz for 1 H, respectively and 75, 125 MHz for 13 C). High-resolution mass spectra HRMS were obtained at Michigan State University Mass Spectrometry Service Center. 118 High pressure liquid chromatography HPLC analyses were performed with two Varian Prostar pumps (model 210) and Varian Prostar detector (model 330). Preparation of allylacetone 144 O O 142 OEt + EtONa, then NaOH, Br 75 °C 65% 143 O 144 Sodium hydride NaH (60% in mineral oil) (63.23 g, 1.58 mol) was added in four portions to 1000 mL of dry ethyl alcohol EtOH under nitrogen flow and cooling reaction flask with ice. Ethyl acetoacetate 142 (226.69 g, 1.74 mmol) in 300 mL of dry ethanol EtOH was added via pressure-equalizing dropping funnel in 30 minutes and nitrogen flow. Thirty minutes after completion of addition, the allyl bromide 143 (210.51 g, 1.74 mmol) was added via pressure-equalizing dropping funnel and nitrogen flow in 15 minutes. After complete addition, the reaction flask was warmed to 75 °C and was stirred for 5 hours. After completion the reaction was cooled, the precipitate filtered and ethanol was removed in vacuum. An aqueous solution of sodium hydroxide NaOH (126.4 g in 1L of water) was added and was kept for 4 hours at 82 °C. Than cold solution was acidified to pH<3 by slow addition of HCl (conc.) (gas ceased). Dichloromethane (300 mL) was added and then extracted by collecting the organic layer. The aqueous layer was washed with dichloromethane (2x300 mL). The combined organic layers were washed with sodium bicarbonate until pH became neutral then dried with magnesium sulfate and solvent was removed under vacuum. The residue was distilled and the fraction at 128-130 °C gave product 144 in 65% yield (155.07 g, 1.58 mol). 119 1 H NMR (400 MHz, CDCl3): δ 2.12 (s, 3H), 2.28 - 2.32 (m, 2H), 2.51 (t, J = 7.2 Hz, 2 H), 4.94 - 5.03 (m, 2H), 5.73-5.83 (m, 1H); 13 C NMR (100 MHz, CDCl3): δ 27.5, 29.6, 42.2, 115.3, 136.6, 207.5. Horner-Wadsworth-Emmons olefination of allylacetone 144 O (EtO) 2POCH 2CO2Et, NaH, DME O OEt 43% 144 140 7:1 E: Z To a suspension of sodium hydride NaH (60% in mineral oil) (4 g, 0.1 mole) in dry dimenthoxyethane DME (330 mL) phosphate (EtO)2POCH2CO2Et (22.42 g, 19.8 mL, 0.1 mole) was added dropwise over 15 minutes under nitrogen flow (at the end of addition reaction became transparent). After five minutes after addition ketone 144 was added dropwise in 15 minutes. The reaction was kept at 35 °C and stirred 1 hour. The reaction mixture was poured onto ice stirrred for 30 minutes and then extracted with diethyl ether (3x150 mL) (last fraction was not UV (256 nm) visible.). The organic layer was dried with magnesium sulfate and solvent was removed under vacuum. The residue was distilled (bp=34-45 °C 1 torr) giving product 140 in 89% yield (14.97 g, 88.9 mmol) E : Z ratio of the product is 7:1. The following data for the E and Z isomers of 140 were extracted from the NMR spectrum of a mixture of the isomers. The assignment of the stereochemistry for 140 is based on assignments in literature where the methyl 120 absorption at δ =2.20 ppm for the E-isomer and the methyl at δ=1.88 ppm for the Zisomer. 1 E-isomer H NMR (500 MHz, CDCl3): δ 1.28 (t, J = 7 Hz, 3H), 2.20 (s, 3H), 2.25 (m, 4 H), 4.14 (q, J = 7 Hz, 2H), 4.99 (d, J = 10 Hz, 1H), 5.04 (d, J = 17 Hz, 1H), 5.68 (m, 1H), 5.81 (m, 1H); 13 C NMR (125 MHz, CDCl3): δ 14.3, 18.7, 31.5, 40.1, 59.4, 115.4, 115.9, 137.2, 158.9, 166.1. 1 Z-isomer H NMR (500 MHz, CDCl3): δ 1.27 (t, J =7.3 Hz, 3H,), 1.88 (d, J = 1.3 Hz, 3H), 2.23 (dt, J = 7.7, 6.5 Hz, 2H), 2.74 (t, J = 7.7 Hz, 2H), 4.14 (q, J = 7.3 Hz, 2H), 4.95 (dd, J = 9.9, 1.2 Hz, 1H), 5.05 (dd, J = 17.1, 1.4 Hz, 1H), 5.67 (br, 1H), 5.84 (ddt, J = 17.1, 9.9, 6.5 Hz, 1H); 13 C NMR (125 MHz, CDCl3): δ 14.1, 25.1, 32.3, 32.4, 59.2, 114.8, 116.4, 137.7, 159.4, 166.0. Preparation of ethyl 3-oxohept-6-enoate 146 O O O OEt 1. NaH 142 2. BuLi, + 0 °C, Br THF 88% 143 O OEt 146 To a suspension of sodium hydride NaH (60% in mineral oil, mineral oil was removed by washing sodium hydride 3 times with dry hexanes) (5.32 g, 0.133 mole) in dry tetrahydrofuran (100 mL) ethyl acetoacetate (15.8 g, 15.5 mL, 0.121 mol) was added dropwise by syringe pump over 15 minutes under nitrogen purge and 0 °C bath temperature to give a light yellow colored solution. After addition, the solution was stirred 15 minutes. A solution of n-butyl lithium (60 mL, 2.12 M 0.127 moles) was added 121 by syringe pump over 15 minutes. After complete addition the solution was stirred at 0 °C for another 15 minutes giving a bright orange solution. Allyl bromide 143 (4.91 g, 3.5 mL, 0.0406 moles) was added to this solution and stirred for 30 minutes. The reaction was quenched by slow addition of aqueous 1N HCl (200mL). The organic layer was extracted with diethyl ether (3x150mL) and then washed with saturated sodium bicarbonate (2x200mL) and brine solutions (2x200mL). Organic layer was dried with magnesium sulfate. Solvent was removed under vacuum. The product was distilled at 75-77 °C (1 torr) giving product 146 in 79% yield (13.4 g, 79.0 mmol) 1 H NMR (500 MHz, CDCl3): δ 1.28 (t, J = 7.2 Hz, 3H), 2.35 (tdt, J = 7.2, 6.5, 1.5 Hz, 2H), 2.65 (t, J = 7.3 Hz, 2H), 3.44 (s, 2H), 4.20 (q, J = 7.2 Hz, 2H), 4.95 - 5.11 (m, 2H), 5.80 (ddt, J = 16.9, 10.2, 6.5 Hz, 1H); 13 C NMR (125 MHz, CDCl3): δ 14.12, 27.43, 42.06, 49.39, 61.38, 115.57, 136.60, 167.15, 201.97. Preparation of (Z)-ethyl 3-((diethoxyphosphoryl)oxy)hepta-2,6-dienoate 147 O O NaH, EtO OEt P O O O OEt (EtO) 2POCl 0 °C, 146 Et 2O 90% OEt 147 To a suspension of sodium hydride NaH (60% in mineral oil mineral oil was removed by washing sodium hydride 3 times with 20 mL of dry hexanes) (3.65 g, 0.0915 moles) in dry diethyl ether (200 mL), β-keto-ester 146 (13.45 g, 0.079 moles) was added dropwise by syringe pump over 20 minutes under a nitrogen purge at 0 °C bath temperature. After addition, the reaction mixture was stirred 20 minutes at room temperature till gas 122 evolution ceased. Neat diethyl chlorophosphate (20.58 g, 17.3 mL 0.119 moles) was added by syringe pump over 5 minutes at 0 °C bath temperature. The mixture was stirred at 0 °C for 15 minutes, then the reaction was quenched by the addition of saturated ammonium chloride NH4Cl (300 mL). The aqueous layer was washed with diethyl ether (2x150 mL) and then the combined organic layers were washed with saturated sodium bicarbonate (2x200mL) and brine (2x200mL) solutions. The organic layer was dried with magnesium sulfate. The solvent was removed under vacuum. The residue (24.35 g, 99% yield) was obtained as a yellow oil was used for next step. Preparation of (E)-ethyl 3-methylhepta-2,6-dienoate 140 EtO OEt P O O O OEt Me 2CuLi, O OEt -78 °C 60% 147 140 To a suspension of dry copper iodide (I) (27 g, 0.143 moles) in 140 mL of dry diethyl ether, a solution of methyllithium (179 mL, 1.6 M, 0.286 moles) was added dropwise via syringe pump over 5 minutes at 0 °C. The yellow precipitate that formed dissolved in 30 minutes. The solution was cooled to -78 °C and the enol phosphate 147 (24.75 g, 0.079 moles) was added as a solution in dry diethyl ether (100 mL) while maintaining an internal temperature below -60 °C. The solution was stirring at -78 °C for 2 hours, and then stired at -45 °C for 2 hours. Methyl iodide (9 mL, 20.6 g, 0.144 moles) was added while stirring at -45 °C over 10 minutes. The reaction mixture was poured on saturated NH4Cl and stirred untill the copper dissolved. The separated organic and aqueous 123 layers were separated, and aqueous layer was washed with diethyl ether (2x150mL). The combined organic layer was washed with water (150 mL), dried with MgSO4 and concentrated under vacuum. The residue was distilled at 35-45 °C (1 torr) giving ester 140 in 60% yield, (8.06 g, 47.9 mmol). The E:Z ratio varied from 1:1 to 7:1 for different 1 preparations. This ratio was determined with H NMR spectroscopy by integrating the methyl hydrogens (δ 2.20 and 1.88 ppm) in the mixture. Preparation of (E)-5-(3,3-dimethyloxiran-2-yl)-3-methylpent-2-en-1-yl acetate 149 OAc OAc NBS, THF/H2O, then KOH >99% 83a O 148 Recrystallized N-bromosuccinimide (18.21 g, 100 mmol) was added in three portions to a stirred solution of geranylacetate 83a (19.88 g, 100 mmol) in tetrahydrofuran (225 mL) and water (100 mL). The mixture was then stirred at room temperature for 30 minutes. A solution of potassium hydroxide (11.32 g, 200 mmol) in water (50 mL) was added after 15 minutes and the mixture was then stirred at room temperature for 1 hour. The mixture was poured into a saturated aqueous solution of ammonium chloride (300 mL) and then extracted with diethyl ether (2 × 250 mL). The combined organic extracts were dried over magnesium sulfate and then concentrated under reduced pressure to leave a pale yellow oil which was directly taken on to the next step. 124 Preparation of (E)-3-methyl-6-oxohex-2-en-1-yl acetate 149a OAc OAc 1. HClO 4, THF/H2O O 2. NaIO 4 65-70% 148 O 149a The crude epoxide 148 from the previous step was dissolved in THF (125 mL) and water was added (125 mL) and then a 70% aqueous solution of perchloric acid (1 mL) was added by syringe. The resulting homogeneous solution was stirred at room temperature for 30 minutes, and then potassium periodate NaIO4 (23.0 g, 100 mmol) was added in three portions over 5 minutes. The mixture was stirred vigorously at room temperature for 30 minutes, then poured into water (250 mL) untill everything dissolves and then aqueous solution was washed with ether (2 × 250 mL). The combined organic extracts were dried over magnesium sulfate and then concentrated under reduced pressure. The remaining oil was loaded onto a column chromatography on of silica gel and the product eluted with 5–20% diethyl ether in hexanes to give the compound 149a (11.1 g, 65% over two steps) as a colorless oil. 1 H NMR (300 MHz, CDCl3): δ 1.73 (s, 3H), 2.06 (s, 3H), 2.39 (t, J = 7.5 Hz, 2H), 2.54- 2.59 (2H, m), 4.59 (d, J = 7.0 Hz, 2H), 5.35 - 5.39 (1H, m), 9.79 (t, J = 1.6 Hz, 1H); NMR (75 MHz, CDCl3): δ 16.5, 20.9, 31.4, 41.6, 61.0, 119.3, 139.9, 171.0, 201.6. 125 13 C Preparation of (E)-3-methylhepta-2,6-dien-1-yl acetate 145a OAc OAc Ph 3PCH 3Br, t-BuOK 20-24% O 145a 149a To a stirred suspension of methyltriphenylphosphonium bromide (23 g, 64 mmol) in dry THF (130 mL), potassium t-butoxide (7.1 g, 63 mmol) was added portionwise over 5 minutes at room temperature and the resulting bright yellow mixture was stirred at room temperature under nitrogen for 1 hour. A solution of the aldehyde 149a (9.0 g, 53 mmol) in THF (130 mL) was cooled in ice bath and the mixture of methyltriphenylphosphonium bromide and potassium t-butoxide was cannulated to the aldehyde solution. The resulting mixture was stirred at 0 °C for 10 minutes. This mixture was poured into a saturated aqueous solution of ammonium chloride (300 mL) and then the resulting mixture was extracted with ether (2 × 250 mL). The combined organic layers were dried over MgSO4 and then the solvent was removed under vacuum to leave yellow oil. This oil was washed with hexanes and triphenylphosphine oxide was filters. Hexane was revoved under vacuum and the residue rinses was purified by flash column chromatography on silica gel using 5% diethyl ether in petroleum ether as eluent to give acetic acid (E)-3-methylhepta-2,6-dienyl ester (2.33 g, 13.8 mmol, 22%) as a colorless oil. Yields are within the 20-24% range for this procedure. 