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FINES will be charged if book is returned after the date stamped below. CONFORMATIONAL EFFECTS IN PHOTOCHEMICAL 5-HYDROGEN ABSTRACTION By Michael Anthony Meador A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry 1983 ABSTRACT CONFORMATIONAL EFFECTS IN PHOTOCHEMICAL 6-HYDROGEN ABSTRACTION by Michael Anthony Meador The photocyclization of various g-alkoxyphenyl ketones was investigated. This proceeds via the intramolecular abstraction of an alkoxy hydrogen by the excited carbonyl oxygen to give rise to a l,5-biradical which cyclizes to a substituted 3-hydroxy-2,3-dihydrobenzofuran; Compari- sons of the hydrogen abstraction rate constants, k“, for these ketones with those of appropriate 2,6-diacylalkoxy- benzenes reveals an excited state equilibrium between a reactive and an unreactive triplet conformer, involving rotation of the alkoxy group about the phenyl-oxygen bond. The considerably lower photocyclization quantum yield for g-benzyloxyacetophenone (ngZOAP) relative to that for g-benzyloxybenzophenone reflects the conformational re- quirements for biradical cyclization. The biradical is initially formed in a conformation favoring disproportion- ation. The C-OH fragment of the biradical must undergo a 90° rotation prior to cyclization. This rotation is Michael Anthony Meador restricted in the g—BZOAP biradical due to the demands of delocalization. The low quantum yield results from this restriction. The photocyclization of a series of a-(g-alkylphenyl)- acetophenones was studied. This involves formation of a l,5-biradical by intramolecular abstraction of an g-alkyl hydrogen by the excited carbonyl oxygen, which cyclizes to the corresponding 2-phenyl-2-hydroxyindane. In all cases, the photocyclization of these ketones is efficient and chemical yields are in excess of 95%. Comparison of the kH values for a-(g—tolyl)acetophenone and a-mesitylaceto- phenone reveals an excited state equilibrium between a reactive and an unreactive triplet conformer, arising from rotation of the a-phenyl ring. The unusually low maximum photocyclization quantum yield for a-mesitylacetophenone suggests a second mode of disproportionation, l,4-hydrogen transfer, which is unaf- fected by the addition of pyridine. To My Wife ii ACKNOWLEDGMENTS The author wishes to express his sincere gratitude to Professor Peter J. Wagner for his guidance throughout the course of this work. His insight, patience, good humor, and encouragement have made by graduate career both a pleasant and fruitful one. I will remember, with mixed emotions, the many trouncings received at his hands during our golf outings. I am grateful to the National Science Foundation and Michigan State University for financial support in the form of teaching and research assistantships. I wbuld also like to thank the Chemistry Department, its faculty and staff for the use of the excellent facilities and their assistance. I would also like to acknowledge Mrs. Peri- Anne Warstler for the fine typing Job. Appreciation is extended to Dr. J. C. Scaiano and the National Research Council of Canada-Chemistry Division for partial financial support and the use of the fine laser facilities while I completed the flash spectroscopy. Tito was a big help in unravelling many of the puzzles that were encountered along the way. A special thanks to my friends and colleagues at MSU for their friendship and help. Rich, Brian, Zebe, and iii the members of the Wagner group have given me a great many fond memories of MSU. I am also grateful to my parents, grandparents, and family for their love and support over the past few years. Most of all, I thank my wife, Mary Ann, for her love, good humor, and constant support which she gave even though she had her own research to complete. iv TABLE OF CONTENTS Chapter LIST OF TABLES. LIST OF FIGURES INTRODUCTION. . . . . . . RESULTS A. ggAlkoxyphenyl Ketones. 1. Identification of Photoproducts 2. Kinetic Results . . . 3. Spectroscopy. . . . . a. Phosphorescence Spectra b. Ultraviolet-visible Absorption Spectra . . . . . . . . . . . . c. Triplet- Triplet Absorption Spectra . . . . . . . . d. 13C - nmr Spectra B. a-(nglkylphenyl)acetophenones. 1. Identification of Photoproducts 2. Kinetic Data. . . . . . . 3. Spectroscopy. a. Phosphorescence Spectra . . b. Ultraviolet-Visible Absorption Spectra . . . . . . DISCUSSION A. g-Alkoxyphenyl Ketones 1. Determination of Meaningful Hydrogen Abstraction Rate Constants Page . viii .xxiii 3O 3O 30 A3 53 53 53 53 6A 6A 614 66 69 69 69 74 Chapter Page a. Steric Effects on Energy Transfer Quenching. . . . . . . . . . 7A b. Contribution of Triplet Decay to the Overall Triplet Lifetime . . . 80 2. Structure - Reactivity Relationships. . . 86 3. Conformational Effects. . . . . . . . . . 87 Evidence for a 1,5-Biradica1 Intermediate. . . . . . . . . . . . . . . . . 105 B. a-(g—Alkylphenyl)acetophenones. . . . . . . . 119 1. Hydrogen Abstraction Rate Constants . . . . . . . . . . . . . . . . 119 2. Glimpses of a 1,5-Biradical Intermediate. . . . . . . . . . . . . . . 121~ 3. Substituent Effects on the Photo- reactivity of a-(o- Alkylphenyl)- acetophenones . . . . . . . . . . . . . 124 A. Mechanistic Implications. . . . . . . . . 125 5. Entropic and Enthalpic Differences Between y- and d-Hydrogen Abstraction . . 132 6. a-(o-Tolyl)acetone and a-(o- Tolyl)acetaldehyde. . . . . . . . . . . . 133 C. Conclusions . . . . . . . . . . . . . . . . . 13A 1. o—Alkoxyphenyl Ketones. . . . . . . . . . 13A 2. a-(g-Alkylphenyl)acetOphenones. . . . . . 135 D. Suggestions for Further Research. . . . . . . 137 1. Laser Detection of 1,5-Biradicals from a-(o-Alkylphenyl)acetophenones . . . 137 2. Synthetic Applications of 6- -Hydrogen Abstraction . . . . . . . . . 139 3. e-Hydrogen Abstraction. . . . . . . . . . 1A0 A. Photochemistry of l-(ogAlkylphenyl)- 1,2-Propanediones and Related Compounds . . . . . . . . . . . . . . . . 141 vi Chapter Page EXPERIMENTAL. . . . . . . . . . . . . . . . . . . . . 143 A. Preparation and Purification of Chemicals . . . . . . . . . . . . . . . . . . 143 1- Solvents and Additives. . . . . . . . . . 143 2. Internal Standards. . . . . . . . . . . . 145 3. Quenchers . . . . . . . . . . . . . . . . 146 4. Ketones . . . . . . . . . . . . . . . . . 146 5. Equipment and Procedures. . . . . . . . . 183 a. Photochemical Glassware . . . . . . . 183 b. Sample Preparations . . . . . . . . . 184 c. Degassing Procedures .. . . . . . . . 184 d. Irradiation Procedures. . . . .3. . . 184 e. Laser Flash Spectrosc0py. . . . . . . 185 f. Analysis Procedures . . . . . . . . . 186 g. Calculation of Quantum Yields . . . . 187 6. Sensitization Studies . . . . . . . . . . 190 B. Isolation and Identification of PhotOproducts . . . . . . . . . . . . . . . . 193 APPENDIX. . . . . . . . . . . . . . . . . . . . . . . 207 REFERENCES. . . . . . . . . . . . . . . . . . . . . . 270 vii Table LIST OF TABLES Photokinetic Data for a Series of Methyl ngryloxyphenyl Glyoxylates. The Effects of PYridine on the Quantum Yields for Photoproduct Formation from grBenzyloxyacetophenone in Benzene at 25°C. . . . . . . The Effects of Pyridine on the Quantum Yields for g and E Photoproducts from gyBenzyloxybenzophenone in Benzene at 25°C. . . . The Effect of Pyridine on the Photo— cyclization Quantum Yield of ofMethoxy- benzophenone in Benzene at 25°C Results of Stern-Volmer Quenching of Various Alkoxyphenyl Ketones with 2,5- Dimethy1-2,4-Hexadiene in Benzene at 25°C. . . . . . Kinetic Data Measured for Some 97 Alkoxyphenyl Ketones in Benzene by Laser Flash Spectroscopy. viii Page 14 41 42 43 46 49 Table Page 7 Kinetic Data Measured for Some 2- Alkoxyphenyl Ketones in Methanol by Laser Flash SpectrOSCOpy. . . . . . . . . . . 50 8 Rate Constants for the Energy Transfer Quenching of Some Phenyl Ketone Trip- lets by Various Dienes in Benzene and Methanol at 27°C. . . . . . . . . . . . . . . 51 9 Arrhenius Parameters for the Energy Transfer Quenching of 2-Keto-2,3-Para- cyclophane and p-MethdxyacetOphenone with Various Quenchers in Methanol. . . . . . 52 10 Arrhenius Parameters for Triplet Decay of Various g-Alkoxyphenyl Ketones in Chlorobenzene and Methanol. . . . . . . . . . 54 11 Triplet Energies of Various o—Alkoxy- phenyl Ketones in EPA and 2-Methyl- tetrahydrofuran at 77°K . . . . . . . . . . . 59 12 Ultraviolet-Visible Absorbtion Maxima for a Series of ofAlkoxyphenyl Ketones in Heptane. . . . . . ... . . . . . . . . . . 61 13 13c Chemical Shifts for the Alkoxy Car- bon and Carbonyl Carbon in Various 0- Alkoxyphenyl Ketones. . . . . . . . . . . . . 65 14 Kinetic Data for Various a-(g-Alkyl- phenyl)acet0phenones in Benzene at 25°C . . . 68 ix Table Page 15 Triplet Energies of Various a-(g—Alkyl- pheny1)acetophenones in EPA and 2-Methy1- tetrahydrofuran at 77°K . . . . . . . . . . . 72 16 Ultraviolet-Visible Absorbtion Maxima for Various a-(g-Alkylphenyl)aceto- phenones in Heptane . . . . . . . . . . . . . 73 17 Kinetic Data Measured for Some 9- Alkoxyphenyl Ketones in Benzene by Laser Flash Spectroscopy. . . . . . . . . . . 76 18 Rate Constants for the Energy Transfer Quenching of the Triplet Lifetime of 2-Keto 2,2-Paracyclophane with Various Triplet Quenchers in Benzene and Methanol at 27°C. . . . . . . . . . . . . . . 78 19 Arrhenius Parameters for the Energy Transfer Quenching of Triplet 2-Keto- 2,2-Paracyclophane and AcetOphenone by Various Triplet Quenchers in Chloro- benzene and Methanol. . . . . . . . . . . . . 79 2O Kinetic Results of Laser Flash Spec- trOSCOpy on a Series of g-Alkoxyphenyl Ketones in Benzene at 25°C. . . . . . . . . . 82 21 Calculated kH Values for Some g-Alkoxy- phenyl Ketones in Benzene at 25°C . . . . . . 84 Table Page 22 Hydrogen Abstraction Rate Constants for 2,6-Diacyla1koxybenzenes and Cor— responding nglkoxyphenyl Ketones in Benzene at 25°C . . . . . . . . . . . . . . . 97 23 130 Chemical Shifts of the Alkoxy Car- bons of Substituted Anisoles. . . . . . . . . 101 24 Excited State Equilibrium Constants for nglkoxyphenyl Ketones in Benzene at 25°C . . . . . . . . . . . . . . . . . . . 104 25 Lifetimes of Some Norrish Type II Bi- radicals. . . . ... . . . . . . . . . . . . . 108 26 Effects of PYridine on Photoproduct Quantum Yields from o-Benzyloxyaceto- phenone in Benzene at 25°C. . . . . . . . . . 111 27 Effects of Pyridine on the Photo- cyclization Quantum Yields for of Benzyloxybenzophenone in Benzene at 25°C. . . . . . . . . . . . . . . . . . . . . 114 28 Effects of Pyridine on the Photocycliza- tion Quantum Yield for geMethoxybenzo— phenone in Benzene at 25°C. . . . . . . . . . 115 29 Photokinetic Parameters for a Series of a-(nglkylphenyl)acetophenones in Benzene at 25°C . . . . . . . . . . . . . . . 120 30 Gas Chromatographic Response Factors for Various Photoproducts . . . . . . . . . . 188 xi Table 31 32 33 34 35 36 37 38 39 Page HPLC Response Factors for Various Photo- Products. . . . . . . . . . . . . . . . . . . 189 Quenching of ngenzyloxyacetOphenone with 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . . . . . . 208 Quenching of ggBenzyloxyacetophenone with 2,5-Dimethy1-2,4-Hexadiene in Ben- zene at 25°C. . . . . . . . . . . . . . . . 209 Quantum Yield Determination for Photo- products from ngenzyloxyacetophenone in Benzene at 25°C. . . . . . . . . . . . . 210 Quenching of ngenzyloxyacetophenone in Benzene Containing 1.02 M Pyridine with 2,5—Dimethy1-2,4-Hexadiene at 25°C . . 211 Effects of Pyridine on Photoproduct Quantum Yield for ngenzyloxyacetophenone in Benzene at 25°C. . . . . . . . . . . . . 212 Quenching of g-Benzyloxybenzophenone in Benzene with 2,5-Dimethyl-2,4-Hexadiene at 25°C . . . . . . . . . . . . . . . . . . 213 Quenching of ggBenzyloxybenzophenone with 2,5-Dimethy1-2,4—Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . 213 Quantum Yield for Photoproduct from of Benzyloxybenzophenone in Benzene at 25°C. . 214 xii Table 40 41 42 43 44 45 46 47 48 Page Quantum Yield for Photoproduct from ggBenzyloxybenzophenone in Benzene at 25°C. . . . . . . . . . . . . . . . . . . . 214 Quenching of ngenzyloxybenzophenone with ggOctyl Mercaptan in Benzene at 25°C. . . . 215 Quenching of ggBenzyloxybenzophenone with geOctyl Mercaptan in Benzene at 25°C. . . . . . . . . . . . . . . . . . . . 215 Quenching of gBenzyloxybenzophenone by 2,5-Dimethy1-2,4-Hexadiene in 1,4— Dioxane at 25°C . . . . . . . . . . . . . . 216 Quenching of ggBenzyloxy-5-Methylbenzo- phenone by 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C. . . . . . . . . . . . . 217 Quenching of g—Benzyloxy-5-Methy1benzo- phenone in Benzene with 2,5-Dimethy1-2,4- Hexadiene at 25°C . . . . . Quenching of 2,2'-Dibenzyloxybenzo- phenone with 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C. . . . . . . . . . . . . 219 Quenching of 2,2'-Dibenzyloxybenzo- phenone with 2,5-Dimethy1—2,4—Hexadiene in Benzene at 25°C. . . . . . . . . . . . . 220 Quenching of g—Methoxybenzophenone with 2,5-Dimethyl-2,4-Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . . . . . 221 xiii Table Page 49 Quenching of ngethoxybenzophenone with 2,5-Dimethyl-2,4—Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . . . . . 222 50 Quantum Yield for Photoproduct from g- Methoxybenzophenone in Benzene at 25°C. . . . 223 51 Quenching of o—Benzyloxyvalerophenone with 2,5-Dimethyl-2,4—Hexadiene in Ben— zene at 25°C. . . . . . . . . . . . . . . . . 224 52 Quenching of geBenzyloxyvalerophenone with 2,5-Dimethyl-2,4-Hexadiene in Ben- zene at 25°C. . . . . . . . . . . . . . . . . 225 53 Quenching of geBenzyloxyvalerophenone with 2,5-Dimethy1-2,4—Hexadiene in Benzene at 25°C. . . . . . . . . . . . . . . . . . . . 226 54 Effects of Pyridine on Quantum Yield for gebenzyloxyacetophenone Formation from g—Benzyloxyvalerophenone in Benzene at 25°C . . . . . . . . . . . . . . . . . . 227 55 Quenching of 2,6-Dibenzoylbenzyloxy- benzene in Benzene with 2,5-Dimethyl-2,4— Hexadiene at 25°C . . . . . . . . . . . . . 228 56 Quenching of 2,6-Dibenzoloxybenzene in Benzene with 2,5-Dimethy1-2,4-Hexadiene at 25°C . . . . . . . . . . . . . . . . . . 229 xiv Table Page 57 Quenching of 2,6-Diacety1benzyloxy- benzene with 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C. . . . . . . . . . . . . 230 58 Quenching of 2,6-Diacety1benzyloxy- benzene in Benzene with 2,5-Dimethy1- 2,4-Hexadiene at 25°C . . . . . . . . . . . 231 59 Quenching of 2,6-Dibenzoylanisole with 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . . . . . 232 60 Quenching of 2,6-Dibenzoy1anisole with ' 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . . . . . 233 61 Quantum Yield for Photoproduct Formation from 2,6-Dibenzoy1anisole in Benzene at 25°C . . . . . . . . . . . . . . . . . . 234 62 Quenching of a-(g—Toly1)acetophenone with 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . 235 63 Quenching of a-(g-Toly1)acetophenone with 2,5-Dimethyl-2,4-Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . 236 64 Quenching of a-(2,5-Dimethy1pheny1) acetophenone with 2,5-Dimethy1-2,4- Hexadiene in Benzene at 25°C. . . . . . . . 237 XV Table Page 65 Quenching of a-(2,5-Dimethy1phenyl) acetophenone with 2,5-Dimethy1—2,4- Hexadiene in Benzene at 25°C. . . . . . . . 238 66 Quenching of o-Mesitylacetophenone with 2,5—Dimethy1-2,4-Hexadiene in Benzene at 25°C. . . . . . . . . . . . . . . . . . . . 239 67 Quenching of a-Mesitylacetophenone with 2,5-Dimethy1-2,4-Hexadiene in Benzene at 25°C . . . . . . . . . . . . . . . . . . 240 68 Quantum Yield for Photoproduct from a-Mesitylacetophenone in Benzene at 25°C. . . . . . . . . . . . . . . . . . . . 241 69 Effects of Pyridine on Quantum Yield for Photoproduct from a-Mesitylaceto- phenone in Benzene at 25°C. . . . . . . . . 241 70 Quenching of a-(2,5-Diisopropy1phenyl)- acetophenone with 2,5-Dimethy1-2,4- Hexadiene in Benzene at 25°C. . . . . . . . 242 71 Quenching of a-(2,5-Diisopropy1phenyl)- acetophenone in Benzene with 2,5-Di- methyl-2,4-Hexadiene at 25°C. . . . . . . . 243 72 Quenching of a-(2,4,6-Triisopr0py1pheny1)- acetOphenone with 2,5-Dimethyl-2,4- Hexadiene in Benzene at 25°C. . . . . . . . 244 xvi Table Page 73 Quenching of a-(2,4,6-TriiSOpropy1- pheny1)acetophenone with 2,5-Dimethy1- 2,4-Hexadiene in Benzene at 25°C; . . . . . 245 74 Sensitization of the Cis-Trans Iso- merization of cis-Piperylene with g: Benzyloxyacetophenone in Benzene at 25°C. I 0 o o o o o o o o o o o o o o o o o 246 75 Sensitization of Cis-Trans Isomeriza- tion of cis-Piperylene with g-Benzyl- oxyacetophenone in Benzene at 25°C. . . . . 247 76 Sensitization of Trans-Cis Isomeriza- tion of trans-Stilbene with g-Benzyloxy- benZOphenone in Benzene at 25°C . . . . . . 248 77 Sensitization of Trans-Cis Isomeriza- tion of trans-Stilbene with g—Benzyl- oxybenzophenone in Benzene at 25°C. . . . . 249 78 Determination of kq for g—Benzyloxy- acetophenone and 2,5-Dimethy1-2,4- hexadiene in Benzene at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 250 79 Determination of kq for geBenzyloxy- acetophenone and 2,5-Dimethy1-2,4-Hexa- diene in Benzene at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . . . . 250 xvii Table 80 81 82 83 84 85 Page Determination of kq for geBenzyloxy- benzophenone and 2,5-dimethy1-2,4- hexadiene at 27°C in Benzene by Laser Flash Spectroscopy. . . . . . . . . . . . . 251 Determination of kq for o-Benzyloxy- valerophenone with 2,5-Dimethy1-2,4- hexadiene in Benzene at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 251 Determination of kq for 2,2'-Dibenzy1- oxybenzophenone with 2,5-Dimethy1-2,4- hexadiene in Benzene at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 252 Determination of kq for 2,6-Dimethoxy- benzophenone with 2,5-Dimethyl-2,4- hexadiene in Benzene at 27°C by Laser Flash Spectrosc0py. . . . . . . . . . 252 Determination of kq for ggMethoxybenzo- phenone with 2,5-Dimethyl-2,4-hexadiene in Benzene at 27°C by Laser Flash Spec- troscopy. . . . . . . . . . . . . . . . . . 253 Determination of kg for geMethoxy- benzophenone and 2,5-Dimethy1-2,4- Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 253 xviii Table Page 86 Determination of kq for 2,6-Dimethoxy- benzophenone and 2,5-Dimethyl-2,4— Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. . . . . . . . . . 254 87 Determination of kq for 2,2'-Dibenzyl- oxybenzophenone and 2,5-Dimethyl-2,4- Hexadiene in Methanol at 27°C by Laser Flash Spectrosc0py. . . . . . . . . . . . . 254 88 Determination of kq for g-Benzyloxy-S- Methylbenzophenone and 2,5;Dimethy1- 2,4-Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. . . . . . . . . . 255 89 Determination of kq for ggBenzyloxy- benzophenone and 2,5-Dimethy1-2,4-Hexa- diene in Methanol at 27°C by Laser Flash Spectrosc0py. . . . . . . . . . . . . 255 90 Determination of kq for g-Benzyloxy- acetophenone and 2,5-Dimethy1-2,4- Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 256 91 Determination of kq for ngenzyloxy- valerophenone and 2,5-Dimethyl-2,4- Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 256 xix Table Page 92 Determination of kq for 2—Keto—[2,2]- Paracyclophane and 2,5-Dimethyl-2,4— hexadiene in Benzene at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 257 93 Determination of kq for 2-Keto-[2,2]- Paracyclophane and Methyl Naphthalene in Benzene at 27°C with Laser Flash Spectroscopy. . . . . . . . . . . . . . . . 257 94 Determination of k for 2-Keto-[2,2]- q Paracyclophane with Methyl Naphthalene in Benzene at 25°C by Laser Flash Spectroscopy. . . . . . . . . . . . . . . . 258 95 Determination of kq for 2—Keto—[2,2]- Paracyclophane and 1,3-Cyclooctadiene in Benzene at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . . . . 258 96 Determination of kq for 2-Keto-[2,2]- Paracyclophane and 2,5-Dimethyl-2,4— Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. . . . . . . . . . . . . 259 97 Determination of kq for 2-Keto-[2,2]- Paracyclophane and 1,3-Cyclooctadiene in Methanol at 27°C by Laser Flash Spectrosc0py. . . . . . . . . . . . . . . . 259 XX Table 98 99 100 101 102 103 104 105 106 107 108 Page Arrhenius Data for kq from 2-Keto-[2,2]- Paracyclophane and 2,5-Dimethy1-2,4- Hexadiene in Methanol . . . . . . . . . . . 260 Arrhenius Data for kq from 2-Keto-[2,2]— Paracyclophane and 1,3-Cyclooctadiene in Methanol . . . . . ; . . . . . . . . . . 260 Arrhenius Data for 1.1 for 2,6-Di- methoxybenZOphenone in Benzene. . . . . . . 261 Arrhenius Data for 1’1 from 2,6-Di- methoxybenZOphenone in Chlorobenzene. . . . 261 Arrhenius Data for geMethoxybenzophenone in Chlorobenzene. . . . . . . . . . . . . . 262 Arrhenius Data for geMethoxybenzophenone in Methanol . . . . . . . . . . . . . . . . 262 Arrhenius Data for g—Benzyloxybenzo- phenone in Chlorobenzene. . . . . . . . . . 263 Arrhenius Data for ngenzyloxybenzo- phenone in Methanol . . . . . . . . . . . . 263 Arrhenius Data for g-Benzyloxyaceto- phenone in Chlorobenzene. . . . . . . . . . 264 Arrhenius Data for geBenzyloxyaceto- phenone in Methanol . . . . . . . . . . . . 264 Arrhenius Data for geBenzyloxyvalero- phenone in Chlorobenzene. . . . . . . . . . 265 xxi Table Page 109 Arrhenius Data for o—Benzyloxyvalero- phenone in Methanol . . . . . . . . . . . . 265 110 Arrhenius Data for o—Benzyloxy-S- Methylbenzophenone in Chlorobenzene . . . . 266 111 Arrhenius Data for o—Benzyloxy-S- Methylbenzophenone in Methanol. . . . . . . 266 112 Arrhenius Data for 2,2'-Dibenzyloxy- benZOphenone in Chlorobenzene . . . . . . . 267 113 Quenching of a-(ggBenzyloxypheny1)- acetophenone with 2,5-Dimethy1-2,4- Hexadiene in Benzene at 25°C. . . . . . . . 268 114 Quenching of a-(g-Benzyloxypheny1)- acetophenone with 2,5-Dimethyl—2,4- Hexadiene in Benzene at 25°C. . . . . . . . 269 xxii Figure 1a lb LIST OF FIGURES A Jablonski diagram depicting the photophysics of an excited state molecule. . . . . Valence bond representations of the n,n* and n,n* ketone triplets Monitoring the photocyclization of o- benzyloxybenz0phenone in d6-benzene by lH-nmr. . . . . . . . The mass spectrum of 2,3-dipheny1—3- hydroxy-2,3-dihydrobenzofuran Mass spectrum of the product arising from the treatment of the crude photoly- sate from o-benzyloxybenzophenone with hydrochloric acid . Mass spectrum of "authentic" 2,3-di- phenylbenzofuran. . . . . . . . The phosphorescence spectrum of o- benzyloxyacetophenone in 2-methy1tetra- hydrofuran at 77°K. . . . . The phosphorescence spectrum of o- benzyloxybenzophenone in 2-methyl- tetrahydrofuran at 77°K . xxiii Page 33 36 37 38 55 56 Figure 10 ll 12 13 14 15 16 The phosphorescence spectrum of 2,6- dimethoxybenzophenone in 2-methy1- tetrahydrofuran at 77°K . . . . . . The phosphorescence spectrum of 2,6-di- benzoylanisole in 2-methyltetrahydrofuran at 77°K . Triplet-triplet absorption spectrum of 2-methoxybenzophenone in benzene The triplet-triplet absorption spectrum of 2,6-dimethoxybenzophenone in benzene 250 MHz lH-nmr spectrum of 2-phenyl-2- hydroxyindane in CD013. The phosphorescence spectrum of a- (gftolyl)acetophenone in 2-methyltetra- hydrofuran at 77°K. . . . The phosphorescence spectrum of a- mesitylacetophenone in 2-methy1tetra— hydrofuran at 77°K. Stern-Volmer plot for the quenching of gebenzyloxybenzophenone with 2,5-di- methyl-2,4-hexadiene in benzene at 25°C. . . . . Stern-Volmer plot for the quenching of ‘g-methoxybenzophenone with 2,5-dimethy1- 2,4-hexadiene in benzene at 25°C. xxiv Page 57 58 62 63 67 70 71 88 89 Figure 17 Page Stern-Volmer plot for the quenching of g-benzyloxyacetophenone with 2,5—di- methyl-2,4-hexadiene in benzene at 25°C. . . . . . . . . . . . . . . . . 