1 H NMR (300 MHz, CDCl3): δ 1.71 (d, J = 1.2 Hz, 3H), 2.06 (3H, s), 2.10 - 2.23 (4H, m), 4.59 (d, J = 7.1 Hz, 2H), 4.94 - 5.06 (m, 2H), 5.36 (tq, J = 7.1, 1.2 Hz, 1H), 5.80 (ddt, J = 126 17.0, 10.2 and 6.3 Hz, 1H); 13 C NMR (75 MHz, CDCl3): δ 16.4, 21.0, 31.8, 38.8, 61.3, 114.7, 118.6, 138.0, 141.6, 171.0. Preparation of (E)-3-methylhepta-2,6-dien-1-ol 145b OAc OH K 2CO3, MeOH 89% 145a 145b To a solution of the acetate 145a (4.2 g, 25.0 mmol) in methanol (50 mL), potassium carbonate K2CO3 (6.91g, 50 mmol) was added in one portion and stirred for 30 minutes at room temperature. The solvent was removed under reduced pressure to leave a colorless oil, which was then partitioned between ether (250 mL) and water (250 mL). The separated aqueous layer was extracted with ether (100 mL) and the combined organic extracts were dried over MgSO4 and then concentrated under reduced pressure to leave the corresponding alcohol 145b (2.81 g, 89%) as a pale yellow oil; 1 H NMR (300 MHz, CDCl3): δ 1.67 (s, 3H), 2.08 - 2.21 (m, 4H), 4.14 (d, J = 6.9 Hz, 2H), 5.04–4.93 (m, 2H), 5.41 (m, 1H), 5.79 (ddt, J = 17.0, 10.3 and 6.3 Hz, 1H); (75 MHz, CDCl3): δ 16.1, 31.9, 38.7, 59.2, 114.6, 123.6, 138.2, 139.0. 127 13 C NMR Preparation of (E)-3-methylhepta-2,6-dienal 135 145b MnO 2, DCM, OH rt, overnight O 135 Alcohol 145b (2.81 g, 21 mmol), without further purification from previous step was 1 dissolved in 100 mL dichloromethane and active manganese dioxide MnO2 (9.8g, 113 mmol) was added in one portion to the solution and stired at room temperature overnight. Reaction mixture was filtered through a silica gel filter. The flask and the residue on the silica gel was washed 6 times with 100 mL of dichloromethane and all solvents were combined. The last wash was checked by TLC did not show any product. After evaporation and drying under high vacuum a 65% yield of aldehyde 135 was obtained (1.80 g, 14.5 mmol) 1 H NMR (500 MHz, CDCl3): δ 2.17 (s, 3H), 2.29 (m, 4H), 4.94 (dd, 1H, J = 1.4, 10.2 Hz), 4.99 (dd, 1H, J = 1.4, 17.1 Hz), 5.78 (m, 1H), 5.88 (d, 1H, J = 8.0 Hz), 9.99 (d, 1H, J = 8.0 Hz); 13 C NMR (125 MHz, CDCl3): δ 17.6, 31.1, 39.7, 115.7, 127.6, 136.8, 163.0, 191.2. 128 Preparation of (E)-tert-butyldimethyl((3-methylhepta-2,6-dien-1-yl)oxy)silane 145d OTBS OTBS Ph 3PCH 3Br NaH THF O 149d 145d Sodium hydride NaH (60% in mineral oil) (2.52 g, 63 mmol) was added in three portions over 5 minutes to a stirred suspension of methyltriphenylphosphonium bromide Ph3PCH3Br (23.0 g, 64 mmol) in dry tetrahydrofuran THF (130 mL) at room temperature. The bright yellow mixture that was formed was stirred at room temperature under nitrogen atmosphere for 1 hour. A solution of the aldehyde 149d (12.83 g, 53 mmol) in tetrahydrofuran THF (130 mL) was cooled in an ice bath. The mixture of methyltriphenylphosphonium bromide (Ph3PCH3Br) and sodium hydride was transferred by cannula to the aldehyde solution. The resulting mixture was stirred at 0 °C for 10 minutes. This mixture was then poured into a saturated aqueous solution of ammonium chloride (300 mL) and then extracted with ether (2 × 250 mL). The combined organic layers were dried over magnesium sulfate and then solvent was removed under vacuum to leave a yellow oil. The product was purified by flash column chromatography on silica gel using 5% diethyl ether in hexanes as eluent to give compound 145d (6.11 g, 25.4 mmol, 48%) as a colorless oil. 1 H NMR (300 MHz, CDCl3): δ 0.08 (s, 6 H), 0.92 (s, 9 H), 1.63 (s, 3 H), 1.98–2.16 (m, 4H), 4.21 (d, J = 6.6 Hz, 2H), 5.04–4.93 (m, 2H), 5.42 (m, 1H), 5.76 (ddt, J = 17.0, 10.3 129 and 6.3 Hz, 1H); 13 C NMR (75 MHz, CDCl3): δ –5.06, 16.32, 25.66, 26.02, 26.38, 39.52, 60.35, 114.6, 123.5, 138.2, 139.1. Preparation of (E)-(((3-methylhepta-2,-dien-1-yl)oxy)methyl)benzene 145e OBn OBn Ph 3PCH 3Br NaH THF O 149e 145e Sodium hydride (60% in mineral oil) (2.52 g, 63 mmol) was added in portions over 5 minutes to a stirred suspension of methyltriphenylphosphonium bromide Ph3PCH3Br (23.0 g, 64 mmol) in dry tetrahydrofuran (130 mL) at room temperature and the bright yellow mixture that formed was stirred at room temperature under a nitrogen atmosphere for 1 hour. A solution of the aldehyde 149e (9.0 g, 53 mmol) in tetrahydrofuran (130 mL) was cooled in an ice bath. The mixture of methyltriphenylphosphonium bromide Ph3PCH3Br and sodium hydride NaH was transferred by cannula to the solution of aldehyde 149e. The resulting mixture was stirred at 0 °C for 10 minutes. This mixture was poured into a saturated aqueous solution of ammonium chloride (300 mL) and the mixture extracted with ether (2 × 250 mL). The combined organic layers were dried over MgSO4 and then the solvent was removed under vacuum to leave a yellow oil. The product was purified by flash column chromatography on silica gel using 5% diethyl ether in petroleum ether as eluent to give compound 145e (9.17 g, 42.4 mmol, 80%) as a colorless oil. 130 1 H NMR (500 MHz, CDCl3): δ 1.69 (s, 3H), 2.04–2.07 (m, 2H), 2.10–2.13 (m, 2H), 4.04 (d, J = 6.7 Hz, 2H), 4.51 (s, 2H), 4.93-5.06 (m, 2H), 5.43 (t, J = 6.7 Hz, 1H), 5.80 (ddt, J = 17.0, 10.3 and 6.3 Hz, 1H), 7.27–7.39(m, 5H); 13 C NMR (75 MHz, CDCl3): δ 16.4, 26.3, 39.5, 66.5, 71.9, 120.8, 123.9, 127.4,127.8, 128.3, 131.6, 138.5, 140.3. Preparation of 145f OTr Ph 3PCH 3Br OTr NaH THF O 149f 145f Sodium hydride (2.52 g, 63 mmol) was added in portions over 5 minutes to a stirred suspension of methyltriphenylphosphonium bromide Ph3PCH3Br (23.0 g, 64 mmol) in dry tetrahydrofuran (130 mL) at room temperature and the bright yellow mixture that formed was stirred at room temperature under nitrogen atmosphere for 1 hour. A solution of the aldehyde 149f (9.0 g, 53 mmol) in tetrahydrofuran (130 mL) was cooled in an ice bath. The mixture of methyltriphenylphosphonium bromide Ph3PCH3Br and sodium hydride was transferred by cannula to the solution of aldehyde 149f. The resulting mixture was stirred at 0 °C for 10 minutes. This mixture was poured into a saturated aqueous solution of ammonium chloride (300 mL) and then extracted with ether (2 × 250 mL). The combined organic layers were dried over MgSO4 and then the solvent was removed under vacuum to a leave yellow oil. The product was purified by 131 flash column chromatography on silica gel using 5% diethyl ether in petroleum ether as eluent to give trityl (E)-3-methylhepta-2,6-dienyl ester (15.62 g, 42.4 mmol, 80%) as a colourless oil 1 H NMR (500 MHz, CDCl3): δ 1.47 (d, J = 1.3 Hz, 3H), 1.88 – 2.02 (m, 2H), 2.02 – 2.18 (m, 2H), 3.60 (d, J = 1.5 Hz, 2H), 4.92 (dd, J = 8.0, 2.2 Hz, 1H), 4.90 – 5.08 (m, 1H), 5.45 (m, 1H), 5.76 – 5.85 (m, , 1H), 7.16 – 7.32 (m, 10H), 7.48 – 7.59 (m, 5H); 13 C NMR (CDCl3): δ 16.48, 32.06, 38.91, 61.25, 86.64, 114.46, 121.70, 126.82, 127.75, 128.71, 137.93, 138.43, 144.41. Preparation of (E)-3,7-dimethyloct-2-ene-1,6,7-triol 154b 1% OsO 4, 5% (DHQD) 2Phal K 3[Fe(CN) 6], K 2CO3 OH 83b OHOH MeSO 2NH 2, 0 °C, t-BuOH/H2O OH 154b Potassium ferricyanide K3Fe(CN)6 (48.026 g, 145 mmol), potassium carbonate (20.16 g, 145 mmol) and methanesulfonamide (4.62 g, 48.6 mmol) were placed into a 1 L round bottom flask equipped with a large magnetic stirring bar. Water (250 mL) was added to completely dissolve all reagents. Osmium tetroxide (0.22 g, 0.48 mmol), was transferred to the reaction mixture and 50 mL of water was used to wash the weighing vial. (DHQD)2Phal (0.8 g, 1.28 mmol) was disolved in 50 mL of t-butanol and added to the reaction mixture. Then reaction flask was cooled with an ice bath and vigorous stirring was maintained at all times. Geraniol 83b (7.5 g, 48.6 mmol) was dissolved in 50 132 mL of tert-butanol and added to the reaction mixture. Another 200 mL of tert-butanol was added and the solution stirred as vigourosly as possible for 12 hours in an ice bath. The slurry turned orange and a yellowish precipitate formed. The reaction was quenched with 48 g of sodium sulfite and stirring continued for 1 hour. The product was extracted with 150 mL of dichloromethane. The aqueous residue was washed twice with 150 mL of dichloromethane and all extracts were combined and dried with magnesium sulfate. After filtration, the solvents were evaporated at reduced pressure. This yielded a clear colorless oil (8.1 g, 43.25 mmol, 89% yield). The product 154b was used without purification for the next step. 1 H NMR (500 MHz, CDCl3): δ 5.44 (m, 1H), 4.12 (m, 2H), 3.32 (m, 1H), 2.45 (b, 1H), 2.26 (m, 1H), 2.14 (b, 1H), 2.11 (m, 1H), 1.68 (s, 3H), 1.59 (m, 2H), 1.42 (m, 1H), 1.18 (s, 3H), 1.14 (s, 3H); 13 C NMR (CDCl3): δ 141.90, 123.93, 78.05, 75.22, 58.92, 35.89, 29.72, 25.74, 25.34, 16.32 Preparation of (E)-6-hydroxy-4-methylhex-4-enal 149b HO HO OH 154b NaIO 4 SiO2 OH O CH2Cl2 149b Preparation of Silica Gel-Supported NaIO4 Reagent. NaIO4 (13.51 g, 63.1 mmol) was dissolved in 20 mL of hot water (70 °C) in a 250 Erlenmeyer flask. To this hot solution was added silica gel (60 g) with vigorous swirling 133 and shaking. The water in NaIO4 is absorbed onto silica gel resulting in a free-flowing powder. Procedure for Glycol Cleavage Oxidations. To a vigorously stirred suspension of all of the silica gel-supported NaIO4 (from previous step) reagent all as prepared above in dichloromethane (100 mL) in a 500 mL round-bottomed flask was added a solution of the diol 154b (8.1 g, 48.6 mmol) in CH2Cl2 (100 mL). The reaction was monitored by TLC until the complete disappearance of the starting material was observed (45 min). The mixture was filtered through a filter funnel, and the silica gel was thoroughly washed with dichloromethane CH2Cl2 (3x50 mL). Removal of solvents from the filtrate afforded the aldehyde 149b in (6.22 g, 48.6 mmol, 99% yield). Rf=0.46 (Hex:EtOAc = 5:1) Aldehyde 149b was used without purification for next step. 1 H NMR (500 MHz, CDCl3): δ 9.68 (t, 1H, J = 1.6), 5.27 (m, 1H), 4.48 (d, 2H, J = 7.0), 2.49 (m, 2H), 2.29 (m, 2H), 1.63 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 201.59, 140.02, 119.28, 61.03, 41.60, 31.43, 16.47. 134 Preparation of (E)-3-methylhepta-2,6-dien-1-ol 145b Ph 3PCH 3Br OH O 149b This procedure was KOt-Bu/t-BuOH THF 0 °C adopted from one OH 145b for a 2 related compound. Methyltriphenylphosphonium bromide Ph3PCH3Br (42.24 g, 118.2 mmol) was placed in 250 mL round bottom flask, 150 mL of dry THF added, and then potassium tbutoxide/t-butanol complex (22.03 g 118.2 mmol) was added. This mixture was stirred at room temperature for 1 hour till the mixture turned yellow. Hydroxyaldehyde 149b (5.55g, 59.1 mmol) was dissolved in 150 mL of dry THF and cooled in an ice bath. The ylide was added via cannula and the resulting mixture stirred 10 min. After that time the starting compound 149b disappeared on TLC. then 100 mL of saturated ammonium chloride solution was added and the mixture was stirred vigorously for 30 min and then extracted with diethyl ether (3x50 mL). The solution was dried over MgSO4 and the solvents were evaporated at reduced pressure. Pentane was added to the brown residue and the precipitate was removed by filtration. This procedure was repeated until till no precipitate formed. After the evaporation of solvent at reduced pressure, the alcohol 145b was obtained in 98% yield (5.40 g, 57.9 mmol) 1 H NMR (500 MHz, CDCl3): δ 5.77 (m, 1H), 5.40 (m, 1H), 4.99 (m, 1H), 4.93 (m, 1H), 4.11 (dd, 2H, J = 11.9, 17.5), 2.16 (m, 2H), 2.08 (m, 2H), 1.64 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 139.05, 138.21, 123.72, 114.57, 59.29, 38.79, 31.92, 16.18 135 Preparation of enyne 162 Cl 160 Mg Et 2O Cl MgCl 20% 161 162 Magnesium (36 g, 1.48 moles, 20 mesh) was placed into a 1 L round bottom flask that was oven dried for 24 h along with a large stir bar sufficient to stir the magnesium at high speed. The flask was filled with a nitrogen atmosphere and the magnesium was “dry stirred” at room temperature overnight. During that time the magnesium was powdered and should not be opened to air (might be pyrophoric). To this was added 300 mL of dry freshly distilled ether and the solution cooled to -10 °C. Allyl chloride 160 (22.57 g, 0.295 moles) was dissolved in 300 mL of dry ether and was added to the vigorously stirred slurry of magnesium in ether at -10 °C. The rate of addition is 16 mL/h (addition is by syringe pump) and the addition took 15 hours. After stirring overnight at 10 °C, The Grignard reagent was transferred by cannula into another 1 L flask to get rid of the unreacted magnesium. The unreacted magnesium was washed with dry diethyl ether and washings were combined and cooled to -20 °C. Propargyl chloride (15.65 g, 0.21 moles) was dissolved in 50 mL of dry ether and added over 0.5 hourand stirring continued for 40 h after addition. A solution of acetic acid (1 mL) in ether 50 mL) was added and mixture was stirred for 1 h. The mixture was warmed to room temperature and washed extracted with 100 mL of a saturated solution of sodium bicarbonate and then washed with the brine solution (100mL) mixtrure was extracted with ether (2x100mL) and combined organic layer was dried with MgSO4 the ether was removed out by distillation. The product was distilled at 65-75 °C. The product was distilled twice 136 (the second time with Vigreux condenser 10 cm. The receiver for the product was chilled with ice. This afforded 4.73 g of alkyne 162 (20% yield). Preparation of vinyl iodide 139 Cl2ZrCp2 162 Me 3 Al I2 I 139 41% To a stirred suspension of zirconocene dichloride ZrCp2Cl2 (18.56, 63.5 mmol) in 150 mL dichloromethane was slowly added 63 mL (129 mmol) of 2.0 M AlMe3 solution in heptane (Aldrich) at RT in a flame-dried 500 mL RB flask equipped with a magnetic stirrer (needle submerge into sovent). The mixture was stirred for 45 min to give a lemon-yellow clear solution. Then, enyne 162 (6g, 63.5 mmol) was added dropwise and the mixture was stirred for 24 h at room temperature. The flask was cooled down in an ice bath, and a solution of iodine (17.88 g, 70.4 mmol) in 50 mL of dry THF was slowly added. The mixture was warmed to room temperature, stirred for 1 h, cooled to 0 °C again and quenched VERY SLOWLY by dropwise addition of a solution of NaHCO3 (1 g) in water (25 mL). After stirring 3 h at room temperature, the mixture was filtered, and the inorganic precipitate was washed 5 times with ether (20 mL). All extracts were combined and washed 2 times with a 10% solution of Na2S2O3*5H2O, 2 times with 50 mL of brine and then dried (MgSO4). Evaporation of 137 the ether and distillation of the product at 70 °C at 5 torr afforded the vinyl iodide 139 (7.39, 41%). 1 H NMR (500 MHz, CDCl3): δ 5.89 (d, 1H, J = 1.1), 5.71-5.80 (m, 1H), 4.93-5.03 (m, 2H), 2.26-2.31 (m, 2H), 2.14-2.22 (m, 2H), 1.83 (d, 3H, J = 1.1 Hz); 13 C NMR (125 MHz, CDCl3): δ 147.3, 137.4, 115.2, 75.0, 38.9, 31.9, 23.9; IR (neat): 3077, 2978, 2934, -1 2847, 1641, 1618, 1448, 1377, 1269, 1144, 992, 912 cm ; mass spectrum m/z (% rel + intensity) 181 (1), 149 (9), 131 (1), 119 (2), 107 (3), 95 M -I (100), 81 (3), 67 (21). Anal calcd for C7H11I: C, 37.86; H, 4.99. Found: C, 38.17; H, 5.00. Colorless oil, bp 56-57 °C at 4 mm Hg, Rf = 0.60 (hexanes). Preparation of alcohol 138 from vinyl iodide 139 OH BuLi I 139 TMS O TMS 163 H 138 65% To a stirred solution of 139 (4.20 g, 18.9 mmol), in 30 mL of diethyl ether, 10 mL (20 mmol) of 2.0 M butyllithium solution in pentane (Aldrich) was added dropwise at –78 °C and the resultant mixture stirred for 1 h. Then a solution of 163 (2.63 g, 20.8 mmol), in 10 mL of diethyl ether was added slowly. The mixture was warmed up to –20 °C and kept overnight. The reaction was quenched the next morning by the slow addition of 2.0 mL (2.10 g, 34.9 mmol) of glacial acetic acid, and this was followed by the addition of 138 ice-cold water (20 mL). The organic layer was separated, and the aqueous layer was extracted with diethyl ether (4x20 mL). The extracts were combined and washed sequentially with 20 mL of water, brine (2x30 mL) and dried with magnesium sulfate MgSO4. The solvent was removed under reduced pressure and residue was fractionally distilled under vacuum (0.15 mm Hg) through a 20 cm distillation column, yielding 2.95 g (13.3 mmol, 70% yield) of pure 138. 1 H NMR (500 MHz, CDCl3): δ 5.71-5.85 (m, 1H), 5.35 (dq, 1H, J = 8.5 Hz, J = 1.3 Hz), 5.06 (d, 1H, J = 4.7 Hz), 5.00-5.04 (m, 1H), 4.92-4.96 (m, 1H), 2.14-2.23 (m, 2H), 2.062.12 (m, 2H), 1.74 (d, 1H, J = 4.8 Hz), 1.70 (d, 3H, J = 1.4 Hz), 0.15 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 139.79, 137.91, 124.66, 114.71, 106.08, 88.87, 59.29, 38.47, 31.64, 16.46, -0.22; IR (neat): 3328 br, 3079, 2961, 2936, 2901, 2174, 1667, 1642, -1 1451, 1416, 1383, 1250, 1030, 957, 912 cm ; mass spectrum m/z (% rel intensity) 168 (42), 167 (46), 149 (34), 125 (62), 117 (41), 99 (43), 95 (47), 91 (37), 75 (99), 73 (100). Anal calcd for C13H22OSi: C, 70.21; H, 9.97. Colorless liquid, bp 80-83 °C at 0.05 torr. Preparation of alcohol 138 via alkynyllithium addition O Li TMS OH TMS 135 138 TMS-acetylene (1.66 g, 16.9 mmol) was dissolved in 10 mL of dry tetrahydrofuran and n-butyllithium (6.7 mL of 2.5 M, 16.9 mmol) solution was added via syringe at room 139 temperature. After gas formation ceased, the reaction mixture was stirred kept stirring at room temperature for 1 hour. Then aldehyde 135 (2.1 g, 16.9 mmol) as a solution in 10 mL dry THF was added via syringe at ice bath temperature. The reaction was exothermic and stirred for one hour. Then the reaction mixture was added to 50 mL of saturated ammonium chloride solution and 50 mL of ether and the mixture stirred for 30 min. Extraction with diethyl ether (2x100 mL) and drying with MgSO4 yielded the alcohol 138 (2.39 g, 10.8 mmol, 64% yield) after the removal of solvents by vacuum. 1 H NMR (500 MHz, CDCl3): δ 5.71-5.85 (m, 1H), 5.35 (dq, 1H, J = 8.5 Hz, J = 1.3 Hz), 5.06 (d, 1H, J = 4.7 Hz), 5.00-5.04 (m, 1H), 4.92-4.96 (m, 1H), 2.14-2.23 (m, 2H), 2.062.12 (m, 2H), 1.74 (d, 1H, J = 4.8 Hz), 1.70 (d, 3H, J = 1.4 Hz), 0.15 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 139.79, 137.91, 124.66, 114.71, 106.08, 88.87, 59.29, 38.47, 31.64, 16.46, -0.22; IR (neat): 3328br, 3079, 2961, 2936, 2901, 2174, 1667, 1642, -1 1451, 1416, 1383, 1250, 1030, 957, 912 cm ; mass spectrum m/z (% rel intensity) 168 (42), 167 (46), 149 (34), 125 (62), 117 (41), 99 (43), 95 (47), 91 (37), 75 (99), 73 (100). Anal calcd for C13H22OSi: C, 70.21; H, 9.97. Colorless liquid, bp 80-83 °C at 0.05 mm Hg, Rf = 0.26 (DCM:hexanes = 1:1). Preparation of (E)-5-methyl-1-(trimethylsilyl)nona-4,8-dien-1-yn-3-ol 138 TMS O 135 TMS i-Pr-MgCl THF 140 OH 138 TMS-acetylene (1.69 g, 16.9 mmol) was dissolved in 10 mL dry THF and was added via syringe to 8.5 mL of a 2M solution (16.9 mmol) of isopropyl magnesium chloride at room temperature. After gas formation ceased the reaction mixture was stirred at room temperature for 1 hour. Then aldehyde 135 (2.1g, 16.9 mmol) as a solution in 10 mL dry THF was added via syringe. The reaction was exothermic and was stirred for 1 hour. Then reaction mixture was added to 50 mL of saturated ammonium chloride solution and 50 mL of ether and the resulting mixture stirred for 30 min. Extraction with diethyl ether (2x100mL) and drying with MgSO4 yielded alcohol 138 (2.82 g, 12.7 mmol, 75% yield) after the removal of solvents under vacuum. 1 H NMR (500 MHz, CDCl3): δ 5.71-5.85 (m, 1H), 5.35 (dq, 1H, J = 8.5 Hz, J = 1.3 Hz), 5.06 (d, 1H, J = 4.7 Hz), 5.00-5.04 (m, 1H), 4.92-4.96 (m, 1H), 2.14-2.23 (m, 2H), 2.062.12 (m, 2H), 1.74 (d, 1H, J = 4.8 Hz), 1.70 (d, 3H, J = 1.4 Hz), 0.15 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 139.79, 137.91, 124.66, 114.71, 106.08, 88.87, 59.29, 38.47, 31.64, 16.46, -0.22; IR (neat): 3328 br, 3079, 2961, 2936, 2901, 2174, 1667, 1642, -1 1451, 1416, 1383, 1250, 1030, 957, 912 cm ; mass spectrum m/z (% rel intensity) 168 (42), 167 (46), 149 (34), 125 (62), 117 (41), 99 (43), 95 (47), 91 (37), 75 (99), 73 (100). Anal calcd for C13H22OSi: C, 70.21; H, 9.97. Found: C, H. Colorless liquid, bp 80-83 °C at 0.05 mm Hg, Rf = 0.26 (DCM:hexanes = 1:1). 141 Preparation of (E)-5-methyl-1-(trimethylsilyl)nona-4,8-dien-1-yn-3-one 137 TMS OH TMS MnO 2, DCM O 138 137 Protected propargylic alcohol 138 (2.39 g, 10.7 mmol) was dissolved in 100 mL of 1 dichloromethane and fresh (brown) manganese dioxide (9.16g, 106 mmol) was added. The mixture was stirred overnight at room temperature and filtered through silica gel yielding 1.61 g (7.28 mmol) of the conjugated ketone 137 (68% yield). 1 H NMR (500 MHz, CDCl3): δ 6.16 (s, 1H), 5.78 (m, 1H), 5.05 (m, 1H), 5.00 (m, 1H), 2.26 (m, 4 H), 2.21 (s, 3H,), 0.24 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 176.27, 161.00, 136.99, 125.50, 115.11, 104.68, 95.94, 40.63, 31.56, 19.83, -0.70; Rf = 0.60 (Hexanes:EtOAc = 5:1). Preparation of chloro-N-methoxy-N-methylacetamide 166 O Cl Cl + 164 H OMe N HCl Me 165 Et 3N Cl CH2Cl2 75% O OCH3 N CH3 166 Triethylamine (28 mL, 200 mmol) was added slowly by 60 mL syringe to a mixture of chloroacetyl chloride 164 (8 mL, 100 mmol) and N,O-dimethylhydroxylamine hydrochloride 165 (9.75 g, 100 mmol), in 250 mL dichloromethane that was cooled in an ice bath and resulting mixture was stirred for 1 h. The mixture was washed with water, 142 brine and saturated sodium bicarbonate. The organic phase was dried over magnesium sulfate and the solvent removed off under vacuum. The residue (10.28 g, 75 mmol, 75% yield) was used as is for next step. 1 H NMR (300 MHz, CDCl3): δ 4.25 (s, 2 H), 3.76 (s, 3 H), 3.24 (s, 3 H); 13 C NMR (125 MHz, CDCl3): δ 167.7, 61.7, 40.6, 32.8. Preparation of phosphate 167 O Cl O O OCH3 P(OEt) 3 (EtO) 2P OCH3 N N 70% CH3 CH3 166 167 Triethylphosphite (13.9 mL, 75 mmol) was added to the unpurified 166 from the previous step (10.28 g, 75 mmol) and the resulting mixture heated at 120°C for 18 h. The product was distilled0 (bp = 125 °C, 0.2 torr) giving 167 (12.55 g, 52.5 mmol, 70% yield). 1 H NMR (500 MHz, CDCl3): δ 4.19 (m, 4H), 3.6 (s, 3H), 3.22 (s, 3H), 2.98 (d, J = 22 Hz, 2H), 1.2 (t, J= 6.7 Hz, 6H). Preparation of Weinreb’s amide 141 via Horner-Wadsworth-Emmons olefination O (EtO) 2P 167 O O O OCH3 N CH3 NaH, 67% 144 N 141 143 OMe To a suspension of sodium hydride (60% in mineral oil, mineral oil was removed by washing sodium hydride 3 times with dry hexanes) (5.32 g, 0.133 mole) in dry tetrahydrofuran (100 mL) phosphate 167 (15.8 g, 0.121 mol) was added under nitrogen atmosphere and 0 °C bath temperature dropwise by syringe pump over 20 minutes to give a transparent solution. After the addition, the solution was stirred 15 minutes. A solution of allylacetone 144 (60 mL, 2.12 M, 0.127 moles) was added by syringe pump over 15 minutes. After complete addition the solution was stirred at 0 °C for another 15 minutes giving a transparent solution. If cloudiness persists, then stirring for an additional 30 minutes should give a transparent solution. The reaction was quenched by the slow addition of saturated aqueous NH4Cl (200mL). The organic layer was extracted with diethyl ether (3x150mL) and then washed with saturated sodium bicarbonate (2x200mL) and brine solutions (2x200mL). Organic layer was dried with magnesium sulfate and the solvent was removed under vacuum. The product was distilled at 75-95 °C (0.2 torr) giving product 141 in 67% yield with 66:34 E:Z mixture (11.45 g, 0.085 moles). 1 E-isomer H NMR (500 MHz, CDCl3): δ 6.12 (s,1H), 5.84-5.5.78 (m, 1H), 5.05 (d, J = 17 Hz, 1H), 4.99, (d, J = 10 Hz, 1H) 3.67 (s, 3H), 3.20 (s, 3H), 2.26 (m, 4H), 2.13 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 137.00, 115.14, 114.29, 61.41, 40.32, 32.27, 31.73, 18.69. 