90 XXV INTRODUCTION Ketone photochemistry has occupied the mainstream of organic photochemistry from its infancy, just as carbonyl chemistry has been in the forefront of organic chemistry. A great deal of knowledge concerning the behavior of excited state carbonyl compounds has been compiled over the years. The study of the photochemistry of carbonyl compounds has helped in the understanding of very fundamental questions in photochemistry, but a great many questions remain un- answered. In that sense, ketone photochemistry, and photo- chemistry itself, is still somewhat in its pioneering stage. A prerequisite to any discussion of photochemistry involves mention of the photOphysics and the nature of the excited states of the system under study. The photophysics of an excited state molecule is best described with the aid of a Jablonskil diagram. Initial absorption of light promotes an electron from the ground state, SO, to an upper excited singlet. For most organic molecules, electronic spins are paired in the ground state. Hence, it is a singlet, having a net elec- tronic spin of zero. The upper excited singlets usually 11_1014s-l)2 decay rapidly (kic = 10 via internal conversion to the lowest excited singlet. From here, the excited Figure la. A Jablonski diagram depicting the photophysics of an excited state molecule. molecule has a number of Options open to it. It can decay to the ground state, emitting a photon of light (fluores- cence). This process usually has a rate constant, kf, on 6 the order of 10 to 1095-1.2 Decay from the excited singlet to the ground state is also possible via radiationless de- cay, with a rate constant kd of from 105 to 108s-l.2 Chem- ical reactions can also occur from the excited singlet, giving rise to products. Finally, the excited singlet can undergo intersystem crossing to an excited triplet state. This proceeds with Spin inversion of an electron, resulting in parallel electronic spins of the two unpaired electrons. The triplet state has a net spin of one, and an overall spin multiplicity of three. Typical rate constants for 10 intersystem crossing, k are on the order of 107 to 10 - s'l.2 Direct population of the triplet state from the isc’ ground state, by absorption of light, is forbidden by spin selection rules. Hence, the intensity of such a transition is extremely low,3 but can be maximized with a laser. As is the case with the excited singlet, the excited triplet has a number of decay modes available to it. Radia- tive decay (phosphorescence) typically proceeds with a rate 1 to lous'l.2 Quenching of the trip— constant, kp, from 10- let state by energy transfer or electron transfer (charge transfer) can occur with a rate constant as high as the rate of diffusion in a given solvent (ilolOM-ls'l).u Triplet-triplet annihilation can occur if the triplets are formed in high enough concentrations, with a bimolecular rate constant close to diffusion.5 This is of particular concern in laser photochemistry. Finally, the triplet state can undergo chemical reactions which give rise to products. In ketones, phenyl ketones in particular, intersystem crossing is both rapid and efficient. The quantum yield for intersystem crossing in phenyl ketones is close to unity.6 The rate constant for intersystem crossing in 10 to 10115.1,7 con- phenyl ketones is on the order of 10 siderably faster than any other process that normally oc- curs from the excited singlet. Therefore, irradiation of a phenyl ketone results in an indirect population of the first excited triplet state. Almost all photochemical re- actions that occur from these compounds, then, arise from the triplet state. Phenyl ketones have two different low lying triplets: a n,n* triplet and an n,n* triplet. Common valence bond representations of these triplets are depicted in Figure 1b. '6:- xi: <—-> 3< R R O 053 ‘0} Figure u), Valence bond representations of the n,n* and n,n* ketone triplets. The (n,n*) triplet arises by promotion of an electron from a non-bonding orbital on the carbonyl oxygen to a n*-antibonding orbital of the aromatic system. The net effect is a slightly electron—deficient oxygen. This de- ficiency gives the n,n* triplet chemical behavior similar to that of an alkoxy radica1.6’8 Reactions arising from the n,n* triplet, then, are those expected of an alkoxy radical, with hydrogen abstraction being the most predominant. The n,n* triplet, on the other hand, arises from promo- tion of an electron from a n-bonding orbital to a n*-anti- bonding orbital. This can result in a shift of electron density from the aromatic n-system to the carbonyl oxygen, creating an electron rich oxygen. This shift can be seen in the middle resonance form for the 3(n,n*) in Figure 2. The n,n* triplet is less susceptible to nucleOphilic attack and radical reactions at the carbonyl oxygen than is the n,n* triplet. However, thermal equilibration6 and quantum mechanical mixing of the two triplets can occur if they are close enough in energy. As a result, ketones with a n,n* lowest triplet do undergo hydrogen abstraction to some extent, but not with the same efficiency as n,n* trip- 1ets.6’9 Ketones with an n,n* lowest triplet readily abstract hydrogen atoms from compounds having reactive hydrogens, e.g., alcohols, ethers, and some alkanes. This reaction was 10 first observed by Ciamician and Silber in the photolysis of benzophenone in ethanol. One of the products observed was benzpinacol, formed by coupling of benzophenone ketyl radicals (Reaction 1). +-CH 3 O 0 Ph m) Ph —-_> o ‘—-"'> R /U\R R/K? HO OH (1) CHOH Ph Intramolecular hydrogen abstraction is also possible. Perhaps the best known example of this is the Norrish Type 11 II reaction (Reaction 2). This reaction involves forma- tion of a 1,4-biradica1l2 via abstraction of a y-hydrogen by the excited carbonyl oxygen. The biradical can either cleave into a smaller ketone and an olefin, or cyclize to a cyclobutanol.ll’13 0H . O h (2) OH Ph Intramolecular hydrogen abstraction carries with it certain geometric constraints. The most obvious is that the hydrogen being abstracted must be physically accessible to the carbonyl oxygen. A good example of this requirement is seen in work reported by Breslow and Winnik.lu This report describes the intramolecular photochemical hydrogen abstrac- tion in a series of p-benzoylbenzoate esters of long chain alcohols (Reaction 3). For this system, there exists a direct correlation between the statistically predicted number of sites of attack on the alkyl chain and the experi- 14,15 mentally determined rate constants. There are a number of examples of conformational effects in ketone photochemistry. Lewis16 has investigated conforma- tional effects in the photochemistry of l-methylcyclohexyl phenyl ketone and a number of substituted analogues. Lewis reports that for l-methylcyclohexyl phenyl ketones, there exist two different ketone triplets each leading to dif- ferent photoproducts (Scheme 1). The ketone conformer with i HH hi isc Iv 5‘39 HO Ph “'9 . , ~\ :cn, Ph 3 * H0 P 1 hv isc \‘ Og—r ~CH3 Ph h 3 H3 - Ji\ CH 3 PhCHO -——4> -__’ d T O A ohv lisc A Ph Ph H L - Scheme 3 Another type of conformational effect, rotational con- trol, is found in the photoenolization of o-alkylphenyl ketones. Wagner and Chen18 have proposed a mechanism in- volving two kinetically distinct ketone rotamers, designated syn and §n§i_(Scheme 4). The short-lived syn triplet can enolize directly upon photolysis (kH = 1095-1). The Egg; triplet must first rotate (krot = 1075-1) into the syn 11 CH3 CH3 R R o IF€>' Exg anti lh‘l’ , isc \th , isc krot 107s"1 3(m) <——— 3(arici)* OH Scheme 4 conformer before enolization can occur. Flash spectroscopy 19 and Scaiano2O supports this mechanism. on this system by Wirz We envisioned that the photochemistry of ggalkoxyphenyl ketones might present another example of this type of rota- tional control. The photochemistry of ggbenzyloxyphenyl carbonyl compounds had been investigated by Pappas,2l"25 and by Lappin and Zannucci,26 but neither group reported ob- serving such conformational effects. These compounds pro- vide an example of photochemical 5-hydrogen abstraction (Reaction 4). 12 CH Ph CH Ph 1’ // ‘ Ph (4) OH This reaction was first observed by Pappas and Black- well21 for gfbenzyloxybenzaldehyde, l. Irradiation of 1 in acetonitrile gave rise to two photoproducts, which readily dehydrated upon treatment with hydrochloric acid to give 2-. phenylbenzofuran. Spectroscopic data revealed the struc- tures of the two photoproducts as g and E - 2—pheny1—3- hydroxy-2,3-dihydrobenzofuran (g and 3 respectively),2l’22 (Reaction 5). [H A more extensive investigation of this reaction, under— 23-25 taken by Pappas, concerns the photochemistry of a series 13 of methyl gfiaryloxyphenyl glyoxylates, 6, (Reaction 6) Again, two isomeric 3-hydroxy-2,3-dihydrobenzofurans, 6 and 6, result from the photolysis of 6. Ph OH O IO\ The stereoselectivity of this reaction is influenced by temperature. For example, in acetonitrile the ratio of 6 to 6 decreases slightly when the reaction temperature is raised from -35°C to 80°C (6:6 = 2.5:1 at —35°C, 6:6 = 1.5:1 at 80°C). A more dramatic example of this was found in heptane when the relative yields of 6 and 6 were measured at 0°C and 100°C. The ratio of 6:6 decreased from 20:1 to 3:1 over this temperature range. This indicates that isomer 6, in which the phenyl and carbomethoxy groups are trans, is the kinetically preferred product. This isomer would also be the thermodynamically preferred product since the two bulkiest groups, phenyl and carbomethoxy, are trans to each other. The stereoselectivity of this reaction also depends on the polarity of the reaction medium (Table l). The relative 14 Table 1. Photokinetic Data for a Series of Methyl ngryloxy- phenyl Glyoxylates.24 CH :r 0” 2A 0 l o 0 Ar 0 “(N O . OH E : cl. 4 Ar = Ph mg Ar = p-CH Ph g Q 6' Ar = p-Cl h ompound Solvent 6/6 ¢§+§ T , 10 s 66 t-BuOH 1.0 (35°C) 0.47 1.3 CH3CN 2.2 (35°C) 0.56 3.7 C6H6 6.7 (35°c> 0.89 u.3 C6H6 14.6 (0°C) -——- --- 66 C6H6 16.0 (0°C) 0.69 3.5 66 C6H6 21.2 (0°C) 0.78 2.1 66-dl CH3CN 2.1 (35°C) 0.52 --- C6H6 7.2 (35°C) 0.86 --- 66-d2 CH3CN 1.9 (35°C) 0.41 --- C6H6 To” (35°C) 0.81 ——- 15 yields of 6 and 6 in benzene are 6.7:1 while they are 1:1 in acetonitrile. Quenching of greater than 80% of the reaction by the ad- dition of 1,3-pentadiene, a known triplet quencher, does not alter the relative yields of 6 and 6. This demonstrates that both photoproducts are formed from the same triplet. Pappas also observed a slight sensitivity of the recipro- cal triplet lifetime to the nature of the aryloxy substi- tuent, e.g., Q6 and 66. Decreases in the photoproduct quantum yield and in the reciprocal triplet lifetime of glyoxylate 66 were observed in polar solvents, such as t-butyl alcohol, versus non- polar solvents. Pappas suggests two possible explanations for such behavior. The first is that t-butyl alcohol sol- vates the hydroxyl group of the biradical and presents a steric barrier to cyclization (Scheme 5). This steric bar- rier is reflected in the decreased photoproduct quantum yield for 66. The same type of behavior has been observed for valero— phenone. Wagner27 reports that added t-butyl alcohol in- creases the quantum yield for acetophenone formation in the photolysis of valerophenone, 7. However, the quantum yield of cyclobutanol products, 9, is decreased in the presence of t—butyl alcohol. Solvation of the biradical, 6, suppresses reverse hydrogen abstraction in the biradical to reform starting ketone. At the same time, this solvation increases on . 0 U by A; 6'— o : ph -H Ph Ph 3 P /C}12PhO/CH"Ph OH ”0030 ha) fillllII[:;:gi‘;;% Scheme 5 the steric barrier to cyclization, thereby lowering the yield of cyclobutanols (Scheme 5). This observation, however, does not explain the decreased reciprocal triplet lifetime in t-butyl alcohol. It is pos- sible that the energies of the n,n* and n,n* triplets of the glyoxylate are inverted in polar solvents. Pappas reports25 a shift in the triplet energy of 66 from 62 to 67kcal/ mole in isopentane and EPA glasses, respectively. This shift, he suggests, is indicative of compounds with an 28 Wagner29 has observed that the trip- n,n* lowest triplet. let lifetimes of pfmethoxyvalerOphenone and pymethylvalero- phenone are longer in polar solvents, indicative of a stabilization of the less reactive n,n* triplet. Pappas suggests that the same type of stabilization may occur for 17 glyoxylate 66 in t-butyl alcohol thereby lowering the recip- rocal triplet lifetime of this compound. Pappas reports that there is essentially no isotope ef- fect on the photocyclization of glyoxylate 66. Wagner30 has reported an isotope effect, kH/kD of 4.8 for y-hydrogen abstraction by nonanophenone in benzene. Therefore, the lack of an isotope effect for d-hydrogen abstraction in glyoxylate 66 suggests that hydrogen abstraction is not the rate determining step in the overall mechanism for the photo- cyclization of this compound. 26 have investigated the photochemistry Lappin and Zannucci of 2—benzyloxy-4-dodecyloxybenzophenone, 66, and report the formation of 2-hydroxy-4-dodecyeloxybenzophenone, 11, in addition to the expected photocyclization products, 6% (Re- action 7). Cfiémi O 0 OH O I | Ph hi 'h ——-> R0 39 no ;_1_ R (7) 18 This hydroxybenzophenone probably arises from a photo- Fries rearrangement involving cleavage of the benzyloxy C-O bond. Similar behavior has been observed for a number of alkoxybenzenes (Scheme 6). For example, benzyl phenyl o o H OCH Pb 0' CH Ph 43’ + 'CH Ph 5 w 2 ____—e’ 2 l CHZPh 1 m3 CHéHi 0H CSZPh CH \3” 0 00 00H3 0 O —* - ”O H . CH3 3 CH3 Scheme 6 l9 ether photochemically rearranges to both 2- and 4-benzy1- phenol via initial cleavage of the benzyloxy C-O bond fol- lowed by recombination of the resulting benzyl and phenoxy radicals. Leary and Oliver310 have reported that the same cleavage occurs for both 2,5—dimethoxyben20phenone and 2,4,6-trimethoxybenzophenone in carbon tetrachloride to produce the corresponding 2-hydroxybenzophenones. The same photocleavage is also observed for g—methoxybenzo- phenone both in carbon tetrachloride solutions and in the 310 31d report that irradia- solid state. Jones and Sullivan tion of 2-allyloxyacetophenone in methanol gives rise to 2-methoxyacetophenone in 12% yield, as well as the expected 3-methy1—2-vinylbenzofuran (1% yield). Cleavage of the allyloxy C-O bond, followed by interception of the result- ing phenoxy radical by methanol would give rise to 2- methoxyacetophenone (Scheme 6). Prolonged irradiation of 2-benzyloxy—4-dodecycloxy- benzophenone also produced 2,3-dipheny1benzofuran, l3, (presumably as a secondary photoproduct arising from the photochemical dehydration of 3-hydroxy-2,3-dihydrobenzo- 26 furan, 62) in 64% yield (Reaction 7). Photolysis of 2-is0propoxy-4-methoxybenzophenone,26 66, produced the expected benzofuranols, l6, 2-hydroxy-4- methoxybenzofuran, $6, and 2,2-dimethyl-4-phenyl-8-methoxy- 1,3-benzodioxane, 61 (Reaction 8). 20 P o 0 OH OH 0 3!. Ph Ph + + ‘15 CH 0 3 $6, CH30 12 Solvent 6 g 12 R Cyclohexane 0.26 0.15 Acetonitrile 0.023 0.005 hv CH O 3 1i ph OH Irradiation of 2,3-dimethyl-3-hydroxy-3-pheny1-2,3-di- hydrobenzofuran, 66, produced 2-hydroxy-4—methoxybenzo- phenone, 66, indicating that 66 is formed as a secondary photOproduct from 16. The benzodioxane, 61, is not formed as a secondary photo- product. Lappin is unable to provide a definite mechanism for its formation, but suggests that it may be formed as the product of a bimolecular reaction between ketone 66 and its 21 biradical. Another plausible mechanism involves cycliza-' tion of the biradical to a spiro epoxide which rearranges to the observed benzodioxane, 67 (Scheme 7). .— 0 ____,h" CH 0 OH CH30 3 - Scheme 7 Both Lappin and Pappas report rate constants for hydro- gen abstraction in g-benzyloxyphenyl carbonyl compounds on the order of 1075-1. Wagner32 has reported a rate constant of 1-2 x 107s—l for photochemical hydrogen abstraction in B-ethoxypropio- phenone (Reaction 9). Turro and Lewis33 report rate constants for y-hydrogen abstraction in a series of a-alkoxyacetophenones in ben- zene on the order of 1093"1 (Reaction 10). 22 Ph Ph can a ~08 82 ‘10) ° 4 —->..j\ Ph,/JL\~/’ Ih//f\\.//£3 Ph1R2 Ketone Rl , R2 . ¢ k , 109s'1j *““‘ ——- —— t2 r . 18 a H H 0.42 3.2 18 b H CH3 0.59 8.4 18 c CH3 CH3 0.40 8.2 Intramolecular photochemical y-hydrogen abstraction has been found to be much faster in cyclic ketones than in 34 acyclic ones. This is due to an immobilization of the possible rotations involved in the formation of the six- center transition required for y-hydrogen abstraction.35 34 2-Benzoylnorborane requires about the same activation energy for hydrogen abstraction as valerophenone (3.6: 0.2 kcal/mole). However, the activation entropy for hydrogen abstraction in 2-benzoylnorborane is approximately 8 eu 23 more than for valerophenone (Scheme 8). Therefore, the rate enhancement observed for y-hydrogen abstraction in 2-benzoy1norborane is purely the result of easing the en- tropic requirements necessary for transition state forma- tion. As can be seen in Scheme 8, an approximate ten fold increase in the rate of hydrogen abstraction accompanies an immobilization of each carbon-carbon bond.3u’35 8 Phi 88-1 6.0 x 10 s'1 7 x 109s" kH 1.2x10 Scheme 835 In light of the results above, a comparison of B- ethoxypropiophenone and a-alkoxyacetophenones with 97 benzyloxyphenyl ketones provides an estimated rate constant 8 1 of at least 10 s' , ten times greater than what is reported! '£TQ%§M RH 107s."1 109$“1 10 s: Epredicted) observed) 24 One possible explanation for this discrepancy is sum- marized in Scheme 9. Scheme 9 The scheme shown is similar to that suggested by Wagner and Chen for gfalkylphenyl ketones.18 Hence, it is pos- sible that there are two different triplet rotamers for 35 benzyloxyphenyl ketones - a syn triplet, 3(265)*, and an 25 222$ triplet, 3(gga)*, 6-hydrogen abstraction can occur directly only from the nyn triplet. However, the 2221 triplet can give rise to hydrogen abstraction by first rotating to the nyn triplet. The rate constant for such a rotation has been measured by Wagner18 as 1078'1 for 97 alkylphenyl ketones. This is approximately the same value 21'25 and Lappin26 for the rate reported by both Pappas constant for d-hydrogen abstraction in nfbenzyloxyphenyl carbonyls! The object of the first portion of this thesis deals with the reexamination of the photochemistry of gfalkoxy- phenyl ketones with particular emphasis on elucidating any special conformational effects. Although it is not as common as y-hydrogen abstraction, photochemical d-hydrogen abstraction has been observed in a number of systems besides ngalkoxyphenyl carbonyl compounds. Bergmark36 reports that photolysis of 2,5-di-ngnn—butyl- acetophenone, 21, did not give rise to any detectable amounts of 2,5-di-nnnn-butylacetophenone, the expected photoproduct of y-hydrogen abstraction (Reaction ll). Bergmark suggests 'that a highly competitive d-hydrogen abstraction occurs to Ixroduce biradical 3%. This biradical does not cyclize, Fu?esumably for steric reasons, but rapidly disprOportionates tC> starting material. Bergmark cites the observation by Porter37 that the quantum yield for the photoreduction of 2-tert—butylbenzo- Phedflone in iSOpropanol is only half that of benzophenone. 26 He suggests that the same highly reversible a-hydrogen ab- straction is responsible for this decreased quantum yield. HO (CH2)30H3 In fact, O'Connell38 has reported such a o-hydrogen ab- straction for 2,4-di-tert-butyl-6-methoxybenzophenone fol- lowed by cyclization to l,l-dimethyl-Z-hydroxy-4-methoxy-2- phenyl-6—tert-butylindane (Reaction l2). qH 0H ' 2 Ph h, ‘ Ph Ph ——-) ——> (12) OCH3 OCH3 OCH? 27 Wagner32 has reported that both y-methoxyvalerophenone and y,y-dimethylvalerophenone readily undergo photochemical 0-hydrogen abstraction (Reactions l3, l4). OCH3 15 —->“ Ph CH3 0 h.” l .___——€> . ‘%> Eh U %‘(14) ‘ bH dHB A few years prior to Wagner's work on B—ethoxypropio- phenone, Stephenson and Parlett39 reported that both 4-methyl- 4-methoxy-2-pentanone, £36, and 4—methy1-4-ethoxy-2-pentanone, €36, undergo facile photochemical o-hydrogen abstraction to produce the corresponding 5-substituted-2,2,4-trimethyl- 4-hydroxytetrahydrofuran, 66 (Reaction 15). RH2GS\O z’u\\//k: h” 0 CH3 CH 3 g}, a HaH gg’ (15) b TECH ' 3 28 Aoyama and co-workersl4O have reported photochemical 6-hydrogen abstraction in a series of N,N-dialkyl-2-oxa- cycloalkylcarboxamides, 66, giving rise to the correspond- ing lactams, %6 (Reaction l6). (l6) Schlessinger and co-workersul have reported that l- benzoyl-8-benzylnaphtha1ene, 61’ undergoes 5-hydrogen ab- straction followed by cyclization to the corresponding alcohol, 66, in 91% yield (Reaction 17). Perhaps the most elegant application of photochemical' G-hydrogen abstraction was reported by Paquetteu2 in the total synthesis of dodecahedrane (Reaction 18). The second portion of this thesis will deal with a new example of photochemical 6-hydrogen abstraction found for 29 OH OH 9. .9 9' __> v29} v29} 52"" a series of d-(o-alkylphenyl)-acetophenones. Particular cemphasis will be placed on the conformational effects that manifest themselves in this reaction. Although a great deal has been published concerning the behavior of 1,4-biradicals, very little is known about 1,5-biradical behavior. This topic will be addressed in this thesis, in particular the behavior of 1,5-biradicals produced from o-alkoxyphenyl ketones. RESULTS A. o-Alkoxyphenyl Ketones 1. Identification of Photoproducts Irradiation of degassed 0.02 to 0.04 M benzene solu- tions of various gfalkoxyphenyl ketones at 313 nm produced the corresponding 2,3-disubstituted 3-hydroxy-2,3-dihydro- benzofurans (both E and g isomers) as the major photo- products (Reaction 19). E and g refer to the positions of the 2-substituent and the hydroxyl group. hv °5H6 jn3nm. (l9) Structural assignments were based upon spectral data obtained for these compounds (1H and 13C nmr, i.r., and 1H nmr proved particularly useful in mass spectrum). assigning the stereochemistries of the diastereomeric benzo- furanol photoproducts. Pappas22 has reported that the diastereomer of 2-methyl-3-phenyl-2,3-dihydrobenzofuran in which the phenyl and methyl substituents are cis has a 30 31 methyl signal at 0.74 ppm. The methyl group in the trans isomer appears at 1.37 ppm (Scheme 10). Pappas , O o O “'0“: CH 3 'h Ph 9 , 1.37 ppm- 80H 0.74 ppm 3 O O 5““ OH Ph 2.51mm. Lewis Ph H Ph CH3 H HO 3 H0 0.60 m 50H 1 .10 ppm. PP Scheme 10 32 Lewis and Hilliard”3 observed the same effect for the two diastereomers of 2—methy1-l-phenylcyclobutanols (Scheme 10). The same is also true for the hydroxyl proton in the two diastereomers of 2-phenyl-3-hydroxy-2,3- dihydrobenzofurans (Scheme 10). Pappas22 has found that the hydroxyl proton in the gin isomer is shielded and appears upfield of the hydroxyl proton of the EEEEE isomer. The stereochemical assignments of the dihydrobenzo- furanol photOproducts were based upon these considerations. Thus, the methyl group of E-2-pheny1-3-methy1-3-hydroxy- 2,3-dihydrobenzofuran (phenyl and hydroxyl are Ennnng phenyl and methyl are gin) appears upfield of the methyl group of the E isomer, because it is in the shielding cone of the benzene ring (Scheme 11). Similarly, the hydroxyl proton of the E isomer is shielded and appears upfield of the hydroxyl proton of the E isomer. Both the hydroxyl proton and C-2 proton of Z-2,3-dipheny1-3-hydroxy-2,3- dihydrobenzofuran are shielded by adjacent benzene rings and appear upfield of their respective signals for the E isomer (Scheme 11). In some cases, the benzofuran photoproducts were pro- duced in quantitative yields. In such instances, it was possible to monitor the progress of the photoreaction by l H nmr spectroscopy. An example of this is seen in Figure 2. In this experiment, a solution of o-benzyloxybenzophenone 33 \ -1 .L A “—4A AAA .A.‘ -4 vv—w— rvw-vv—rv—w—vr— v—y va v 1 - - l - L - l l L - - I 1 - 1 l 0 )0 I. I ‘l- . Ilulik . , ( -L ..lil . to Figure 2. Monitoring the photocyclization of ngbenzyl- oxybenzophenone in d6-benzene by lH-nmr. 34 88. 8 h 8C 8a 5.77 5.66 5b 2.62 1.95 Scheme 11 in d6-benzene was placed in a 5 mm nmr tube, degassed with a steady stream of nitrogen, and irradiated at 313 nm. As the reaction progressed, the methylene peak at 4.5 ppm was lost and replaced by the methine proton resonance of the photoproduct (5.5 ppm). The upper spectrum in Figure 12 corresponds to the reaction mixture at 100% ketone con- version. Treatment of this sample with deuterium oxide resulted in the disappearance of the singlet at 1.9 ppm, 35 confirming the presence of the hydroxyl group in the photoproduct. A number of these 3—hydroxy-2,3-dihydrobenzofuran photoproducts readily fragment in the mass spectrometer, with loss of water, as would be expected.uu An example of this can be seen in Figure 3, the mass spectrum of 2,3- dipheny1-3-hydroxy-2,3-dihydrobenzofuran (produced by the photolysis of nfbenzyloxybenzophenone). The base peak (M/e = 270) corresponds to the molecular weight of 2,3- diphenylbenzofuran. The 3-hydroxy-2,3-dihydrobenzofuran photoproducts readily dehydrate upon treatment with hydrochloric acid. 21 Thus, treatment The same behavior was observed by Pappas. of a sample of 2,3—diphenyl—3-hydroxy-2,3-dihydrobenzofuran with hydrochloric acid gave rise to a compound whose mass spectrum correlates well with that of an authentic sample of 2,3-diphenylbenzofuran (Figures 4 and 5). Irradiation of degassed samples of 2,6-diacylalkoxy- benzenes produced photoproducts which underwent secondary photoreactions. This is not surprising since these photo- products are themselves ggalkoxyphenyl ketones and would absorb strongly at 313 nm (Reaction 20). In cases where photoproduct quantum yields and triplet lifetimes were measured, ketone conversions were kept at 5 e 10% to mini- mize the possibility of such secondary reactions. The structures of these secondary photoproducts were not 36 .cmpsmonconoaphsfioum.mlmxoLGS£IMIH>CoSQHo|m.m Lo Sappooom name 029 .m opzwfim mom sum .mmm~_ uo~m .Km.¥tm£$ awn mmw com um“ can “ca maafivzdé mmm. mu .chqo nm— ow~ and 00— on mm: . ..L..-»_.L.. m. V C _ IV C .... k ..o.on _m ..@.oo~ uvmu u mwma macaw: mumu ”unmzcm mflumu + oanmmumu om\vo\m® rambowmm mmq: CDCIu-L 9.....1 - lluc €- 37 «num— .cfiom QHLOH:00pozS nufiz ococozaouconzxoazncoplm Eopm ouMmEHOpona bongo on» no phospmmnp on» Eopm wcfimfipm posooma one go Exppooam mmmz .: opswflm u~ . on w\: day W-HJ— ‘oLidpplp. .l. ... ..h...t _ To. 8 _ S E 8 _— m—— Nb 8" T m: I mmN . I r900 A r L . ; own {6.8— mmm: ... mwm. . 39....“- vwm— “gm .voNNn no; ma. .5“. 3.10 2&— + @06qu 3A3de own ...: wmqm mwm' «N "3.3 Schowam mm? 38 «mum .cmpzmoucmnamconafioam.m acaucmzusme mo Esauooam mmmz .m cndwfim own nmw ohm .o~m- .u~¢ 0mm aux: mmcm 8N mm" mum Now ma— 2N mm— m. .36 3.10 mm: m" ”3.3 on— m3 vo— 3— on an we 8 mm“ 9— Km mm a: mu Nu. .. mm: g! 9.3— “ml—gm mouN + gnawin— om...mm\no ghommm mmcz u\t :1. 9. I065 [9.3— 39 determined since knowledge of their structure had no direct bearing upon this project. No photoproducts attributable to 5-hydrogen abstrac- tion were detected from the irradiation of nfbenzyloxy- valerophenone, 66. Instead, nebenzyloxyacetophenone, 36 arising from y-hydrogen abstraction, was the only photo- product observed (Reaction 21). (21) 2—Acety1benzophenone was produced as the major photo- product from n—benzyloxyacetophenone, in addition to 40 Ef2-phenyl—3-methyl-3-hydroxy-2,3-dihydrobenzofuran and a trace amount of the E isomer (Reaction 22). . Ph CHZPh Ph 0 ° 0 OH hv CH3 0 H3 "9 <22) 0 0H 3 Photolysis of nfbenzyloxyacetophenone in benzene con- taining varying amounts of pyridine resulted in a dramatic increase in the amounts of E and Eg2-phenyl-3-methyl-3- hydroxy-2,3-dihydrobenzofurans. The quantum yield of 2- acetylbenzophenone was essentially unaffected. The stereo- selectivity of the photocyclization was also affected by added pyridine. In the absence of pyridine, the photo- cyclization strongly favored formation of the less hindered E isomer. However, the quantum yields of E and E isomers are nearly equal in benzene containing 2.2 M pyridine (Table 2). Added pyridine also affected the stereoselectivity of the photocyclization of nebenzyloxybenZOphenone. There is almost no stereoselectivity in benzene containing 2.2 M pyridine. The overall quantum yields for photocycliza- tion are reduced (Table 3). This reduction is also ob- served for nemethoxybenzophenone in the presence of added 41 Table 2. The Effects of Pyridine on the Quantum Yields for Photoproduct Formation from o-Benzyloxyaceto- phenone in Benzene at 25°C. Ph CH (fllPh §Ih 3 2 s 0/’ 0 0 O hv 'CH I ~\\ H3 CH3 3 /’ _z_ .11 Z—Ach Ph [Pyridine]: M °E °§ ¢2~ACBP °total 0.0 0.0226 0.00 0.0589 0.0815 0.544 0.0598 0.0301 0.0670 0.157 1.09 0.0872 0.0528 0.0579 0.198 1.63 0.101 0.0666 0.0517 0.219 2.18 0.118 0.0811 0.0456 0.245 Table 3. The Effects of Pyridine on the Quantum Yields for E and E Photoproducts from o-Benzyloxybenzo- phenone in Benzene at 25°C. ’/,CHéH1' o 0 0.11 [Pyridine], M ¢§ ¢§ ¢total 0.00 0.831 0.108 0.939 1.24 0.358 0.290 0.648 2.47 0.323 0.293 3 0.616 43 Table 4. The Effect of Pyridine on the Photocyclization Quantum Yield of gyMethoxybenzophenone in Benzene at 25°C. CH() 0 1912.9 O Ph H [Pyridine], M ¢cyc 0.00 0.299 1.24 0.157 2.47 0.151 'v 44 pyridine (Table 4). 2. Kinetic Results 45 Stern-Volmer quenching was used to measure the trip- let lifetime of a number of gfalkoxyphenyl ketones. In these experiments, a conjugated diene, e.g., 2,5-dimethyl- 234-hexadiene, is used to quench the triplet ketone by energy transfer. A mathematical relationship holds between the ratio of photoproduct in the absence and presence of quencher and the concentration of quencher used. This rela- tionship is given in Equation 1. o %7 = 1 + kq TT [Q] Equation 1 quantum yield in the absence of quencher 22 D" (D ’1 CD 6- 0 ll ¢ = quantum yield in the presence of quencher IT = ketone triplet lifetime [Q] = concentration of quencher kq = rate constant for energy transfer quench- ing by the diene Thus, a plot of 00/0 versus [Q] should give a straight line with an intercept of 1.0 and a slope of kth. In most cases, energy transfer quenching by dienes is close to the rate of diffusion in a given solvent.“6 For ex- ample, k is known to equal 5-6 x 109M715"l in benzene at q Ch 45 25°C.