144 Preparation of ketone 137 via alkynyllithium addition O O N 141 OMe TMS BuLi TMS 137 A solution of n-butyllithium (24 mL, 2.5 M, 60 mmol) was added slowly (5 minutes) to a solution of TMS acetylene (6.01 g, 60.0 mmol) in tetrahydrofuran THF (100 mL) under nitrogen atmosphere and kept in an ice cold bath. After addition and the bubbles had ceased forming solution was stirred for one hour in the ice bath. This solution was transferred by cannula to the pre-cooled (0 °C) solution of E-isomer Weinreb’s amide 141 (10 g, 54 mmol). After complete addition the reaction was continued to stir for one hour at room temperature. The reaction was quenched by the slow addition of saturated aqueous NH4Cl (100mL). The organic layer was extracted with diethyl ether (3x100mL) and then the combined washed ether layers with saturated sodium bicarbonate (2x100mL) and brine solutions (2x100mL). The organic layer was dried with magnesium sulfate and the solvent was removed under vacuum giving 137 in 65% yield (7.84 g, 35.1 mmol). 1 H NMR (500 MHz, CDCl3): δ 6.16 (s, 1H), 5.78 (m, 1H), 5.05 (m, 1H), 5.00 (m, 1H), 2.26 (d, 4H, J = 2.9 Hz), 2.21 (s, 3H,), 0.24 (s, 9H); 13 C NMR (125 MHz, CDCl3): δ 176.27, 161.00, 136.99, 125.50, 115.11, 104.68, 95.94, 40.63, 31.56,19.83, -0.70; Rf = 0.60 (Hexanes:EtOAc = 5:1). 145 Preparation of ketone 137 via alkynylmagnesium chloride addition O O OMe N ClMg TMS Me THF 141 95% TMS 137 A solution of i-propylmagnesium chloride (31 mL, 2M solution, 61.3 mmol), was added slowly (in 5 minutes) to a solution of TMS acetylene (6.02 g, 61.3 mmol) in 100 mL of dry tetrahydrofuran under nitrogen atmosphere and at 0 °C. After addition and after bubbles had ceased forming the mixture was stirred for one hour in an ice bath. This solution was transferred by cannula to the solution of Weinreb’s amide 141 (5.62 g, 30.6 mmol) cooled by ice bath. After addition, the mixture was stirred for one hour at room temperature The reaction was quenched by slow addition of saturated aqueous NH4Cl (100mL). The organic layer was extracted with diethyl ether (3x100mL) and then the combined organic layers washed with saturated sodium bicarbonate (2x100mL) and brine solutions (2x100mL). The organic layer was dried with magnesium sulfate MgSO4. Solvent was removed under vacuum giving 137 in 86% yield (5.80 g, 26.3 mmol) 1 H NMR (500 MHz, CDCl3): δ 6.16 (s, 1H), 5.78 (m, 1H), 5.05 (m, 1H), 5.00 (m, 1H), 2.26 (d, 4H, J = 2.9 Hz), 2.21 (s, 3H,), 0.24 (s, 9H); 13 C NMR (125 MHz, CDCl3): δ 176.27, 161.00, 136.99, 125.50, 115.11, 104.68, 95.94, 40.63, 31.56, 19.83, -0.70; Rf = 0.60 (Hexanes:EtOAc = 5:1). 146 Separation of E and Z isomers of Weinreb’s amide 141 O N OMe 141 Distillation of Weinreb amide 141 The distillation of 3 g of the amide 141 (Table 2.5) that was a 72:28 mixture of E:Z isomers is done under high vacuum (0.2 torr) in the temperature range of 79-90 °C. The distillate was collected in two fractions: the first fraction gave 1.6 g with a boiling point range from 79 to 81 °C (0.2 torr) and contained 54% of the E-isomer and the second fraction gave 1.4 g with a boiling point range of 81 to 90 °C (0.2 torr) and contained 92% of the E-isomer. This result demonstrated that fractional distillation can be used to partially resolve the isomers of 141. Depending on the type of apparatus and proper of the heat adjustment, it was possible to get fractions of 5-10 grams of 141 which were 85-95% E-isomerand fractions of 20 g which were 66-75% E-isomers of 141 1 For the determination of the stereoisomer ratio the H NMR peaks at 1.89 (Z-isomer) and 2.13 ppm (E-isomer) were integrated and GC peaks with retention times (oven temperature 120 °C) Rt= 4.756 min (Z-isomer) and 6.012 min (E-isomer) were integrated. Column Chromatography After distillation, the first fraction (1.6 g, 54:46 (E:Z)) was subjected to further isomer enrichment by silica gel chromatography with a 10:1 mixture of hexane/EtOAc. This was 147 performed with 250 g silica gel in a 10 cm diameter column. Fifteen fractions were collected from the silica gel column. The last nine fractions gave 0.8 g of amide 141 as the pure E-isomer (more than 99% E-isomer) after removal of solvent. The fractional distillation becomes very efficient on large scales (10-30 g scale). Isomerization of Weinreb’s amide 141 from Z to E isomer O MeO N Me 1. PhSLi -78 °C 2. H 2O O OMe N Me 141-E 66% E-isomer 141-Z 90% Z-isomer N-Butyllithium (2.183 mL, 2.5 M, 5.46 mmol) was added to a THF (100 mL) solution of thiophenol (0.601 g, 5.46 mmol) at 0 °C then cooled to -78 C. A solution of the Z isomer (1 g , 5.46 mmol, 90% Z) was added and was stirred overnight at -78 °C. The reaction was quenched with 100 mL of water, warmed to rt and extracted with diethyl ether (2x150 mL). Ratio 66% E isomer and 34% Z isomer. 148 Preparation of compound 174 Ph N H 177 Ph OH + Cl Ph OH Ph OH N HO Ph Ph OH N Cl 174 3 Adopted from Ding’s procedure. (S)-Diphenyl(pyrrolidin-2-yl)methanol 177 (1.672 g, 6.60 mmol) and potassium carbonate K2CO3 (3.649 g, 26.40 mmol) were dissolved in dry dimethyl formamide DMF (20 mL) at 0 °C. 2,6-Bis(chloromethyl)-4-methylphenol (0.615 g, 3.00 mmol) was added to this stirred solution and the resulting mixture was stirred at room temperature for 12 h before being diluted with water (70 mL) and diethyl ether Et2O (70 mL). The organic layer was collected and the aqueous phase was washed with diethyl ether Et2O (3×50 mL). The organic phases were washed with water (2×50 mL), brine and then dried with magnesium sulfate. After removal of the solvent, the product was purified by column chromatography on silica gel using hexanes/EtOAc (from 20:1 to 5:1) as the eluent to yield 174 (1.793 g, 94%) as a white amorphous solid. 1 H NMR (300 MHz, CDCl3): δ 1.43–1.63 (m, 4H), 1.75–1.82 (m, 2H), 1.97–2.04 (m, 2H), 2.14 (s, 3H), 2.33–2.41 (m, 2 H), 2.76–2.83 (m, 2H), 3.21 (d, J=12.3 Hz, 2 H), 3.36 (d, J=12.6 Hz, 2 H), 3.94 (dd, J=4.5, 9.3 Hz, 2H), 6.58 (s, 2 H), 7.10–7.32 (m, 12H), 7.55 (d, J=8.4 Hz, 4H), 7.68 ppm (d, J=8.4 Hz, 4H); 149 13 C NMR (75 MHz, CDCl3): δ 20.38, 24.01, 29.61, 54.99, 57.77, 71.36, 78.88, 123.98, 125.93, 125.98, 126.38, 126.60, 127.12, 127.95, 128.19, 128.82, 146.40, 146.98, 152.61 ppm. These data 3 matched data that reported for this compound. Preparation of alcohol S-171 via Trost’s protocol O TMS 3 eq 135 10 mol% 174 Me 2Zn (3 eq) toluene, 4 °C 170 OH TMS 171 ee 65-70% To a solution of Me2Zn (4.80 mL, 2.0 M in toluene, 9.6 mmol, 2.95 equiv) in dry toluene (20 mL) was added TMS acetylene (1.30 mL, 9.2 mmol, 2.8 equiv) at room temperature under a nitrogen atmosphere. After initial agitation, the clear solution stood at room temperature without stirring for 90 minutes, then was transferred via syringe to another 100 mL round bottom flask containing the neat diprolinol ligand 174 (200mg, 0.325 mmol). After 10 minutes the bubbling ceased and aldehyde 135 (0.403 g, 3.25 mmol) was added. The reaction flask was sealed and cooled to 4 °C for 20 hours at which point it was quenched with saturated aqueous ammonium chloride (40 mL) and stirred vigorously for 15 minutes. The organic phase was separated and the aqueous phase was washed with diethyl ether Et2O (3x100 mL). The organic phases were combined, dried with magnesium sulfate, concentrated under vacuum and purified by silica gel chromatography giving 171 in 16% yield (0.1154 g, 0.52 mmol) 150 1 H NMR (500 MHz, CDCl3): δ 5.71-5.85 (m, 1H), 5.35 (dq, J = 8.5 and 1.3 Hz, 1H), 5.06 (d, J = 4.7 Hz, 1H), 5.00-5.04 (m, 1H), 4.92-4.96 (m, 1H), 2.14-2.23 (m, 2H), 2.06-2.12 (m, 2H), 1.62 (d, J = 4.8 Hz, 1H), 1.72 (d, J = 1.4 Hz, 3H), 0.17 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 140.07, 138.02, 124.74, 114.80, 106.09, 89.09, 59.48, 38.58, 31.76, 16.57, -0.12; the enantiomeric excess was determined 65-70% by HPLC using Chiracel OD column (n-hexane/i-PrOH 99.6:0.4, 25 °C) at 1.5 mL/min, UV detection at 205 nm: tR : (major) = 17.786 min, (minor) = 20.423 min. Preparation of alcohol 173 O CO2Me 3 eq, 135 172 10 mol% 174 Me 2Zn (3 eq) OH CO2Me toluene, 4 °C Ph OH Ph N Ph HO Ph 173 racemic OH N 174 To a solution of Me2Zn (4.80 mL, 2.0 M in toluene, 9.6 mmol) in dry toluene (2 mL) was added TMS acetylene (1.30 mL, 9.2 mmol) at room temperature under an atmosphere of argon. After initial agitation, the clear solution stood at room temperature without stirring for 90 minutes, then was transferred via syringe to another test tube containing neat diprolinol ligand 174 (20.1 mg, 0.0325 mmol, 0.1 equiv). After 10 minutes the 151 bubbling ceased and aldehyde 135 was added (0.403 g, 3.25 mmol). The reaction was sealed and cooled to 4 °C for 20-48 hours at which point it was quenched with saturated aqueous NH4Cl (2 mL) and while vigorously stirred for 15 minutes. The organic phase was separated and the aqueous phase was extracted with diethyl ether Et2O (3x10 mL). The organic phases were combined and concentrated. The unpurified alcohol 173 was not active in the polarimeter, so purification was not done. Preparation of alcohol 171 O Zn(OTf)2, Et 3N TMS (+)-N-methylephedrine OH TMS 23 °C, toluene 135 170 171 0% ee A 10 mL flask was purged with nitrogen for 15 minutes and was then charged with Zn(OTf)2 (400 mg, 1.1 mmol, )and (+)-N-Methylephedrine (216 mg, 1.2 mmol). Toluene (3mL) and triethylamine (Et3N 0.120 g, 1.2 mmol) were added to this flask and then the reaction mixture was stirred at room temperature for 2 hours. Alkyne 170 (0.1176 g, 1.2 mmol) was added in one portion by syringe. Aldehyde (0.1240 g, 1.0 mmol) was added after 15 minutes. The reaction was quenched after 20 hours by slow addition of aqueous ammonium chloride (60mL). The organic layer was extracted with diethyl ether (3x40mL) and then washed with saturated sodium bicarbonate (2x40mL) and brine solutions (2x40mL). The organic layer was dried with magnesium sulfate. The solvent 152 was removed under vacuum and product was purified by silica gel column chromatography to give 171 in 17% yield (0.038 g, 0.17 mmol) 1 H NMR (500 MHz, CDCl3): δ 5.71-5.85 (m, 1H), 5.35 (dq, J = 8.5 and 1.3 Hz, 1H), 5.06 (d, J = 4.7 Hz, 1H), 5.00-5.04 (m, 1H), 4.92-4.96 (m, 1H), 2.14-2.23 (m, 2H), 2.06-2.12 (m, 2H), 1.62 (d, J = 4.8 Hz, 1H), 1.72 (d, J = 1.4 Hz, 3H), 0.17 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 140.07, 138.02, 124.74, 114.80, 106.09, 89.09, 59.48, 38.58, 31.76, 16.57, -0.12; the enantiomeric excess was determined to be 0% by HPLC using Chiracel OD column (n-hexane/i-PrOH 99.6:0.4, 25 °C) at 1.5 mL/min, UV detection at 205 nm: tR : (major) = 17.786 min, (minor) = 20.423 min. Preparation of N-(Benzyloxycarbonyl)-S-proline 178 O OH NH 4 O CbzCl NaOH 177 OH N Cbz 178 A 250-mL, three-necked, round-bottomed flask was equipped with two pressure equalizing dropping funnels (25- and 25-mL), a thermometer and a magnetic stirrer. The flask was charged with 50 mL (0.1 mol) of a 2 M aqueous solution of sodium hydroxide and cooled with an ice-salt bath. To this stirred solution 12.5 g (0.10 mol) of S-proline 177 was added. The resulting solution was maintained at 0 to -5 °C while 18 mL (20.0 g, 0.12 mol) of benzyl chloroformate (Aldrich) and 35 mL (0.14 mol) of 4 M aqueous solution of sodium hydroxide were added dropwise over 1 h with vigorous stirring. The 153 reaction mixture was stirred for another 1 h at 0 to -5 °C and then washed with ethyl ether (2 x 25 mL). The aqueous solution was acidified to pH 2 (ice bath cooling) by the dropwise addition of 6 M hydrochloric acid and the resulting mixture was saturated with sodium sulfate and extracted with ethyl acetate (3 x 50 mL). The organic extracts were combined, dried over anhydrous sodium sulfate (2 portions), and evaporated under reduced pressure to give a colorless oil, which was dissolved in 25 mL of ethyl acetate and diluted with 100 mL of hexane. Crystallization of the resulting mixture was induced by cooling and scratching with a glass rod. The crystals were collected by filtration and washed with 20 mL of petroleum ether. After drying under vacuum, 96% yield (23.9 g, 0.096 mol) of colorless crystals of 128 were obtained, mp 69-74 °C,. 1 H NMR (500 MHz, CDCl3): δ 7.37 – 7.24 (m, 5H), 5.22 – 5.09 (m, 2H), 4.39 (ddd, J = 15, 8.6, 3.4 Hz, 1H), 3.63 – 3.40 (m, 2H), 2.25 (dd, J = 20.7, 12.2 Hz, 1H), 2.12 (q, J = 16.0, 12.8 Hz, 1H), 2.03 – 1.89 (m, 2H). This data matched that reported in the 4 literature. Preparation of N-Benzyloxycarbonyl-S-proline Methyl Ester 178 O O OH N Cbz BF 3⋅Et 2O MeOH 177 4 OMe N Cbz 178 A 1-L, one-necked, round-bottomed flask equipped with a magnetic stirrer and a Liebig condenser fitted with a rubber septum was charged with 23.9 g (0.096 mol) of N- 154 (benzyloxycarbonyl)-S-proline 177 and 400 mL of anhydrous methanol, and the contents were placed under dry nitrogen. After the addition of 24.6 mL (28.4 g, 0.20 mol) of boron trifluoride etherate to the stirred mixture, the solution was heated at reflux for 1 h. The solvent was removed under reduced pressure and the residue was vigorously stirred with 200 mL of ice-water and extracted with ethyl acetate (3 x100 mL). The organicextracts were combined and successively washed with brine, 1 M aqueous sodium bicarbonate solution, and brine, and then dried over anhydrous sodium sulfate. After the removal of the solvent under reduced pressure, the residual colorless oil was dried by twice dissolving in 100 mL of dry toluene and removing solvent under reduced pressure to give 35.9 g (0.096 mol) of methyl ester 178 as a colorless oil in >99%yield. 1 H NMR (500 MHz, CDCl3): δ 7.41 – 7.21 (m, 5H), 5.19 (d, J = 12.6 Hz, 1H), 5.12 (d, J = 12.5 Hz, 1H), 5.05 (d, J = 12.5 Hz, 1H), 4.37 (ddd, J = 27.2, 8.7, 3.7 Hz, 1H), 3.74 (d, J = 1.6 Hz, 2H), 3.67 – 3.43 (m, 4H), 2.21 (dddd, J = 18.8, 15.1, 11.9, 8.9 Hz, 1H), 2.06 – 1.84 (m, 3H). Preparation of S-2-(Diphenylhydroxymethyl)pyrrolidine 179 O OMe 2 eq. PhMgCl 4 Ph Ph OH NH N Cbz 179 178 A dry 1-L, three-necked, round-bottomed flask was equipped with a pressure-equalizing 250-mL dropping funnel, a thermometer, a rubber septum, and a large magnetic stirrer. The contents of the flask were placed under nitrogen, and 400 mL of a solution (2 M, 155 0.8 mol) of phenylmagnesium chloride in THF was added. A solution of N(benzyloxycarbonyl)-S-proline methyl ester 178 (19 g, 0.072 mol) in 100 mL of dry THF was added to the phenylmagnesium chloride solution over 1 h at 0 to -10 °C with cooling with an ice-salt bath. After the addition, the cooling bath was removed and the reaction mixture was allowed to warm to room temperature and was stirred for 16 h. The reaction mixture was poured with stirring into 300 g of crushed ice and 60 g of ammonium chloride in 100 mL of water. The resulting mixture was concentrated under reduced pressure to remove the tetrahydrofuran and the resulting aqueous mixture was extracted with ethyl ether (3x150mL). The ethereal extract was washed with brine, dried over anhydrous potassium carbonate, and concentrated in a rotary evaporator to a total volume of 500 mL. Dry hydrogen chloride gas was bubbled into the solution with stirring until the mixture was acidic. The precipitated amine hydrochloride was collected by filtration, washed with ether, and dissolved in 150 mL of hot methanol. To this solution was added 600 mL of ethyl ether, and the resulting mixture was stirred and cooled with an ice bath. The precipitate was filtered, washed with ether, and dried to give 16.7 g of crude product. The hydrochloride salt was suspended in 300 mL of ether and treated with 60 mL of 2 M aqueous sodium hydroxide solution with vigorous stirring. The resulting mixture was stirred vigorously for 45 min and extracted with ethyl ether. The extracts were washed with brine, dried over anhydrous potassium carbonate, and evaporated under reduced pressure to give a solid, which was recrystallized from methanol (15 mL) and water (3 mL) to give 13.3 g (0.0527 mol, 52.7% yield) of colorless crystals of 179 (50.8% yield based on S-proline), mp 76.5-77.5 °C, [α]D 3.0, MeOH, 99% ee) 156 20 = 58.0 (c = 1 H NMR (500 MHz, CDCl3): δ 7.59 – 7.53 (m, 2H), 7.49 (dt, J = 7.2, 1.1 Hz, 2H), 7.35 – 7.22 (m, 4H), 7.19 – 7.11 (m, 2H), 4.57 (s, 1H), 4.24 (t, J = 7.7 Hz, 1H), 3.02 (ddd, J = 9.2, 6.7, 4.9 Hz, 1H), 2.93 (dt, J = 9.1, 7.5 Hz, 1H), 1.80 – 1.50 (m, 5H); 13 C NMR (125 MHz, CDCl3): δ 146.38, 143.69, 128.16, 127.86, 127.62, 127.16, 81.61, 66.00, 61.90, 47.74, 29.68, 22.97, 14.64. Preparation of oxazoborolidine 183 N H 4 Ph toluene Ph + HO OH reflux B OH 179 182 Ph N B Ph O 183 Diphenylprolinol 179 (8.4 g, 33.2 mmol) and methyl boronic acid 182 (2.0 g, 33.3 mmol) were mixed and 50 mL of dry toluene was added to dissolve both compounds. The mixture was vigorously refluxed with a Dean-Stark device under nitrogen for 1 hour till water separated and gave calculated amount (0.9 mL). The reaction mixture was cooled to room temperature and toluene was evaporated at reduced pressure. The residue was distilled at 140-145 C at 0.03 torr. The liquid crystallized in 30 min giving 95% yield (8.0 g, 31.54 mmol) of product 183. 1 mp 124–127°C (dec); H NMR (500 MHz, CDCl3): δ 7.62 (m, 2 H),7.39-7.20 (m, 8 H), 4.66 (t, 1 H, J = 7.9), 3.37–3.43 (m, 1 H), 3.19–3.24 (m, 1 H), 1.89–2.00 (m, 2 H), 1.56– 1.68 (m, 1 H), 1.28–1.37 (m, 1 H), 0.77 (s, 3 H), 157 13 C NMR (125 MHz, CDCl3): δ 144.58, 143.47, 128.23, 128.09, 127.29, 127.08, 125.89, 125.00, 90.62, 76.21, 57.69, 31.40, 24.87. Preparation of S-proline-N-carboxyanhydride 184 O CO2H N H 1. COCl2 2. Et 3N O N O 177 184 To a cold water-cooled suspension of s-proline 177 (12 g, 0.104 mol) in 120 mL of tetrahydrofuran THF in a dry 500 L flask, phosgene (64 mL of 20% in toluene, 0.1878 mol) was added via pressure-equalizing addition funnel over 0.5 hour maintaining a temperature of not more than 20 °C. After addition, the solution was kept at 35 °C for 0.5 hour and the reaction mixture become homogeneous. When homogeneous, it was concentrated under reduced pressure. Dry tetrahydrofuran (THF) (120 mL) was added and the mixturecooled to 0-5 °C in an ice bath. Triethylamine (14.5 mL) was added dropwise over 15 minutes. The precipitate was filtered and washed with dry THF (3x30 mL). The filtrates were combined and concentrated under vacuum. Due to its instability the anhydrous 184 was used immediately for next step as it is. Preparation of diphenylprolinol 179 from 184 O N 184 O PhMgBr O 158 N H 179 57% Ph Ph OH Phenylmagnesium chloride (160 mL, 2M, 0.320 mol) was placed in a 1L flask and cooled with an ice/salt bath (-10- -5°C). To this solution was added the solution of 184 from previous reaction in 100 mL in tetrahydrofuran. Stir overnight at room temperature. The reaction mixture was quenched with 210 mL of 2N sulfuric acid. The reaction mixture was filtered and filter cake was washed with water (5 °C, 2x15mL) and ethyl acetate (3x40 mL). The cake (diphenylprolinol sulfate) was placed into a 500 mL beaker and treated with 2M sodium hydroxide (55 mL) and tetrahydrofuran 55 mL. After aging for 30 minutes, 150 mL of toluene was added and the mixture was partitioned into two phases. The organic layer was dried with magnesium sulfate and concentrated under reduced pressure resulting in 15.02 g, (57% yield from proline) of 179 after crystallization from hexane. Mp 76-77 °C Combined procedure of Corey and Mathre for preparation of 183 N H 179 Ph Dean Stark Ph + HO B OH toluene OH 182 Ph N B 183 B O Ph O + 179 O B B O Ph 185 N B Ph O 183 Extremely pure after distillation 4 The following is a modification of the procedures by Corey 5 and Mathre. Diphenylprolinol 179 (16.8 g, 66.4 mmol) and methyl boronic acid 182 (3.97 g, 66.4 mmol) were mixed and 100 mL of dry toluene was added to dissolve both compounds. The mixture was vigorously refluxed with a Dean-Stark trap under nitrogen for 1 hour till water separated and gave the correct calculated amount (1.8 mL). Additional methyl 159 boronic acid (0.5 g) was added and refluxed with a Dean-Stark trap for one hour. The toluene was distilled off and fresh toluene (100 mL) was added and then removed by distillation to remove the excess methyl boronic acid. The mixture was cooled to room temperature and 0.1 mL of trimethylboroxine was added and the mixture stirred overnight under a nitrogen atmosphere. The solvent was removed by distillation and 10 mL of dry toluene was added and distilled off. This process was repeated untill no crystals were separated. The solvent was removed under vacuum and residue was distilled (175 °C (0.1 torr)) giving 13.80 g, (49.8 mmol) of 183 (75% yield) 1 mp 124–127°C (dec); H NMR (500 MHz, CDCl3): δ 7.62 (m, 2 H),7.39-7.20 (m, 8 H), 4.66 (t, 1 H, J = 7.9), 3.37–3.43 (m, 1 H), 3.19–3.24 (m, 1 H), 1.89–2.00 (m, 2 H), 1.56– 1.68 (m, 1 H), 1.28–1.37 (m, 1 H), 0.77 (s, 3 H), 13 C NMR (125 MHz, CDCl3): δ 144.58, 143.47, 128.23, 128.09, 127.29, 127.08, 125.89, 125.00, 90.62, 76.21, 57.69, 31.40, 5 24.87. These data match that reported for this compound. Preparation of preparation of (S,E)-5-methyl-1-(trimethylsilyl)nona-4,8-dien-1-yn-3ol 171 Ph Ph O N B 183 O 137 TMS BH 3⋅Me 2S -20 °C, CH2Cl2 160 OH 171 TMS Method A. Freshly prepared oxazoborolidine 183 the solution was stirred (0.92 g, 3.3 mmol) was dissolved in 5 mL of dry dichloromethane (DCM). The solution was stirred under nitrogen atmosphere while 3.4 mL of a 1M solution of borane*dimethylsulfide complex in DCM was added via syringe at room temperature. The resulting solution was stirred for 30 min at room temperature. The catalyst solution was cooled to -20 °C and then 0.73 g (3.3 mmol) of ketone 137 was diluted with DCM to 2 mL total in a syringe. The ketone was addedvia syringe pump over 30 min the solution was stirred for 30 min and then 2 mL MeOH was added by syringe pump over 30 min. The reaction mixture was stripped of solvents under reduced pressure. The product 171 was purified by column chromatography (Pentane: Ether= 5:1). The product was afforded in 95% yield (0.7025 g, 3.12 mmol). The ee was determined to be 89 % as described below. [α]D 20 = +59.3° (c = 0.282, CH2Cl2, 89% ee) Method B. Freshly prepared oxazoborolidine 183 in (0.063g, 2.3 mmol) was dissolved in 5 mL of dry DCM. This solution was stirred under nitrogen atmmosphere while 2.3 mL of a 1M solution of borane*dimethylsulfide complex in DCM was added via syringe at room temperature. The resulting solution was stirred for 30 min at room temperature. The catalyst solution was cooled to -20 °C and then ketone 137 (0.5 g, 2.3 mmol) as a solution in DCM was diluted to 2 mL total in a syringe. Ketone 137 was added via syringe pump over 5 hours. After addition, the reaction mixture was stirred for 30 min and then 2 mL MeOH was added by syringe pump over 30 min. The reaction mixture was evaporated under reduced pressure. The product was purified by column 161 chromatography (Pentane: Et2O= 5:1). The alcohol 171 was afforded in 65% yield (0.3279 g, 1.495 mmol). 1 H NMR (500 MHz, CDCl3): δ 5.71-5.85 (m, 1H), 5.35 (dq, , J = 8.5 and 1.3 Hz, 1H), 5.06 (d, J = 4.7 Hz, 1H), 5.00-5.04 (m, 1H), 4.92-4.96 (m, 1H), 2.14-2.23 (m, 2H), 2.062.12 (m, 2H), 1.62 (d, J = 4.8 Hz, 1H), 1.72 (d, J = 1.4 Hz, 3H), 0.17 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 140.07, 138.02, 124.74, 114.80, 106.09, 89.09, 59.48, 38.58, 31.76, 16.57, -0.12; The enantiomeric excess was determined to be 78% ee by HPLC using Chiracel OD column (n-hexane/i-PrOH 99.6:0.4, 25 °C) at 1.5 mL/min, UV detection at 205 nm: tR : (major) = 17.786 min, (minor) = 20.423 min.; [α]D 20 = +59.3 (c = 0.282, CH2Cl2, 89% ee). Preparation of enyne 194 Cl 197 Mg -10 °C Et 2O Cl MgCl 187 -20 °C Et 2O, 194 44 hours Magnesium (36.9 g, 1.48 moles) that is 20 mesh (it is important!!!) was placed into a 1 L round bottom flask that was oven-dried for 24 h and abig stir bar sufficient to stir the magnesium at high speed. The magnesium was “dry stirred” under nitrogen atmosphere” at room temperature for 2 days. During that time magnesium becomes powdered, and not recommended to open this to the air since it might be pyrophoric. 