“7 Therefore, the triplet lifetime can be calculated from the slope of the Stern-Volmer plot. The photoproduct quantum yields and triplet lifetimes of a number of gralkoxyphenyl ketones are given in Table 5. Intersystem crossing quantum yields were measured for o-benzyloxybenzOphenone and ngbenzyloxyacetophenone and each was found to be 1.0. These measurements were made using the ketone to sensitize the isomerization of either Ennnnestilbene or nEn—piperylene.u8 A number of nfalkoxyphenyl ketones were studied by nano- second 1aser flash spectroscopy using a Molectron nitrogen laser as the excitation source (Aexc = 337.1 nm, Eexc = 3 to 10 mJ). This technique involves monitoring the ab- sorbance of a traisient species, e.g., a ketone triplet, at a fixed wavelength as a function of time. The result is a simple first-order decay curve, where in ——————— = k t Equation 2 infinite (baseline) absorbance of the where A0° transient At = absorbance of the transient at time, t kexp = transient decay rate constant Thus, the triplet lifetimes can be measured directly from 46 wAmm.ov o.ooao.oom no.0“ om.o m mmomflmmov ea aa>onrm m.mam.mo Hoo.oa 63.6 m eaAONmoeavnm ea camonHo-.m.m o.oao.moa mo.oa mm.o mmoum on as camozumuonum o.oomm 1a-: m mmo ha eaaohmtm o.omao.omsa aoo.oaommo.o m mzo ea ciaonum o.ommao.owmm mo.oa om.o m ea : camoozum oao.oaommm.o ---- m ea ea o.camosm-m m.Hm 63.0 3 ea ea camoamnm omoo.oa moa.o A.HHO.HOH I omo.oa mm.o m as ea samonuo 9.Huz .96 ex pose x .m m ocooox x woomm pc ocoscom ca oeoficcxoeua.muasecoefiaum.m spa: monouox Hzconazxoxa mo mcfinozosa poEHo>ICLCBm mo madamom .m manna . ELI: u EZCU . 9 .0 ~.Q~...~. 47 mo coaumELom map pom papa» 53908300 .0000: omfizmonpo mmoacs Lozososv mm 00m: ocofipmxoc flagposflmlmxmx .LoEomfi mean» on» .LoEomfi mac 020 no soameLom pom paofiz 5:000:00 .0omm pm ozoncon CH ocouox no mGOHuSHOm 2 No.0 commmwoo no coapmfipmhsfi EC mam: .ocfiofimza z 0.H wcficfimucoo ozoncon CH nonamuno UHWHz 5502030 wouaefixme on» mucommpaon momozpconmm :H osam> .ococmcoouoowzxoaznconlo no :oHumEpom map mom papa» Educmsaw .ocfipfipmq z 0.H mcficfimpcoo ocmucon CH ocouox mo mCOfipzaom 2 =0.0 00mmmw00 mo coaumfiompna Sc mama .oomm um ocoNcon :0 U mHIZNOH x a H .Oomm an x apococosv mm 00m: cmpnmopoe Hmpoouco m H- H-200H x :.m n x .mcwxofiplz.a CH mcouox mo wCOHuBHom 2 20.0 pommmwop no cofiumHUMLHH EC mamp .LoEomH news» on» no coapmspom on» now 0000» 53000300 .Lmsoma mac 0:» mo cofipmshom on» now oaofiz 5:000:02 .mcmNCmQ CH mfloumx MO mCOfiUSHOm S 30.0 Gmmmmwmfi MO COHumHUmhhH EC MHMG 0.0mao.000 000.0“ ss.0 0000-0 00 0 «0010.0 m.m00.me 000.06 00H.0 mmooou0 mmo ea 0000-0.0 0.Ham.aa 000.00 00.0 m.H90.mH H00.04. 00.0 0000-0 00 ea 000:0.0 x.HIE .99 0x @000 x .m m econox .0oscficco0 .0 cases O Q V 48 the decay curve. In addition, Stern-Volmer quenching can be used to not only measure the triplet lifetime, but also the rate constant for energy transfer quenching, k . For 9 this experiment, kexp is plotted as a function of quencher concentration. The following relationship holds - + k [Q] . Equation 3 The slope of the line is k and the intercept is 1E1. q, The results of nanosecond laser spectroscopy of a num— ber of gralkoxyphenyl ketones”9 in benzene and methanol are presented in Tables 6 and 7. Note that the value of kq for many of these ketones is approximately one-half that of the accepted value for ketones, 5.0 x 109M-ls'l. Rate constants lower than 'normal' values were also observed for the energy transfer quenching of triplet 2- keto-[2,2]-paracyclophane, 2-KPCP, by a number of triplet quenchers in both benzene and methanol. These values are summarized in Table 8. In an attempt to better understand the quenching process for this ketone, Arrhenius parameters were determined for the quenching of triplet 2-KPCP by 2,5-dimethyl-2,4-hexadiene and 1,3-cyclooctadiene in methanol. These values are presented in Table 9. Arrhenius parameters were also determined for the triplet l\ I} u)— R .— nt~ — Vi .d- I 49 0.mma 00.0 0.000.00 0 000010000 00 0>000-m 00.0 0.000 0.00 000-0 00 00 0002-0-000-m 00.0000.0 0.000.00 0.000.00 0 0010000000-0 00 0000000-.0.0 00.0000.0 00000.0000 0.000.0000 0000-0 00 m 0000200-0.0 00.0 0.0000 0.0000.000 0 000 00 00000-m 00.0 0.000 0.000.00 0 00 00 00000-0 00.0 0.0000 0.0000 0 00 0 mmooz-m 0-00-2000 .00 H-2 .00 00 060: .00 x .0 0 ocopmx .. 0 o \O 0 0000 .zaoomopuooqm £0000 pommq an ocmwcom :0 monouox Hzconaaxoxa00mnm 00.0 0.0000 0.000 000-0 :0 :0 0002-0-on-m 00.0 0.000 0.000 0 0000020000-0 00 mmon0o-.0.0 00.0 0.000 0.000.000 0000-0 00 0 0000:00-0.0 00.0 0.0000 0.000 0 000 00 000N0-0 00.0 0.000 0.00 z :0 00 mmon-m 0.0 0.0000 0.000 m 00 m mmomz-m 0-m0-Zmo0 .00 Be ax 0mm: .90 x .m m weepmx ... Q _ c \\mV 00:0 1 .zaoomonuomam nm00m medq an 00203002 :0 mmCOpmx 00cmnazxox0o-m.0 mchQ00o>ommelmm.NQIOpmmIm om.m 0ocmnpmz mcm0vwxmzlz.m-0mcme0Q-m.m mcan00o>QMmenmm.mH-oumxlm 000.0 mcmwcmm mcm0©muOOO0o>olm.0 mcan00o>ompmmnmm.mu-oumm-m 00.0 mcmwcmm mcm0mnp£QmC0z£umzl0 mchQ00000000m-mm.NHIOpmxlm 00.0 mcmucmm mcm0omxmn-0.mn0znme0Q-m.0 mcanO0ozompmm-mm.mg-Opmx-m 0100-2000 .vx ucm>0om pmnocmsa mcoumx .0000 pm 00:0:002 new mcmucmm :0 mmcm0a m300pw> an muo0Q0pe mcoumx 00cmzm mEom no w:0:ocm30 memCMAB zwpmcm ma» non mucmumcoo mumm .w m0nma 52 .0003000 00:000nsm:s .o:000om .o .00 00.0 00.00 0:00o0x0:-0.m-0>:Q0E0Q-m.0 00:0:0:0000o00xo:u0z-Q 000.0000.0 00.0000.0 00000000000000-0.0 00000000000000-00.00-0000-0 00.0000.0 00.0000.00 000000000-0.0-00000500-0.0 02000000000000-00.00-0000-0 0005\00ox .mm < 000 0030:020 0:000x .0o:0:p0z :0 000:0:030 050000> :00: 0:0:02009000000:902Lm 0:0 0:0:000000 I000m-m.mlou0xlm mo w:0:o:050 0000:009 mmn0:m 0:» non 0000080000 0:0:0:00< .m 00n09 53 decay of a number of ofalkoxyphenyl ketones in chloro- benzene and methanol. These values are summarized in Table 10. 3. Spectroscopy a. Phosphorescence Spectra - Representative phos- phorescence spectra of some ogalkoxyphenyl ketones are shown in Figures 6-9. Phosphorescence spectra of all o—alkoxyphenyl ketones studied in this thesis were recorded in two different sol- vent glasses at 77°K - EPA and 2-methyltetrahydrofuran. The triplet energies for these ketones were calculated from the highest energy (0,0) band are are reported in Table 11. b. Ultraviolet-visible Absorption Spectra - Ultra- violet—visible absorption spectra were recorded for all g- alkoxyphenyl ketones studied in this thesis in n-heptane. The wavelengths of the absorption maxima and their corres- ponding extinction coefficients are reported in Table 12. c. Triplet-Triplet Absorption §pectra - Triplet- triplet absorption spectra of all ketones studied by laser flash spectroscopy were recorded in both benzene and methanol. Representative spectra are shown in Figures 10 and ll. 54 mmomfimmov 00 0>onnm 00.0000.m 00.00m0.: :m.ofizz.o0 3:.OH-.: : In: ....... mm.ofimm.m om.OH~o.m 0 cmflommozmvnm :0 0000000-.m.0 m0.ofioo.m mH.OHmo.m Hm.ofiam.m 00.OHNH.: 0 :0 0 00002-0 3.330 2.320 2.385 8.380 0 m5 ca . 085-0 om.ofimm.m mm.oflm0.m 0m.oam.oa m:.oaom.: mmoum :0 gm 0002:0aonam < 000 0002\0000 a 000 0005\0000 x .0 m 0:0000 «m «.m 0 0 Hoc0c00z . 0000:0no0oazo x .m g c N \\b 006 I .Hoc00002 0:0 0:00:0no0oaso 0H 0000000 H000nazxoxa mo A0009 00HQH09 000 0000080000 03H00£00¢ .oa 0H00e 55 L l l l l I l l I L4 J J l 1 1 L \[0 I I l I T 1 I 1 I l T f l I [ F 00 % 0 nm 0 Figure 6. The phosphorescence spectrum of o-benzyloxy- acetophenone in 2-methyltetrahdeofuran at 77°K. 56 \ l, 1 l, 1 1 41 J 1 1 1 1 1 1 ll L 1 1 T I I T’ I I l I I I I I I I T I I V’ u: 8 nm (8 Figure 7. The phosphorescence spectrum of o-benzyloxy- benzophenone in 2-methyltetrahydrofuran at 77°K- -.-\1 b 00 57 _J 1 1 1 J 1 I I I 1 I I J L 1 LI'TIT'IIITInll¥tII—Ir 0 run. . U1 0 a Figure 8. The phosphorescence spectrum of 2,6-dimethoxy- benzophenone in 2-methyltetrahydrofuran at 77°K. —lr—- 09€"” Figure 9. 58 099 ——— The phosphorescence spectrum of 2,6-dibenzoyl- anisole in 2-methyltetrahydrofuran at 77°K. 0.00 00: 0.00 00: 000010 00 00 00010.0 m 59 0.00 :00 0.00 00: 000010 00 00 00010.0 0.00 000 0.00 000 000010 00 0 «0010.0 m.00 2000 mm: 0.00 2000 000 m00010 00 0 000020010.m 0.00 mo: 0.00 so: 0 mmomflmmov 00 0000010 0.00 00: 0.00 00: 0 002000000010 00 00000001.m1m 0.00 000 0.00 mm: mmoum 00 00 000210100010 0.00 00: 0.00 00: 0 00 0 0000210 0.00 00: 0.00 00: 0 00 00 0000010 0.00 m0: 0.00 000 0 m00 00 0000010 0HoE\H0ox Es 0Hoe\H0ox E: x .m m 0CO000 0.00 0 02 0 00 0 00 000 02000210 <00 mm:o\ .xot. 00 0003000003 I00000H0£00zlm 0:0 <00 :0 0000000 H000000xoxH mo 00000000 0000008 .HH 0H00B 60 .mm .0m .00 .m000 ..0.2 .0000 302 .000000 000002 .=20000E00000000 00 00000000: .>o0:2 .0 .00 0.m0 mam 0.00 00m 000oc0£0O00o< 0.00 00: 0.00 m0: 0000:0£QON00m 00oEm00ox m: 00oe\00ox an x .m m 00o00x a a 0 CM 0 OK 0 cm 0 oK 000 00000210 000 .Umdcfl0soo .HH mant .mpcmfiofimmmoo COHpocfipxm Lwaoe mp0 mmmmnpcmpmq :H 005H0>0 61 “mamav 000 Aofim.00v 000 000000000000000000000000-0.0 A0000V :0 000 A000.mfiv 0:0 0000000000000000u0.0 A00m0v :0 000 A000.mav 0:0 0000:00000000000000000000u0.0 Azmmav :0 mom .A00o0v 000 A000.HHV mz0 00000000000m Iaznumelmlzxoammcmmno Ammmzv 00m A00000 mm0 00000000000000000000000-.0.0 Awmmzv 0mm Aomm.aav cam meccmzaopmam>>xoazmcmmnm Aom.0mv :0 0mm .AHO.:0V :0 mam .A00.:0V :0 00m .Aommav 00 000 .A000mv :0 000 .Aoummv :0 000 A000.mHV 0:0 000000000000000000efiaum.0 Ammm0v :0 000 .A00m0v 000 I A000.0HV :m0 .Aoo:.mav 0:0 .A00:.:0v mz0 A000.0HV :0 0M0 0:000:000000000000zuo Aoommv wwm Aoommv omm 0:0:03Q0pmowmxoam0cmmum Am0oav :0 00m A000Hv 000 “00:00 m00 00000200000000000000mum 050x02 COfipnpomn¢ pmnpo 04 mCOumx I .0c0990m CH 00:0p0x Hzcmzqzxoxanumaoa>0puab .mH magma 62 .mcmucmn :0 0:0:mnaoucmnzxonumelm mo Ezppomam coapmpomnm pmaafipplpmaafipe .oa mpswfim _ . 1523003.. 00.0. . 8h 00m . won no... as» — J. _ _ . _ q .q .. ‘ n . . . .. 0 4 .q 4 4 Q d‘ ‘ ‘ ‘ 4 4 0e 4 Q 4 4 ‘ 4 4 63 .mC0acmn :0 0co20£Q00cmnmxonmeHUum.m no Edppomam COHumpomnm pmaafipplpmaafipp 029 .HH mpswfim 396490.... 80 80 can can 80 0 J .0 _ .1 1 a. a. 00 1: c 4 d C 4 1 6H d. 130 — nmr Spectra - 130 - nmr spectra (250 MHz) were recorded for a number of gfalkoxyphenyl ketones in kl-chloroform. In general, it was found that the chemical shift of the alkoxy carbon of 2,6-diacyclalkoxybenzenes were 6-10 ppm downfield of the alkoxy carbons of their monoacyl counterparts. These chemical shifts, as well as those of the carbonyl carbons are presented in Table 13. B. a-(o-Alkylphenyl)acetophenones 1. Identification of Photoproducts Irradiation of 0.10 M cyclohexane solutions of a number of a-(gyalkylphenyl)acetophenones under an argon atmos- phere with a medium pressure mercury lamp filtered through Pyrex afforded the corresponding 2-phenyl-2-hydroxyindane in quantitative yield (Reaction 23). No purification of the photo lysate was required . CHE 2 Ph R' R. (23) Structural assignments of all photoproducts were based 13 upon spectral data (1H and C nmr, i.r., and mass spectrum). A 1H nmr spectrum (250 MHz, CDCl3) of 2-phenyl-2-hydroxy- indane, formed by the photolysis of a-(gftolyl)acetophenone 65 Table 13. 130 Chemical Shifts for the Alkoxy Carbon and Carbonyl Carbon in Various ggAlkoxyphenyl Ke- tones.a CHZR ’// 0 o ‘0 R' X Ketone R R' .. X GOCHg-R 60:0 O-BZOBP Ph Ph H 68.65 192.3 O-BZOS-MeBP Ph Ph 5-CH3 69.32 196.8 2,2'-D1BZOBP Ph 2-(PhCH20)Ph Pi 70.00 195.5 O-BZOAP Ph CH3 H 70.6 199.8 o-BzOVP Ph (CH2)3CH3 H 70.66 203.7 2,6-DBB Ph Ph 6-COPh 77.12 195.5 2,6-DAB Ph CH3 6-COCH3 79.4 200.0 2,6-Dicyanobenzyloxybenzene 76.90 ----- O-MeOBP H Ph H 55.33 196.2 2,6-D1MeOBP H Ph 6-OCH3 55.70 195.2 2,6-DBA H Ph 6—COPh 61.6 195.5 Anisole 514.07n aSpectra recorded in CDCl3/TMS at 250 MHz. Chemical shifts are reported from TMS (6 = 0.0). 66 in cyclohexane is shown in Figure 12. A common feature of the 1H nmr spectra of these 2—phenyl-2-hydroxyindanes is an AB quartet occurring from 3.0 to 4.0 ppm and correspond- ing to the methylene protons of the indane ring. Such a photocyclization does not occur for either a- (o-tolyl)acetone or a-(o-tolyl)acetaldehyde. 1,2-Di-(9f tolyl)ethane, formed by acyl cleavage is the only photo- product isolated (Reaction 24). 3 . *9 (2n) .2 @ Spectral data for all 2-phenyl-2-hydroxyindane photo- products is presented in detail in the Experimental Section. 2. Kinetic Data Triplet lifetimes of some a-(gfalkylphenyl)acetophenones were measured by Stern—Volmer quenching in benzene at 25°C. These lifetimes and the corresponding photoproduct quantum yields are presented in Table 1“. 67 .maooo Ca osmocfimxopozznmlazcmcoum mo Sappomdm Leanna 0:2 0mm .mH mpswfim .EQR 0.0 o.“ o.N o.m w 0.5 o.® . L D Ll L ~ Ir W‘00111"+1111+<1+4‘++1111++‘1‘++1+«111‘*1 \I‘l+14++41+1‘+‘1 < 0%? .600: 003 mCmHU 1020C12.muH2Cumechm.m moCoumx CoCuo HHm Com .C0CoCmsU mm @005 0C0H©020C0Hozolm.H© .mCHwHC2Q 2 H .mm wCHCHmpCoo 0C00Coo CH UmCHmpno onHm Esprsq nonvoCQOCOCC UmuHEmee 0C» mpCmmoComC mHmmeCoCmd CH 03H0>o 0 0e0 .oomm um 0C00Cmn CH EmOH x o.m u x wCHECmmm x EOCM UmpmHCOHwo 0 HI HI 9 .oomm pm 0C00Cmo CH mCOHusHom mCOCox z mmo.o commmwmu Co COHpmHUCCCH EC MHmm 68 2.00 0m0.0 000.0000.m m00.00020.0 0202m2ov2ovu0.0 m20 0020090n0 0.02 000.0 00.000m.m 00.000:.0 02020020-m Mme 0020000-0 0.00 0m0.0 00.000m.: 0o.002:.0 0Am2ovnm.: 2 002-0 m0.0 ow.m 02.00 0.00 :0.0000.0 mmoum 2 00202QVI0 m0.0 00.0 m.00 0.0m m0.0000.0 2 2 009-0 3H. 3H. «B U DUQ HummOH H\H 2000C H HIE e x e .m m 0C0p02 rm . 0 0020 .Oomm p0 0C00Com CH 00COC0CQOC000AH2C0CCH22H Com mama 0Hp0CH2 .2H mHnme 69 3. Spectroscqpy a. Phosphorescence Spectra — Phosphorescence spectra were recorded for all a-(gyalkylphenyl)acetophenones in both EPA and 2-methyltetrahydrofuran glasses at 77°K. Repre- sentative phosphorescence spectra are shown in Figures 13 and l“. Triplet energies calculated from the wavelength of the 0,0 band are reported in Table 15. b. Ultraviolet-Visible Absorption Spectra - Ultra- violet visible spectra were recorded for all a-(gfalkyl- phenyl)acet0phenones studied. The wavelengths of the ab- sorption maxima and their corresponding extinction co- efficients are reported in Table 16. 70 —r— —L—. _ ... '-. .... _. .. _. h.- '- .. _ .. 099-“- Figure 13. The phosphorescence spectrum of a-(ggtolyl) acetophenone in 2-methyltetrahydrofuran at 77°K. 71 I I I I l I I I I I I I I I I I ..- I I I I I I I I I I I I I I I I E: nm 16 0 ° 0 Figure 14. The phosphorescence spectrum of a-mesitylaceto- phenone in 2-methyltetrahydrofuran at 77°K. 72 .000 .2020 .0020 .m .000202 .z .m .CmCHmodEQm .m .< .CmCm03 .2 .m .202000 zoom .mm C .mmemnoHomonCums CH .222000 000 .0m ..2020 .mmm .0 ..mm mm .00002 .0 .2 .0000000022002I0 000 m.:2 nmCOCmCQoCmH0> o.mw 0CHomCmnzxooQ 22m 2.m2 22m 0.m2 0A0Am2ov2ova.2 m2o 0222020I0 00m 0.00 000 0.m0 02m20020Im m20 002000VI0 000 0.00 00m 0.00 020200-0.s 2 002-0 Ham 0.m2 02m m.m2 2 2 229I0 EC mHoE\Hmox EC oHoE\H002 .m m 0Couox .0.02 .0.02 .0.02 .0.00 000000002200000022002I0 <02 0220 I .202» p0 CapsmonszwpumszCuoz IN CCm mo mmeCmCm umHCHCB .mH mHome 73 .mmme0C00md CH 000 mpCmHOHmmmoo COHuoCHuxm CmHozm oCOCmCC00oow 200.000 00m .00.000v 000 .Amm0av 200 2000.000 0M0 IAH20000020000000000I0.0.0VI0 AamHv mmm 0C0C0C000000 .Ao.0000 020 .200000 200 .000m0v 000 0000.000 0M0 I202000002000000000Im.0VIa Am.mmv mmm 0CoC0Cooumom 20.0000 020 .20.0000 200 .00.000v 200 000000 0M0 -202000002000000Im.0VI0 202.m0v 00m .20.m000 200 .20.0020 200 Am0o.0av 2m0 0000000000000200002I0 20m.mzv 20m I .Ao.0mmv mmm .Am.momv mum .Am.Hmmv Hum Amoomv mmm 0C0C0CQ00000AH2HoeIoVI0 000002 0000000000 00000 00 000002 .mCmuQmm CH 00C0C0CQ IoumomaHmCmCoH22H¢Ivaa mCoH00> Com mmewaz CoH000omn< 0H0HmH>IpmH0H>000HD .mH mHnme DISCUSSION A. grAlkoxyphenyl Ketones 1. Determination of Meaningful Hydrogen Abstraction Rate Constants a. Steric Effects on Energy Transfer Quenching - The importance of determining accurate values of energy trans- fer rate constants, kq's, is obvious. Without reliable kq values, it is not possible to determine accurate excited state (singlet or triplet) lifetimes by Stern-Volmer quench- ing. Thus, a great deal of activity has dealt with the careful determination of kq values for a number of excited state molecules and appropriate quenchers.u’50-l56 It is widely accepted that the rate constant for the quenching of triplets by energy transfer in benzene at 25°C is 5.0 - 6.0 x 109M'ls'1.57’58 Scaiano51 has undertaken a rather extensive study of the energy transfer quenching of various triplet organic molecules with a number of triplet quenchers and has found this value to be accurate. Turro59 has examined the quenching of acetone phosphorescence by a number of acyclic 1,3-dienes and found kq values ranging -1 from 3.0 - 6.0 x 109M-ls The quenching rate constants 7H 75 of these dienes are slightly dependent upon the electronic nature of the diene. 50 has shown that the rate constants for the quench- Wagner ing of the Norrish Type II reaction of a,a-dimethylvalero- phenone and valerophenone with 2,S-dimethyl-Z,H-hexadiene vary similarly with viscosity in a number of different hydro- carbon and primary alcohol solvents. Wagner and Chen58 have found the same trend for the quenching of the Norrish Type II reaction of o—methyl-y-methylvalerophenone and valerophenone with 2,5-dimethy1-2,4-hexadiene in a number of primary alcohol solvents of varying viscosities. Hence, energy transfer is not strongly sensitive to either a-di- methyl or o-methyl substitution. 6 In order to further test the steric sensitivity of energy transfer, kq values were measured by nanosecond laser flash spectroscopy for a number of g-alkoxyphenyl ketones, having o-alkoxy substituents of various sizes. 2,5-Dimethyl-2,U- hexadiene was used as the triplet quencher. These results, presented in Table 17, demonstrate that energy transfer is sensitive to the degree of steric congestion orthg to the carbonyl. Only the least congested ketone, gamethoxybenzo- phenone, has a 'normal' kq value in benzene. The most sterically crowded ketone, 2,2'-dibenzyloxybenzophenone, has the smallest kq value in benzene, 8.“ x 108M'ls'l. All other ketones have kq values on the order of 2.9 x -1S-1 109M , nearly one-half the normal value of 5-6 x 109M Hence, steric bulk ortho to the carbonyl does 76 00.0 0.000 0.000.00 2 020020200 00 20000-0 No.0 o.mmH 0.20 mmoum C2 Cm mmszmIoumIm No.000m.o 0.000.00 o.m00.02 2 ConNmoCvam C2 2m00mHoI.m.m 2m.oamm.m oom00.0mm0 o.muo.onH mmOOIw C2 2 mmomzHaIm.m 00.0 0.003 0.300.220 2 m20 02 Baum-m 00.0 0.0: 0.0 0.0.0. 2 02 02 22002-0. :0 0.003 0.0200 2 02 2 22002-m 0 0 H072000. 2 HI2 .0; 2 0000 .00. 2 .2 2 000002 .. Q o o 2020\ I .mdoomoppomdm CmmHm 0000A 20 0C00C0m CH mmCoumx H2C0CC2202H2pd .02020om .o .20 02.0002.2 00.0002.0 20000002 000-m.2 00002-0 00.0000.2 mm.0000.02 20000002 0220-m.0 00002-0 00.0000.2 0m.0000.0 0000000000200 000-m.2 00002-0 0m.200.2 m0.0000.02 0000000000200 0220-0.m 00002-0 00.002m.0 00.0000.0 0000000000200 0000-m.2 0000000000000 mm.00m0.2 00.0000.02 0000000000200 00220-m.m 0000000000000 0208\2002 .0m < woq pcm>20m hmnocmsa onu02 .2oc0zumz 050 0:00:00 .oQO2no :2 020002030 0022209 030200> an mcochQOp00< 0:0 0000202020020m|mm0mu Ioumxlm pmHQHQB mo w22nocmza Lommc029 ampocm on» 20% 0209080202 ms2cmnan< .m2 0200B 80 magnitude less than those for the quenching of triplet aceto- phenone. These lower A factors indicate a greater entropic requirement for energy transfer from triplet 2-KPCP than from triplet acetophenone. Efficient energy transfer from triplet to quencher re- quires maximum overlap of the orbitals of both ketone and 50 Cram63 has found that the carbonyl and benzene quencher. rings of 2-KPCP are orthogonal in the ground state of this ketone. Since the molecule is quite rigid, the excited state geometry must also have some lack of co—planarity between the carbonyl and aromatic n-system. Hence, the low A fac- tors for the energy transfer quenching of triplet 2-KPCP probably reflect the inability of the quencher orbitals to completely overlap with both the carbonyl and aromatic n-orbitals of the ketone. The steric bulk of the o-alkoxy substituents of g—alkoxy- phenyl ketones also prevent complete overlap of the n—orbitals of ketone and quencher. The result is a lower than normal kq value for these ketones. b. Contribution of Triplet Decay_to the Overall Trip- let Lifetime Reciprocal triplet lifetimes were calculated from the slopes of Stern-Volmer quenching plots (kth) assuming that k = 2.9 x 109M'ls'l for all ketones except g-methoxybenzo- q phenone and 2,6-dibenzoylanisole (2,6-DBA). Although kq 81 values were not measured for diketones 2,6-DBB, 2,6-DBA, and 2,6-DAB, it was assumed that they were nearly equal to thoseof their monoketone analogues. These reciprocal triplet lifetimes are presented in Table 20. The reciprocal triplet lifetime, 1E1, is a sum of the rate constants for hydrogen abstraction, kH, and triplet decay, kd. That is - Hence, the contribution of triplet decay to the overall triplet lifetime must be determined and kd subtracted from 151 in order to obtain an accurate appraisal of kH. Typical values for Rd in phenyl ketones are on the order 6 29a of 105 to 10 3'1.65 Wagner has found kd values for 27 methoxyphenyl alkyl ketones on the order of 1.6 x 1065-1. Turro and Lewis66 have reported that kd for pfmethoxybutyro- phenone measures 6.0 x 105s"1 in benzene. Favaro67 has measured kd values for U-methoxybenzophenone and A,H'-di- methoxybenzophenone in benzene of 1.7 x 1053'1 and 6.25 As—l x 10 , respectively. It is unlikely that the k values for 90 and pealkoxy- d phenyl ketones differ greatly from each other. There is no known reason why kd values should be sensitive to the nature of the alkoxy substituent, i.e., kd's for gamethoxy- phenyl ketones and g-benzyloxyphenyl ketones should be equal. 82 100220020 20022 20002v 00220222 2022222 no w222o2020 2mE2o>I22mpm 22 00220220 m:20> .Amaoo 2 .202008202 2020022 no w22202030 2mE2o> 22mum 22 00220220 0:20>0 00.0 0.02 0.002 0.00m 2 m20020200 00 0>002-m 00.0 0.000 0.0002 0.0002 2 m20 00 02002-m 02.0 0.00 0.00 2.20 2 0020020000-0 00 0200220-.0.0 20.0 0.0002 0.0200 ----- m200-0 00 2 0000220-0.0 00.0 0.02 0.002 0.m02 020-0 00 00 0202-0-002-m 00.0 0.0002 0.0020 0 0200 2 00 2 02002-m 20.2 0.00. 0.022 0 202 2 00 00 02002-m m z 02 .02 0002 .2 z . 20 z 0 202 x m m .020202 2- 2- 0 2- 0 2- 0 . 2 .0 Q . 0 \ 2W20 2220222202221m mo 0022mm 0 2o 22000022002m 20022 20002 no 022200m 0220222 .oomm p0 m2mu2mm 22 0020202 .ON 02208 83 'Wagner2ga has shown that kd values for p—methoxyphenyl alkyl ketones do not change with different alkyl groups. Therefore, kd values for gealkoxyphenyl ketones can be ap- proximated by those for their pfmethoxy analogues. That is, kd for gfbenzyloxybenzophenone can be approximated by kd for p¢methoxybenzophenone. 6-Hydrogen abstraction rate constants calculated from reciprocal triplet lifetimes and assumed kd values are presented in Table 21. The quantum yield for photoproduct formation from these ketones can be represented by - ¢pdt = ¢1sc kHTTa where ¢isc = intersystem crossing quantum yield for the ketone kH = rate constant for é-hydrogen abstraction TT = ketone triplet lifetime 0 = efficiency with which the intermediate (biradical) converts to product Intersystem crossing quantum yields for g-benzyloxybenzo- phenone and gebenzyloxyacetophenone are both 1.0. There is no reason why ¢isc should not equal 1.0 for all the g— alkoxyphenyl ketones studied. If a is 1.0, then ¢pdtTTl equals kH. If a is less than unity, this product represents a lower limit for kH. For the sake of comparison, values 8H m 000.0 00.0 00.0 002.0 2000-0 20 02 000-000 00.2 02.0 20.0 00.0 2000-0 20 2 <00-0.0 0.20 0.20 0.20 000.2 0200-0 20 20 000-0.0 020.0 000.0 000.0 0200.0000.0 2 020020200 20 0>000-m 0000.0 000.0 002.0 0200.000000.0 2 020 22 02000-0 20.2 20.2 00.2 02.0 2 0020020000-0 20 0000020-.0.0 000.0 00.2 00.2 00.0 020-0 20 20 0002-0-000-m 0000.0 002.0 202.0 00.0 2 00 2 00002-m 00.0 00.0 00.0 020.0 2 20 20 00000-q 2-0002 2-0002 2-0 002 0000 2 .2 2 .000002 2 2 a 02 02 2-2 ... G .00mm 20 020N20m 22 0020202 22202222022<1m 0200 202 00220> m 2 0000200200 .2N 02209 85 .0202202000 02 20220 0222222 20220002 002 02 02202220 20 20222000 002 20 00220200 002022 2222020 000222202 220002002 00000220200 22 00220>0 .0202002002000 202022200200 02202002 0200 202 02020 2222020 202090 .2\2 020 00200220>0 20230 2020 20 20200200 . - . 0 . u 0 00 0000020 .0 0 000 2- 202 x 00 0 2 00.200-0.0 0:0 .200 10.m a0020200000200220220-m 220 202 2|0m02 x 0.2 u 02 000000-0.0 0:0 .2>000-m .00000-0 200 2-0002 2 0.2 u 02 00220000 .0\2 2000 00002002000 .00002 .000020000 .20 02000 86 calculated from both assumptions are presented in Table 21. Discrepancies between the two calculated k values can H arise from a number of sources. The assumed triplet decay rate constants may not be correct for o—alkoxyphenyl ke- tones. This is probably the case for o-benzyloxyaceto; phenone since the calculated kH value is much less than its lower limit. The other source of discrepancies comes when a is less than one. Biradical inefficiencies are well known in ketone photochemistry, and will be addressed later in this thesis. 2. Structure - Reactivity Relationships g—Benzyloxybenzophenone is approximately fifty times more reactive than g-benzyloxyacetophenone. This difference in reactivity is directly attributable to the nature of the lowest excited triplet of each ketone. g-Benzyloxybenzo— phenone, like 2-benzyloxy-Ll-dodecycloxybenzophenone,26 has a n,n* lowest triplet. g-Benzyloxyacetophenone, like 29a g-methoxyvalerophenone, has a n,n* lowest triplet. Since n,w* triplets are inherently more reactive than 6 it is n,n* triplets in hydrogen abstraction reactions, not surprising to find that g—benzyloxybenzophenone is more reactive than g—benzyloxyacetophenone. G-Hydrogen abstraction rate constants for g-alkoxy- phenyl ketones are sensitive to the reactivity of the alkoxy hydrogens. g-Benzyloxybenzophenone is thirty times 87 more reactive than g-methoxybenzophenone, reflecting the greater reactivity of a benzylic hydrogen in comparison with a methyl or primary hydrogen. Walling68 has reported an eighty-fold difference in the reactivity of a methyl hydrogen and a benzyl hydrogen in the photoreduction of benzophenone. Wagner69 reported a fifty-fold difference in the rate constants for y-hydrogen abstraction in y-phenyl- butyrophenone and butyrophenone. 3. Conformational Effects Hydrogen abstraction rate constants for o-benzyloxy— benz0phenone, g-methoxybenzophenone, and g—benzyloxyaceto- 6 phenone are in the same range (10 - 1073-1) as that re- ported by Pappas25 for methyl g-benzyloxyphenyl glyoxylates 26 for 2-benzyloxy-u-dodecycloxybenZOphenone. and by Lappin Stern-Volmer quenching plots for these ketones (cf. Figures 15-17) are linear, and, hence, do not reveal the presence of more than one triplet,“b contrary to what was anticipated. However, as mentioned previously, these kH values are at least an order of magnitude lower than what is predicted for these ketones. It is tempting to assume that this de- creased reactivity is the result of the presence of two rapidly interconverting triplets, one reactive and the other unreactive. If this conformational interconversion is faster than hydrogen abstraction, the observed reciprocal triplet lifetime is actually the linear sum of the products h.0 3-5 3.0 QI‘Q 2.5 88 0 no 51.0 16.0 15.0 zofio 25.0 36.0 [Q] . 