162 Then 300 mL of dry freshly distilled ether was added and the mixture was cooled to -10 °C. Methallyl chloride 197 of (26.85 g, 0.295 moles) was dissolved in 300 mL of dry ether and was added to the vigorously stirred magnesium in ether at -10 °C. The rate of addition is 16 mL/h (addition is by syringe pump). It took 15 hours for addition. The reaction mixture was stirred overnight at -10 °C. The Grignard reagent was transferred by cannula into another 1 L flask to get rid of unreacted magnesium. The magnesium residue was washed with dry ether and the washing was combined and the mixturecooled to -20 °C. Propargyl chloride (15.76 g, 0.21 moles) was dissolved in 50 mL dry ether and added over 0.5 hour and the resulting mixture was stirred for 40 hours. A solution of acetic acid in ether was then added. The mixture was stirred for 1 hour and the mixture was allowed to warm to room temperature, The reaction mixture was washed with 100 mL of saturated sodium bicarbonate and then brine. The aqueous layer was extracted with ether (2x200 mL) and the combined organic layer was dried with MgSO4. The ether was removed by distillation. The product was distilled at 65-75 °C and 20 torr. The product was distilled twice (second time with 10 cm Vigareaux column with the reciever for the product was chilled with ice. This afforded alkyne 194. 22% yield (4.43 g, 46.2 mmol). 1 H NMR (500 MHz, CDCl3): δ 4.78 (d, J = 1.49 Hz, 1H), 4.74 (d, J = 1.49 Hz, 1H), 2.34 (m, 2H), 2.24 (t, J = 7.2 Hz, 2H), 1.96 (t, J = 3.8 Hz, 1H), 1.74 (s, 3H); MHz, CDCl3): δ 143.89, 110.93, 84.08, 68.51, 36.57, 22.26, 17.18. 163 13 C NMR (125 Preparation of hex-5-yn-2-one 192 O O Cl K 2CO3 EtOH 188 206 O 192 35% Potassium carbonate (15.41 g, 0.111 mmol), propargyl chloride (7.1 g, 0.095 mmol) and 2,4-pentadione (10 g, 0.100 mmol) were mixed and stir under reflux in ethanol for 24 hours. After cooling to room temperature, water 100 mL was added and extracted with diethyl ether (3x100 mL). The combined organic phase was washed with brine (100 mL) and dried with magnesium sulfate. The solution was concentrated on rotary evaporator and the product was distilled (60 °C, water aspirator) giving 192 as an oil in 35% yield (3.25 g, 33.2 mmol). 1 H NMR (500 MHz, CDCl3): δ 2.66 (t, J = 10 Hz, 2H), 2.37 (m, 2H), 2.14 (s, 3H) 1.91 (t, J = 3.8 Hz 1H); 13 C NMR (125 MHz, CDCl3): δ 206.4, 82.6, 68.5, 42.4, 12.8, 29.5. Preparation of enyne 194 Ph 3PCH 2Br O BuLi 194 3% 192 Butyllithium (18.8 mL, 2.5 M, 47 mmol) was added to a stirred suspension of methyltriphenylphosphonium bromide (Ph3PCH3Br) (16.79 g, 47 mmol) in dry tetrahydrofuran THF (130 mL) at room temperature and the bright yellow mixture that formed was stirred at room temperature under a nitrogen atmosphere for 1 hour. A 164 solution of the ketone 192 (3.25 g, 33.7 mmol) in tetrahydrofuran THF (130 mL) was cooled in an ice bath. The mixture of methyltriphenylphosphonium bromide Ph3PCH3Br and butyllithium was transferred by cannula to the solution of ketone 192. The resulted mixture was stirred at 0 °C for 1 hour. This mixture was poured into a saturated aqueous solution of ammonium chloride (300 mL) and then extracted with ether (2 × 250 mL). The combined organic layers were dried over MgSO4 and then the solvent was removed under vacuum to leave a yellow oil. The residue was distilled and enyne 194 was obtained as as a colourless oil (0.097 g, 1.01 mmol 3% yield). 1 H NMR (500 MHz, CDCl3): δ 4.78 (d, J = 1.49 Hz, 1H), 4.74 (d, J = 1.49 Hz, 1H), 2.34 (m, 2H), 2.24 (t, J = 7.2 Hz, 2H), 1.96 (t, J = 3.8 Hz, 1H), 1.74 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 143.89, 110.93, 84.08, 68.51, 36.57, 22.26, 17.18. Preparation of ethyl 4-methylpent-4-enoate 207 Cl 197 O O O OEt EtO 206 OEt 207 Diethyl malonate 206 (53.07 g, 33 mmol) was added to a mixture of sodium hydride (60% mineral oil, 13.2 g, 33 mmol) in tetrahydrofuran (750 mL). Then methallyl chloride 197 (30 g, 33 mmol) was added dropwise over 15 minutes. The reaction mixture was refluxed for 36 hours and then quenched with ammonium chloride. The aqueous layer was washed with diethyl ether (2x150 mL) and the combined organic layer dried with magnesium sulfate. The solvents were removed solvent under vacuum and the residue was dissolved in 450 mL DMSO and sodium chloride (114 g, 2 moles) was added and 165 the mixture stirred at 185 °C for 24 hours. After cooling to room temperature, water (200 mL) and ethyl acetate (200 mL) were added. The organic layer was separated and solvents removed by rotory evaporator. The residue was distilled at 105-110 °C with a water aspirator giving product 207 in 50% yield (20 g, 1 mole). 1 H NMR (500 MHz, CDCl3): δ 1.25 (t, J = 7.2 Hz, 3H), 1.74 (s, 3H), 2.33 (t, J = 8.0 Hz, 2H), 2.45 (t, J = 8.0 Hz, 2H), 4.13 (q, J = 7.1 Hz, 2H), 4.69 (s, 1H), 4.74 (s, 1H); 13 C NMR (125 MHz, CDCl3): δ 14.25, 22.48, 32.68, 32.73, 60.31, 110.35, 144.14, 173.27. Preparation of aldehyde 193 O OEt O 193 33% 208 The solution of ester 208 (20 g, 140 mmol) in dichloromethane (400 mL) was cooled to 78 °C and then DIBAL-H (73 mL, 2.5 M, 0.182 mmol) was added by syringe. After addition, the reaction mixture was stirred at -78 °C for 4 hours. The reaction was quenched with 30 mL of methanol and 60 mL of water the mixture was warmed to room temperature and stirred with Rochelle’s salt overnight. After extraction, drying organic layer and concentrating under vacuum the residue was distilled at 55 °C (water aspirator) giving aldehyde 193 in 33% yield (4.5 g, 46.2 mmol). 1 H NMR (500 MHz, CDCl3): δ 1.75 (s, 3H), 2.34 – 2.37 (m, 2H), 2.55 – 2.58 (m, 2H), 4.69 (s, 1H), 4.77 (s, 1H), 9.77 (t, J = 1.5 Hz, 1H); 22.69, 29.88, 41.81, 110.72, 143.77, 202.08. 166 13 C NMR (125 MHz, CDCl3): δ Preparation of dibromide 209 O Br CBr 4, Ph 3P Br 209 76% 193 Carbon tetrabromide (43.93g, 132 mmol) was dissolved in 100 mL of dry dichloromethane, cooled in an ice bath and then triphenylphosphine (69.48 g, 264 mmol) was added as a solution in 250 mL of dry dichloromethane. During the addition, the solution turned red and later brown with some precipitate formation. The mixture was stirred for 10 minutes after the addition and then aldehyde 193 (6.5 g, 66.2 mmol) was added at room temperature for 2 hours. The precipitate was filtered and washed with hexanes. The solvent was removed from combined filtrate under vacuum, and the product was purified by silica gel chromatography with hexanes: DCM 5:1 as eluent. After removal of solvent, the product was afforded in 76% yield (12.75 g, 50.3 mmol) Preparation of iodide 211 Ph 3P, Imidazole OH 210 I 2, 4 h, DCM 41% I 211 To a solution of triphenylphosphine (44.06 g, 168 mmol) in dichloromethane (350 mL), imidazole (11.44 g, 168 mmol) was added carefully. Then iodine (42.64 g, 168 mmol) was added at 0 °C. After 15 minutes alcohol 210 (16.22 mL, 160 mmol) was added dropwise. The reaction mixturewas stirred at room temperature for 4 hours. The mixture was then concentrated under reduced pressure and diluted with hexanes. Then reaction 167 mixture was filtered through silica gel and celite. Then the solvent was removedunder reduced pressure. The residue was distilled at 75 °C water aspirator giving compound 211 in 41 % yield (11.14 g, 65.6 mmol) 1 H NMR (500 MHz, CDCl3): δ 4.85 (s, 1H), 4.75 (s, 1H), 3.25 (t, J = 8 Hz, 2H), 2.58 (t, J = 8 Hz, 2H), 1.73 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 143.9, 112.3, 41.7, 21.6, 3.5. Preparation of enyne 190 TMS TMS I Li 211 190 N-Butyllithium (31 mL, 2.5 M, 77 mmol, 1.5 equiv.) was added to a tetrahydrofuran solution (250 mL) of TMS acetylene (7.59 g, 77 mmol, 1.5 equiv.) under nitrogen atmosphere and cooled in an ice bath and stirred for 1 h. Then iodide 211 (10.1 g, 51.5 mmol) was added via syringe and the solution heated at 55 °C for 24 h (conversion 88%). The reaction was quenched with ammonium chloride (100 mL), the aqueous layer was extracted with diethyl ether (2x150 mL) and combined organic layers were dried with magnesium sulfate. The product was distilled (45 °C, 6 torr, 110-115 water aspirator) to give 5.86 g, (35.5 mmol) of 190 (69% yield) 1 H NMR (500 MHz, CDCl3): δ 0.17 (s, 9H), 1.73 (s, 3H), 2.23 (t, J = 10 Hz, 2H), 2.34 (t, J = 10 Hz, 2H), 4.70 (s, 1H), 4.75 (s, 1H); 13 C NMR (125 MHz, CDCl3): δ 0.19, 18.84, 22.35, 36.88, 84.75, 107.09, 110.84, 144.14. 168 Deprotection of TMS group towards enyne 194 TMS TBAF (cryst) 190 194 The dissolved enyne 190 (7.06 g, 0.047 mmol) was dissolved in dry diethyl ether (150 mL) and then cooled in ice bath. Crystalline TBAFx3H2O (4.46 g, 0.0141 mmol) was added in three portions and the mixture stirred for 2 hours. The mixture was stirred with 100 mL of water for 1 hour. The organic layer was separated and washed with water (3x150mL). and then dried with magnesium sulfate. The solvent was removed under reduced pressure in rotory evaporator with water bath at no more than 15 °C. The residue was distilled at 90-95 °C giving enyne 194 in 61% yield (2.42 g, 0.028 mmol) 1 H NMR (500 MHz, CDCl3): δ 1.74 (s, 3H), 1.96 (t, J = 3.8 Hz, 1H), 2.24 (t, J = 7.2 Hz, 2H), 2.34 (m, 2H), 4.74 (s, 1H), 4.78 (s, 1H); 13 C NMR (125 MHz, CDCl3): δ 17.18, 22.26, 36.57, 68.51, 84.08, 110.93, 143.89. Prepraration of diene 214 Cl MgCl Cl 187 Cl 214 47% 213 Methallylmagnesium chloride 187 was prepared according to the method for compound 194 (page 42) (Magnesium 39 g, 1.6 moles; chloride 213 31.7 g, 352 mmol). Compound 213 (22 g, 198 mmol) was added and the reaction mixture was stirred overnight at room 169 temperature. The reaction was quenched with ammonium chloride the aqueous layer was separated and extracted with diethyl ether (2x100 mL) and the combined organic layer was dried with magnesium sulfate. The solvents were removed under reduced pressure to provide 12.17 g (93.6 mmol) of compound 214 in. (47% yield) 1 H NMR (500 MHz, CDCl3): δ 1.74 (s, 3H), 2.28 (t, J = 10 Hz, 2H), 2.47 (t, J = 10 Hz), 4.60-4.82 (m, 2H), 5.13 (s, 1H), 5.16 (s, 1H). Prepraration of enyne 191 OH 2 eq. LDA than acetone Cl 214 191 15% Compound 214 (12.17 g, 94 mmol) from the previous step above was added to a solution of freshly prepared LDA (2 equiv) in 400 mL of THF at -78 °C and the resulting solution stirred for 2 hours. The alkynyllithium intermediate was reacted with acetone (18.49 g, 318 mmol, 3.4 equiv.) afforded the corresponding acetone adduct 191 in 2.15 g (15% yield). 1 H NMR (500 MHz, CDCl3): δ 1.47 (s, 6H), 1.49 (s, 1H), 1.74 (s, 3H), 2.24 (t, J = 7.2 Hz, 2H), 2.33 (m, 2H), 4.75(s, 1H), 4.77 (s, 1H); 13 C NMR (125 MHz, CDCl3): δ 17.23, 22.26, 31.92, 36.57, 65.40, 82.61, 85.67, 110.78, 143.76. Prepraration of 194 from 191 OH OH 3% KOH toluene 191 194 170 20% Compound 191 (2.15 g, 14 mmol) was heated under reflux for 1 h in the presence of one pellet of sodium hydroxide in 15 mL of toluene. The product 194 was purified by distillation at 95 °C which gave (0.2770 g, 2.8 mmol, 20 % yield). 1 H NMR (500 MHz, CDCl3): δ 1.74 (s, 3H), 1.96 (t, J = 3.8 Hz, 1H), 2.24 (t, J = 7.2 Hz, 2H), 2.34 (m, 2H), 4.74 (s, 1H), 4.78 (s, 1H); 13 C NMR (125 MHz, CDCl3): δ 17.18, 22.26, 36.57, 68.51, 84.08, 110.93, 143.89. Preparation of vinyl iodide 195 I + AlMe3 + ZrCp2Cl2 194 I2 DCE, rt, 24 h 195 To a stirred suspension of zirconocene dichloride (ZrCp2Cl2) (18.56, 63.5 mmol) in 150 mL dichloromethane in a flame-dried 500 mL RB flask equipped with magnetic stirrer was slowly added 63 mL (129 mmol) of a 2.0 M solution of AlMe3 in heptane at room temperature. The mixture was stirred for 45 min to give a lemon-yellow clear solution. Then, enyne 194 (5.96 g, 63.5 mmol) was added dropwise and stirred for 24 h at room temperature. The flask containing the reaction mixture was cooled down in an ice bath, and a solution of iodine (17.88 g, 70.4 mmol) in 50 mL of abs THF was slowly added. The mixture was warmed to room temperature, stirred for 1 h, cooled to 0 °C again and quenched VERY SLOWLY by the dropwise addition of NaHCO3 (1 g) solution in water (25 mL). After stirring 3 h at room temperature, the mixture was filtered; the inorganic precipitate was 171 washed 5 times with ether (20 mL). The organic layer and extract were combined and washed 2 times with a 10% solution of Na2S2O3*5H2O, 2 times with 50 mL of brine and dried (MgSO4). Evaporation of ether and distillation of the product at 70 °C at 5 torr afforded vinyl iodide 195 (3.29 g, 14.0 mmol, 22% yield). 