10% Figure 15. Stern—Volmer plot for the quenching of o— benzyloxybenzophenone with 2,5-dimethyl:2,u- hexadiene in benzene at 25°C. 89 8.0 t 6.0 v- Ellri 0'0 .L e : 0.0 5.0 10.0 15.0 [Q] . IO’ZM Figure 16. Stern-Volmer plot for the quenching of g- methoxybenzophenone with 2,5-dimethyl-2,H- hexadiene in benzene at 25°C. 9O 0.0 n '1 1 1 1 0.0 10.0 20.0 30.0 40.0 50.0 [Q] , 1044M Figure 17. Stern-Volmer plot for the quenching of of benzyloxyacetophenone with 2,5-dimethyl-2,u- hexadiene in benzene at 25°C. 91 of the reciprocal triplet lifetimes, T11, and fractional populations of each triplet conformer, Xi.7O That is - -1 , -1 Tobsd = i Xi T1 In such cases, only one triplet lifetime would be observed by Stern-Volmer quenching.70 The existence of two triplet conformers for these ketones, therefore, could go unde- tected. (Note that if such a conformational change is occurring in ggalkoxyphenyl ketones, it must be faster than hydrogen abstraction since k 's for these ketones are sen- H sitive to the reactivity of the g—alkoxy hydrogens.) Two important internal rotations are available to éf alkoxyphenyl ketones. Each rotation produces two different conformers. Therefore, if both rotations occur freely, four different rotational isomers are produced. Of these four rotamers, only one, the (syn,§yn) conformer, is re- active. Because both the alkoxy oxygen and the carbonyl conju- gate with the benzene ring, rotations of these substituents are somewhat restricted in the ground state. Since this conjugation is even more important in the excited state,71 these rotations are more restricted. It was not possible to predict the relative importance of each of these rota- tions on the overall mechanism for 6-hydrogen abstraction in these ketones. Therefore, model compounds were 92 R R a (f/J l\\c R' R' b ax <———7— syn,syn anti,syn b b J R O L\ R' 0 R' O a <————- _-} syn,anti anti,anti synthesized and studied in order to test the effects of each rotation on the efficiency of hydrogen abstraction in these ketones. g—Alkoxybenzophenones have a special conformational problem. Hoffmann71 has shown that in the excited state of benzophenone, only one benzene ring is coplanar with the carbonyl. Montaudo and co-workers72 suggest that 1H 93 nmr and dipole moment measurements reinforce earlier notions73 that in solution the ground state conformation of benZOphenone is 'propellor-like' with each benzene ring tilted approximately 20° out of the plane of the carbonyl. However, orthg substitution increases the dihedral angle between the carbonyl and the substituted ring to as much as “5°,72 depending upon the size of the ortho substituent. Based upon this ground state preference, it is unlikely that the alkoxy substituted ring is coplanar with the carbonyl. It is possible, then, that the alkoxy hydrogens may not be as available to the carbonyl oxygen in this ar- rangement as they would be if the alkoxy substituted ring was coplanar with the carbonyl (Scheme 12). Hence, G-hydro- gen abstraction may not be very efficient from this con- formation. QEEQQ benzyloxy substitution of both benzene rings, as in 2,2'-dibenzyloxybenzophenone, would ensure that one benzyloxy substituted ring remains nearly coplanar with the carbonyl at all times. Hence, the efficiency of hydrogen abstraction and RH would be increased. However, RH for 2,2'-dibenzyloxybenzophenone is only 1.5 times larger than RH for o—benzyloxybenzophenone. The smallest increase possible would be due to the increased statistical favorability of two benzyloxy groups, i.e., a factor of two. The observed increase is less than that and would suggest that the efficiency of 6-hydrogen abstraction in gealkoxybenzophenones is not severely affected by this type of excited state conformational preference. 9“ Scheme 12 Rotation about the acyl-phenyl bond has been found to be an important conformational factor in the photochemistry 18 It was envisioned that if such of ggalkylphenyl ketones. a rotation is important to hydrogen abstraction in o- alkoxyphenyl ketones, 2,6-dialkoxyphenyl ketones might be more reactive than ggalkoxyphenyl ketones. For example, 2,6-dimethoxybenzophenone should have a shorter lifetime than.gfmethoxybenzophenone (Scheme 13). The triplet life- time of 2,6-dimethoxybenzophenone (determined by laser flash SpectPOSCOPY) is more than twice that of ggmethoxybenzo— phenone, determined by the same technique! Rotation about the acyl-phenyl bond, therefore, does not have a significant effect on the rate of hydrogen abstraction in o—alkoxyphenyl ketones. 2,6-Diacyl substitution about the alkoxy group can help determine the importance of alkoxy group rotations to 6-hydrogen abstraction in o—alkoxyphenyl ketones (Scheme 114'). 95 Scheme 13 Scheme 1“ 96_ 2,6-Diacylalkoxybenzenes, then, are models for the (syg,§yg) conformer. If alkoxy rotations are of any sig— nificance in the mechanism of o-hydrogen abstraction, kH values for 2,6-diacylalkoxybenzenes should be much larger than those of their monoacyl counterparts. In all cases, this rate enhancement is observed for 2,6-diacylalkoxy- 29b have shown benzenes (Table 22)! Wagner and Siebert that metagacyl substitution has no effect on the rate constant for y-hydrogen abstraction in valerophenones. Hence, the larger kH values for 2,6-diacylalkoxybenzenes are a true indication of the effect that rotation of the alkoxy group has on the efficiency of d-hydrogen abstrac- tion in gfalkoxyphenyl ketones. Although the large kH values for 2,6-diacylalkoxy- benzenes indicate that alkoxy group rotation is important to the overall hydrogen abstraction mechanism, the exact mechanism of the interconversion of the two conformers resulting from such a rotation has yet to be established. Three basic mechanisms have been proposed for such inter- 16 rate determining 1? conversions - ground state equilibrium, 18 excited state rotation, or excited state equilibrium. Proton nmr.“l indicates, not surprisingly, that the preferred ground state conformation of g-substituted anisoles is one in which the methoxy group is rotated a full 180° away from the ortho substituent. The same ground state preference should also be true for all 97 Table 22. Hydrogen Abstraction Rate Constants for 2,6- Diacylalkoxybenzenes and Corresponding g—Alkoxy- phenyl Ketones in Benzene at 25°C. 0/ CHZR I R" 7 -l I! ' R R R opdt RH, 10 s H Ph Ph 0.914a 2.70 COPh Ph Ph 1.00a 2u.70 H H Ph 0.30 ' 0.177 COPh H Ph 0.77 2.19 H Ph CH3 0.0226 0.0532 COCH3 Ph CH3 0.119 3.82 aTotal quantum yield for the formation of both 3-hydroxy-2,3- dihydrobenzofuran isomers. 98 ggalkoxyphenyl ketones, since steric repulsions between the alkoxy group and carbonyl should be equal to if not greater than those felt in the anisoles described above. There- fore, if ground state equilibrium populations of the two ketone conformers limited the efficiency of hydrogen abstraction, quantum yields for photoproduct formation could not be more than 0.5 and could be much smaller. However, the photoproduct quantum yield for orbenzyloxy- benzophenone is 1.0. Hence, a ground state equilibrium between these two conformers does not have a significant effect on the efficiency of hydrogen abstraction in these ketones. Rate determining rotation of the alkoxy group would make kH values for these ketones insensitive to the C-H 99 bond strength of the alkoxy hydrogens. As pointed out earlier, kH values for g-alkoxyphenyl ketones are sensitive to the reactivity of the alkoxy hydrogens. Therefore, alkoxy group rotation is not the rate determining step in the mechanism for 6-hydrogen abstraction. This leaves an excited state equilibrium between the two triplet conformers as the only mechanistic alternative. A mechanism based upon this excited state equilibrium is sum- marized in Scheme 15. \_.. 02 OH OH Scheme 15 100 The 13C nmr chemical shifts of the alkoxy carbons in 2,6-diacyalkoxybenzenes are a full 7 to 10 ppm downfield relative to those of their monoacyl counterparts (Table 23). Similar chemical shift differences have been observed by Strothers7n for a series of 2,6-dialkylanisoles (Table 23). In this system, increasingly bulky alkyl substituents force the methoxy group out of the plane of the benzene ring, thereby disrupting conjugation of the methoxy oxygen with the aromatic system. This loss of conjugation is mani- fested by the higher chemical shift values of the methoxy carbons of these compounds. These results are substan- tiated by other 13C nmr studies75 and by electronic ab- sorption spectroscopy.76 Since the chemical shift dif- ferences in 2,6-diacylalkoxybenzenes are of the same magni- tude and direction as those reported by Stothers for 2,6- dialkylanisoles,7h it is reasonable to assume that the same conformation is preferred in these compounds as well. That is, the alkoxy group of 2,6-diacylalkoxybenzenes is actually orthogonal to the plane of the central benzene ring, Just as it is in 2,6-di-t-butylanisole.7Ll 2R :'H R' O R' 101 Table 23. 130 Chemical Shifts of the Alkoxy Carbons of Substituted Anisoles. ! H R R R 60_CH2_R. ppm H COPh H 55.33 Ph copn H 68.65 Ph COCH3 H 70.60 Ph ON ON 76.90 Ph COPh COPh 77.12 Ph COCH3 COCH3 79.u0 H COPh COPh 61.60 H H H 514.0a a H CH3 CH3 57.9 a H CH(CH3)2 CH(CH3)2 61.2 a aReference 7h. 102 Furthermore, the exact geometry of the (syn,§yn) con- former is most likely one in which the alkoxy group is not totally COplanar with the aromatic system, but approaches co-planarity as far as steric repulsions from the carbonyl will allow it. This conformation is still reactive since the alkoxy hydrogens are still quite accessible to the carbonyl oxygen. Excited state equilibrium constants can be calculated from the ratio of kH for an gealkoxyphenyl ketone to that of its 2,6-diacylalkoxybenzene analogue. This calculation assumes that the 2,6-diacylalkoxybenzenes provide an ac- curate measure of kH for the (syn,§yn) conformer of the cor- responding gyalkoxyphenyl ketones. That is, kH for 2,6- diacylalkoxybenzenes represent the intrinsic kH values for their corresponding g—alkoxyphenyl ketone analogues. The calculation of these excited state equilibrium constants in- vokes the Winstein—Holness relationship.77 This relation- ship, which holds only for systems in which conformational changes are faster than reaction, states that - obs int kH - Kex kH where kabs = observed rate constant for hydrogen abstraction (kH for an g—alkoxyphenyl ketone Kex = excited state fractional equilibrium population of the reactive conformer 103 kfint = intrinsic hydrogen abstraction rate constant (kH for the appropriate 2,6-diacylalkoxybenzene). These excited state equilibrium constants are summarized in Table 24. The Kex values for both ggbenzyloxybenzophenone and o- methoxybenZOphenone are surprisingly similar. This would seem to indicate that the magnitude of Kex is not strongly influenced by the size of the alkoxy substituent. Excited state equilibrium favors the unreactive con— former in ofbenzyloxyacetophenone by nearly 99:1! This is almost an order of magnitude larger than the excited state -preference for the unreactive conformer of g-benzyloxybenzo- phenone. The larger Kex value for gebenzyloxybenzophenone may reflect the fact that the benzyloxy substituted ring is probably not coplanar with the carbonyl groups, as it must be in g—benzyloxyacetophenone. Hence, the steric repulsions due to the carbonyl group are not as strong in the benZOphenone as they are in the acetOphenone. CHth CH R CH 10“ Table 2”. Excited State Equilibrium Constants for gs Alkoxyphenyl Ketones in Benzene at 25°C. n ' 7 -l R R' R kH, 10 s Kex Ph ' Ph H 2.70 0.109 Ph . Ph COPh 2u.70* Ph CH3 H 0.0532 0.0139 Ph CH3 COCH 3.82* H Ph H 0.177 0.0808 H Ph COPh 2.19* ! Note that these values are assumed to be the intrinsic kH values for the corresponding g-alkoxyphenyl ketones. 105 The intrinsic rate constant for o-hydrogen abstraction in ogbenzyloxybenzophenone is in good agreement with the predicted value of 1088-1. Correction of the intrinsic kH for o-methoxybenzophenone for the reduced reactivity of an gfmethoxy group, also brings it within the predicted range. The intrinsic kH for o-benzyloxyacetOphenone is also somewhat lower than the predicted kH. It has been estab- lished that the excited state reactivities of both 3- 29a methoxyvalerophenone and o-benzyloxyvalerophenone are approximately one—eighth that of valerophenone. An 9? alkoxy substituent stabilizes the fl,fl* triplet relative to 29a the n,n* triplet of these ketones by resonance. Since the n,w* triplet is lowered in energy there is more n,n* character in the triplet of these ketones and the excited d.29a Assuming that the same is state reactivity is reduce true for o—benzyloxyacetophenone, correction of the intrin- sic k for this reactivity decrease puts it in good agree- H ment with the predicted value. Evidence for a 1,5-Biradical Intermediate n-Alkyl mercaptans are known to trap biradicals with rate constants on the order of l x 107M'ls-l.78 Attempts to trap the presumed biradical formed from ggbenzyloxybenzo- phenone with n-octylmercaptan, a known biradical trapping‘ agent,780 were unsuccessful. Instead, the lifetime value obtained indicates that the ketone triplet was quenched. 106 Mercaptans are known to quench ketone triplets, as well, with similar rate constants.7u Therefore, if the ketone triplet is substantially longer lived than the biradical, it will be quenched preferentially. This is the case here, indicating that the biradical lifetime is much shorter than the ketone triplet lifetime. For the same reason, it was not possible to observe the biradical directly by nanosecond laser flash spectroscopy. Absorptions from the longer lived ketone triplet masked those of the biradical. In such cases, it is possible to "fine- tune" the system.80 This is accomplished by adding suf- ficient amounts of a diene quencher to shorten the triplet lifetime enough to make it shorter lived than the biradi- cal, thereby making the biradical spectrum visible. At- tempts to observe the biradical by this technique in ben- zene solution were unsuccessful. However, addition of 1.0 M pyridine did make the biradical formed from g-benzyloxy— benzophenone visible (TBR = 13 nsec).81 Hence, in the ab— sence of pyridine this biradical is too short-lived to be observed on the nanosecond time scale of the laser appa- ratus. The effects of pyridine on the lifetime of this biradical will be discussed later. It has been shown that l,u-biradicals which have an oxygen atom incorporated in their backbone have dramatically shorter lifetimes than their pure hydrocarbon analogs. Caldwell82 has found that the Norrish Type II biradicals 107 formed from benzyl phenacyl ethers have lifetimes two orders of magnitude less than their hydrocarbon counter- parts (Scheme 16). Caldwell82 has also found that pre- oxetane biradicals (Scheme 16), formed from the Paterno- Bfichi reaction of benzophenone with various olefins, have similarly short lifetimes, on the order of 1.5 to “.0 nsec depending upon the olefin and experimental conditions. Peters83 reported similar lifetimes for the Paterno-Bfichi biradical formed from benzophenone and dioxene. This effect has only been observed in circumstances where the biradical backbone contains an oxygen atom, and is not observed if there is an alkoxy substituent on the biradical. The lifetime of the Norrish Type II biradical formed from y-methoxyvalerophenone (30 i 6 nsec)82 is close to the 38 nsec lifetime of the biradical produced from valerophenone by the same process. Two explanations have been put forth82’83 to account for the shorter lifetime of these biradicals. One is that resonance with the oxygen decreases the average distance between the two radical centers and thereby destabilizes the biradical (Scheme 17). 1.=’hJ:H\/ll {—9 ”)1ng Scheme 17 108 Table 25. Lifetimes of Some Norrish Type II Biradicals. CHEER -CR R 0 1 2 OH I 1 2 0 X o x ‘ R1 2 H 41> --—> 3 X Methanol Heptane R1 R2 X TBR, nsec TBR’ nsec Ph Ph 0 H.9t1.5 6.4il.6 Ph H O 1.3 - 1.7 Ph 1 Ph CH2 222.:18. ll3.il3. Ph H 'CH2 146.118. 55.: 8. OCH3 H CH2 70.: 5. 30.: 6. R R R 0 -—J-R 0 I/Ji\\P hv /\H E R . ' Ph«—L——d Ph h Ph £_- Ph Ph Alternatively, some biradical conformations have an angle of 90° between a 2p oxygen orbital and the half-filled orbital of the adjacent radical center. Spin-orbit coupling from these conformations is enhanced thereby enhancing the 109 rate of intersystem crossing (believed to be the rate de- termining step in biradical decay8u) and reducing the triplet lifetime. However, these conformations should also exist in the biradical formed from y—methoxyvalerophenone. Since this biradical has a 'normal' lifetime, it is unlikely that the latter explanation is a correct one. Since the biradical formed from gebenzyloxybenzophenone contains an oxygen atom in its backbone, it is not surpris- ing that it is extremely short-lived in the absence of pyridine. Wagner85 has demonstrated that pyridine and other weak Lewis bases, such as t-butyl alcohol, solvate Norrish Type II biradicals and suppress disprOportionation of the bi- radical to starting ketone (Reaction 25). The quantum OHW 0 ‘ elim. dis PhiA \(25) P P$£ éyé:::Z:m{ H0 yields of elimination products are enhanced, while those of cyclization products are diminished slightly, for 110 steric reasons. In the case of ggalkoxyphenyl ketones, there are only two competitive reactions possible from the biradical - cyclization and disproportionation (Reaction 26). Addition of pyridine should totally suppress disprOportionation while offering a slight steric barrier to cyclization. The net result should be an overall enhancement of the photocycliza- tion quantum yield. Although the photocyclization quantum yield for o—benzyloxybenzophenone in the absence of pyridine is already close to 1.0, addition of pyridine (ca. 2 M) increases the photocyclization quantum yield for o—benzyl- oxyacetophenone nearly ten-fold (Table 26)! R I O R! hv Eisprop The effect of added pyridine on the photocyclization JWr 3' (26) quantum yield for o-benzyloxyacetOphenone is rather dram- atic compared to its effect on the Norrish Type II reaction. For example, pyridine increases the quantum yield for the formation of g—benzyloxyacetophenone from o—benzyloxyvalero- phenone by a factor of only 1.8. 111 Table 26. Effects of Pyridine on Photoproduct Quantum Yields from o—Benzyloxyacetophenone in Benzene at 25°C. - Ph H CHZPh 0 0’/’ 0 0 H 0 W“ Ph Ph 0H 0H 0 V" . _z_ E Z-AcBP CH [Pyridine], M ¢g ¢§ ¢2-AcBP 0.00 0.0226 Trace 0.0589 0.500 0.0598 0.0301 0.0670 1.63 0.101 0.0666 0.0517 2.18 0.118 0.0811 0.0u56 The biradical derived from oebenzyloxyacetophenone is initially formed in a conformation which favors dispro- portionation (Scheme l7) over cyclization. To avoid dis- proportionation, the biradical must undergo rotation about 86 bond a. Conradi and co-workers have measured the line broadening of the epr spectrum of benzaldehyde ketyl radi- cal. They deduce a rate constant for bond rotation on the order of 103s.l at 25°C. This is somewhat lower than what would be expected for such a rotation. Molecular orbital 112 CHZPh CH-Ph CH-Ph /’ o// ’I R O OH O hv ° ' OH R ____, a R 0 Ph OH R Scheme 17 calculations87 predict a barrier to rotation in this system of approximately 8 kcal/mole. Based upon this value, one would expect a rate constant for rotation on the order of 107s'1. Coincidentally, this is the same value found for rotation in the electronically similar triplet ketone.18 Regardless of whether or not the experimentally de- termined value is correct, it is clear that the requirement that the C-OH fragment remain 00planar with the benzene ring, in order to maximize delocalization of the odd 113 electron, demands that rotation about bond a is highly restricted. Therefore, the biradical formed from of benzyloxyacetophenone initially exists in a conformation favoring disprOportionation and would not be able to under- go rotation fast enough to make cyclization competitive with disproportionation. However, pyridine solvates the ketyl portion of the biradical and prevents disprOportionation from this con- formation, giving the biradical more time to undergo rota- tion and subsequent cyclization. This solvation would also inorease the steric bulk at the ketyl radical center and may force rotation about bond a, i.e., increase the rate of rotation. Pyridine solvation of the biradical also results in a loss of stereoselectivity for biradical cyclization. In the absence of pyridine, cyclization of biradicals derived from gfbenzyloxyacetophenone and g-benzyloxybenZOphenone clearly favors formation of the kinetically preferred product. That is, cyclization of these biradicals in the absence of pyridine favors the isomer in which the less bulky hydroxyl group is gig to the C-2 phenyl (§_isomer). Ad- dition of pyridine increases the steric bulk of the hydroxyl group, since the pyridine is now hydrogen bonded to the hydroxyl proton. Since the hydroxyl group is now com- parable in size to a methyl (in the o—benzyloxyacetophenone derived biradical) or a phenyl (in g—benzyloxybenzophenone 11h derived biradical), cyclization proceeds with no stereo- chemical preference. The photocyclization quantum yields for both g—benzyl- oxybenZOphenone and o—methoxybenzophenone are reduced by the addition of pyridine. At the same time, however, addi- tion of pyridine to both of these ketones results in the formation of a new photoproduct, whose structure is presently undetermined (Tables 27 and 28). Laser flash spectroscopy Table 27. Effects of Pyridine on the Photocyclization Quantum Yields for ggBenzyloxybenzophenone in Benzene at 25°C. Ph ’/,CH2Ph 0H “Ph Ph rufi E a [Pyridine], M g E unknown total 0.0 0.831 0.108 0.00 0.939 1.24 0.358 0.290 0.280 0.928 2.A7 0.323 0.293 0.310 0.926 aEstimated 115 Table 28. Effects of Pyridine on the Photocyclization Quantum Yield for ngethoxybenzophenone in Benzene at 25°C. Ph ' CH 23,—) 0 Ph o 3 W H0 CH3 [Pyridine], M ¢cyc ¢unknown ¢total 0.0 0.299 0.0242 0.323 1.2M 0.157 0.110 0.267 2.H7 0.151 0.135 0.286 reveals that the triplet lifetime of gebenzyloxybenzophenone is only slightly affected by the addition of pyridine (TBR a 58 nsec in benzene, 75 nsec in benzene containing 1M pyridine).81 Hence the lower photocyclization quantum yield for g—benzyloxybenzophenone is not due to quenching of the ketone triplet. Therefore, the lower photocycliza- tion quantum yield for o—benzyloxybenzophenone must be due to some interaction of pyridine with the biradical. The lifetime of the g—benzyloxybenzophenone derived biradical is an order of magnitude larger in benzene containing 1M pyridine (13 nsec)81 than it is in the absence of pyridine 116 81 It may be possible that solvation of (less than 4 nsec). the biradical reduces the rate constant for cyclization enough to make some other biradical process competitive. It is this process which gives rise to the new photOproduct. Unfortunately, this product was too unstable to be isolated by flash chromatography.88 Hence, any discussion of its origin is purely speculative. Spectral analysis of the photoproduct formed from of methoxybenzophenone in the presence of pyridine reveals it is probably gymethoxybenzhydrol. It is likely that this product arises from photoreduction of o—methoxybenzophenone. The quantum yield for the formation of 2-acetylbenzo- phenone, 33, from o—benzyloxyacetophenone, 30, is not affected by the addition of pyridine (see Table 26). This suggests that 2-acetylbenzophenone may be formed from the biradical via a pathway which is not affected by the pres- ence of pyridine. Such a pathway is outlined in Scheme 18. According to this mechanism, the biradical has two competitive cyclization reactions available to it - one leads to formation of the usual benzofuranol photoproducts, the other leads to formation of the quinoid structure, 31. Addition of pyridine would not affect the rate with which the biradical cyclizes to 31, since such a cyclization does not involve the hydroxyl proton. Rearrangement of 31 to 2-acetylbenzhydrol, 32, should be fast since it involves a rearomatization of the benzene ring. Hence, the overall rate constant for the formation of 2-acetylbenzhydrol 117 from the o-benzyloxyacetophenone biradical should be unaf- fected by the addition of pyridine. It is not clear whether the oxidation of 2-acetylbenzyhydrol to 2-acetylbenzo- phenone proceeds photochemically or thermally. CH Ph - / 2 /CH Ph 0 0 0 0H hv . CH ——-> CH O o 3 (5— o 3—> O P. Sme HO CH 1/ 3 Ph Ph OH OH 0 0 ( 3A .2; CH > 3 —-—> Ph 3 O O CH 3 ' 0 Scheme 18 Both radicals and biradicals are known to undergo ring coupling reactions which give rise to compounds with structures similar to 31. Benzyl radicals couple to form 1-alkyliden-2,5-cyclohexadienes.89 The same coupling re- action has been found to occur with the semi-benzpinacol radicals formed from the photoreduction of benzophenone.90 Steel has shown that these ring coupled products are formed in yields on the order of a few percent from the 118 91 photoreduction of benzophenone. Pitts and co-workers92 have reported that photolysis of butyrophenone produces a trace amount of material whic they believe may be a-tetralone (as well as the usual Type II products). They postulate that it is formed from the cyclization of the Norrish Type II biradical. OH 1 l CH CH 0 3 OH 2 Ph Ph ' 7 ‘ 0 / Hence, the mechanism described in Scheme 18 provides a plausible and rather attractive explanation for the forma- tion of 2-acety1benzophenone via the photolysis of of benzyloxybenzophenone. 119 B. a-(ggAlkylphenyl)acetophenones 1. Hydrogen Abstraction Rate Constants The rather short triplet lifetimes for d—(g—alkyl- phenyl)acetophenones suggest that hydrogen abstraction is the predominant process from the triplet. Acyl cleavage is not competitive with hydrogen abstraction since rate constants for such a process in a-phenylacetophenones are 6 l 93 on the order of 10 s- . Lewis reports that kc for a- 6 1 (A-methylphenyl)acetophenone is 3.6 x 10 s' in benzene. Furthermore, hydrogen abstraction is much faster than trip- let decay in this system. The photocyclization quantum yield for a-(g-tolyl)acetophenone (Table 29) is noteworthy, since such a value is possible only if kH is much larger than both kd and ka. Lewis93 has reported a kd value on 68-1 for a-(H-methylphenyl)acetophenone in the order of 10 benzene. Assuming that the kd values for a-(N-methylphenyl)- acetophenone and a-(g-methylphenyl)acetophenone are similar, non-reactive decay accounts for less than 1% of the over- all triplet lifetimes of these ketones. Hence, the recip— rocal triplet lifetimes of these ketones are in accurate measure of the rate constant for hydrogen abstraction, kH. These values are presented in Table 29. 120 .ocfiofipmd 2H wcficfiMucoo ocmucon :fi oomfimpno .oaofiz Ewucmsv coaummfiaozo Iouond omuaefixmz .Oomm pm ocoucon CH m Emoaxmu x wcfiezmmm .Be x Eopm woumHSonom Q HI HI sm.a mo.o mm.m Hso.o mimeovmo-o.s mmo aaAeHeV-a as.a mso.o om.m . ms.o Ngmeovmo-m meo saxsuovus mo.H mm.o mo.: oflsm.ovss.o mmoum.: z mazua mom.o em.m o.mH mo.o mmo-m m saxazovus moH.o sfi.e s.om oo.H z : aaeus aunmoa some .wt HI: .eeox cone .m m ocooox .mxu90\fi .m cm o memo I .oomm um ocoucmm CH monocmzoouoomAazcozoazxa«loViv mo weapom m pom whouoempmm oHpocfixouonm .mm manna 121 2. Glimpses of a 1,5—Biradical Intermediate The quantum yield for the formation of 2-phenyl-2- hydroxyindanes from a-(gfalkylphenyl)acetophenones can be represented by - k ¢pdt ¢isc TT H It has been established that kH and 1/T are essentially equal. The photocyclization quantum yield of 1.0 for d- (g-toly1)acetophenone indicates that ¢isc must be 1.0, as we well. Varying the alkyl substituent on the a-phenyl ring should not affect the value of the intersystem crossing yield. Lewis93’9LI has measured intersystem crossing quan- tum yields for a number of a-phenylacetophenones and found them all to be 1.0. Therefore, photocyclization quantum yields less than one are attributable to some inefficiency in cyclization of the presumed 1,5-biradica1 (Reaction 27). . OH OH ° .. O O. O . ——+ -—» Ph Ph Ph (27) There is no direct evidence for the intermediacy of this biradical. Attempts to trap the biradical with n-dodecyl- 78 mercaptan were unsuccessful, presumably due to the 122 unreactive nature of a benzyl radical towards radioal scavengers. There is, however, some rather convincing indirect evidence for its existence. Recall that pyridine increasestflmephotocyclization of g-benzyloxyacetOphenone by suppressing disproportionation of the biradical to starting material. Added pyridine also increases the photocyclization quantum yield of a-mesityl- acetophenone, albeit to a much lesser extent (from 0.44 to a maximum of 0.54). This result is reminiscent of typical biradical behavior and points toward the existence of a 1,5-biradical in this reaction. It is interesting that the maximum photocyclization quantum yield for a-mesitylacetOphenone is only 0.54, especially since that for a—(g-tolyl)aCetophenone is 1.0. This would suggest that there may be another mode for bi- radical disproportionation, which is unaffected by the 32b have found that presence of pyridine. Wagner and Chiu the 1,5-biradica1 formed by the photolysis of B-ethoxy- propiophenone undergoes two different modes of dispropor- tionation - 1,6-hydrogen transfer (the expected mode) and 1,4-hydrogen transfer (Reaction 28). 1,4-Hydrogen trans- fer (enolization), does not involve the hydroxyl proton, and hence is unaffected by addition of pyridine. Enoliza- tion is also the major disproportionation reaction from this biradical. 123 CH C C HO ' O kv 0 CH3 0 9L; —-> I; -—>H <+————- . Ph 1.6-H . Ph transfer 1,4-H HO h (28) ‘§\\\\\\ transfer CH ~ 3 The same disprOportionation pathway is available to 1,5- biradicals produced from (gealkylphenyl)acetophenones (Re- action 29). /1,4-H \ transfer (29) This added mode of disproportionation would also account for the unusually low photocyclization quantum yield for 124 a-(2,4,6-triis0propy1phenyl)acetophenone, as well as explain- ing why ¢ma for a—mesitylacetophenone is less than 1.0. x The biradical essentially has two options available - dis- proportionation (via both 1,4- and 1,6-H transfer) and cyclization. Although cyclization is much faster than dis- proportionation in a-(g—tolyl)acet0phenone, added substi- tution of both the d-phenyl ring and the g-methyl carbon reduces the rate of cyclization. Disproportionation is also affected, but to a much lesser extent. Therefore, ketones with bulky R or R' substituents should have photocycliza- tion quantum yields less than unity, as is observed in the extreme for a-(2,4,6-triisoprOpylphenyl)acetophenone. 3. Substituent Effects on the Photoreactivity of a-(ggAlkylphenyl)acetOphenones The photocyclization of a-(g—alkylphenyl)acetophenones is quite sensitive to the reactivities of the gfmethyl hydrogens (Table 29). This sensitivity manifests itself in two different effects. First of all, alkyl substitution of the ofmethyl group increases the rate of hydrogen abstraction. For example, a-(2,5-diisopropylphenyl)acetophenone is approximately six times more reactive than a-(2,5-dimethylphenyl)acetophenone. Wagner and Leavitt95 have found that cumene (iSOpropyl- benzene) is approximately 2.5 times more reactive than toluene in the photoreduction of acetophenone, reflecting 125 the added reactivity of a tertiary benzylic hydrogen over a primary benzylic one. Alkyl substituents on the a—phenyl ring also increase the rate of hydrogen abstraction. For example, a-(2,5- dimethylphenyl)acetophenone is twice as reactive as a- (getolyl)acet0phenone. Similar rate enhancements have been observed in the photoreduction of aromatic ketones with 95’96 These rate en- various alkyl substituted toluenes. hancements are, in part, the result of inductive effects on the reactivity of the benzylic hydrogens. 4. Mechanistic Implications Such inductive effects, however, cannot explain the observation that a—mesitylacetophenone is nearly seven times more reactive than a-(g-tolyl)acetophenone. Several literature reportsgfr'g9 indicate that inductive effects result in only a 1.2 to 1.8 fold greater reactivity for mesitylene relative to toluene in benzylic hydrogen ab- straction. Correction of kH for a—mesitylacetophenone for this inductive increase still leaves a four fold difference in kH's of a-mesitylacetophenone and a-(ggtolyl)aceto- phenone. One possible explanation is that hydrogen abstrac- tion in a-(g-toly1)acetophenone experiences some conforma- tional restrictions which are not present in a-mesityl- acetophenone. 126 Karabatsos and Fenoglioloo have shown that the preferred ground state conformation of a-phenylacetaldehyde is one in which the a-phenyl ring eclipses the carbonyl. E= 0.3 Real/mole This conformation should be even more preferred in the ground state of a-phenylacetophenones since the ortho hydrogens of the two benzene rings interact strongly in the gauche conformation.lOl Assuming that the a-phenyl ring eclipses the carbonyl in a-(g-alkylphenyl)acetophenones, there are three con- formers possible for these ketones. 127 The preferred conformer would have the a-phenyl ring rotated such that the g-methyl group is a full 180° away from the carbonyl (anti conformer), thereby minimizing steric interactions between the methyl and carbonyl. 5-Hydrogen abstraction is not possible in this con- former, since the g-methyl hydrogens are not accessible to the carbonyl oxygen. The a-phenyl ring can rotate to give rise to the syn conformer. Examination of Dreiding molecular models reveals that the o—methyl cannot become co-planar with the carbonyl, for steric reasons. There- fore, the syn conformer is one in which the a-phenyl ring rotates far enough to allow hydrogen abstraction to occur, 128 but not far enough to create serious steric interactions between the nfmethyl and the carbonyl. Symmetric 2,6-dimethyl substitution of the a-phenyl ring, as in a-mesitylacetophenone, would eliminate the possibility of an anti conformer, leaving only the syn and skewed conformers. Hence, the four-fold difference in kH's for a-mesitylacetophenone and a-(nftoly1)aceto— i phenone is due to the lack of any unreactive anti conformer for a—mesitylacetophenone. The Winstein-Holness relation- ship can be applied to this system, since conformational changes are faster than hydrogen abstraction. The four fold difference in kH's for these two ketones means that the fractional population of the nyn conformer is four times greater for a-mesitylacetophenone than it is for a-(n—tolyl)acetophenone. Given that - S+A+G=1=S'+G' where S, A, and G refer to the fractional popula- tions of the syn, anti, and skewed conformers of a-(n—tolyl)acet0phenone, and S' and G' are the fractional populations of the nyn and skewed conformers of a—mesityl- acetophenone. Since - S' = 48, then, S + A + G = 4S + G'. 129 Reorganization of the above equation gives - +G-' ASG=3 Wagner and Chen18 have found an anti/syn ratio of ap- proximately 4 for n—methylacetophenone. The anti/syn ratio for a-(ngtoly1)acetophenone should be similar to that for nemethylacetophenone, since the steric inter- actions in both systems are nearly the same. Hence, the anti/syn ratio for a—(n—tolyl)acetophenone is approximately 3. This means that (G - G') is negligible. It is unlikely that a-mesitylacetophenone and a-(n—tolyl)acetophenone should have equal populations of skewed conformers. There- fore, the populations of skewed conformers for both these ketones must be minimal, making the (G - G') term unim- portant. Although the nature of the conformational effect has been established for this system, the mechanism of this interconversion has not. The usual three possibilities l6 exist - ground state equilibrium, rate determining rota- tion,18 and excited state equilibrium.l7 Since a ground state equilibrium between syn and anti conformers clearly favors the anti conformers, photocycliza- tion quantum yields would be much less than 0.50 if there were no excited state interconverSion. However, ¢pdt for a-(n—toly1)acetophenone is 1.0. Hence, ground state equilibrium populations of the syn and anti conformers do not 130 limit the efficiency of hydrogen abstraction in a-(n—tolyl)- acetophenone. Rate determining rotational control can be eliminated, since the kH values for these ketones vary with the reac- tivity of the nemethyl hydrogens. The only mechanistic alternative that remains is an excited state equilibrium between syn and anti conformers. A mechanism based upon this equilibrium is summarized in the scheme on page Assuming that excited state equilibrium populations of the skewed conformer are negligible gives an excited state equi- librium constant of 0.25 for the interconversion of anti and syn triplets. Using this Kex value and invoking the Winstein—Holness relationship, the intrinsic value for the hydrogen abstrac— tion rate constant can be estimated as 6.5 x 1083-1. An apparent contradiction to this mechanism is found when comparing the k values of a-(2,5—diisopropy1phenyl)- H acetophenone and a-(2,4,6-triisopropylphenyl)acetophenone. These rate constants are the same within experimental error! Since the value of kH would have no effect on the value of Kex’ the higher Kex value must be due to something else. The similar kH values for a-(2,5-diisopropylphenyl)- and a-(2,4,6-triisopr0pylphenyl)acetophenones suggest that the fractional equilibrium populations of syn conformers are identical for both ketones. This means that - A+G=G' 131 R R' IN Ph Ph R ’ R R ' 0H 0H -—-——-* Ph Hence, the fractional equilibrium population of the skewed conformer of d-(2,4,6-triis0prOpylphenyl)acetOphenone cannot 132 be negligible. This is not unreasonable since the added steric bulk of an n—isopropyl group may prevent the triplet ketone from attaining the syn or reactive conformation as easily as it does in the case of a-(n—tolyl)acetophenone. 5. Entropic and Enthalpic Differences Betweengle and 8-Hydrogen Abstraction a-(n—Alkylphenyl)acetophenones are merely one carbon higher homologs of n—alkylacetophenones. It might be use- ful, at this point, to compare G-hydrogen abstraction in the former with y-hydrogen abstraction in the latter. Wagner18 has measured the rate constant for y-hydrogen abstraction in nemethylacetophenone as 3 x 1093-1. The intrinsic hydrogen abstraction rate constant for a-(g- 8 1 tolyl)acetOphenone is 6.5 x 10 s' It has been determined 102 that d-phenyl substitution affects ketone photoreactivity as much as n—methyl substitution does.l8 Hence, the nearly five-fold difference in rate constants between these two ketones reflects the relative ease of y- and G-hydrogen abstraction. Both systems have essentially the same degree of rotational freedom. Therefore, this reactivity difference represents the enthalpic disfavorability of the formation of a seven-center transition state (d-hydrogen abstraction) relative to formation of a six center transi- tion state (y-hydrogen abstraction). Wagner32 had found a twenty-fold difference in the rates 133 of Y‘ and 6- hydrogen abstraction in freely rotating acyclic systems. It was never clear what the relative contributions of entrOpic and enthalpic factors were to this rate difference. In light of the previous comparison, it appears that entropic and enthalpic factors contribute equally to this twenty-fold rate difference. 6. a-(ngTolyl)acetone andcp49eTolyl)acetaldehyde A brief mention should be made concerning the photo- chemistry of a-(n—tolyl)acetone and a-(n—tolyl)acetaldehyde. Irradiation of each of these compounds failed to produce any of the desired photocyclization products. Instead, products arising from acyl cleavage (Norrish Type I reactionlOB) were obtained (Reaction 30). Ogata1014 has also reported .. O O 0“ R=Ph R h-i CH3 WP. -—> 3 852 the same results for the photolysis of a-(n—tolyl)acetone. 0105- V Cleavage rate constants on the order of 1 l have been reported for dibenzyl ketones.9u Therefore, since cleavage should be 100 times faster than G-hydrogen abstraction, no photocyclization products should be formed. 134 C. Conclusions l. n—Alkoxyphenyl Ketones The mechanism of d—hydrogen abstraction in nfalkoxy- phenyl ketones involves an excited state equilibrium prior to hydrogen abstraction. This equilibrium is brought about by rotation of the alkoxy group about the phenyl- oxygen bond, and favors the unreactive (nnni,nyn) con- former. The (nyn,nyn) triplet conformer readily undergoes hydrogen abstraction, giving rise to a 1,5-biradica1. The (nnEi,§yn) conformer cannot undergo hydrogen abstraction directly, but can equilibrate with the (nyn,nyn) triplet, thereby leading to hydrogen abstraction. Rotation about -1)18 the phenyl—acyl bond (kr0 m 1078 can occur from the t (nnEi,nyn) triplet, but is not rate determining since hydrogen abstraction in these ketones is no faster than such a rotation. There is no evidence that phenyl-acyl bond rotation is taking place in the (nn£$,nyn) triplet, although this rotation may be masked by the kinetics of the excited state equilibrium involving the alkoxy group rota- tion. The 1,5-biradical formed from these ketones must under— go rotation about the ketyl radical center in order to avoid rapid disproportionation to starting ketone and in order to cyclize to benzofuranol products. This rotation is severely restricted if R'=CH3, meaning that the yield 135 of photocyclization products is quite low (¢ = 0.0226). However, if R' = Ph, this rotation is rapid, cyclization is quite efficient, and the photocyclization quantum yields in such cases approach unity. Intrinsic hydrogen abstraction rate constants are in good agreement with the values previously predicted for this system.105 2. a-(g—Alkylphenyl)acetophenones The mechanism for hydrogen abstraction in a-(n—tolyl)- acetophenone also involves an excited state equilibrium between two triplet ketone conformers. Only the nyn con- former is reactive, since it is only in this conformation that the nemethyl hydrogens are accessible to the carbonyl oxygen. However, excited state equilibrium for a-(g- tolyl)acetophenone favors the unreactive conformer by by 3:1, due to the steric repulsions between the nemethyl group and the carbonyl. Hydrogen abstraction occurs from the nyn triplet with a rate constant of 6.5 x 108s'l. This equilibrium situation breaks down for a-(n—iso- propylphenyl)acetophenones, where steric bulk forces the a-phenyl ring to tilt into a skewed conformation. The percentage of skewed conformer in a—(2,4,6-triis0propyl- phenyl)acetophenone is probably quite substantial and re- duces the value of k for this ketone. H The photocyclization of a-(n-tolyl)acetophenone proceeds 136 RI 137 with unit efficiency. However, photocyclization quantum yields of other d-(n—alkylphenyl)acetOphenones are less than 1.0. Addition of pyridine increases the photocycliza- tion quantum yield for d-mesitylacetophenone to 0.54. It is unlikely that unreactive triplet decay would account for the extra 46% of the quantum yield. This suggests that there are two modes of biradical disprOportionation 32b - 1,4- and 1,6-hydrogen transfer. 1,6-Hydrogen transfer is suppressed by the presence of pyridine, while 1,4-hy- drogen transfer is not. D. Suggestions for Further Research 1. Laser Detection of 1,5-BiradiCals from a-(g—Alkyl- phenyl)acetophenones It would be useful to examine a-(n—alkylphenyl)aceto- phenones by laser flash spectroscopy to determine whether such biradicals are detectable. These biradicals should be longer lived than those produced from n—alkoxyphenyl ketones for reasons discussed previously. Such a study would determine whether heteroatoms in the backbone of 1,5- biradicals shorten their lifetimes as they do in 1,4-bi- radicals. This study would also provide further informa- tion on the mechanism for this effect on biradical life- times. Deuteration of the a-methylene group would help ascer- tain whether 1,4-hydrogen transfer is an important pathway 138 hv isc 1,6- CH3 1, 4-H Hydrogen OH PTransfer Transfer / Ph 0H o .. 139 for 1,5-biradical disproportionation in a-(g-alkylphenyl)— acetophenones. 2. Synthetic Applications of d-Hydrogen Abstraction The remarkably high chemical yields for 2-phenyl-2- hydroxyindanes produced from the photocyclization of a- (n-alkylphenyl)acetophenones prompt a more extensive study of the synthetic potential of this photoreaction. A number of modifications come to mind. It would be especially interesting to replace the phenone ring or the a-phenyl ring with another aromatic system, e.g., furans. hv V W \/ 30 h” \/ 0H .... .\ J 0 hr > . \. 0H It has been shown that the methylene analogs of n- alkylphenyl ketones undergo efficient y-hydrogen 140 abstraction.106 The same reaction may be possible for the methylene derivative of a-(ngalkylphenyl)acetophenones and provide a photochemical route to indanes. CH CH3 3 H . 3 / llliII//u\C h” 3 ”K by CH3 Ph 3. e-Hydrogen Abstraction Preliminary studies indicate that 2,3-dipheny1-3- hydroxy-3,4-dihydrobenzopyran is formed in approximately 80% yield from the photolysis of a-(n-benzyloxyphenyl) acetophenone. This reaction warrants a more extensive study from both a synthetic and mechanistic standpoint. CHémi / . Ph 0 - 0 hv Ph Ph 0H 141 4. Photochemistry of l-(ngAlkylphenyl)-l,2-Propane- diones and Related Compounds Ogata and Takagilou report that the photocyclization of l-(n—tolyl)-1,2-propanedione proceeds via formation of a photoenol. As a method of proof, they have trapped the enol with dimethyl acetylenedicarboxylate. 0H 002Me CH 30 hr . 0 ---€> H Me 02Me COZMe 002Me o H 02Me Results obtained for d—(n-to1y1)acetophenones suggest an alternative mechanism. It is likely that there are two different ketone triplets for this system. These rota- mers, designated a and b, are in equilibrium. Rotamer a leads solely to 6-hydrogen abstraction. Rotamer 6 leads only to enolization. It would, therefore, be interesting to reexamine this compound and a number of its derivatives 142 to ascertain which of the above mechanisms is the correct one . 3 ' * 3 f. a * 7 CH3 7 O O .7: e Me O L - L CH3 J 0H 002Me EXPERIMENTAL A. Preparation and Purification of Chemicals 1. Solvents and Additives Benzene.107 - One gallon of thiophene free reagent grade benzene (Mallinkrodt) was repeatedly stirred with 200 ml portions of sulfuric acid for 12-24 hr periods until the sulfuric acid remained water white. The benzene and sulfuric acid were separated and the benzene washed, first with 400 ml distilled water, and then with sufficient amounts of a saturated aqueous sodium bicarbonate solution until the aqueous phase remained basic to pHydrion paper. The benzene was separated from the sodium bicarbonate solu- tion, dried over magnesium sulfate, and filtered into a clean, dry 5.0 2 round bottom flask. Phosphorus pentoxide (100 g) was added to this and the solution refluxed over- night. After refluxing, the benzene was distilled through a one meter column packed with stainless steel helices at a rate of 100 ml/hr. The first and last 10% were discarded. 108 Dioxane. -Scintillation grade 1,4-dioxane was re- fluxed over calcium hydride for 12 hr and then distilled 143 144 through a one meter column packed with glass helices. The first and last 10% were discarded. Cyclohexane - Spectral grade cyclohexane (Fisher) was used as received. Heptane - MCB Omni-Solv grade heptane was used as received. Pyridine109 - Pyridine (Mallinkrodt) was refluxed over barium oxide for 12 hr and distilled through a one meter column packed with glass helices. The first and last 10% were discarded. EPA Mixed Solvent - MCB phosphorimetric grade EPA mixed solvent (ethyl ether:iSOpentane:ethyl alcohol, 5:5;2) was used as received. 110 - 2-Methyltetrahydrofuran 2-Methyltetrahydrofuran (Aldrich) was refluxed over cuprous chloride for 12 hr and distilled. The first and last 10% were discarded. The middle fraction was then distilled from lithium aluminum hydride through a 60 cm Vigreaux column. The initial and final 10% were discarded. 145 2. Internal Standards Pentadecane - Pentadecane (Columbia Organics) was washed with sulfuric acid and distilled (10 Torr., b.p. 131°C) by Dr. Peter J. Wagner. Hexadecane - Hexadecane (Aldrich) was purified by washing with sulfuric acid, followed by distillation, b.p. 105°C (10 Torr) by Dr. Peter J. Wagner. Nonadecane - Nonadecane (Chemical Samples Company) was purified by recrystallization from ethanol. Heneicosane - Heneicosane (Chemical Samples Company) was purified by recrystallization from ethanol. Eicosane - Eicosane (Aldrich) was purified by recrystal- lization from ethanol. Docosane - Docosane (Aldrich) was purified by recrystal- lization from ethanol. Tetracosane - Tetracosane (Aldrich) was used as received. Hexacosane - Hexacosane (Pfaltz and Bauer) was used as received. 146 3. Quenchers 1,3-Pentadiene - 1,3-Pentadiene (Chemical Samples Com- pany) was used as received. trans—Stilbene - trans-Stilbene (Fisher Photochemical Grade) was used as received. 2,5-Dimethyl-2,4-hexadiene - 2,5-Dimethyl-2,4-hexadiene (Chemical Samples Company) was allowed to sublime in the refrigerator. 1,3-gyclohexadiene - 1,3-Cyclohexadiene (Aldrich) was used as received. n-Dodecylmercaptan - n-Dodecylmercaptan (Aldrich) was distilled at reduced pressure. n-Octylmercaptan - n-Octylmercaptan (Aldrich) was distill- ed at reduced pressure. 4. Ketones Benzophenone - Benzophenone (Eastman) was purified by Dr. P. J. Wagner, by recrystallization from ethanol. 147 AcetOphenone - Acetophenone (Mallinkrodt) was purified by Dr. A. E. Puchalski by passing the ketone through a short pad of alumina followed by spinning band distillation under reduced pressure (b.p. 105°C, 17 Torr). 111 Valerophenone - Valerophenone was prepared by Friedel- Crafts acylation of benzene with valeryl chloride in the presence of an aluminum chloride catalyst. Normal work-up procedures afforded the crude product which was vacuum dis- tilled to yield a water white liquid (b.p. 105°C, 2.0 Torr). ortho-Benzyloxybenzophenone (gngOBP) — 2-Hydroxybenzo- phenone (Aldrich, 10.0 g, 55.5 mmole) was added to a stirred solution of sodium methoxide (Fisher, 3.0 g, 55.6 mmole) in 100 m1 methanol. The resulting deep red solu- tion was stirred under nitrogen for 1 hr. Benzyl bromide (Eastman, 6.6 m1, 55.6 mmole) in 25 ml of methanol was added dropwise and the resulting solution refluxed under nitrogen overnight. The methanol was removed on a rotary evaporator and the residue taken up into 150 ml diethyl ether. The ether was washed with saturated sodium bi- carbonate (3 x 150 ml). The aqueous layers were combined and washed with ether. The ether extracts were combined, dried (MgSOu), and the solvent removed on a rotary evaporator to afford a yellow oil. This oil was dissolved in hot 148 chloroform—hexanes and cooled to afford 6.6 g of pure 9: BzOBP as white needles (45.4% yield). m.p. 65-6700 (lit. 6200112). lH-nmr (60 MHz,CDCl3); a=6.7-7.8 (m,7H, Ar-H's), 4.9 (s, 2H, O-CH2-Ph) ppm. l3C—nmr (250 MHz, 00013;: 5=196.1 (C=O), 138.3, 132.7, 131.9, 129.7, 128.2, 126.5, 120.9, 112.7, 69.97 (O-QH2Ph) ppm. mass spectrum: (m/e) 288 (M+), 197, 105, 91 (Base), 77. -1 -1 i.r. (CClu): 1675 cm (C=O), 1250 cm (Ar-O-C). ortho-Methoxybenzophenone (geMeOBP) - A solution of 2- hydroxybenzophenone (Aldrich, 5.0 g, 25.3 mmole) in 25 ml methanol was added dropwise to a stirred solution of sodium methoxide in methanol (freshly prepared by the addition of 0.6 g of sodium metal to 50 m1 methanol under nitrogen). The resulting solution was stirred under nitrogen at room temperature. Dimethyl sulfate (Mallinkrodt, 3.8 g, 30.0 mmole) was added dropwise, and the reaction refluxed over- night. The solvent was removed on a rotary evaporator and the remaining residue taken up into 200 ml diethyl ether. The ether was extracted with aqueous 10% potassium hydroxide (3 x 100 ml). The ether layer was dried (NaZSOu) and the V solvent removed on a rotary evaporator to afford a pale yel- low oil. This oil was dissolved in hot ethanol and cooled to afford 3.2 g (60% yield) of pure neMeOBP as white needles. 149 m.p. 36-38°C (lit. 39°C).113 1 H-nmr (60 MHz, CDC13): 6=6.7-7.8 (m, 3H, Ar-H's), 3.6 (s, 1H, OCH3) ppm. l3C-nmr (250 MHz, 00013): 6=l96.2 (C=O), 157.1, 137.6, 132.7, 131.7, 129.5, 129.3, 128.6, 120.3, 111.2, 55.33 (OCH3) ppm. mass spectrum: (m/e) 212 (M+), 195, 135 (Base), 105, 92, 77. i.r. (CClQ): 1680 cm‘1 (C=O), 1260 cm‘1 (Ar-O-C). Ortho-Benzyloxyacetophenone (n—BzOAP) - 2-Hydroxyaceto- phenone (Aldrich, 4.0 g, 29.4 mmole) was added to a stirred solution of potassium hydroxide (Fisher, 2.5 g, 44.6 mmole) in 100 m1 of methanol under a nitrogen atmosphere. The solution was stirred at room temperature for 1 hr, after which benzyl chloride (Fisher, 5.0 ml, 44.6 mmole) was added dropwise and the solution refluxed overnight. The solvent was removed on a rotary evaporator and the resi- due taken up into 200 ml ether. The ether was washed with 10% aqueous potassium hydroxide (3 x 150 m1) and dried (Na2SOu). The ether was removed on a rotary evaporator to provide a pale yellow oil. This oil was dissolved in hot chloroform-hexane and cooled to afford pure n-BzOAP as white crystals (5.6 g, 83% yield). m.p. 39-41°C. lH-nmr (250 MHz, 00013;: 6=6.9-7.7 (m, 9H, Ar-H's), 5.15 (s, 2H, O-CH2Ph), 2.50 (s, 3H, CH3) ppm. 150 l3C-nmr (250 MHz, 00013): 6=199.8 (C=O), 158.0, 136.1, 133.5, 130.4, 128.2, 127.5, 120.8, 112.7, 70.6, 70.55 (0- QHZPh) ppm. mass spectrum: (m/e) 226 (M+), 208, 183, 121, 107, 91 (base), 77. i.r. (0014): 1680 cm“1 (C=O), 1260 cm"1 (Ar-O-C). 