1 H NMR (500 MHz, CDCl3): δ 5.83-5.88 (m, 1H); 4.71 (s, 1H), 4.66 (s, 1H), 2.31-2.34 (m, 2H), 2.11-2.14 (m, 2H), 1.83 (s, 3H), 1.70 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 147.51, 144.58, 110.47, 74.86, 37.75, 35.93, 23.84, 22.29; IR (neat): 3075, 2969, 2936, -1 2915, 2851, 1649, 1617, 1447, 1375, 1269, 1142, 1055, 889 cm ; mass spectrum m/z + (% rel intensity) 181 (18), 127 (4), 109 M -I (100), 91 (8), 81 (19), 79 (12), 67 (57). Anal calcd for C8H13I: C, 40.70; H, 5.55. Found: C, 40.99; H, 5.73. Colorless liquid, bp 70-71 °C at 4 mm Hg, Rf = 0.59 (hexanes). Prepraration of Fischer carbene complex 134 1. nBuLi I 2. Cr(CO)6 3. MeOTf 195 Cr(CO)5 OMe 134 80% To a stirred solution of vinyl iodide 195 (5g, 21.2 mmol) in 70 mL of diethyl ether in a 250 mL flame dried round bottom flask was added dropwise 10 mL (2.0 mmol) of 2.0 M BuLi solution in pentane at –78 °C and the resulting mixture stirred at this temperature 172 for 30 min. The resulting clear solution was transferred by cannula to a suspension of chromium hexacarbonyl (Strem Chemicals, 4.4 g, 20.00 mmol) in 350 mL of diethyl ether that had been cooled to –78 °C. The mixture was warmed to room temperature and stirred for 2 h. The mixture was cooled to 0 °C and 2.5 mL of methyl triflate, (3.63g, 22.1 mmol), was added and the mixture was stirred for 30 min at room temperature. The reaction mixture was concentrated under reduced pressure and the product was purified by silica-gel chromatography (eluent: hexanes, Rf = 0.34) to give 134 as a dark red oil, which was dried at 0.05 mm Hg overnight. Yield of 134 is 5.5 g (16.0 mmol, 80%). 1 H NMR (500 MHz, CDCl3): δ 7.22 (s, 1H),4.74 (s, 1H), 4.70 (s, 4H), 2.22 (s, 4H), 1.83 (s, 3H), 1.73 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 340.23, 224.01, 216.74, 144.30, 142.02, 140.93, 110.78, 66.12, 39.04, 35.83, 22.19, 20.37; IR (neat): 3079, 2957, 2853, -1 2058, 1917, 1651, 1586, 1455, 1377, 1250, 1186, 1094, 1042, 982, 891 cm ; mass + + + spectrum m/z (% rel intensity): 344 M (2), 288 M -2CO (8), 260 M -3CO (6), 232 M + + -4CO (22), 204 M -5CO (42), 172 (95), 148 (95), 107 (60), 91 (81). Anal calcd for C15H16CrO6: C, 52.33; H, 4.68. Found: C, 52.68; H, 4.76. Deep red oil, Rf = 0.19 (hexanes). 173 Prepraration of propargyl alcohol 215 OH OH TBAF, THF TMS 171 215 To a stirred solution of 171, 0.4939 g (2.22 mmol) in 10 mL of dry tetrahydrofuran, was added slowly 2.4 mL (2.4 mmol) of 1.0 M TBAF solution in THF at room temperature and the resulting mixture was stirred at this temperature for 1 h. The reaction mixture was then added slowly to a vigorously stirred mixture of 25 mL of brine and 50 mL of overlaid ether. The two layers were stirred was stirred for additional 15 min. The layers were separated and the aqueous layer was extracted with ether (3x25 mL). The combined organic layers, washed with brine (3*50 mL) and dried with magnesium sulfate MgSO4. The ether was distilled off under reduced pressure and the crude product was purified by silica-gel chromatography (eluent: DCM) to give pure 215 as a light yellow liquid (0.33 g, 2.15 mmol, 99%). 1 H NMR (500 MHz, CDCl3): δ 5.71-5.84 (m, 1H); 5.36-5.40 (m, 1H), 5.05-5.09 (m, 1H), 4.92-5.04 (m, 2H), 2.47 (d, J = 2.2 Hz, 1H), 2.14-2.23 (m, 2H), 2.07-2.12 (m, 2H), 1.78 (d, 1H, J = 4.9 Hz), 1.71 (d, 3H, J = 1.4 Hz); 13 C NMR (125 MHz, CDCl3): δ 140.38; 137.91, 124.34, 114.81, 84.39, 72.49, 58.82, 38.47, 31.67, 16.52; IR (neat): 3398, 3079, -1 2961, 2932, 2860, 1728, 1642, 1451, 1379, 1275, 1125, 1073, 1020, 966, 912 cm ; + mass spectrum m/z (% rel intensity) 150 M (9), 57 (11), 70 (9), 71 (9) 104 (5), 149 174 (100), 167 (18). Anal calcd for C10H14O: C, 79.96; H, 9.39. Found: C, 79.98; H, 9.46. Light yellow liquid with a distinctive odor, Rf = 0.29 (DCM). [α]D 20 = +54.4 (c = 0.604, CH2Cl2). Preparation of compound 216a Ph Ph Ph O OH 215 TrCl DBU, DCM 2 days 216a 93% To a stirred solution of alcohol 215 (1.0 g, 6.6 mmol) and trityl chloride TrCl (2.78 g, 10 mmol) in 10 mL of DCM, of DBU (1.5 g, 10 mmol) was added slowly and the resulting mixture was stirred at room temperature for 18 hours. Reaction mixture was then added slowly to 50 mL of stirred water. The mixture was stirred for additional 5 min and the layers were then separated. The aqueous layer was extracted with DCM (25 mL) and combined organic layers were washed with 50 mL of water, 30 mL of a saturated solution of NaHCO3, brine (2*30 mL) and then dried (MgSO4). The solvent was distilled off under reduced pressure and product was purified by chromatography on silica gel (eluent: ether:pentane =1:9, Rf = 0.60) to give 216 as an almost colorless yellowish viscous oil, which was dried under high vacuum for overnight. This gave 1.55 g (4.0 mmol, 60% yield) of 216a. 1 H NMR (500 MHz, CDCl3): δ 7.42-7.48 (m, 6H), 7.11-7.24 (m, 9H), 5.63-5.77 (m, 1H), 5.17-5.21 (m, 1H), 4.86-4.97 (m, 2H), 4.67 (d, J = 8.1, 1H), 2.04 (d, J = 2.1 Hz, 1H), 175 1.96-2.02 (m, 2H), 1.84-1.90 (m, 2H), 1.28 (d, J = 1.2 Hz, 3H); 13 C NMR (125 MHz, CDCl3): δ 144.34, 138.24, 136.34, 128.98, 127.71, 127.02, 124.34, 114.56, 88.25, 83.27, 72.10, 61.95, 38.35, 31.74, 16.70; IR (neat): 3295 (br s), 3059, 3034, 2978, 2928, -1 1640, 1491, 1449, 1221, 1156, 1086, 1028, 1003, 990, 912 cm ; mass spectrum m/z + + (% rel intensity): 244 Ph3C +1 (34), 243 Ph3C (88), 166 (12), 165 (57), 115 (10), 105 (100), 91 (41), 79 (16), 77 (70). Anal calcd for C29H28O: C, 88.73; H, 7.19. Found: C, 88.60; H, 7.08. Colorless needles: solidified after standing at +2°C for several weeks, mp 47-48 °C, Rf = 0.60 (ether:hexanes = 1:9). Preparation of (S,E)-((4-methoxyphenyl)(5-methylnona-4,8-dien-1-yn-3- yloxy)methylene)dibenzene 216 OMe (4-OMe-Ph)(Ph) 2CCl OH DBU, 24 hours 215 O Ph Ph 216b To a stirred solution of alcohol 215,(0.33g, 2.13 mmol) and 4-OMe-TrCl (1.85 g, 4.30 mmol) in 3 mL of DCM, slowly 0.5 mL (0.509 g, 3.34 mmol) of DBU was added and then resultant mixture was stirred at RT for 32 h. The reaction mixture was then added slowly to 50 mL of stirred water. The mixture was stirred for an additional 5 min, and the layers were then separated. Aqueous layer was extracted with DCM (25 mL), extracts were 176 combined, organic layer was washed with 50 mL of water, 30 mL of saturated solution of NaHCO3, brine (2*30 mL) and dried (MgSO4). The solvent was distilled off under reduced pressure and product was purified by chromatography on silica gel (eluent: ether:pentane =1:10, Rf = 0.44) to give 216b as almost colorless yellowish viscous oil, which was dried under high vacuum overnight. Giving 216b in 93% yield (0.837 g, 1.98 mmol,). 1 H NMR (500 MHz, CDCl3): δ 7.53 (ddt, J = 1.3, 8.3, 11.1 Hz, 4H), 7.40 (m, 2H), 7.27 (dddd, J = 1.0, 3.6, 4.8, 7.1 Hz, 4H), 7.22 (m, 2H), 6.81 (dd, J = 1.3, 9.0 Hz, 2H), 5.78 (m, 1H), 5.27 (dd, J = 1.3, 8.1 Hz, 1H,), 5.02 (m, 1H), 4.96 (m, 1H), 4.75 (dt, J = 1.8, 8.1 Hz, 1H,), 3.78 (d, J = 0.8 Hz, 3H), 2.16 (dd, J = 1.3, 2.1 Hz, 1H), 2.08 (ddd, J = 4.0, 7.3, 7.9 Hz, 2H), 1.96 (dd, J = 6.8, 13.6 Hz, 2H), 1.38 (t, J = 1.3 Hz, 3H); 13 C NMR (125 MHz, CDCl3): δ 158.67, 144.87, 144.82, 138.21, 136.22, 136.02, 130.01, 128.65, 128.63, 127.67, 126.85, 124.43, 114.54, 112.97, 87.93, 83.40, 72.06, 61.82, 55.16, + 38.34, 31.74, 16.72; HRMS (TOF-ESI) calc’d for C30H30O2Na ([M+Na] ) 449.2457. Found: 449.2497. [α]D 20 = +11.0 (c = 0.180, CH2Cl2, 89% ee). 177 Preparation of DMT-protected alcohol 216 O Ph OH 215 O DMTCl DBU, DCM 18 h O 216c 62% To a stirred solution of alcohol 215,(0.33g, 2.13 mmol) and 4-OMe-TrCl (1.85 g, 4.30 mmol) in 3 mL of DCM, 0.5 mL (0.509 g, 3.34 mmol) of DBU was added and then resultant mixture was stirred at RT for 18 h. The reaction mixture was then added slowly to 50 mL of stirred water. The mixture was stirred for an additional 5 min, and the layers were then separated. Aqueous layer was extracted with DCM (25 mL), extracts were combined, organic layer was washed with 50 mL of water, 30 mL of saturated solution of NaHCO3, brine (2*30 mL) and dried (MgSO4). The solvent was distilled off under reduced pressure and product was purified by chromatography on silica gel (eluent: ether:pentane =1:10, Rf = 0.32) to give 216c as almost colorless yellowish viscous oil, which was dried under high vacuum overnight giving 216c in 62% yield (0.597 g , 1.32 mmol). 1 H NMR (500 MHz, CDCl3): δ 1.41 (s, 3H), 1.93 – 2.04 (m, 2H), 2.07 – 2.14 (m, 2H), 2.19 (d, J = 2.1 Hz, 1H), 3.81 (s, 6H), 4.77 (d, J = 8.0 Hz, 1H), 4.99 (d, J = 10.2 Hz, 1H), 5.05 (d, J = 17.1 Hz, 1H), 5.28 (d, J = 8.1 Hz, 1H), 5.75 – 5.88 (m, 1H), 6.84 (dd, J = 178 6.4, 4.8 Hz, 4H), 7.19 – 7.25 (m, 1H), 7.26 – 7.34 (m, 2H), 7.40 – 7.48 (m, 4H), 7.51 – 7.58 (m, 2H); 13 C NMR (125 MHz, CDCl3): δ 16.78, 31.80, 38.39, 55.21, 61.75, 72.04, 83.56, 87.69, 113.01, 113.20, 114.57, 124.54, 126.74, 127.70, 128.40, 130.41, 136.21, 136.61, 138.28, 145.40, 158.59. Preparation of (S)-4-methoxy-2-((S,E)-1-((4-methoxyphenyl)diphenylmethoxy)-3methylhepta-2,6-dienyl)-6-methyl-6-(3-methylbut-3-enyl)cyclohexa-2,4-dienone 221 O O Ph Ph Cr(CO)5 Ph Ph O + O 60 °C, CH3CN 21 h H 216b O O OMe 221b 134 Chromium carbene complex 134 (0.88 g, 2.5 mmol), ether 216b (1.08 g, 2.5 mmol) and 128 mL of dry acetonitrile CH3CN were put into a flame-dried 500 mL Schlenk flask equipped with stopcock and a magnetic stir bar. The mixture was deoxygenated with freeze-thaw method (3 cycles). Then, the reaction was warmed to 60 °C under vacuum and kept at that temperature for 20.5 h. The flask was opened to air, and the reaction mixture was stipped of solvents under reduced pressure then 50 mL of ether-DCM (1:1) was added to the flask and the mixture was stirred with contact to air (septum, Pasteur pipette bubbling with technical air) 24 hours. 179 The resulting green solution was filtered, and the solvent was distilled off at reduced pressure. The crude product was checked by NMR but the peaks are too broad, due to presence of Cr (III). TLC shows 2 spots. The product was finally purified and separated by chromatography on silica gel using 1:1:50 DCM:Et2O:pentane mixture, Rf (desired product) = 0.21, Rf (opposite diasteromer) = 0.22. this gave 221b as a yellow oil (1.0 g, 65% yield). 1 H NMR (500 MHz, CDCl3): δ 0.95 (s, 3H), 1.36 (m, 3H), 1.53 (s, 3H), 1.58 (s, 3H), 1.80 (m, 1H), 2.01 (m, 2H), 2.12 (m, 2H), 3.52 (s, 3H), 3.73 (s, 3H), 4.47 (s, 1H), 4.55 (s, 1H), 4.71 (s, 1H), 4.93 (d, 1H, J = 10.0 Hz), 5.01 (d, 1H, J = 20.0 Hz), 5.06 (d, 1H, J = 5.0 Hz), 5.30 (d, 1H, J = 15.0 Hz), 5.78 (d, 1H, J = 7.1 Hz), 6.66 (s, 1H), 6.71 (d, 2H, J = 8.3 Hz), 7.25 (m, 8H), 7.49 (d, 4H, J = 7.1 Hz); 13 C NMR (125 MHz, CDCl3): δ 17.06, 22.43, 26.97, 31.93, 32.31, 32.45, 39.06, 41.34, 48.67, 54.63, 55.10, 66.92, 87.57, 109.46, 109.51, 112.95, 114.44, 125.49, 126.64, 126.69, 127.64, 127.69, 128.44, 128.67, 130.79, 136.05, 136.38, 138.40, 138.79, 145.00, 145.52, 145.56, 150.53, + 158.38, 202.88; HRMS (TOF-ESI) calc’d for C41H50NO4 ([M+NH4] ) 620.3740. Found: 620.3768. [α]D 20 = +112.0 (c = 0.705, CH2Cl2), on 89% ee material. 