2-Hydroxyvalerophenonellu - Phenyl valerate (16.5 g, 92.7 mmole, prepared from valeryl chloride and phenol) in 100 ml petroleum ether (b.p. 60-110°C) was added to a stirred suspension of aluminum chloride (Fisher, 24.7 g, 0.105 mole) in 100 m1 petroleum ether under a nitrogen atmosphere. The resulting mixture was refluxed with stirring under nitrogen for 3 hr. The reaction was then cooled to room temperature and the mixture poured over crushed ice. After the ice had melted, the aqueous solution was extracted with ether (3 x 200 ml). The ether was dried (Na2SOu) and the solvent re— moved on a rotary evaporator. The resulting liquid was vacuum distilled (1.0 Torr, b.p. 60-90°C) to afford 6.0 g (36% yield) of 2-hydroxyvalerophenone. Spectral data 114 were consistent with those in the literature. lH-nmr (60 MHz,CDCl3): 12.2 (s, 1H, OH), 6.5—7.5 (m, 4H, Ar-H's), 2.9 (t, 2H, C5200), 2.0-0.9 (m, 7H, CHZCHZCH2) ppm. mass spectrum: (m/e) 178 (M+), 149, 136, 121 (Base), 93, 65. 151 ortho-Benzyloxyvalerophenone (n—BzOVP) - 2—Hydroxyva1ero- phenone (10.0 g, 56.2 mmole) was added to a stirred solution of potassium hydroxide (Fisher, 3.2 g, 57.0 mmole) in 20 m1 of methanol under a nitrogen atmosphere. This solution was stirred at room temperature for 1 hr, after which benzyl chloride (Eastman, 6.7 ml, 56.4 mmole) was added dropwise. The resulting solution was refluxed under nitrogen for 2 hr, cooled to room temperature, and the solvent removed on a rotary evaporator. The resulting residue was taken up into 200 ml of ether, and the ether washed with 200 ml distilled water. The ether layer was dried (NaZSOu) and the solvent removed on a rotary evaporator. The crude product was vacuum distilled to afford 8.0 g (53.1% yield). This oil was crystallized from hot hexanes to afford 6.7 g of n- BzOVP as white platelets. m.p. 26-28°C. lH-nmr (250 MHz, CDC13): 5=6.96—7.68 (m, 9H, Ar-H's), 5.12 (s, 2H, OCH2Ph), 2.94 (t, 2H, J=7.32 Hz, CO-CHZ), 1.60 (m, 2H, COCHZCH2), 1.22 (m, 2H, CH3), 0.82 (t, 3H, J=7.32 Hz, CH3) ppm. l3C-nmr (250 MHz, CDC13): 5=203.7 (C=O), 157, 136, 133, 130, 129, 128.7, 128.2, 127, 121, 112, 70.7 (O-QHZPh), 43, 26, 22, 14 ppm. mass spectrum: (m/e) 268 (M+), 211, 121, 91 (Base), 77. i.r. (C014): 1680 cm"1 (C=O), 1270 cm"1 (Ar-O-C). 152 2,2'-Dibenzyloxybenzophenone (2,2'-DiBzOBP) - 2,2'- Dihydroxybenzophenone (Aldrich, 5.0 g., 23.4 mmole) was alkylated with benzyl bromide (Eastman, 5.6 ml, 46.8 mmole) in a solution of potassium hydroxide (Fisher, 2.6 g, 46.8 mmole) in methanol following the procedure described for nebenzyloxyacetophenone. Recrystallization of the residue obtained after work up from hot ethanol afforded 2.6 g (28.2% yield) of 2,2'-DiBzOBP as white needles. m.p. 98-99.5°C. lH-nmr (60 MHz, CDCl ): 6=6.6-7.5 (m, 18H, Ar-H's), 4.7 3— (s, 4H, OCH2Ph) ppm. l3C—nmr (250 MHz, 00013): 0=l95.5 (C=O), 157.2, 136.3, 132.5, 130.4, 128.1, 127.3, 126.5, 120.8, 112.5, 70.0 (O-QHZPh) ppm. mass npectrum: (m/e) 394 (M+), 376, 303, 211, 183, 91 (Base), 77. i.r. (00141: 1650 cm‘1 (C=O), 1280 cm‘ l (Ar-O-C). 2-Benzyloxy-5-methylbenZOphenone (geBzO-S-MeBP) - 2- Hydroxy-5-methy1benzophenone (Aldrich, 5.0 g, 23.6 mmole) was alkylated with benzyl bromide (Eastman, 2.8 ml, 23.6 mmole) in a solution of potassium hydroxide (Fisher, 1.3 g, 23.6 mmole) according to the procedure described for 97 benzyloxyacetophenone. The residue obtained after work up was recrystallized from hot methanol to afford pure n-BzO-S-MeBP as white needles (3.0 g, 42% yield). 153 m.p. 77-78°C. lH-nmr (250 MHz, 00013;; 5=6.89-8.55 (m, 8H, Ar-H's), 4.95 (s, 2H, OCH2Ph), 2.32 (s, 3H, CH3) ppm. l3C-nmr (250 MHz, 000131: 6=196.8 (C=O), 138.3, 136.4, 132.5, 132.2, 130.3, 130.1, 129.5, 129.1, 128.1, 127.4, 126.5, 112.8, 70.1 ((-QH2Ph), 20.28 ppm. mass spectrum: (m/e) 302 (M+), 284, 224, 135, 105, 91 (Base), 77. i.r. (00141: 1675 cm"1 (C=O), 1280 cm"1 (Ar-O-C). 2,6-Dimethoxybenzophenone (2,6-DiMeOBP) - 2,6-Dimethoxy- benzophenone was prepared according to the procedure des- cribed by Levine and Sommers.115 Thus, nfdimethoxybenzene (Aldrich, 13.8 g, 0.100 mole) was added dropwise to a stirred solution of nebutyllithium (Aldrich, 1.6 M, 0.100 mole) in 100 ml anhydrous ether under a nitrogen atmosphere. The resulting solution was refluxed under nitrogen for 2 hr. Methyl benzoate (MCB, 13.6 g, 0.100 mole) in 100 m1 anhydrous ether was added dropwise and the solution refluxed for an additional 5 hr. After the solution had cooled to room temperature, it was poured over 200 g crushed ice and 20 ml concentrated hydrochloric acid. The ether layer was separated and the aqueous layer extracted with ether (2 x 200 ml). The ether extracts were combined and neutralized with a saturated aqueous sodium bicarbonate solution. The ether layer was dried (Na2SOu) and the solvent removed on a rotary evaporator. Vacuum distillation of the residue 15“ afforded 3.0 g of 2,6-DiMeOBP. The distillate was re- crystallized from hot methanol to afford pure 2,6-DiMeOBP as white platelets. m'po 98-10000 (lit. 9705-980C).ll6 l H-nmr (250 MHz, CDCl3l‘ 6=6.58-7.85 (m, 4H, Ar-H's), 3.65 (s. 3H. 00113) ppm. l3c-nmr (250 MHz, 000131: 5=195.2 (0:0), 157.5, 133.0, 129.2, 128.3, 103.9, 55.7 (OQH3) ppm. mass spectrum: (m/e) 2H2 (M+), 225, 165 (Base), 151, 105, 91, 77. i.r. (CClul; 1675_cm‘l (C=O); 1290, 1310 cm“1 (Ar—O-C). 2,6-Dibenzoylanisole and 2,6-dibenzoylbenzyloxybenzene were both prepared from 2,6-dibenzoylphenol, which was synthesized by the following route. CH CH {/ 3 0./’ 3 H 0 0H H0 0 00 H 3 3 KMnOh, K0H 2 2 H20, 80"? -1.) 5001 2 . 2.) A1C13/ Benzene O OH 0 Ph fllliii ph 155 Anisole-2,6-Dicarboxylic Acid - 2,6-Dimethylanisole (prepared from the alkylation of 2,6-dimethyl phenol with dimethyl sulfate in a solution of potassium hydroxide in methanol) (20.0 g, 0.147 mole) was added to a vigorously stirred solution of potassium hydroxide (Fisher, 18.3 g, 0.325 mole) and potassium permanganate (Fisher, 103.7 g, 0.657 mole) in 700 m1 of distilled water. The reaction mixture was heated to 80°C and maintained at this tempera- ture for 3 hr. The solution was then cooled to room tempera- ture, filtered to remove manganese dioxide, and acidified with concentrated hydrochloric acid. After this solution had cooled, it was filtered and the crystalline product air dried to afford 22.8 g (79% yield) of anisole-2,6- dicarboxylic acid. m.p. 219-221°C. mass spectrum: (m/e) 196 (M+), 178, 165, 149, 132, 120, 105, 91, 77. 2,6-Dibenzgylphenol - Anisole-2,6—dicarboxy1ic acid (15.0 g, 91.5 mmole) was added to 100 ml thionyl chloride (MCB), and the mixture refluxed under nitrogen until all of the acid had dissolved. The excess thionyl chloride was removed under vacuum and the resulting residue vacuum dis- tilled (0.8 Torr, 105-110°C) to afford the desired diacyl chloride (9.5 g, “2% yield). The diacyl chloride was dissolved in 100 m1 of dry 156 benzene and added to a stirred suspension of aluminum chloride (Fisher, 10.“ g, 78 mmole) in 50 m1 dry benzene. The resulting yellow mixture was refluxed under nitrogen for 8 hr. After the solution had cooled to room temperature it was poured into 200 g crushed ice and 20 ml concentrated hydrochloric acid. This was extracted with ether (2 x 200 ml). The ether extracts were combined and washed with aqueous saturated sodium bicarbonate until neutral by pHydrion paper. The ether was dried (Na2SOu) and the sol- vent removed on a rotary evaporator to afford an orange oil. Trituration of this oil with hexanes afforded crysal- line 2,6-dibenzoyl phenol (7.2 g, 61% yield). lH-nmr (60 MHz,CDC13l: 0=13.8 (s, 1H, 0H), 6.7-8.0 (m, 13H, Ar-H'S) ppm. 2,6—Dibenzgy1benzyloxybenzene (2,6eDBB) - 2,6-Dibenzoy1- phenol (3.0 g, 9.93 mmole was alkylated with benzyl bromide (Eastman, 1.2 ml, 9.93 mmole) in a solution of potassium hydroxide (Fisher, 0.6 g, 9.93 mmole) in 50 m1 methanol following the procedure described for ggbenzyloxyaceto- phenone. Trituration of the residue resulting from work up with hexanes afforded 3.0 g (41% yield) of 2,6-DBB as colorless needles. mop. 104-105°C. lH-nmr (250 MHz, 00013;: 6=6.63-7.87 (m, 18H, Ar-H's), 4.69 (s, 2H, OC§2Ph) ppm. 157 l30-nmr (250 MHz, 000131: 6=l95.5 (C=O), 159.4, 137.0, 135.5, 133.8, 133.9, 131.9, 129.9, 128.3, 127.9, 127.8, 123.5, 77.00 (OC_H2Ph) ppm. mass spectrum: (m/e) 392 (M+), 315, 286, 181, 105, 91 (Base). 77. ’ i.r. (001“): 1680 cm”1 (C=O), 1250 cm’1 (Ar-O-C). 2,6-Dibenzoy1aniso1e (2,6-DBA) - 2,6-Dibenzoylphenol (12.0 g, 39.8 mmole) was alkylated with dimethyl sulfate (Mallinkrodt, u.0 ml, U3.3 mmole) in a solution of potas- sium hydroxide (Fisher, 2.4 g, 93.3 mmole) in 200 ml methanol following the procedure described previously. Chromatography of the oil obtained from work up on 200 g alumina using dichloromethane: hexanes (1:9) as the eluent afforded 5.0 g of a water white oi1. Crystallization of this oil from carbon tetrachloride afforded 3.0 g (29% yield) of pure 2,6-DBA as a white powder. m.p. 37-38°C. lH-nmr- (250 MHz, 000131: 0=7.2-8.0 (m, 13H, Ar-H's), 3.93 (s, 3H, OCH3) ppm. l3c-nmr (250 MHz, 000131: 6=195.5 (C=O), 136.9, 133.4, 133.0, 131.8, 129.8, 128.5, 123.1, 61.6 (09H3) ppm. mass spectrum: (m/e) 316 (M+), 299, 285, 239, 225, 211, 181, 1N7, 105 (Base), 91, 77. i.r. (CClfl): 1680 cm".1 (C=O), 1250 cm.1 (Ar—O—C). 158 2,6-Diacetylbenzyloxybenzene was prepared according to the following scheme. /CH3 /CH 0 a 0 3 0 HO 0 00 H . ". 2 2 1.) 5001 Bus C C S Bu 2.) n"Bu§ iLi(Me)2Cu/ THF 0’5 0 0’ 0 CH 3 2,6-Diacetylanisole - Di-(nebutyl)anisole-2,6-dicar- boxylic acid dithioester was prepared by the treatment of the diacyl chloride with two equivalents of n—butyl mer- captan in ether containing two equivalents of pyridine.118 Lithium dimethyl cuprate117 was prepared by the addi- tion of 102 m1 methyl lithium (Aldrich, 1.6 M) to a solu- tion of 16.0 g anhydrous cuprous iodide (Fisher) in 50 m1 anhydrous THF at 0°C under nitrogen. This solution was 159 stirred for 15 min, and cooled to —50°C. A solution of the dithioester in 50 m1 anhydrous THF was added and the 118 After resulting solution stirred at -50°C for 3 hr. the solution had warmed to room temperature, it was poured into 400 m1 of aqueous saturated ammonium bicarbonate solu- tion. This was extracted with ether (3 x 200 ml). The ether extracts were combined and dried (NaZSOu). The sol- vent was removed on a rotary evaporator to afford 9.8 g of a brown liquid. Vacuum distillation of this liquid afforded pure 2,6-diacetylanisole (1.0 Torr, 125-130°C, 6.0 g, 70% yield). 1 H-nmr (60 MHz, CDCl3l: 07.1 (t, 1H, p-Ar-H), 7.7 (d, 2H, Ar-H's), 3.8 (s, 3H, O-CH3), 2.6 (s, 6H, CH3's) ppm. 2,6-Diacetylphenol - 2,6-Diacetylanisole (5.0 g, 26.0 mmole) was added to a stirred solution of sodium iodide (MCB, 10.0 g, 65.0 mmole) and chlorotrimethylsilane (Aldrich, 8.5 ml, 65.0 mmole) in 70 m1 acetonitrile under a nitrogen atmosphere at room temperature.119 The reaction mixture was refluxed under nitrogen for 20 hr. After the solution had cooled to room temperature, it was poured into 100 m1 dilute hydrochloric acid and extracted with ether (3 x 150 ml). The ether extracts were combined and extracted (3 x 150 ml) with a 10% aqueous potassium hydroxide solu- tion. These extracts were combined, acidified with con- centrated hydrochloric acid, and extracted with ether 160 (3 x 150 ml). The ether extracts were combined, dried (NaZSOu), and the solvent removed on a rotary evaporator to afford 7.0 g of a brown oil (69.1% yield). This oil, which crystallized upon standing, was recrystallized with hot methanol to afford pure 2,6-diacetylphenol. lH-nmr (60 MHz, 000131: 6=13.1 (s, 1H, OH), 7.8 (d, 2H, m—Ar-H's), 6.8 (t, 1H, p-Ar-H), 2.6 (s, 6H, CH3's) ppm. 2,6-Diacetylbenzyloxybenzene (2,6-DAB) - 2,6-Diacetyl- phenol (8.2 g, “6.1 mmole) was alkylated with benzyl bro- mide (Eastman, 6.0 m1, 50.7 mmole) in a solution of potassium hydroxide (Fisher, 2.8 g, 50.7 mmole) in 100 ml methanol following the previously described procedure. Work up afforded 7.0 g (53% yield) of a brown liquid after removal of the solvent. This liquid was crystallized from hot methanol to afford pure 2,6-DAB as white crystals. m.p. 69-70°C. lH-nmr (250 MHz, 000131: 8:7.71 (d, 2H, m-AryH's), 7.36 (8, 5H, OCH2EQ), 7.25 (t, 1H, p-Ar-H), 5.0 (s, 2H, CflzPh), 2.59 (8, 6H, CH3'S) ppm. l3c-nmr- (250 MHz, 000131: 6=(200.0 (0:0), 135.4, 135.1, 132.8, 128.6, 128.3, 129.3, 79.9 (O-QHZPh), 30.66 ppm. mass spectrum: (m/e) 268 (M+), 253, 235, 225, l“7, 91 (Base). 77. i.r. (CClul: 1700 cm-1 (0=0), 1290 cm"1 (Ar—O-C). 161 a-(QrTolyl)acetophenone (a-TAP) - g—Xylyl lithium was 120 prepared by the procedure described by Broaddus from gfxylene (Fisher, 61.0 ml, 0.512 mole), nebutyl lithium (Aldrich, 1.2 M, 110 ml, 0.121 mole) and tetraethylene- diamine (Aldrich, 15.2 g, 0.128 mole) in 100 m1 anhydrous ether under nitrogen. Benzoic acid (Fisher, 7.8 g, 0.06“ mole) in 100 ml anhydrous ether was added dropwise and the solution refluxed under nitrogen for “ hr. The reaction mixture was cooled and poured into 300 ml dilute hydro- chloric acid. This solution was extracted with ether (2 x 200 ml). The ether extracts were combined and washed with aqueous sodium bicarbonate solution (200 ml). The ether layer was dried (NaZSOM) and removed on a rotary evaporator to afford a dark liquid. This liquid was vacuum distilled to afford “.8 g of a-TAP (35.8% yield based upon the amount of benzoic acid). The distillate was recrystallized from hot ethanol to afford white plates. m.p. 67-68.5°C (lit. 67-6800)121. lH-nmr (60 MHz, 000131: 5=6.9-8.1 (m, 9H, Ar-H's), 9.2 (s, 2H, Oge-Ar), 2.3 (s, 3H, ar-Cg3) ppm. l30-nmr (250 MHz, 000131: 5=197.u (C=O), 136.8, 133.u, 133.1, 130.3, 130.25, 128.6, 128.3, 127.2, 126.1, 93.9, 19.7 ppm. mass spectrum: (m/e) 210 (M+), 105 (Base), 89, 77. i.r. (0014): 1690 cm"1 (C=O). 162 a-MesitylacetOphenone was prepared by the reaction of phenyl lithium with a-mesitylacetonitrile, prepared by the procedure described by Fuson and Rabjohn.122 a-Mesitylacetonitrile - Mesitylene (Aldrich, 100 g, 0.83 mole) was dissolved in concentrated hydrochloric acid (Mallinkrodt, 500 m1) and formaldehyde solution (Mallin- krodt, 35% formaldehyde, 32 ml). The mixture was heated to 55°C and hydrogen chloride bubbled into the solution through a gas dispersion tube. After 3 hr, another 32 ml of formaldehyde solution were added and the reaction heated for another 3.5 hr. The reaction mixture was cooled to room temperature and extracted with benzene (3 x “00 ml). The benzene extracts were combined, dried (Nastu), and the solvent removed on a rotary evaporator. Vacuum distilla- tion of the resulting liquid (0.6 Torr, 100-12000) afforded 73.6 g of 2,“,6-trimethylbenzyl chloride. lH-nmr (60 MHz, 000131: 5=6.8 (s, 2H, Ar-H's), 9.6 (s, 2H, 052-01), 2.9 (s, 6H, 2,6-0H3's), 2.2 (s, 3H, “—CH3) ppm. 2,“,6-Trimethy1benzyl chloride (71.3 g, 0.“3 mole) was added dropwise to a mixture of sodium cyanide (Mallin— krodt, 37.3 g, 0.76 mole) in 5“ ml distilled water and 78 ml ethanol. The mixture was heated on a steam bath with stirring for 5 hr. After the solution had cooled to room temperature, it was extracted with benzene (3 x 200 m1). 163 The benzene extracts were combined, dried (Na280u), and the solvent removed on a rotary evaporator. Vacuum distil- lation of the resulting residue provided 36.9 g (5“% yield) of a-mesitylacetonitrile. lH-nmr- (60 MHz, 00013;: 6:6.9 (s, 2H, Ar-H's), 3.6 (s, 2H, Cflg’CN): 2.“ (s, 6H, 2,6-CH3's), 2.2 (s, 3H, “-CH3) ppm . a-Mesitylacetophenone (a-MAP) - Phenyl lithium (Ald- rich, 1.9 M, 36.0 ml, 69.7 mmole) was added dropwise to a stirred solution of a-mesitylacetonitrile (10.0 g, 62.9 mmole) in 250 ml anhydrous ether at room temperature under nitrogen. After the addition of phenyl lithium was com- plete, the reaction was refluxed for 3 hr. The solution was then cooled to room temperature and extracted (3 x 200 ml) with dilute hydrochloric acid. The acidic extracts were combined and refluxed for “ hr. After this solution had cooled to room temperature, it was extracted with ether (3 x 200 ml), the ether extracts were combined and dried (Na2SOu). The solvent was removed on a rotary evaporator to afford 9.2 g (61% yield) of cream colored crystals. . Recrystallization of these crystals afforded pure a-MAP as white needles. m.p. 196.5-198°C (lit. 197-11800) 123 lH-nmr- (60 MHz,CDCl3l: 8=7.8-8.2 (m, 5H, Ar-H's), 6.8 (d, 2H, mesityl-H's), 9.3 (s, 2H, CHZAr), 2.3 (s, 3H, 9-CH3), 16“ 2.2 (s, 6H, 2,6-CH3's) ppm. l30-nmr (250 MHz, 00013): 5=197.1 (0:0), 137.1, 136.8, 136.3, 133.1, 129.5, 129.2, 128.8, 128.6, 128.0, 39.23, 20.90, 20.29 ppm. mass spectrum: (m/e) 238 (M+), 223, 209, 197 (Base), 119: ‘05: 919 77- i.r. (0014): 1700 cm”1 (C=O). d-(2.5-Dimethy1phenyl)acetophenone was prepared by the reaction of phenyl magnesium bromide with 2,5—dimethyl— benzyl cyanide, prepared from 2-bromo-p-xy1ene by the fol— lowing route. 0H3 Br 1..)Mgfim;0 2.)c 0H3 CH3 NaCN CH2Cl DMSO CH 165 2,5-Dimethylbenzoic Acid - 2-Bromo—p-xylene (Aldrich, 27.6 ml, 0.200 mole) in 50 m1 anhydrous ether was added dropwise to magnesium turnings (MCB, 5.3 g, 0.220 mole) and 50 ml anhydrous ether at room temperature under a nitrogen atmosphere. After the addition was complete, the mixture was refluxed under nitrogen for 1 hr to insure com- plete formation of the Grignard reagent. The solution was cooled to room temperature and poured over 200 g of powdered dry ice. After all of the dry ice had sublimed, the resi- due was dissolved in 200 ml ether and extracted with 10% potassium hydroxide solution (3 x 150 ml). The aqueous ex- tracts were combined, acidified with concentrated hydro- chloric acid, and extracted with ether (3 x 200 ml). The ether extracts were combined, dried (Na2SOu), and the sol- vent removed on a rotary evaporator to afford 2,5-dimethy1- benzoic acid as cream colored crystals (23.7 g, 73% yield). 2,5:Dimethylbenzyl Alcohol - A solution of 2,5-dimethyl- benzoic acid (23.7 g, 0.158 mole) in 150 ml anhydrous ether was added dropwise to a stirred suspension of lithium alum- inum hydride (Aldrich, 12.7 g, 0.317 mole) in 50 m1 an- hydrous ether at room temperature under nitrogen. The re- sulting mixture was refluxed overnight, cooled to room temperature, and the excess lithium aluminum hydride de- composed by careful addition of methanol. Acidic work up afforded 2,5-dimethy1benzyl alcohol as a pale yellow oil (21.5 g, 100% yield). 166 lH-nmr (60 MHz, 000131: 5=6.8—7.2 (m, 3H, Ar-H's), 9.6 (s, 2H, GHQ-OH), 2.35 (s, 3H, Ar-CH3), 2.25 (s, 3H, Ar- CH3) ppm. 2,5-Dimethy1benzyl Chloride - 2,5-Dimethylbenzyl alcohol (21.5 g, 0.158 mole) was added dropwise to a stirred solu- tion of thionyl chloride (MCB, 20 ml) in 150 ml benzene. The solution was refluxed under nitrogen for 3 hr, cooled to room temperature, and poured into 300 ml distilled water. The layers were separated and the aqueous phase extracted with ether (3 x 200 ml). The ether extracts were combined, washed with saturated sodium bicarbonate solution (2 x 200 m1) and dried (NaZSOu). The solvent was removed on a rotary evaporator to afford 22.0 g of 2,5-dimethylbenzyl chloride as a brown oil (93%). This oil was not purified, but used directly for the next reaction. 2,5-Dimethylbenzyl Cyanide - A mixture of sodium cyanide (Fisher, 9.9 g, 0.215 mole) in 100 m1 dimethyl sulfoxide was heated at 80°C until all of the sodium cyanide had dissolved. 2,5-Dimethy1benzyl chloride (22.0 g, 0.1“3 mole) was added to this solution and the mixture stirred at this temperature for “ hr. The mixture was cooled to room temperature and poured into 500 ml distilled water. The resulting solution was extracted with ether (2 x 150 ml). The ether layers were combined, washed with x ,7/—1 167 distilled water (3 x 150 m1), and dried (NaZSOu). The solvent was removed on a rotary evaporator to afford 15.3 g of 2,5-dimethylbenzyl cyanide (50% yield) as a brown solid. The crude product was used without further purification. lH-nmr (60 MHz, 00013;: 5:6.8-7.2 (m, 3H, Ar-H), 3.5 (s, 2H, CE2-CN), 2.3 (s, 3H, Ar-CH3), 2.1 (s, 3H, Ar-CH3) ppm . a-(2,5-Dimethy1phenyl)acetophenone (a-(DMP)AP) - A solution of 2,5-dimethylbenzyl cyanide (15.3 g, 0.106 mole) in 50 ml anhydrous ether was added dropwise to a stirred solution of phenyl magnesium bromide (prepared from 3.1 g magnesium turnings and 13.“ ml bromobenzene in 100 m1 anhydrous ether) under a nitrogen atmosphere at room temperature. The resulting mixture was refluxed under nitrogen for “ hr, cooled to room temperature and extracted with hydrochloric acid (concentrated HCl:water, 1:1) (3 x 200 ml). The acidic extracts were combined and re- fluxed for 6 hr. After the solution had cooled to room temperature, it was extracted with ether (3 x 200 ml). The ether extracts were combined, washed with saturated sodium bicarbonate (2 x 200 m1) and dried (Nastu). The ether was removed on a rotary evaporator to afford 7.0 g of crude product (29.5% yield). The crude product was chromatographed on 50 g alumina using petroleum ether as the eluent to afford pure a-(DMP)AP. 168 m.p. 52-53°C. 1H-nmr (250 MHz, 000131: 5=6.9—8.2 (m, 8H, Ar-H's), 9.62 (s, 2H, Ar-CEZ), 2.8 (s, 3H, Ar-CH3), 2.21 (s, 3H, Ar- CH3) ppm. l3c-nmr (250 MHz, 00013;: 5=198.0 (C=O), 135.5, 133.3, 133.1, 131.0, 130.3, 128.7, 128.0, 93.36, 20.83, 19.21 ppm. mass spectrum: (m/e) 22“ (M+), 119, 105 (Base), 91, 77. 1 i.r. (001”): 1690 cm‘ (C=0). d-(2,5-Diis0propy1phenyl)acetophenone was prepared from p-diisoprOpylbenzene by the following route (page 169). 2,5-DiiSOpropy1bromobenzene.l2” - p—Diisopropylbenzene (Aldrich, 58 ml, 0.31 mole) was dissolved in 30 ml anhydrous dimethyl formamide and cooled to -20°C (dry-ice/carbon tetra- chloride). A solution of bromine (Mallinkrodt, 32 ml, 0.62 mole) in 20 m1 dimethyl formamide (NOTE: bromine was added to dimethyl formamide at -20°C to avoid a violently exothermic reaction) was added and the resulting solution stirred at -20°C for 3 hr. The solution was allowed to warm to room temperature and quenched by the addition of “00 ml of a saturated aqueous sodium sulfite solution. This mixture was extracted with carbon tetrachloride (2 x 300 ml). The organic layers were combined and washed with a saturated aqueous sodium bicarbonate solution (300 ml) and 300 ml distilled water. After drying (Na2SOu), the solvent 169 BrZ-DMF Br 1.)Mg/Et 0 -ZC°C 5 2.5002 5 JIZLiAlHu/Et 0 .CH2C1 SOCl CHZOH P:>(:i go/IFO -50° CH CN-H 02 reflux 3 2’ Ph was removed on a rotary evaporator. The resulting liquid was vacuum distilled through a 10 cm Vigreaux column to 170 provide “9.5 g of the desired bromide (“.0 Torr, 110-115°C, 33% yield). lH-nmr (60 MHz, 000131: 6=7.2 (s, 1H, Ar-H ortho to Er), 7.0 (s, 2H, Ar-H's), 3.2 (m, 1H, -C§(CH3)2 ortho to Er), 2.7 (m, 1H, —C§(CH3)2), 1.3 (d, 12H, CH3's) ppm. mass spectrum: (m/e) 2“2 (M+), 227, 211, 199, 183, 171, 161, 1“6, 131, 115, 103, 91, 80. 2,5-Diisopropy1benzoic Acid - 2,5-DiiSOpropylbromoben- zene (“9.5 g, 0.21 mole) in 50 m1 anhydrous ether was added dropwise to magnesium turnings (MCB, 5.6 g, 0.23 mole). After addition of the bromide was complete, the mixture was refluxed under nitrogen for 1 hr to insure complete for- mation of the Grignard reagent. The solution was then cool- ed to room temperature and poured over 600 g powdered dry ice. After all of the dry ice had sublimed, 300 m1 dilute hydrochloric acid was added, and the mixture extracted (3 x 300 ml) with ether. The ether extracts were combined, dried (MgSOu), and the solvent removed on a rotary evaporator to afford “1.6 g (89.1% Yield) of 2,5-diis0propylbenzoic acid as cream colored crystals. No further purification was attempted. 2,5-Diisopropy1benzyl Alcohol - A solution of 2,5- diiSOpropylbenzoic acid (“1.6 g, 0.187 mole) in 50 m1 anhydrous ether was added drOpwise to a stirred suspension 171 of lithium aluminum hydride (Aldrich, 15.0 g, 0.375 mole) in 100 ml anhydrous ether under nitrogen. After the addi- tion was complete, the mixture was refluxed under nitrogen for 2 hr. The mixture was then cooled in an ice bath and the excess lithium aluminum hydride decomposed by the care- ful addition of methanol. Distilled water (300 ml) was added and the mixture extracted with ether (2 x 300 ml). The ether extracts were combined, dried (Naasou), and the so solvent removed on a rotary evaporator to afford 25.“ g of a dark liquid (70.7% yield, 90% pure by glc). lH-nmr (60 MHz, CDCl3l: 5=7.1 (s, 3H, Ar—H's), “.6 (s, 2H, Cfl2OH), 3.0 (m, 2H, -Cfi(CH3)2), 1.3 (d, 12H, Cfl3's) ppm . 2,5-Diisopropylbenzyl Chloride - A solution of thionyl chloride (MCB, 15.0 ml, 0.198 mole) in 50 ml chloroform was added dropwise to a stirred solution of 2,5-diisopropy1- benzyl alcohol (25.“ g, 0.12 mole) in 50 m1 chloroform. The reaction mixture was refluxed under nitrogen for 6 hr. After the solution had cooled to room temperature, the solvent and excess thionyl chloride were removed under re- duced pressure. The residue was dissolved in 300 ml ether and washed with 200 m1 of a saturated aqueous sodium bi- carbonate solution. The ether was dried (NaZSOu) and the solvent removed on a rotary evaporator. Vacuum distilla- tion of the resulting liquid afforded 12.3 g (0.5 Torr, 87-89°C, ““.“% yield) of 2,5-diisopropylbenzyl chloride. 172 lH-nmr (60 MHz, 000131: 6=6.9-7.2 (m, 3H, Ar-H's), 9.6 (s, 2H, CH2C1), 2.5-3.5 (m, 2H, -C§(CH3)2), 1.9 (overlapp- ing d, 12H, CH3's) ppm. a-(2,5-Diisopropylphenyl)acetophenone (d—(DIP)AP) - g—Butyl lithium (Aldrich, 1.7 M, 38.0 ml, 69.6 mmole) was added to a stirred solution of 2-pheny1-1,3-d1th1ane125 in 100 ml anhydrous tetrahydrofuran under nitrogen ar-50°C. The resulting solution was stirred at -50°C for 6 hr.126 A solution of 2,5-diisopropy1benzy1 chloride (12.3 g, 69.6 mmole) in 100 m1 anhydrous tetrahydrofuran was added drop- wise and the mixture stirred under nitrogen overnight. The reaction mixture was then poured into 500 ml distilled water and extracted with dichloromethane (2 x 300 ml). The organic extracts were combined and washed with a 10% potassium hydroxide solution (2 x 300 ml). The organic layer was dried (Na2SOu) and the solvent removed on a rotary evaporator to afford a pale yellow oil. This oil was added to a stirred suspension of mercury (11) chloride (Mallinkrodt, 35.0 g, 0.129 mole) and mercury (11) oxide (Mallinkrodt, 28.0 g, 0.192 mole) in “00 ml acetonitrile:water (1:1) under a nitrogen atmosphere.127 The mixture was refluxed for “.5 hr, during which time the mixture turned color from milky yellow to milky white. The reaction mixture was cooled, filtered through a pad of Celite, and the solvent removed on a rotary evaporator. 173 The residue was taken up into 500 ml distilled water and “00 m1 dichloromethane. The organic layer was separated and washed with 500 m1 of a half-saturated solution of am- monium acetate in water and 500 ml distilled water. The organic phase was dried (Na2SOu) and the solvent removed on a rotary evaporator to afford 17.0 g of a pale yellow liquid. Vacuum distillation of this liquid afforded pure d-(DIP)AP (1.0 Torr, 180-185°C, 22% yield). lH-nmr (250 MHz, CDC13): 0=6.95-8.0 (m, 8H, Ar-H's), “.32 (s, 2H, Cfiz-Ar), 2.92 (m, 1H, -C§(CH3)2, 2.82 (m, - 1H, -cp(CH3)2), 1.19 (d, 6H, -0H(CH_3)2 pggpp to CH2CO), 1.17 (d, 6H, -CH(Cfl3)2) ppm. 13C-nmr (250 MHz, 000131: 5=197.7 (C=O), 195.8, 136.9, 132.9, 131.“, 128.9, 128.5, 128.1, 125.“, 125.3, “3.06, 33.36, 29.21, 23.82, 23.72 ppm. mass spectrum: (m/e) 280 (M+), 175, 105 (Base), 77. 1 i.r. (09141: 1700 cm“ (C=0). d-(2,“,6-Triisopropylpheny1)acetophenone was synthesized from the reaction of phenyl magnesium bromide and a-2,“,6- triisoprOpylbenzyl cyanide, prepared following the same procedure used to prepare 2,5-dimethy1benzy1 cyanide. 2,“,6-Triis0propy1bromobenzene - A solution of 1,3,5- triiSOpropylbenzene in anhydrous dimethyl formamide was brominated at -20°C with bromine-dimethyl formamide solution 17“ following the procedure described for 2,5-diisopropylbromo- benzene. Vacuum distillation of the crude product afforded the desired bromide (b.p. 100°C, 1.0 Torr) in 78% yield. 2,9,6-Triisopropylbenzoic Acid — 2,9,6-Triisopropyl- benzoic acid was prepared by the carboxylation of 2,9,6- triisopropylphenyl magnesium bromide with dry ice following the procedure described for 2,5—diisopropy1benzoic acid. The usual work up afforded 19.0 g of the desired acid (53.3% yield). 2,“,6-TriiSOpropy1benzy1 Alcohol - Borane-THF complex in tetrahydrofuran (Aldrich, 1.0 M, 200 ml) was added dr0p- wise to a stirred solution of 2,“,6-trii50propylbenzoic acid (19.0 g, 56.5 mmole) in 50 ml anhydrous tetrahydro- furan under a nitrogen atmosphere. The resulting solution was stirred overnight under nitrogen and then poured into “00 m1 of a 20% aqueous potassium hydroxide solution. The aqueous and organic phases were separated and the aqueous phase extracted with ether (2 x 200 ml). The organic extracts were combined, dried (MgSOu), and the solvent re- moved on a rotary evaporator to afford 2,“,6-triisopr0pyl- benzyl alcohol as a colorless liquid (13.2 g, 56.5 mmole, 100% yield). lH-nmr (60 MHz, 000131: 5=6.9 (s, 2H, Ar-H's), 5.6 (s, 2H, 052-0H), 2.8-3.8 (m, 3H, -CH(CH3)2), 3.5 (br s, 1H, 0H), 1.3 (d, 18H, CEB'S) ppm. 175 2,9,6-Tri150propylbenzyl Chloride - 2,“,6-Triisopropy1- benzyl chloride was prepared frdm 2,9,6-triisopr0py1benzyl alcohol and thionyl chloride according to the usual pro- cedure. Normal work up afforded the desired chloride in 76% yield as a pale yellow oil. i.r. (neat): shows no -OH at 3500 cm-1. mass spectrum: 252 (M+). 2,“,6-Triisopropylbenzy1 Cyanide - 2,“,6-Triis0propyl- benzyl cyanide was prepared from 2,“,6-triisopropylbenzyl chloride and sodium cyanide following the procedure used to prepare 2,5-dimethylbenzyl cyanide. The solvent was re- moved after the usual work up to afford 8.0 g of a dark oil which solidified upon standing (75.3% yield). No further purification was attempted. lH—nmr (60 MHz, 00013): 6=6.9 (s, 2H, Ar-H's), 3.7 (s, 2H, Cflz-CH), 2.5-3.9 (m, 3H, -CH(CH3)2), 1.9 (d, 12H, -cp(CH3)2vs ortho to CH20N), 1.2 (d, 6H, -CH_(CH3)2 para to CEZCN) ppm. a-(2,“,6-Triisopropylppenyl)acetophenone (a(TIP)AP) - d-(2,“,6-Triis0propylphenyl)acetophenone was prepared from the reaction of phenyl magnesium bromide with 2,“,6-tri- isopropylbenzyl cyanide following the procedure used to prepare a-(2,5-dimethylphenyl)acetophenone. Removal of the solvent following the usual work up afforded 3.0 g of 176 a brown oil which solidified upon standing (29.6% yield). Recrystallization of this solid from methanol afforded pure a-(DIP)AP as white crystals. m.p. 101.5-102.5°C (lit. 113.5-11“.5°C).128 1H-nmr (250 MHz, 000131: 5=8.1 (d, 2H, Ar-H's ortho to CO), 7.55 (m, 3H, other phenone H's), 7.05 (s, 2H, - phenyl H's), “.96 (s, 2H, CEZ-CO), 2.86 (m, 3H, -C§(CH3)2'S), 1.23 (overlapping d's, 18H, -C§(CH3)2) ppm. l3c—nmr (250 MHz, 000131: 5=197.7 (0:0), 197.1, 137.1, 133.1, 128.7, 128.0, 126 5, 120.9, 37.63, 39.19, 30.25, 23.98 ppm- mass spectrum: (m/e) 322 (M+), 217, 203, 105 (Base. i.r. (001,): 1710 cm"1 (C=0). 2-(35Tolyl)ethanol - A solution of p—tolylacetic acid (Aldrich, 10.0 g, 66.7 mmole) in 150 m1 anhydrous ether was added dropwise to a stirred suspension of lithium aluminum hydride (Aldrich, 5.1 g, 0.133 mole) in 100 ml anhydrous ether at room temperature under nitrogen. The mixture was refluxed for 6 hr, cooled to 0°C, and the excess lithium aluminum hydride decomposed by the careful addition of acetone. The reaction mixture was poured into “00 ml distilled water, acidified with concentrated hydro- chloric acid, and extracted with ether (2 x 200 ml). The ether extracts were combined, washed with saturated aqueous sodium bicarbonate, and dried (Na280u). Removal of the 177 solvent afforded 8.2 g of 2-(getolyl)ethanol (91% yield). as a pale yellow oil. No further purification was at- tempted. lH-nmr (60 MHz, 000131: 5=7.0 (s, 9H, Ar-H's), 3.7 (t, 2H, ch-OH), 2.8 (t, 2H, CEZ—Ar), 2.5 (br, s, 1H, 0H), 2.3 (s. 3H, Ar-Cfi3) ppm- 'E:(ngolyl)aceta1depyde - Chromium trioxide (Fisher, 18.1 g, 0.181 mole) was added to a stirred solution of pyridine (Fisher, 28 ml) in 300 ml dichloromethane.129 The orange colored solution was stirred for an additional 15 min, after which a solution of 2—(3—toly1)ethanol (9.1 g, 30.2 mmole) in 25 m1 dichloromethane was added. The resulting green solution was stirred for 30 min. The methyl- ene chloride was decanted from the inorganic precipitate and the precipitate washed with ether (3 x 150 ml). The organic solutions were combined and washed with 350 m1 of a saturated sodium bicarbonate solution. After drying (MgSOu) the solvent was removed on a rotary evaporator to afford 3.3 g of a-(p—tolyl)aceta1dehyde (70% yield). 111mm (60 MHz, 00013;: 5=9.9 (s, 1H, CHO), 7.1 (s, 9H, Ar-H's), 3.6 (d, 2H, Cfi2CHO), 2.2 (s, 3H, Ar-CH) ppm. mass spectrum: (m/e) 139 (M+), 91 (Base), 77. i.r. (neat): 1725 cm.1 (C=0). 178 a-(prolyl)acetone - g-Butyl lithium (Aldrich, 1.7 M, 90 ml) was added to a stirred solution of 2-methyl-l,3— dithiane127 (20.2 g, 0.151 mole) in 100 m1 anhydrous tetra- hydrofuran under nitrogen at -20°C. This solution was maintained at -20°C for 1.5 hr, whereupon it was cooled to -70°C. A solution of d-bromo-pgxylene (Aldrich, 27.7 g, 0.17“ mole) in 50 m1 tetrahydrofuran was added drop- wise and the solution stirred at -70°C for an additional 2 hr.126 The solution was warmed to room temperature and poured into 300 ml distilled water. The layers were separated, and the aqueous layer was extracted with 200 ml ether. The organic layers were combined, washed with 300 m1 of a saturated sodium bicarbonate solution, dried (MgSOu), and the solvent removed on a rotary evaporator. The resulting pale yellow oil was added to a vigorously stirred suspension of mercury (II) oxide (Mallinkrodt, 71.9 g, 0.332 mole), mercury (11) chloride (Mallinkrodt, 90.1 g, 0.332 mole) in “00 ml acetonitrile:water (1:1). The resulting mixture was stirred at reflux under nitrogen for 6 hr. After it had cooled to room temperature, the solu- tion was filtered through a pad of Celite. The filtrate was concentrated and the residue dissolved in 900 ml di- chloromethane and 900 ml water containing 30 m1 concentrated hydrochloric acid. The layers were separated and the aqueous layer extracted with 200 ml dichloromethane. The organic layers were combined, washed with 300 m1 of a saturated 179 sodium bicarbonate solution, and dried (MgSOu). The sol- vent was removed on a rotary evaporator and the resulting liquid vacuum distilled (b.p. 109-119°C, 12.0 Torr; lit. 10“ b.p. 110-113°C, 1“ Torr) to afford 5.0 g (22% yield) of pure d-(pftolyl)acetone. Spectral data matched that in the literature.lol4 lH--nmr (60 MHz, 000131: 5=7.0 (s, 9H, Ar-H's), 3.5 (s, 2H, C§2CO), 2.2 (s, 3H, CO‘CE3): 2.1 (s, 3H, Ar—CEB) ppm. mass spectrum: (m/e) 198 (M+), 133, 119, 105, 91, 77, “3. a-(prenzyloxyphenyl)acetophenone was prepared from 3- benzyloxybenzyl chloride and 2-lithio—2-phenyl-l,3-dithiane following the procedure used to prepare a—(2,5-diis0propyl- phenyl)acetophenone. ‘g-Benzyloxybenzyl Chloride - p—BenZyloxybenzaldehydel35 (20.0 g, 99.3 mmole) in 50 ml anhydrous ether was added dropwise to a stirred suspension of lithium aluminum hydride (Aldrich, 2.0 g, “8.8 mmole) in 100 ml anhydrous ether at room temperature under nitrogen. This solution was refluxed overnight, cooled to room temperature, and the excess lithium aluminum hydride decomposed by the careful addition of methanol. The resulting mixture was poured into “00 ml distilled water and 50 ml concentrated hydro- chloric acid. This solution was extracted with ether (3 x 150 ml). The ether extracts were combined, washed with 300 m1 of an aqueous sodium bicarbonate solution, and 180 dried (Na280u). The solvent was removed on a rotary evapor- ator to afford 20 g of p—benzyloxybenzyl alcohol as a pale yellow oil. Thionyl chloride (MCB, 22 ml) in 20 ml benzene was added dropwise to a solution of the crude alcohol in 100 m1 benzene. The resulting solution was refluxed under nitrogen for 6 hr. After the solution had cooled to room temperature, the solvent and excess thionyl chloride were removed under reduced pressure. Vacuum distillation of the resulting residue afforded “.0 g of p—benzyloxybenzyl chloride (20% overall yield, b.p. 128-138°C at 0.1 Torr). lH-nmr (60 MHz, 00013): 6:6.6-7.5 (m, 9H, Ar-H's), 5.0 (s, 2H, O-ngPh), “.5 (s, 2H, Cfi2-C1) ppm. mass spectrum: (m/e) 232 (M+), 197.91 (Base), 78. Note: no peak at 21“ (corresponding to the molecular weight of the alcohol) was observed. a-(p-Benzyloxyphenyl)acetophenone (a-(p-BzOPh)AP - p- Butyl lithium (Aldrich, 1.7 M, 11.1 ml, 18.9 mmole) was added dropwise to a stirred solution of 2-phenyl-1,3-di- thiane125 (3.“ g, 17.2 mmole) in 100 ml anhydrous tetra- 126 The resulting hydrofuran at -75°C under nitrogen. solution was warmed to -50°C and stirred at this tempera- ture for 6 hr. p—Benzyloxybenzyl chloride (“.0 g, 17.2 mmole) in 50 m1 anhydrous tetrahydrofuran was added drop- wise and the reaction mixture allowed to warm to 0°C. After the solution had stirred overnight, it was poured 181 into 500 ml distilled water, and extracted with methylene chloride (2 x 200 ml). The organics were combined and washed, first with 500 ml distilled water, then an aqueous 5% potassium hydroxide solution, and finally with distilled water (2 x 200 ml). The methylene chloride solution was dried (MgSOu) and the solvent removed on a rotary evapora- tor to afford a pale yellow oil. This oil was added to a vigorously stirred suspension of mercury (11) chloride (MCB, 10.3 g, 37.8 mmole) and mercury (11) oxide (MCB, 8.2 g, 37.8 mmole) in 250 ml acetonitrile-distilled water (9:1) at room temperature under nitrogen. This mixture was refluxed under nitrogen for “.5 hr, cooled to room temperature, and filtered through a pad of Celite. The filtrate was concentrated on a rotary evaporator and the residue taken up into 500 ml distilled water and “00 ml methylene chloride. The layers were separated and the organic layer washed first with 500 ml of a half-saturated aqueous ammonium acetate and then with 500 ml distilled water. The methylene chloride solution was dried (MgSOu) and the solvent removed on a rotary evapora- tor to afford 6.0 g of a bright yellow oil which crystal- lized upon standing. Recrystallization of this solid from ethanol afforded pure a-(g-BzOPh)AP as cream colored crystals. m.p. 102-109°C. lH-nmr (250 MHz,CDCl3l: o=6.8—8.1 (m, 19H, Ar—H's), 182 5.02 (s, 2H, O-CfiZPh), 9.28 (s, 2H, cpz—Co) ppm. 13C-nmr (250 MHz, 000131: 5=197.9 (C=O), 156.2, 136.8, 132.8, 131.1, 128.3, 127.8, 127.6, 127.1, 129.1, 120 8, 111.8, 69.85 (O-CHZPh), 39.95 ppm. i.r. (0014;: 1680 om‘l (C=O), 1280 om‘l (Ar-O-C). mass spectrum: (m/e) 302 (M+), 211, 105, 91 (Base), 77. 2-Keto-[2,2]-Paracyclophane (2-KPCP) - 2-Keto-[2,2]- paracyclophane was synthesized according to the procedure described by Cram and Hegelson.63 Thus, a solution of [2,2J-paracyclophane (Union Carbide, 9.5 g, “5.6 mmole), N—bromosuccinimide (MCB, 13.0 g, 73.0 mmole) and benzoyl peroxide (Fisher, 100 mg) in 300 ml anhydrous carbon tetrachloride was refluxed under nitrogen for 10 hr. During this time, the solution was irradiated with a high intensity visible lamp. The solution was then cooled to room tem- perature and filtered. The filtrate was concentrated on a rotary evaporator and the residue dissolved in 70 ml ben- zene. The benzene solution was adsorbed on a 1.5 Kg silica gel column, and the column eluted with ether-pen- tane (1:1) to provide 2.0 g of cream colored crystals. Recrystallization of these from hot ethanol afforded pure 2-KPCP. Spectral data agrees with that in the litera- ture.63 m.p. 198-201°C (lit. m.p. 195—196°C).63 lH-nmr (250 MHz, 000131: 8=6.9-6.6 (m, 9H, Ar-H's), 3.87 (s, 1H, 03200), 3.09 (s, 2H, Ar-cp2) ppm. 183 l3c--nmr (250 MHZ; 000131: pom mLOpomm omcoomom afinomhmoomaopno mmc .om canoe 189 .p0poopoo E: 05m .popmzuoafipoficoooo< .CESHoo walmmo oponommpoaso .poooouoo E: 05m .Aoauomv oompoo< Hmnomnoomxom .QESHoo Hm oponqmmpuaao .poooouop E: cum .Amummv oompoo< amnomuocmxom .CESHoo Hm oponommpoabo .zHo>Hpoommop .mpoEomH mcwpp pom mHo mo .m.mm nmzmo.o m:o:o:ooooo< ommH.o demonssxoseseumuasoosoomssoue.suaseononmnaseooeHonfi.H ammo.o osmocfiszLUznnmlahoopoomfilmIazconmlmlaznooefiola.H ommmo.o mopedssxososeumnaseoeoumnaseoozum osmo.o mesonsaxosoaeumuamsoooumlaseooeHouo.3 ommao.o nonsmouoooopomcfiolm.mlazouconlwlszAUznlmIamconmum oomH.o seosooNeooosossHenm.muasooosususxososeumuasnooEumuHsooemum o.emsdo.o .mmao.o eesscoseooososefioum.m-Hsoesoous-ssososeum7Hseoeosoum.m omomo.o sesscoosooososefioum.mnsxososeumuazeooEumuHssoedum omsmo.o emssooueooososnsoum.musxososeumnaseoedum o.esmmo.o .mmo.o cesscowsooososefioum.musxosossumuassosofionm.m .m.m podepaouonm .mposoopoooozm mzoapm> pom whooomm omcoomom 04mm .Hm oHQmB 190 solution was irradiated in parallel with the samples to be analyzed. Upon completion of the irradiation the valero- phenone sample was analyzed for acetophenone, using the following equation - AP = (R.F.[int. std.] (AAP/Astd) The intensity of the light absorbed by each sample, in ein 1'1, can be calculated from the acetophenone concentra- tion knowing that pdt for valerophenone is 0.33 - -1 _ [AP] I (ein l ) - 0.3 6. Sensitization Studies The sensitized isomerization of either gisepiperylene or pggpsestilbene by triplet ketone were monitored by gas chromatography. Eli? and Epspsestilbene were analyzed on a 6' column containing 20% SE-30 on Chromsorb G maintained at 180°C. gise and ppgps—piperylene were analyzed on a 25' column containing 25% 1,2,3-tris(cyanoethoxy)propane held at 60°C. The area percents of the newly isomerized alkene were calculated from the g.c. peak areas by the following equation - 191 Ax 8: Ax + Ay where Ax = area of newly isomerized alkene Ay = area of unisomerized alkene. This area percent was corrected for any reisomerization of the alkene product, using - v = C1 8 aln 3:8 where a = photostationary state of isomerized alkene B' = corrected area percent of isomerized alkene 98 d = 0.55 for cis-piperylene 0.596 for trans-stilbene.”8 The concentration of the newly isomerized alkene can be calculated from 8', since - [isom. alkene] = B'Ealkene]° where [alkene]° = initial concentration of alkene. Actinometer solutions were prepared from a stock solution of acetophenone or benzophenone and an apprOpriate concentra- tion of alkene. Concentrations of acetOphenone or 192 benZOphenone were adjusted such that the absorbance of the actinometer at 313 nm (for piperylene) or 366 nm (for stil- bene) was identical to that of the ketone solutions studied. If the concentration of alkene used was greater than 0.5 M, separate actinometers were used for each of the ketone solutions in the experiment, such that each sample in the experiment had an actinometer of identical alkene concen— tration. This was done to correct for any changes in the characteristics of the solvent that might occur in such a high concentration of alkene. In all other cases, the concentration of alkene used in the actinometer was a value in the middle of the range of concentrations used for ketone solutions. The intensity of absorbed light can be calcu- lated from - 1 B acttalkenejact d (ein. light)1-l = Thus the quantum yield for the ketone sensitized iso- merization can be represented by - 8'[alkene]° ¢ = c o isom BactEalkene]act A straight line was obtained from a plot of a/¢isom versus [alkeneJ-l. This line had an intercept of 03:0, 193 the reciprocal of the intersystem crossing quantum yield for the ketone sensitizer. The ratio of the intercept to the slope equals k TT, where TT is the lifetime of the q ketone sensitizer triplet. B- Isolation and Identification of Photoproducts In most cases, photoproducts were obtained by prepara- tive scale photolysis of 0.01 to 0.1 M solutions of the apprOpriate ketone in spectral grade cyclohexane or hep- tane under a nitrogen atmosphere. A medium pressure Hano- via mercury vapor lamp was used as the irradiation source. For pgalkoxyphenyl ketones, this light was filtered through uranium glass. A Pyrex filter was used for the irradia- tion of a-(pgalkylphenyl)acetophenones. Photoproducts from g-alkoxyphenyl ketones were isolated by flash chromatography88 on ICN Silica Gel (0.032 to 0.063 mm) using hexanes:ethyl acetate (95:5) as the eluent. Photo- products from d-(g-alkylphenyl)acetophenones were formed innearly quantitative yields and did not require any further purification. Structural assignments were based upon standard spectros- copic techniques - 1H and 13C nmr spectroscopy, infrared spectroscopy, and mass spectrometry. lH nmr spectra were recorded on either a Varian T-60 Nuclear Magnetic Reson- ance Spectrometer or on a Bruker WM-250 250 MHz Fourier Transform Nuclear Magnetic Resonance Spectrometer. l3C 19“ nmr spectra were recorded on the Bruker WM-250 instrument. All spectra were calibrated using tetramethylsilane as an internal standard (6=0.0 ppm). Infrared spectra were re- corded on a Perkin-Elmer Model 237 B Grating Infrared Spectrophotometer. Mass spectra were recorded on a Finni- gan “000 GC/MS using the direct inlet mode. This instrum- ent was Operated by Mr. Ernest A. Oliver. Ultraviolet- visible absorption spectra were recorded on a Varian Carey 219 Spectrophotometer. Melting points were recorded on a Thomas Hoover Capillary Melting Point Apparatus and are un- corrected. p—Benzyloxyacetophenone - Irradiation of a 0.1 M solu- tion of p—benzyloxyacetophenone in spectral grade heptane (100% ketone conversion) afforded containing 2M pyridine afforded a mixture of three photoproducts. These three products were separated by flash chromatography and are listed in order of elution. gy2-phenyl-3-methyl-3-hydroxy-2,3-dihydrobenzofuran. lH-nmr (250 MHz, 000131: 5=6.9-7.55 (m, 9H, Ar-H's), 5.3 (s, 1H, O-CfiPh), 1.7 (s, 3H, CH3), 1.95 (br s., 1H, OH) ppm. i.r. (neat): 3970 om‘l (OH), 3080, 3060, 3030 cm”1 (Ar- CH), 2960, 2910, 2870 cm"1 (sat. C—H), 1260 cm"1 (Ar-O-C). mass spectrum: (m/e) 266 (M+), 208, 121, 105, 91 (Base), 77. 195 §-2-phenyl-3-methyl-3-hydroxy-2,3-dihydrobenzofuran. lH—nmr (250 MHz, 000131: 5=6.9-7.9 (m, 9H, Ar-H's), 5.52 (s, 1H, o-cpgph), 2.98 (s, 1H, 0H), 1.11 (s, 3H, CH3) ppm. l3c-nmr (250 MHz, 00013): 6=159.“, 139.9, 132.0, 130.9, 128.8, 128.6, 127.1, 123.9, 121.5, 110.7, 92.90, 78.20, 25.1“ ppm. i.r. (00141: 3580 cm"1 (OH), 3060, 3030 cm"1 (Ar-CH), 2970, 2950 om“1 (sat. C-H), 1260 om‘l (Ar-O—C). mass spectrum: (m/e) 226 (M+), 208 (Base), 121, 105, 91, 77. 2—Acetylbenzophenone lH-nmr (250 MHz, 000131: 5=7.25—7.95 (m, 9H, Ar-H's), 2.52 (s. 3H, CH3) ppm. l3c-nmr (250 MHz, 000131: 5198.6, 197.9 (C=O), 191.0, 137.7, 137.3, 133.0, 132.2, 129.8, 129.“, 129.3, 128.5, 128.“, 120.“, 112.7, 27.39 (Cfi3)ppm. i.r. (001,): 1680, 1660 om‘l (0:0), (lit. 1680, 1660 om‘l).136 mass spectrum: (m/e) 229 (M+), 209, 181, 197, 105, 77. 133 m.p.: 78-80°C (lit. 99°C). grBenzyloxybenzophenone — Irradiation of a 0.2 M solution of pgbenzyloxybenzophenone in heptane containing 2 M pyri- dine (100% ketone conversion) resulted in the formation of three compounds (by HPLC). The first and last peaks were isolated by flash chromatography. The middle peak 196 was unstable to chromatographic conditions. The two com- pounds isolated are listed in order of elution. £52,3—diphenyl-3-hydroxy-2,3—dihydrobenzofuran. lH-nmr (250 MHz, CDClB); 6=6.6-7.9 (m, 19H, Ar-H's), 5.66 (s, 1H, o-cggph), 1.95 (br s, 1H, 0H). l30-nmr (250 MHz, 00013;: o=160.3, 192.9, 139.0, 130.7, 129.6, 128.8, 128.5, 128.3, 127.7, 127.6, 127.0, 126.8, 125.5, 122.0, 110.8, 95.3, 83.2 ppm. i.r. (0014;: 3500 om'l (OH), 3080, 3060, 3030 om‘l (Ar— C-H), 2960, 2910 om‘l (sat. C-H), 1275 cm"1 (Ar-O-C). mass spectrum: (m/e) 288 (M+), 270, 181, 121, 105, 91 (Base), 8“, 77. §:2,3-diphenyl-3-hydroxy-2,3-dihydrobenzofuran. lH-nmr (250 MHz, 00013): 8=6.9-7.96 (m, 19H, Ar-H's), 5.77 (s, 1H, O-CfiePh), 2.62 (br, s, 1H, CH) ppm. i.r. (CHepgzl: 3570 om"l (OH), 3010 our1 (Ar-CH), 2995 om‘l (Sat. C-H), 1225 cm“1 (Ar-O-C). mass spectrum: (m/e) 288 (M+), 270, 181, 121, 105, 91 (Base) 89,77. prMethoxybenzophenone - Irradiation of 0.2 M solution of pgmethoxybenzophenone in spectral grade heptane con- taining 2 M pyridine (100% ketone conversion) afforded a 197 mixture of two photoproducts. These photoproducts were isolated by flash chromatography and are listed in the order of their elution. peMethoxybenzhydrol. lH-nmr (250 MHz, 000131: 5=6.7=8.1 (m, 9H, Ar-H's), 5.95 (S: 1H: CEfOH): 3335 (5, 3H: O-CH3) ppm° l3c-nmr (250 MHz, 000131: 5=167.1, 157.7, 195.5, 139.9, 132.3, 129.2, 127.9, 126.1, 125.6, 120.0, 113.9, 82.7 (CH-OH), 56.16 (O-CH3) ppm. . i.r. (00141: 3500 om‘l (OH), 3090, 3010 cm"1 (Ar-CH), 2950, 2925 cm"1 (sat. C-H). mass spectrum: (m/e) 213, 195 (Base), 135, 121, 105, 77. m.p.: 177-178°C (lit. l“l).l3u 3-Phenyl-3-hydroxy-2,3-dihydrobenzofuran. lH-nmr (250 MHz,00013l: o=6.88-7.50 (m, 9H, Ar-H's), 9.98, “.66 (AB quartet, J=10.29 Hz, 2H, O-CH2-), 1.92 (br, s, 1H, OH) ppm. l3c-nmr (250 MHz, CDCl3l: 5=166.8, 192.5, 132.2, 130.6, 128.3, 127.—, 126.1, 129.9, 121,9, 110.8, 86.13, 82.59 ppm. i.r. (neat): 3930 om’l (OH), 3080, 3060, 3030 om‘1 (Ar- CH), 2980, 2950, 2890 om‘l (sat. C-H), 1225 om‘1 (Ar-O-C). mass spectrum: (m/e) 212 (M+) (Base), 199, 181, 165, 121, 105, 91, 77. 198 p:Benzy1oxy-5-methy1benzophenone - A degassed solution of p—benzyloxy-5—methylbenzophenone was irradiated at 313 nm (100% ketone conversion). Proton nmr of the crude photolysate revealed it to be mainly 2,3-dipheny1-5-methyl- 3-hydroxy-2,3-dihydrobenzofuran. lH-nmr (250 MHz, 00013): 6=6.8-7.9 (m, 19H, Ar-H's), 5.65 (s, 1H, O-CHPh), 2.26 (s, 3H, 053), 1.8 (br, s, 1H, 0H) ppm. 2,6-Diacetylbenzyloxybenzene - 2-Phenyl-3-methyl-7- acety1-3-hydroxy-2,3-dihydrobenzofuran was isolated by flash chromatography of the crude photolysate from 2,6- diacetylbenzyloxybenzene in spectral grade cyclohexane (50% ketone conversion). Based upon the proton chemical shift of the methyl protons and the hydroxyl proton it was assigned the Z-stereochemistry. The structural assignment was based upon the following spectral data. lH—nmr (250 MHz, 000131: 5=7.0—8.0 (m, 8H, Ar—H's), 5.96 (s, 1H, O-CHPh), 2.69 (s, 3H, cocp3), 1.77 (s, 3H, C(OH)CH3), 1.98 (br, s, 1H, OH) ppm. l3c-nmr (250 MHz,_CDC13): 6=199.9 (c=0), 190.7, 175.9, 199.6, 130.6, 129.0, 128.8, 128.7, 126.9, 125.7, 121.6, 93.62, 77.30, 31.3“, 25.38 ppm. i.r. (00191: 3560 cm"1 (OH), 3050 cm'1 (Ar C-H), 2970 cm-1 (sat. C-H), 1260 cm-1 (Ar-O-C). 199 mass Spectrum: (m/e), 268 (M+), 253, 225, 197 (Base), 119, 105, 91, 77, “3. 2,6-Dibenzoylbenzyloxybenzene - Irradiation (313 nm, 12 hr) of a degassed solution of 2,6-dibenzoy1benzyloxy- benzene (50% ketone conversion) in benzene produced a mixture of two photoproducts and starting material. These products were separated by flash chromatography and are listed in the order of elution. g—2p3-diphenyl-7-benzoy1-3-hydroxye2,3-dihydrobenzofuran. lH-nmr (250 MHz, 000131: o=7.0-7.9 (m, 18H, Ar-H's), 5.69 (s, 1H, O-CflPh), 2.19 (br. S, 1H, OH) ppm. l3c-nmr (250 MHz, 000131: o=195.0 (C=O), 192.3, 138.0, 139.5, 133.0, 132.8, 131.7, 129.9, 128.8, 128.6, 128.9, 128.3, 128.2, 127.9, 127.8, 126.5, 121.6, 95.76, 82.23 ppm. i.r. (0H29121: 3550 om‘l (OH), 3010, 3000 om“l (Ar C-H), 1 2900, 2880, om‘l (sat. C—H), 1270 om‘ (Ar-O-C). mass spectrum: (m/e) 392 (M+), 379, 285 (Base), 181, 105, 91, 77. £72,3-diphenyl-7—benzoyl-3-hydrogy-2,3-dihydrobenzofuran. lH-nmr (250 MHz, dg-acetone): 0=6.8-8.2 (m, 18H, Ar-H's), 5.81 (s, 1H, O-CHPh), 5.70 (s, 1H, OH). 1 i.r. (CH2912): 3570 cm"1 (OH), 3020 om‘ (Ar-C-H), 2960, 200 2900 om‘l (sat. C-H), 1290 om‘l (Ar-O-C). mass spectrum: (m/e) 392 (M+), 37“ (Base), 285, 181, 105, 91, 77. 216-Dibenzoy1anisole - 3-Phenyl-7-benzoyl-3-hydroxy-2,3- dihydrobenzofuran was isolated by flash chromatography from the photolysate of 2,6-dibenzoylanisole in spectral grade cyclohexane (50% ketone conversion). Structural assignment was based upon the following spectral data. 3-Phenyl-7-benzoy1-3-hydroxy-2,3-dihydrobenzofuran. lH-nmr (250 MHz, 000131; 6=6.92-7.99 (m, 13H, Ar-H's), 9.97, 9.65 (AB quartet, J=10.5 Hz, 2H, 0-0p2), 1.2 (br. s, 1H, OH) ppm. l304nmr (250 MHz, CDC13l: 5=199.1 (C=O), 157.8, 137.8, 132.8, 132.1, 130.2, 129.9, 128.9, 128.3, 128.2, 127.8, 126.0, 122.3, 122.2, 121.2, 86.76, 81.79 ppm. i.r. (CH2C12): 3570 cm"1 (OH), 3095 cm'1 (Ar C-H), 2950 om‘l (sat. C-HO, 1260 om’l (Ar-O-CO) mass spectrum: (m/e) 316 (M+), 298, 221 (Base), 165, 105, 91, 77. QrBenzyloxyvalerophenone - GC/MS of the photolysate from p—benzyloxyvalerophenone in benzene (313 nm irradia- tion) contained only g-benzyloxyacetophenone. The mass Spectrum of the photoproduct was identical to that of 201 authentic p—benzyloxyacetophenone. There was also good agreement between the retention times of the photoproduct and authentic sample. a-(ngolyl)acetophenone - a-(g—Tolyl)acetophenone (200 mg) in 300 ml spectral grade cyclohexane was irradiated under a nitrogen atmosphere to 100% ketone conversion (ap- proximately 6 hr). HPLC analysis (Ultrasphere Si column; hexane/ethyl acetate, 95:5; 2.0 ml/min) of the photolysate (200 mg) revealed one major component (>99% pure). The photoproduct was identified as 2-pheny1-2-hydroxyindane on the basis of the following spectral data. lH—nmr (250 MHz, CDC13): 0=7.l-7.8 (m, 9H, Ar-H's), 3.99, 3.2“ (AB quartet, J=16.“ Hz, “H, CHZPh), 2.15 (br. s, 1H, OH) ppm. l3c-nmr (250 MHz, 000131: o=195.8, 190.9, 128.9, 127.2, 126.9, 125.2, 125.0, 83.32, “9.13 ppm, 1 i.r. (neat): 3770 our1 (OH), 3080, 3060, 3020 om‘ (Ar C-H), 2920, 2850 om'l (sat. C-H). mass Spectrum: (m/e) 210 (M+), 192, 105 (Base), 91, 77. d-(2,5-Dimethylphenyl)acetophenone - a-(2,5-dimethy1- phenyl)acetophenone (200 mg) in 300 ml spectral grade cyclo- hexane was irradiated under a nitrogen atmosphere to 100% ketone conversion. Removal of the solvent on a rotary evaporator afforded 200 mg of crude photolysate (colorless 202 oil) which HPLC analysis (same conditions as a-TAP) re- vealed to contain one major component (>99% pure). Spec- tral analysis of the crude photolysate identified the photo- product as 2-pheny1-5-methyl-2-hydroxyindane. Structural assignment was based upon the following spectral data. lH—nmr (250 MHz, 00013): o=6.88-7.91 (m, 8H, Ar-H's), 3.29, 3.02 (AB quartet, J=16.28 Hz, “H, CE -Ph), 2.21 (s, 2 3H, Ar-CH3) ppm. l3c-nmr (250 MHg,,000131: o=195.9, 191.2, 138.0, 136.9, 128.3, 128.25, 127.6, 127 0, 125 7, 125.2, 129.7, 83.36, “9.09,.