180 Preparation of compound 221a Cr(CO)5 OMe + 134 O OTr OTr MeCN, 55 °C 0.02 M OTr + OMe 221a 216a O OMe 222a Chromium carbene complex 134 (0.2819 g, 819 mmol), enyne 216a (0.3440 g, 819 mmol) and 40.2 mL of dry acetonitrile CH3CN were put into a flame-dried 100 mL Schlenk flask equipped with stopcock and magnetic stir bar. The mixture was deoxygenated by freeze-thaw method (3 cycles). Then, it was warmed to 60 °C and kept at the temperature for 20.5 h. The flask was opened to air, and the reaction mixture was concentrated under reduced pressure, 50 mL of ether-DCM (1:1) was added to the flask and the mixture was stirred with contact to air (septum, Pasteur pipette bubling with technical air) for 24 hours. The resulting green solution was filtered, and the solvent was distilled off at reduced pressure. The crude product was checked by NMR but the peaks are too broad due to presence of Cr(III). TLC shows 2 spots were both collected. The product was finally purified and separated by chromatography on silica gel using 1:1:50 DCM:Et2O:pentane mixture, Rf (desired product) = 0.24, Rf (opposite diasteromer) = 0.32. this gave 221a as a yellow oil (0.3463g, 70% yield). 1 H NMR (500 MHz, CDCl3): δ 0.94 (s, 3H), 1.30-1.33 (m, 3H), 1.53 (s, 3H), 1.57 (s, 3H), 1.77-1.83 (m, 1H), 1.99-2.02 (m, 2H), 2.10-2.12 (m, 2H), 3.51 (s, 3H), 4.46 (s, 1H), 4.55 181 (s, 1H), 4.71 (s, 1H), 4.94 (d, J = 10.0 Hz, 1H), 5.02 (d, 1H, J = 20.0 Hz), 5.07 (d, 1H, J = 5.0 Hz), 5.30 (d, 1H, J = 15.0 Hz), 5.77 (d, 1H, J = 7.1 Hz), 6.67 (s, 1H), 7.25 -7.35 (m, 12H), 7.46-7.55 (d, J = 7.1 Hz, 3H); 13 C NMR (125 MHz, CDCl3): δ 17.07, 22.44, 26.99, 32.32, 32.47, 39.07, 41.35, 48.68, 54.64, 66.93, 87.58, 109.46, 109.51, 112.95, 114.44, 125.49, 126.64, 126.69, 127.64, 127.69, 128.44, 128.67, 130.79, 136.05, 136.38, 138.40, 138.79, 145.00, 145.52, 145.56, 150.53, 158.38, 202.88. Preparation of compound 221c Cr(CO)5 OMe + 134 O ODMT ODMT MeCN, 55 °C 0.02 M O ODMT + OMe OMe 221c 216c 222c Ph O DMT O Chromium carbene complex 134 (0.822, 2.386 mmol), ether 216c (1.08, 2.386 mmol) and 105 mL of dry acetonitrile CH3CN were put into flame-dried 250 mL Schlenk flask equipped with stopcock and magnetic stirrer. The mixture was degassed by three cycles of the freeze-thaw method. Then, without nitrogen filling, it was warmed to 60 °C and kept at the temperature for 20 h. 182 The flask was opened to air, and the reaction mixture was concentrated under reduced pressure, 50 mL of ether-DCM (1:1) was added to the flask and the mixture was stirred with contact to air (septum, Pasteur pipette bubling with technical air) 24 hours. The resulting green solution was filtered, and the solvent was distilled off at reduced pressure. The crude product was checked by NMR but the peaks are too broad, due to presence of Cr (III). TLC shows 2 spots. The product was finally purified and separated by chromatography on silica gel using 1:1:50 DCM:Et2O:pentane mixture, Rf (desired product) = 0.2, Rf (opposite diasteromer) = 0.21. Compound 221c was obtained as a yellow oil (1.05 g, 70 % yield). 1 H NMR (500 MHz, CDCl3): δ 0.94 (s, 3H), 1.30-1.33 (m, 3H), 1.54 (s, 3H), 1.60 (s, 3H), 1.77-1.83 (m, 1H), 1.99-2.02 (m, 2H), 2.10-2.12 (m, 2H), 3.52 (s, 3H), 3.73 (s, 3H), 3.74 (s, 3H), 4.47 (s, 1H), 4.56 (s, 1H), 4.72 (s, 1H), 4.94 (d, J = 10.0 Hz, 1H), 5.02 (d, 1H, J = 20.0 Hz), 5.07 (d, 1H, J = 5.0 Hz), 5.30 (d, 1H, J = 15.0 Hz), 5.76-5.83 (m, 1H), 6.66 (d, J = 5 Hz, 1H), 6.71-6.75 (m, 4H), 7.00 -7.55 (m, 9H); 13 C NMR (125 MHz, CDCl3): δ 17.09, 22.44, 26.95, 32.33, 32.48, 39.08, 41.36, 48.69, 54.65, 55.25 66.81, 87.28, 109.46, 109.51, 112.95, 114.44, 125.49, 126.64, 126.69, 127.64, 127.69, 128.44, 128.67, 130.79, 136.05, 136.38, 138.40, 138.79, 145.00, 145.52, 145.56, 150.53, 158.38, 202.93. 183 Preparation of macrocycle 226a O O OTr Me OTr Me Grubbs II OMe toluene 110 °C, 3 h 221a OMe 226a A 500 mL one neck round bottom flask with condenser was filled with nitrogen and compound 224a (109.14 mg, 0.191 mmol) was added and diluted with 185 mL of dry toluene to give a 0.00102 mM solution. The reaction mixture was brought to reflux. Then 2 nd Generation Grubbs Catalyst (Aldrich) (17.6 mg, 0.02 mmol) was added as a solution in 10 mL toluene solution by syringe. The resulting mixture was refluxed for 3 h. The mixture was cooled to room temperature and filtered through a plug of silica gel (10 g) to remove the catalyst. The solvent was removed by a rotory evaporator that gave a yellow solid. Purification by preparative TLC (eluent: Et2O:DCM:hexanes = 1:1:30, Rf = 0.28) gave 47.5 mg (82.6 mmol, 20%) of pure product 226a. A small part of 226a was recrystallyzed from MeOH to get a pure sample with mp 209212 ºC 1 H NMR (500 MHz, CDCl3): δ 7.47-7.42 (m, 6H), 7.22-7.17 (m, 6H), 7.10-7.14 (m, 3H), 6.64 (dd, J = 3.2, 0.6 Hz, 1H), 5.23 (d, J = 8.6 Hz, 1H), 4.84 (d, J = 9.4 Hz, 1H), 4.62 (d, J = 3.2 Hz, 1H), 4.41 (d, J = 11.5 Hz, 1H), 3.51 (s, 3H), 2.28-2.12 (m, 3H), 2.00 (td, J = 12.5, 4.8 Hz, 1H), 1.86-1.81 (m, 2H), 1.67-1.55 (m, 2H), 1.45 (s, 3H), 1.43 184 (s, 3H), 0.79 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 201.67, 150.73, 144.76, 139.23, 135.32, 134.83, 134.39, 128.86, 127.65, 127.29, 126.78, 124.62, 109.89, 87.72, 66.92, 54.62, 49.12, 39.37, 37.93, 36.17, 30.43, 25.54, 15.63, 15.03. Preparation of (2S,3E,7E,11S)-13-methoxy-2-((4methoxyphenyl)diphenylmethoxy)-4,8,11-trimethylbicyclo[9.3.1]pentadeca1(14),3,7,12-tetraen-15-one 226 O O OMMT Me OMe Grubbs 2nd gen. catalyst toluene, 0.1 mM reflux 12 h 224b OMMT Me OMe 226b A 500 mL round bottom flask was filled with nitrogen and compound 224b (1 g, 1.65 mmol) was added and diluted with 150 mL of dry toluene. The reaction mixture was nd brought to reflux. Then 2 Generation Grubbs Catalyst (Aldrich) (70.4 mg, 0.08 mmol) was addedas a solution in 10 mL toluene by syringe. The reaction mixture was refluxed for 3 h. The mixture was cooled to room temperature and filtered through silica gel (10 g) to remove catalyst. Solvent was removed by a rotary evaporator which gave yellow solid. Purification by preparative TLC (eluent: Et2O:DCM:hexanes = 1:1:30, Rf = 0.25) gave 0.2383 g (25%) of pure product. 185 1 H NMR (500 MHz, CDCl3): δ 7.49 (d, 4H, J = 7.5 Hz), 7.31 (d, 2H, J = 8.9 Hz), 7.18 (6H, m), 6.70 (d, 2H, J = 9.0 Hz), 6.66 (d, 1H, J = 3.1 Hz), 5.22 (d, 1H, J = 9.4 Hz), 4.87 (d, 1H, J = 9.5 Hz), 4.65 (d, 1H, J = 3.1 Hz), 4.43 (d, 1H, J = 11.1 Hz), 3.72 (s, 3H), 3.53 (s, 3H), 2.26-2.14 (m, 1H), 2.04-1.99 (m, 1H), 1.88-1.76 (m, 2H), 1.71-1.52 (m, 4H), 1.48 (s, 3H), 1.45 (s, 3H), 0.81 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 201.68, 158.29, 150.78, 145.63, 145.01, 139.42, 136.44, 135.41, 134.80, 134.38, 130.75, 128.67, 128.64, 128.40, 127.70, 127.63, 126.66, 126.60, 124.65, 112.93, 109.90, 87.45, 66.81, 55.07, 54.62, 49.15, 39.40, 37.99, 36.20, 30.29, 29.37, 25.57, 15.66, 15.05; HRMS + (TOF-ESI) calc’d for C39H42O4Na ([M+Na] ) 597.2981. Found: 597.2958; [α]D 20 = +74.6 (c = 0.435, CH2Cl2) 89% ee material. Preparation of macrocycle 226 O O ODMT Me OMe ODMT Me Grubbs II Toluene, 110 °C, 3h 224c OMe 226c A 500 mL round bottom flask was filled with nitrogen and compound 224c (0.71 g, 1.12 mmol) was added and diluted with 374 mL of dry toluene. The reaction mixture was nd brought to reflux. Then 2 Generation Grubbs Catalyst (Aldrich) (53mg, 0.062 mmol) was added as a solutionin 10 mL toluene by syringe. The reaction mixture was refluxed for 3 h. 186 The mixture was cooled to room temperature and filtered through silica gel (10 g) to remove the catalyst. Solvent was removed by rotory evaporator which gave yellow compound. Purification by preparative TLC (eluent: Et2O:DCM:hexanes = 1:1:30, Rf = 0.21) gave 441 mg, 0.729 mmol, (65%) of pure product. 1 H NMR (500 MHz, CDCl3): δ 0.85 (s, 3H), 1.48 (s, 3H), 1.51 (s, 3H), 1.55-1.75 (m, 4H), 1.80-1.95 (m, 2H), 2.00-2.10 (m, 1H), 2.15-2.35 (m, 1H), 3.57 (s, 3H), 3.75 (s, 3H), 3.76 (s, 3H), 4.47 (d, J = 11 Hz, 1H), 4.68 (d, J = 3 Hz, 1H), 4.89 (d, J = 9.5 Hz, 1H), 5.24 (d, J = 9.4 Hz, 1H), 6.70 (d, J = 3 Hz, 1H), 6.72-6.77 (m, 4H), 7.12-7.28 (m, 2H), 7.33 (m, 3H), 7.50-7.55 (m, 4H); 13 C NMR (125 MHz, CDCl3): δ 15.06, 15.67, 25.57, 30.21, 36.21, 38.00, 39.40, 54.64, 55.14, 66.69, 87.14, 109.91, 112.92, 124.65, 126.49, 127.18, 127.26, 127.68, 128.18, 129.14, 130.23, 130.40, 130.80, 134.38, 134.77, 135.44, 136.73, 137.26, 139.53, 145.83, 150.79, 158.19, 201.71. Preparation of alcohol 246 O OH OTIPS OTIPS MeMgCl OMe OMe 224d 246 Ketone 224d (0.77 g, 1.58 mmol) was dissolved in dry THF (33 mL) and cooled in an ice bath. Then an ethereal solution of MeMgBr (5.27 mL of 3 M solution, 15.8 mmol) was added dropwise and then the reaction mixture warmed to room temperature over 187 30 minutes. The reaction was quenched with ammonium chloride and the aqueous layer was separated and extracted with ethyl acetate (2x15 mL) and then the combined organic layer was dried with magnesium sulfate. The product was purified on silica gel with hexanes: EtOAc (10:1) giving 0.27 g (33.9% yield) 1 H NMR (500 MHz, CDCl3): δ 1.05 (m, 21 H), 1.20-1.25 (m, 3H), 1.30 (s, 3H), 1.40- 1.45 (m, 1H), 1.63 (s, 3H), 1.68 (s, 3H), 1.90-2.00 (m, 3H), 2.05-2.20 (m, 4H), 3.52 (s, 3H), 4.05 (s, 1H), 4.40 (s, 1H), 4.52-4.65 (m, 1H), 4.63 (s, 1H), 4.90-5.05 (m, 3H), 5.57 (s, 1H), 5.62 (d, J= 10 Hz, 1H), 5.85-5.92 (m, 1H) Deprotection of TIPS protecting group to obtain 246 O O OTIPS OH TBAF OMe OMe 221 246 A solution of the TIPS protected alcohol 221 (0.4889 g, 1.004 mmol) was dissolved in tetrahydrofuran (60 mL) and TBAF solution (2 mL, 2 M, 2.009 mmol) was added and the mixture was stirred for 15 hours. The reaction mixture was washed with water (50 mL), and then the aqueous phase was separated and washed with diethyl ether (2x40 mL) and then the combined organic phase was concentrated under reduced pressure. The product was purified on a silica gel column with Hexanes:EtOAc (from 10:1 to 5:1) giving product 246 0.2157 g (65% yield) 188 1 H NMR (500 MHz, CDCl3): δ 5.85 – 5.72 (m, 1H), 5.33 – 5.25 (m, 3H), 5.05 (d, J = 3.1 Hz, 1H), 5.04 – 4.93 (m, 2H), 4.62 (dtd, J = 27.9, 1.4, 0.7 Hz, 2H), 3.63 (s, 3H), 2.28 – 2.06 (m, 6H), 1.85 – 1.72 (m, 1H), 1.70 (d, J = 0.9 Hz, 3H), 1.68 – 1.62 (m, 3H), 1.54 (ddd, J = 12.8, 11.8, 4.3 Hz, 1H), 1.31 – 1.22 (m, 1H), 1.22 (s, 3H); 13 C NMR (125 MHz, CDCl3): δ 206.26, 150.18, 145.42, 139.40, 138.18, 138.09, 137.58, 124.61, 114.80, 110.95, 110.05, 66.89, 54.88, 49.93, 40.31, 38.88, 33.17, 32.00, 27.11, 22. 48, + 16.77; HRMS (TOF-ESI) calc’d for C21H31O3 ([M+H] ) 331.2273. Found: 331.2267. [α]D 20 = +50.6(c = 0.488, THF) on 89% ee material ) One-pot cyclohexadienone annulation and ring closing metathesis Cr(CO)5 OMe 134 O OTr + toluene OTr Me 60 °C, 0.01M Grubbs II 110 °C OMe 216a O 221a OTr Me OMe 226c Chromium carbene complex 134 (0.263 g, 0.764 mmol), ether 216a (0.3 g, 0.764 mmol) and 76 mL of dry toluene were put into flame-dried 250 mL Schlenk flask equipped with stopcock and magnetic stirrer. The mixture was deoxygenated by the freeze-thaw method (3 cycles). Then, without nitrogen filling, it was warmed to 60 °C and kept at that temperature for 21 h. Then 2 nd Generation Grubbs Catalyst (Aldrich) (17.6mg, 0.02 189 mmol) was added as a solution in 10 mL toluene by syringe . The resultant mixture was heated in the Schlenk flask at 110 °C for 3 hours. The mixture was cooled to room temperature and filtered through silica gel (10 g) to remove the catalyst. Solvent was removed by rotary evaporator which gave a yellow compound. Purification by preparative TLC (eluent: Et2O:DCM:hexanes = 1:1:30, Rf = 0.28) gave 0.184 g (42 %) of pure product. A small part of 226 was recrystallyzed from MeOH to get pure sample with mp 209-212 1 ºC. The H NMR and 13 C NMR data matched that given above for this compound. 190 BIBLIOGRAPHY 191 BIBLIOGRAPHY (1) Fatiadi, A. J. Synthesis 1976, 65. (2) Schlosser, M.; Christmann, K. F. Angew. Chem. Int. Ed. 1964, 3, 636. (3) Xiao, Y.; Wang, Z.; Ding, K. Chem. Eur. J. 2005, 11, 3668. (4) Corey, E. J.; Shibata, S.; Bakshi, R. K. J. Org. Chem. 1988, 53, 2861. (5) Xavier, L. C.; Mohan, J. J.; Mathre, D. J.; Thompson, A. S.; Carroll, J. D.; Corley, E. G.; Desmond, R. Org. Synth. 1997, 74. 192