“8.77, 21.18 ppm. i.r. (neat): 3590, 3920 cm“1 (OH), 3080, 3060, 3030, 3010 om‘l (Ar—C-H), 2990, 2920 om”l (sat. C-H). mass spectrum: (m/e) 229 (M+), 206, 191, 119, 105 (Base), 91, 77. a-Mesitylacetophenone - d-Mesitylacetophenone (200 mg) in 300 ml spectral grade cyclohexane was irradiated under a nitrogen atmosphere to 100% ketone conversion (12 hr). The solvent was removed on a rotary evaporator to afford 200 mg of a pale yellow oil. HPLC analysis of this oil revealed one major component in >99% purity. Spectral analysis identified the photoproduct as 2—pheny1-9,6-di- methyl-2-hydroxyindane on the basis of the following data. 203 lH-nmr (250 MHz, 00013): o=6.81-7.99 (m, 7H, Ar-H's), 3.29, 3.02 (AB quartet, J=l6.3 Hz, “H, CH2Ph), 2.27 (s, 3H, Ar-CH3), 2.16 (s, 3H, Ar-Cp3), 1.26 (br. s, 1H, 0H) ppm- l3c-nmr (250 MHz, 0D013): 6=197.6, 190.8, 136.7, 136.9, 133.7, 128.5, 128.1, 126.8, 125.0, 122.8, 82.76, 99.27, 97.60, 21.09, 18.8“ ppm. 1 1 i.r. (neat): 3520, 3370 cm" (0H), 3080, 3060, 3020 cm“ (Ar C-H), 2960, 2920, 2860 cm"1 (sat. C-H). mass spectrum: (m/e) 238 (M+), 220, 133, 105 (Base), 91, 77. a-(2,5-DiiSOpropylphenyl)acetophenone - a-(2,5-Diiso- propylphenyl)acetophenone (200 mg) in 300 ml spectral grade cyclohexane was irradiated to 100% ketone conversion (12 hr) under a nitrogen atmosphere. The solvent was removed on a rotary evaporator to afford 200 mg of a pale yellow oil. HPLC analysis of the oil showed only one major com- ponent in >99% purity. Spectral analysis of the crude photolysate identified the photoproduct as 1,1-dimethyl-2- phenyl—5-isopropyl-2-hydroxyindane on the basis of the following data. lH-nmr (250 MHz, 00013): o=7.1-7.7 (m, 8H, Ar-H's), 3.29, 2.99 (AB quartet, J=l6.01 Hz, 2H, CHZPh), 2.90 (m, 1H, -CH— (CH3)2), 2.03 (br. s, 1H, OH), 1.35 (s, 3H, CH3), 1.28 (d, 6H, -CH(CH3)2), 0.76 (s, 3H, CH3) ppm. 209 l3c-nmr (250 MHz, 00013): 8=197.9, 191.9, 138.8, 127.6, 127.0, 126.9, 125.2, 123.2, 123.1, 122.6, 87.23, 93.98, 33.88, 27.80, 29.11, 19.53 ppm. i.r. (neat): 3920 om"l (OH), 3080, 3060 om‘l (Ar C-H), 2960, 2860 cm"1 (sat. C—H). mass spectrum: (m/e) 280 (M+), 161, 105 (Base), 91, 77. a-(2,9,6-Triis0propylphenyl)acetOphenone - a-(2,“,6- Triisopropylphenyl)acetophenone (200 mg) in 300 ml spectral grade cyclohexane was irradiated to 100% ketone conver- sion (29 hr). HPLC analysis of the pale yellow oil (200 mg) obtained after the solvent had been removed indicated only one major component in 95% purity. Spectral analysis of the crude photolysate identified the photoproduct as 1,1- dimethyl-2-phenyl—9,6-diisopropyl-2-hydroxyindane on the basis of the following spectral evidence. lH-nmr (250 MHz, 00013): 0=6.9-7.63 (m, 7H, Ar-H's), 3.81, 3.08 (AB quartet, J=l6.l Hz, 2H, CHZPh), 2.92 (m, 2H, -CH(CH 2.19 (br. s, 1H, OH), 1.36 (s, 3H, cp3), 1.29 3),). (d, 6H,-CH(CH3)2),0.78 (s, 3H, CH3). l30-nmr (250 MHz, CD013): 6:198.9, 199.8, 190 8, 133.6, 127.7, 127.1, 126.6, 129.1, 121.5, 118.9, 87.21, 51.62, 92.19, 39.39, 31.06, 28.09, 29.28, 23.07, 22.90, 19.62. i.r. (neat): 3920 cm"1 (OH), 3080, 3060, 3020 om‘1 (Ar C-H), 2970, 2900, 2860 cm"1 (sat. C-H). mass spectrum: (m/e) 322 (M+), 231, 217, 203 (Base), 105, 91,77. 205 a-(g-Benzyloxyphenyl)acetophenone - A solution of 100 mg a-(g-benzyloxyphenyl)acetOphenone in 300 m1 spectral grade cyclohexane was irradiated under a nitrogen atmos- phere to 100% ketone conversion (2“ hr). HPLC analysis (Ultrasphere ODS-l8 column; acetonitrile/water; 2.0 ml/min) revealed one major component in the crude photolysate (80% pure). Homodecoupled l H-nmr revealed the presence of two AB quartets. Spectral analysis of the crude photolysate identified the photoproduct as a mixture of g and E—2,3- diphenyl-3-hydroxy-3,9-dihydrobenzopyran (E/E = 1.6:1 by proton nmr). The structural assignment was based upon the following spectral data. lH—nmr (250 MHz, 00013): o=6.7-7.5 (m, 19H, Ar-H's), 5.15 (overlapping s's, 2H, O-CHPh); 3.67, 300 (AB quartet, E- isomer, J=l7.11 Hz, 2H, Ar-CH2); 3.9“, 3.08 (AB quartet, E-isomer, J=16.33 Hz, 2H, Ar-CHZ), 1.26 (br. s, 1H, OH). (Homodecoupling experiments helped to unravel both AB 1 systems in the H-nmr.) l3c—nmr (250 MHz, 00013): 6=159.l, 137.3, 130.1, 129.9, 128.0, 127.9, 127.5, 127.3, 127.1, 126.9, 125.9, 121.3, 121.1, 116.7, 116.5, 89.65, 83.00, 72.08, 90.53, 36.77 ppm. i.r. (0014): 3580 cm“1 (OH), 3080, 3060, 3030 om‘l l 1 (Ar C-H), 2950, 2920 cm‘ (sat. C-H), 1280 cm“ (Ar-O—C). mass spectrum: (m/e) 302 (M+), 289, 211, 196, 183, 165, 152, 133, 105 (Base),9l, 77. 206 g:(p—Tolyl)acetone and d-(p-Tolyl)aceta1dehyde - 1,2- Di(p—tolyl)ethane was the only photoproduct visible in the proton nmr spectrum of the crude photolysate from either a-(prtolyl)acetone or a-(p—tolyl)acetaldehyde in spectral grade cyclohexane. Structural assignment was based upon both the proton nmr and the mass spectrum of the crude photolysate. lH-nmr (60 MHz, 00013): a: 7.0 (s, 9H, Ar-H's), 2.8 (s, 2H, Ar-CHZ), 2.1 (s, 3H, Ar-CH3) ppm. mass spectrum: (m/e) 210 (M+), 105 (Base). APPENDIX The tables in this Appendix contain the raw data from quantum yield measurements, Stern-Volmer quenching, and sensitization studies. Analysis conditions, appropriate concentrations of the materials used, as well as other pertinent experimental conditions are also furnished. In all cases, g.c. or HPLC peak areas are the average of at least two injections. 207 208 Table 32. Quenching of o-Benzyloxyacetophenone with 2,5- Dimethyl-2,“4Hexadiene in Benzene at 25°C.a qu1 = 1750 M‘1 00 Analysis: 5' 3% QF-l on Chrom. G qu2 = 2920 M'1 Column at 220°C. Aphoto/Astd ¢°/° [Q], 10"3 M #1 7 #2 #1 #2 0.0 0.199b 1.18°’° —--- -——— 0.303 0.103 0.703 1.95 1.68 0.606 0.0753 0.566 1.98 1.68 1.21 0.0976 0.301 3.13 3.92 1.82 0.0397 0.188 “.29 6.28 2.92 0.0253 0.118 t 5.89 10.0 a[Ketone] = 0.0388 M, [020] = 1.29 x 10‘3 M, [VP] = 0.110 M, [c 7.92 x 10"3 M. 151 z b 1 Actinometer (VP): moles AP = 6.68 x 10‘3; I = 0.0202 ein 1‘ moles photoproduct #1 = 2.56 x 10’“; 0 0.0177 moles photoproduct #2 = 2.02 x110'3; 0 0.100 cphotoproduct #l = g—2-phenyl—3—methy1-3-hydroxy—2,3-di- hydrobenzofuran; photoproduct #2 = 2-Acetylbenzophenone. 209 Table 33. Quenching of gyBenzyloxyacetOphenone with 2,g- Dimethyl-2,9-Hexadiene in Benzene at 25°C.a: 1 HPLC Analysis: Ultrasphere Si Column, qu = 1690 M 270 nm Hexane: EtOAc (95:5) Flow: 2.0 ml/min [QJ’ 10-3 M (Aphoto/Abenzene) x 100 ¢o/¢ 0.0 2.15 ---- 0.991 1.91 1.52 0.881 0.919 2.3“ 1.76 0.538 “.00 2.6“ 0.326 6.61 3.53 0.222 9.68 a[Ketone] = 0.039 M. bQuenching of the formation of gf2—pheny1-3-methy1-3-hydroxy- 2,3-dihydrobenzofuran. 210 Table 39. Quantum Yield Determination for Photoproducts from o-Benzyloxyacetophenone in Benzene at 25°C.a HPLC Analysis: Ultrasphere Si, 270 nm Hexane: EtOAc (95:5) Flow: 2.0 ml/min Aphoto/Abenzene mmoles photo c c c c c c Tube #1 #2 #1 #2 ¢#l ¢#2 A 0.0190 0.0303 B 0.0171 0.0355 Average 0.0181 0.0329 0.653 1.07 0.027 0.059 VP 0.101 9.53b a[Ketone] = 0.0381 M; [VP] = 0.111 M. b 1 I = 0.0289 ein l- . 0#1 = g—2-phenyl-3-methy1-3-hydroxy-2,3-dihydrobenzofuran. #2 2-Acetylbenzophenone. 211 Table 35. Quenching of gyBenzyloxyacetophenone in Benzene Containing 1.02 M Pyridine with 2,5-Dimethyl-2,“— Hexadiene at 25°C.a qul = 2250 M'1 HPLC Analysis: Ultrasphere Si, 270 nm qu2 = 1920 M-1 Hexane: EtOAc (95:5) qu3 = 2250 M.1 Flow: 2.0 ml/min [Q], Aphoto/Astd ¢o/¢ 10'3 M #1b #2b #3b '#1b #2b #3b 0.0 0.115 .0675 0.0361 ---- ---- ---- 0.383 0.0726 .0““2 0.0296 1.58 1.53 1.97 0.766 0.0“28 .0286 0.0165 2.91 2.36 2.19 1.53 0.0260 .0155 0.00927 “.“2 “.35 3.89 2.30 0.0177 .0105 0.00637 6.50 6.93 5.67 3.06 0.0195 .00895 0.0051“ 7.93 7.99 7.02 aEKetone] = 0.0902 M. b#1 #2 #3 2—Acetylbenzophenone. g-2-phenyl-3-methyl-3-hydroxy-2,3-dihydrobenzofuran. §-2-pheny1-3-methyl-3-hydroxy-2,3-dihydrobenzofuran. 212 Table 36. Effects of Pyridine on Photoproduct Quantum Yield for p-Benzyloxyacetophenone in Benzene at 25°C.a HPLC Analysis: Ultrasphere Si, 270 nm Hexane: EtOAc (95:5) Flow: 2.0 ml/min [Per’ M . Aphoto/Astd 9 0.0 0.0130 0.0226 0.599 0.0360 0.0629 1.09 0.0550 0.0958 1.63 0.0670 0.116 2.18 0.0821 0.193 a[Ketone] = 0.0197 M, photoproduct = gg2-phenyl-3-methy1_3_ hydroxy-2,3-dihydrobenzofuran. 213 Table 37. Quenching of ggBenzyloxybenzophenone in Benzene with 2,5-Dimethyl-2,“-Hexadiene at 25°C.a qu = 100.1 M‘1 00 Analysis: 5' 3% QF-l on Chrom G 180°C [Q] 10‘2 M Ab /A ¢°/¢ ’ photo std 0.0 12.65 ---- 0.518 7.85 1.61 1.0“ 6.97 1.96 2.07 “.02 3.15 3.11 3.08 9.11 a[Ketone] = 0.038 M, [C24]: 7.87 x lO’Ll M, '313 nm b . E and E 2,3-diphenyl-3-hydroxy—2,3-dihydrobenzofuran have the same retention. Table 38. Quenching of prenzyloxybenzophenone with 2,5- Dimethy1-2,“-Hexadiene in Benzene at 25°C.a qu = 112.9 M‘1 -2 b [01, 10 M AphotO/Astd ¢°/¢ 0.0 6.71 ---- 0.987 9.38 1.53 0.979 3.17 2.11 1.95 2.0“ 3.29 2.92 1.50 9.98 3.90 1.28 5.2“ a[Ketone] = 0.0908 M, [C29] = 9.82 x 10"H M, 313 nm. b; and Ee2,3-diphenyl-3-hydroxy-2,3-dihydrobenzofuran. 219 Table 39. Quantum Yield for Photoproduct from peBenzyloxy- benzophenone in Benzene at 25°C.a GC Analysis: 5' 3% QF-l on Chrom G 180°C Sample Aphoto/std Moles Photoproduct ¢pdt A 7.60 0.019 B 7.63 0.0138 Average 7.62 0.0139 0.938 VP 0.260 9.89 x 10'3 a[Ketone] = 0.0395 M, [02“] = 1.36 x 10’3 M; [VP] = 0.111 M, [C 0.01 M; 313 nm. 1 15J = b: = 0.0198 ein 1' cs and g- 2,3-diphenyl-3-hydroxy-2,3-dihydrobenzofuran. Table “0. Quantum Yield for Photoproduct from ngenzyloxy- benzophenone in Benzene at 25°C.a HPLC Analysis: Ultrasphere Si, 270 nm Hexane: EtOAc (93:7) Flow: 1.0 ml/min Aphoto/Abenzene moles photo c c c c c c Sample #1 #2 #1 #2 ¢#1 ¢#2 A 0.93“ 0.0593 B 0.375 0.0966 Average 0.905 0.050“ 0.015“ 0.002 0.831 0.108 VP 0.0599 0.00611b a[Ketone] = 0.09 M, [VP] = 0.108 M, 313 nm. bl = 0.0185 ein 1‘1 0#1 #2 £32,3-diphenyl-3-hydroxy-2,3-dihydrobenzofuran. E52,3-diphenyl-3-hydroxy-2,3-dihydrobenzofuran. 215 Table “1. Quenching of p—BenzyloxybenZOphenone with n-Octyl Mercaptan in Benzene at 25°C.a qu = 0.58b M"1 00 Analysis: 5' 3% QF-l on Chrom 0 180°C C [Q]: M Aphoto/Astd ¢o/¢ 0.0 7.60 _ ---- 0.159 6.78 1.12 0.319 6.15 1.29 0.638 5.65 1.35 0.957 “.90 1.55 1.28 “.“6 1.71 a[Ketone] = 0.0395 M, [C29]: 1.36 x 10'3 M, 313 nm. hr = 90 nsec assuming kq = l.“ x 107M'ls'l. CBoth E and E benzofuranols. Table 92. Quenching of ngenzyloxybenzophenone with n-Octyl Mercaptan in Benzene at 25°C.a = -1 qu 0.612 M c [Q]: M Aphoto/Astd ¢o/¢ 0.0 17.26 ---- 0.153 15.13 1.1“ 0.306 13.37 1.29 0.612 11.97 1.51 0.918 10.09 1.72 1.22“ 10.02 1.78 a[Ketone] = 0.0911 M [C29] = “.79 x lO-D M, 313 nm. bT = “0.1 nsec. CBoth p and g benzofuranols. 216 Table “3. Quenching of p—Benzyloxybenzophenone by 2,5- Dimethyl-2,“-Hexadiene in 1,9-Dioxane at 25°C.8 kg: = 51.5 M"'1 00 Analysis: 5' 3% QF-l on Chrom 0 180°C [Q] 10"2 M Ac /A ¢°/¢ ’ photo std 0.0 5.77b ---- 0.695 9.31 1.39 1.29 3.17 1.82 2.58 2.“8 2.31 3.87 1.95 2.96 5.16 1.53 3.77 VP 0.383b 9 a[Ketone] = 0.093 M, [02,] = 6.21 x 10' M, [VP] = 0.103 M, [015] = 9.76 x 10'3 M, 313 nm. b[AP] in aceinometer = 3.93 x 10‘3 M; 1 = 0.0109 ein 1‘l [PhotOproduct] = 9.78 x 10"3 M; = 0.96. ¢pdt CBoth E and g benzofuranols. 217 Table “9. Quenching of p-Benzyloxy-S-Methylbenzophenone by 2,5-Dimethyl-2,“-Hexadiene in Benzene at 25°C.a qu = 160 M"1 00 Analysis: 5' 3% QF-l on Chrom G 205°C -2 c [0], 10 M Aphoto/Astd ¢°/¢ 0.0 0.787b ---- 0.768 0.338 2.33 1.59 0.220 3.58 3.07 0.139 5.87 9.61 0.103 7.63 6.1“ 0.0707 11.13 VP 0.206b -“ a[Ketone] = 0.0395 M, [C26] = 7.6 x 10 M, [VP] = 0.108 M, [C15] = 0.0118 M, 313 nm. b[AP] = 9.57 x 10‘3 M; I = 0.0138 ein 1‘1, [Photoproduct] -3 . » = 7.87 x 10 M, ¢pdt 0.57. c2,3-diphenyl-5-methyl-3-hydroxy-2,3-dihydrobenzofuran, stereochemistry of the photoproduct is undetermined. 218 Table “5. Quenching of peBenzyloxy-5-Methylbenzophenone in Benzene with 2,5-Dimethyl-2,9-Hexadiene at 25°C.8 qu = 169 M’l. GC Analysis: 5' 3% QF-l on Chrom G 205°C -2 mmoles [Q]’ 10 M photoproductC ¢°/¢ 0.0 7.67b --—- 0.552 3.92 1.96 1.10 2.61 2.99 2.21 1.59 9.98 3.31 1.18 6.50 9.92 0.901 8.81 VP 9.87b a[Ketone] = 0.0902 M, [026] = 1.99 x 10'3 M, [VP] = 0.110 M, - -3 [015] - 5.57 x 10 M. b[AP] = “.87 x 10"3 M; I = 0.0198 ein 1'1, [Photoproduct] = 7.67 x 10'3 M; = 0.520. ¢pdt c2,3-Diphenyl-5-methyl-3-hydroxy-2,3-dihydrobenzofuran, photoproduct stereochemistry is undetermined. 219 Table 86' Quenching 0f 2:2'-Dibenzy10xybenzophenone with 2:5'Dimethyl-2,“-Hexadiene in Benzene at 25°C.a’c qu = 71.7 M‘1 GC Analysis: 6' 5% 0v-101 on Chrom G 250°C [01. M Aphoto/Astd °°/° 0.0 2.09b ---- 0.0188 - 0.982 2.08 0.0377 0.607 3.36 0.0753 0.318 6.93 0.113 0.239 8.91 0.151 0.179 11.59 VP 0.170b a[Ketone] = 0.0387 M; [C26] = 1.37 x 10‘3 M; [VP] = 0.108 M; [015] = 6.13 x 10’3 M, 313 nm. b[AP] = 1.95 x 10"3 M; I = 5.92 x 10'3 ein 1’1, [Photo- 3 -3 ° = product] 2.69 x 10 M, ¢pdt 0.955. CPhotoproduct assumed to be 2-phenyl-3-(gfbenzyloxyphenyl)- 3-hydroxy-2,3-dihydrobenzofuran. 220 Table ”7' Quenching 0f 2:2'-Dibenzyloxyben20phenone with 2sS'Dimethyl-2,“-Hexadiene in Benzene at 25°C.a’c qu = 65.8 M‘1 GC Analysis: 6' 5% OV-101 on Chrom G 250°C [0], M Aphoto/Astd ¢°/¢ 0.0 2.09b ---— 0.0196 0.982 2.08 0.0391 0.597 3.92 0.0782 0-359 5.76 0.117 0.291 8.“8 VP 0.196b a[Ketone] = 0.0906 M, [026] = 1.31 x 10‘3 M, [VP] = 0.106 M, [C15] = 5.00 x 10‘3 M, 313 nm. b[AP] = 1.89 x 10'3 M; 1 = 5.58 x 10'3 ein 1‘1, [Photo- product] = 2.57 x 10"3 M; 0 = 0.961. CPhotoproduct was assumed to be 2-phenyl-3-(pfbenzyloxy- phenyl)—3-hydrogen—2,3—dihydrobenzofuran. 221 Table “8- Quenching Of p—Methoxybenzophenone with 2,5- Dimethyl-2,9-Hexadiene in Benzene at 25°C.a’c qu = 2330 M"1 GC Analysis: 6' 3% QF-l on Chrom G 180°C -“ [01, 10 M AphotO/Astd ¢°/¢ 0.0 2.70b ---- 0.205 2.60 1.01 0.908 2.5“ 1.06 0.816 2.27 1.19 1.22 2.08 1.30 1.63 1.99 1.39 VP 0.191b a[Ketone] = 0.0905 M, [C21] = 1.32 x 10"3 M, [VP] = 0.119 M, [015] = 0.0139 M, 313 nm. b[AP] = 5.00 x 10"3 M; I = 0.0152 ein 1‘l , [Photoproduct] = 5.35 x 10'3 M; o = 0.352. CPhotoproduct = 3-phenyl-3-hydroxy-2,3-dihydrobenzofuran. 222 Table “9. Quen0hing of p—Methoxybenzophenone with 2,5- Dimethyl-2,9-Hexadiene in Benzene at 25°C.a’c qu = 2810 M‘1 GC Analysis: 6' 3% QF-l on Chrom G 180°C '3 [Q], 10 M Aphoto/Astd ¢°/¢ 0.0 3.78b ---— 0.183 2.66 1.98 0.366 2.09 1.88 0.732 ' 1.26 3.11 1.10 0.906 9.92 1.96 0.709 5.61 VP 0.959b a[Ketone] = 0.0911 M, [C21] = 1.39 x 10'3 M, [VP] = 0.103 M, [015] = 2.55 x 10’3 M, 313 nm. b[AP] = 9.6 x 10‘3 M; I = 0.0139 ein l'l , [Photoproduct] = 5.63 x 10"3 M; o = 0.909. CPhotoproduct = 3-phenyl-3-hydroxy-2,3-dihydrobenzofuran. 223 Table 50. Quantum Yield for PhotOproduct from ngethoxy- benzophenone in Benzene at 25°C.a HPLC Analysis: Ultrasphere Si Hexane: EtOAc (95:5) Flow: 2.0 ml/min 270 nm mmoles 0 Sample Aphoto/Astd photo. ¢ A 0.158 B 0.172 Average 0.161 5.5“ 0.299 VP 0.0599 6.11b a[Ketone] = 0.0370 M; [VP] = 0.099 M, 313 nm. bl = 0.0185 ein 1'1. CPhotoproduct = 3-phenyl-3-hydroxy-2,3-dihydrobenzofuran. 22“ Table 51° Quenching 0f QrBenzyloxyvalerophenone with 2,5- Dimethyl-2,“-Hexadiene in Benzene at 25°C.a’c qu = 273 M’1 GC Analysis: 5' 3% QF-l on Chrom G 220°C -2 [Q], 10 M Aphoto/Astd ¢°/¢ 0.0 3.88b ---- 0.397 1.75 2.22 0.699 1.26 3.08 1.39 0.751 5.17 2.08 0.983 8.03 2.78 0.938 8.85 VP 0.699b a[Ketone] = 0.0901 M, [022] = 1.26 x 10"3 M, [VP] = 0.105 M, [C 0.0103 M, 313 nm. l5J = bEAP] = 0.0135 M; I = 0.0909 ein 1'1, [Photoproduct] = 7.77 x 10‘3 M; 0 = 0.19. cPhotoproduct = p—benzyloxyzcetophenone. 225 Table 52. Quenching Of g-BenzyloxyvalerOphenone with 2,5- Dimethy1-2,9-Hexadiene in Benzene at 25°C.a’c qu = 309 M‘1 GC Analysis: 5' 3% QF-l on Chrom G 220°C -2 [Q]. 10 M Aphoto/Astd ¢°/¢ 0.0 0.692b ---- 0.182 0.319 2.16 0.369 0.231 2.99 0.727 0.152 9.59 1.09 0.117 5.90 1.95 0.0913 7.56 VP 0.0917b a[Ketone] = 0.091 M, [022] = 2.95 x 10"3 M, [VP] = 0.105 M, [C 0.0196 M. 15] = b[AP] = 3.38 x 10'3 M; I = 0.0102 ein l"1 , [Photoproduct] = 2.69 x 10"3 M; 0 = 0.260. CPhotOproduct = p-benzyloxyacetophenone. 226 Table 53. Quenching of peBenzyloxyvalerophenone with 2,5- Dimethyl-2,9-Hexadiene in Benzene at 25°C?"c qu = 295 M‘1 GC Analysis: 5' 3% QF-l on Chrom G 220°C -3 [Q]. 10 M Aphoto/Astd °°/° 0.0 2.37b ---- 1.08 1.55 1.53 2.16 1.11 2.19 “.32 0.886 2.67 6.98 0.668 3.55 8.6“ 0.678 3.50 VP 0.292b a[Ketone] = 0.0392 M, [C22] = 1.9 x 10'3 M, [VP] = 0.103 M, [015] = 0.0109 M, 313 nm. b[AP] - 5.98 x 10"3 M; I = 0.0181 ein 1'1, [Photoproduct] = 5.27 x 10‘3 M; 9 = 0.291. cPhotoproduct = p—benzyloxyacetophenone. 227 Table 5“. Effects of Pyridine on Quantum Yield for 97 benzyloxyacetophenone Formation from ngenzyloxy— valerophenone in Benzene at 25°C.a HPLC Analysis: Ultrasphere Si Hexane: EtOAc (95:5) Flow: 1.7 ml/min 270 nm [Pyrj’ M Aphoto/Astd °II 0.0 0.0956 0.300 0.226 0.0675 0.999 0.953 0.0768 0.505 0.679 0.0783 0.515 0.906 0.0799 0.526 a[Ketone] = 0.0195 M, 313 nm. 228 Table 55. Quenching of 2,6-Dibenzoylbenzyloxybenzene in Benzene with 2,5-Dimethyl-2,“-Hexadiene at 25°C.a qul = 19.7 M"1 HPLC Analysis: Ultrasphere Si qu2 = 13.9 M'1 Hexane: EtOAc (9:1) Flow: 2.2 ml/min 270 nm ephoto/Astd ¢o/¢ [0], M #1 #2 #1 #2 0.0 0.361b 0.0990b ---- ---- 0.0192 0.219 0.0659 1.58 1.51 0.0399 .195 .0595 1.76 1.67 0.0789 .193 .0936 2.90 2.27 0.118 .129 .0377 2.77 2.63 0.158 .100 .0308 3.92 3.22 VP 0.0192b a[Ketone] = 0.0911 M, [VP] = 0.112 M, 313 nm. b[AP] = 1.81 x 10'3 M; I = 5.99 x 10-3 ein 1'1, [Photoproduct 1] = 9.62 x 10‘3 M; p = 0.892, [Photoproduct 2] = 1.91 x 10"3 M; 0 = 0.257. Photoproduct #1 = §-2,3-diphenyl-7- benzoyl-3-hydroxy-2,3-dihydrobenzofuran. Photoproduct #2 =‘§-isomer. 229 Table 56. Quenching of 2,6-Dibenzoyloxybenzene in Benzene with 2,5-Dimethyl-2,9-Hexadiene at 25°C.a qul = 19.2 M‘1 HPLC Analysis: Ultrasphere Si qu2 = 13.5 M‘1 Hexane: EtOAc (9 1) Flow: 2.2 ml/min 270 nm Aphoto/Astd °°/° [01. M #1 #2 #1 #2 0.0 0.192b 0.0920b ---- ---- 0 0226 0.0818 0.0252 1.79 1.67 0.0952 0.0652 0.0201 2.18 2.09 0.0909 0.0962 0.0197 3.03 2.87 0.136 0.0393 0.0123 3.61 3.91 0.181 0.0302 0.0095 9.70 9.92 VP 0.0069b a[Ketone] = 0.0207 M, [VP] = 0.102 M. 9 l b[SP = 6.51 x 10' M; 1 = 1.97 x 10‘3 ein l‘ , [Photoproduct 1] = 1.82 x 10'3 M; 0 = 0.92, [Photoproduct 2] = 6.17 x 10'“ M; m = 0.31, Photoproduct #1 = EgBenzofuranol; photo- product #2 = g—Benzofuranol. 230 Table 57. Quenching of 2,6-Diacetylbenzyloxybenzene with 2,5-Dimethyl-2,“-Hexadiene in Benzene at 25°C.a qu = 69.5 M.1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (9:1) Flow: 2.0 ml/min 270 nm -2 [Q]’ 10 M Aphoto/Astd ¢o/¢ 0.0 0.0239b ---- 0.993 0.0117 ' 1.86 1.89 0.0085 2.57 3.77 0.00579 3.77 5.60 0.00926 5.12 7.59 0.00337 6.98 VP 0.00916 M APb a[Ketone] = 0.02 M, [VP] = 0.110 M. b[AP] = 0.00916 M; 1 = 0.0267 ein 1'l , [Photoproduct] = “.53 x 10'3 M; 0 = 0.163; Photoproduct = E-2-pheny1-3- methyl-7-acetyl-3-hydroxy-2,3-dihydrobenzufuran. 231 Table 58. Quenching of 2,6-Diacetylbenzyloxybenzene in Benzene with 2,5-Dimethyl-2,9-Hexadiene at 25°C.a qu = 76.1 M'1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (9:1) Flow: 2.0 ml/min 270 nm -2 [Q], 10 M (AphOtO/Astd) x 100 ¢°/¢ 0.0 ‘ 1.79b ---- 0.973 ’ 0.917 1.90 1.95 0.650 2.68 3.89 0.929 7 “.06 5.89 0 318 ' 5.98 7.79 0.293 7.16 VP 6.23 x 10'3 M APb a[Ketone] = 0.0193 M, [VP] 0.107 M, 313 nm. bEAP] = 6~23 X 10'3 M; I = 0.0189 ein 1'1, [Photoproduct] = 3.31 x 10'3 M; 0 = 0.175; PhotOproduct = Z-benzofuranol. 232 Table 59. Quenching of 2,6-Dibenzoylanisole with 2,5- Dimethyl-2,9-hexadiene in Benzene at 25°C.a qu = 297 M‘1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (9:1) Flow: 2.0 ml/min 270 nm [QJ’ 10-2 M Aphoto/Astd ¢o/¢ 0.0 0.391 ---- 0.197 0.23“ 1.67 0.393 0.185 2.11 0.787 0.126 3.10 1.18 0.0990 3.95 1.57 0.0765 5.11 a[Ketone] = 0.0191 M, 313 nm. Photoproduct = 3-phenyl-7- benzoyl-3-hydroxy-2,3-dihydrobenzofuran. 233 Table 60. Quenching of 2,6-Dibenzoylanisole with 2,5-Di- methyl-2,9-Hexadiene in Benzene at 25°C.a kg: = 206 M'1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (9:1) Flow: 2.0 ml/min 270 nm [Q], 10‘2 M AphOtO/Astd ¢°/¢ 0.0 0.912 ---- 0.201 0.568 1.61 0.902 0.927 2.19 0.809 0.311 2.93 1 21 0.236 3.86 1.61 0.202 9.51 a[Ketone] = 0.0219 M, 313 nm. Photoproduct = 3-phenyl—7- benzoyl-3-hydroxy-2,3-dihydrobenzofuran. 23“ Table 61. Quantum Yield for Photoproduct Formation from 2,6-Dibenzoylanisole in Benzene at 25°C.3 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (9:1) Flow: 2.0 ml/min 270 nm Sample Aphoto/Astd mmoles photo. ¢pdt A 0.906 B 0.398 Average 0.900 5.56 0.77 b VP 0.0253 2.39 aEKetone] = 0.0205 M; [VP] b I = 7.29 x 10‘3 ein 1' 1 0.105 M, 313 nm. ; photOproduct = 3-phenyl-7-benzoyl- 3-hydroxy-2,3-dihydrobenzofuran. 235 oTable 62. Quenching of a-(pgTolyl)acet0phenone with 2,5- Dimethyl-2,9-hexadiene in Benzene at 25°C.a qu = 29.3 M‘1 GC Analysis: 6' 3% QF-l on Chrom 0 185°C [Q], 10'2 M mmoles photOproduct ¢°/¢ 0.0 2.33b ---- .937 1.87 1.25 1.87 1.57 1.99 3.75 1.05 2.22 5.62 0.878 3.65 7.99 0.563 “.1“ VP 0.859b -“ a[Ketone] = 0.0261 M, [C21] = 9.59 x 10 M, [VP] = 0.129 M, [015] = 0.0105 M, 313 nm. bl = 2.85 x 10'3 ein l-l; photoproduct = 2-phenyl-2-hydroxy- indane. 236 Table 63. Quenching of a-(p-Tolyl)acet0phenone with 2,5— Dimethy1-2,9-Hexadiene in Benzene at 25°C.a -1 qu = 31.8 M -2 [Q], 10 M mmoles photoproduct ¢°/¢ 0.0 3.68b ---- 0.893 2.77 1.33 1.69 2.21 1.67 3.37 1.69 2.18 5.06 1.50 2.96 6.7“ 1.17 3.15 L} a[Ketone] = 0.025 M, [C2D] = 7.69 x 10‘ M; photoproduct = 2-pheny1-2-hydroxyindane. 237 Table 6“. Quenching of a-(2,5-Dimethylphenyl)acetophenone . with 2,5-Dimethyl-2,9-hexadiene in Benzene at 25°C.a qu = 18.8 M‘1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (95:5) Flow: 2.0 ml/min 270 nm [0], M Aphoto/Astd ¢°/¢ 0.0 0.109 ---- 0.032 ‘ 0.0729 1.51 0.069 0.0512 2.13 0.128 0.0339 3.22 0.192 0.0226 9.82 0.256 0.0163 6.69 a[Ketone] = 0.0253 M, 313 nm; photoproduct = 2-phenyl-5- methyl-2-hydroxyindane. 238 Table 65. Quenching of a-(2,5-Dimethylpheny1)acetophenone with 2,5-Dimethy1-2,9-Hexadiene in Benzene at 25°C.a qu = 19.6 M-1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (95:5) Flow: 2.0 ml/min 270 nm 0.0 0.110b -—-— 0.0325 .0720 1.52 0.0651 .052“ 2.10 0.130 .0380 3.33 0.195 .023“ “.70 0.260 .016“ 6.71 VP 0.0315b a[Ketone] = 0.0299 M, [VP] = 0.105 M, 313 nm. b[AP] = 2.97 x 10‘3 M; I = 0.009 ein 1'1; [Photoproduct] = 5.08 x 10'3 M; m 2 hydroxyindane. 0.653; photoproduct = 2—phenyl—5-methyl- 239 Table 66. Quenching of a-MesitylaCetophenone with 2,5- Dimethy1-2,“-Hexadiene in Benzene at 25°C.a qu = 9.95 M"1 HPLC Analysis: Ultrasphere ODS-18 CH3CN - H2O Flow: 2.0 ml/min 270 nm [QJ’ 10-2 M Aphoto/Astd ¢°/¢ 0.0 0.559 ——4- 0.889 0.517 1.08 1.78 0.990 1.19 3.56 ' 0.981 1.16 5.33 0.996 1.25 7.11 0.905 1.38 a[Ketone] = 0.0225 M, 313 nm; photoproduct = 2-pheny1-“,6- dimethyl-2—hydroxyindane. 2“0 Table 67. Quenching of a-MesitylacetOphenone with 2,5— Dimethyl-2,“-Hexadiene in Benzene at 25°C.a qu = 9.73 M‘1 HPLC Analysis: Ultrasphere ODS-18 CH3CN - H20 Flow: 2.0 ml/min 270 nm [QJ’ M Aphoto/Astd ¢o/¢ 0.0 0.570 ---- 0.0335 0.987 1.17 0.0670 0.919 1.36 0.13“ 0.365 1.56 0.201 0.286 ' 2.01 0.268 0.251 2.27 a[Ketone] = 0.0221 M, 313 nm; photoproduct = 2-phenyl-“,6- dimethyl-2-hydroxyindane. 291 Table 68. Quantum Yield for Photoproduct from a-Mesityl- acetophenone in Benzene at 25°C.a. mmoles Sample Aphoto/Astd photoprod. ¢pdt A 0.0101 B 0.00965 Average 0.00987 7.99 0.971 VP 0.0600 5.66b a[Ketone] = 0.025 M, [VP] = 0.109 M, 313 nm. b1 = 0.0172 ein 1'l hydroxyindane. ; photOproduct = 2-phenyl-“,6-dimethyl~2- Table 69. Effects of Pyridine on Quantum Yield for Photo- product from a-Mesitylacetophenone in Benzene at 25°C.a [Pyridine], M Aphoto/Astd ¢pdt 0.0 0.0267 0.9“ 0.117 0.0279 0.96 0.233 0.0295 0.986 0.967 0.0309 0.509 0.700 0.0308 0.508 0.933 0.0329 0.592 a[Ketone] = 0.0231 M, 313 nm; photoproduct = 2-phenyl-“,6- dimethyl-7-hydroxyindane. 292 Table 70. Quenching of a-(2,5-Diisopropylphenyl)acetophenone with 2,5-Dimethyl-2,“-hexadiene in Benzene at 25°C.a qu = 3.99 M'1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (95:5) Flow: 2.0 ml/min 270 nm —2 [Q]: 10 M Aphoto/Astd ¢°/¢ 0.0 0.216 —-—- 0.93 0.192 1.13 1.86 0.181 1.20 3.72 0.189 1.17 5.58 0.168 1.29 7.9“ 0.158 1.37 a[Ketone] = 0.0263 M, 313 nm; photoproduct = 1,1-Dimethyl- 2-pheny1-5-isopropy1-2-hydroxyindane. 293 Table 71. Quenching of a-(2,5-Diisopropy1phenyl)aceto- phenone in Benzene with 2,5-Dimethyl-2,“-Hexa- diene at 25°C.a kq¢ = 3.27 M'1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (95:5) Flow: 2.0 ml/min 270 nm [QJ’ M Aphoto/Astd 80/¢ .0 .107b ---, .081 .0799 1.29 .162 .0722 1.91 .329 .0519 1.98 .“86 .0“03 2.53 .698 .0326 3.13 VP 9.96 x 10'3 M AP a[Ketone] = 0.025 M; [VP] = 0.105 M, 313 nm. b 1 I = 0.0150 sin 1‘ : [Photoproduct] = 6.23 x 10‘3 M; 9 = 0.915; photoproduct = l,l—Dimethyl-2-phenyl-5-isopr0pyl-2- hydroxyindane. 2““ Table 72. Quenching of a-(2,9,6-Triisopropylphenyl)aceto— phenone with 2,5-Dimethyl—2,9-Hexadiene in Benzene at 25°C.a k r = 3.51 M'1 q HPLC Analysis: Ultrasphere Si Hexane: EtOAc (99:1) Flow: 2.0 ml/min 270 nm Aphoto/Astd [Q], M x 100 ¢°/¢ 0.0 1.53b ---- 0.123 0.915 1.67 0.296 0.777 1.97 0.992 0.533 2.87 0.737 0.902 3.81 0.983 0.330 9.69 VP 0.839b a[Ketone] = 0.0259 M; [VP] = 0.103 M, [015] = 0.01 M, 313 nm. b[AP] = 0.058 M; I = 0.0978 ein 1'1; [Photoproduct] = 2.03 x 10"3 M; ¢ = 0.0925; photoproduct = 1,1-Dimethyl-2-phenyl- 9,6-diisopropy1-2-hydroxyindane. 295 Table 73. Quenching of a-(2,“,6-Triisopropylphenyl)aceto- phenone with 2,5-Dimethyl-2,“-Hexadiene in Benzene at 25°C.8 qu = 2.98 M‘1 HPLC Analysis: Ultrasphere Si Hexane: EtOAc (99:1) Flow: 2.0 ml/min 270 nm Aphoto/Astd [Q], M x 100 ¢°/¢ 0.0 1.30b ---- 0.126 0.793 1.75 0.252 0.622 2.09 0.50“ 0.960 2.83 0.756 0.378 3.99 1.01 0.299 “.35 VP 0.672b a[Ketone] = 0.0229 M; [VP] = 0.103 M; [C 1 15] = 0.0115 M, 313 nm. b[AP] = 0.0195 M; I = 0.0939 ein 1‘ ; [Photoproduct] = 1.73 x 10'3 M; o = 0.039“; photoproduct = 1,1-Dimethyl-2-phenyl- 9,6-diisopropyl-2-hydroxyindane. 296 Table 7“. Sensitization of the Cis-Trans Isomerization of cis-Piperylene with p—BenzyloxyacetOphenone in Benzene at 25°C.a ' kg: = 62.8 M‘1 GC Analysis: 25' 25% 1,2,3-Tris- ¢isc= 0'97 (2-Cyanoethy1)propane on Chromsorb P -l -1 [C-P] , M Bcorr MC-t O'SS/MC-t 23.9 0.203 0.939 1.25 11.7 0 103 0.996 1.23 7.81 0.0791 0.980 1.15 5.95 0.0561 0.985 1.13 9.67 0.0955 0.992 1.12 3.90 0.0383 0.998 1.11 2.92 0.0298 0.516 1.07 AP 0.0923b a[Ketone] = 1.99 x 10‘3 M; [AP] = 0.102 M, 313 nm. b[o-P] in Actinometer = 0.257 M; 1 = 0.0109 ein 1'1. 297 Table 75. Sensitization of Cis-Trans Isomerization of cis- Piperylene with p-Benzyloxyacetophenone in Ben- zene at 25°C.a kq r= 63.6 M"1 GC Analysis: 25' 25% 1,2,3-Tris- ¢isc=l.00 (2-cyanoethy1)propane on Chromsorb P -1 -1 [C-P] , M 800?? MC-t O'SS/MC-t 23.20 0.0698 0.“9“ 1.18 11.60 0.103. 0.985 1.13 7.75 0.0698. 0.99“ 1.11 5.78 0.0598 0.517 1.06 “.63 0.0995 0.527 1.09 3.86 0.0382 0.593 1.01 2.90 0.0387 0.5“3 1.01 AP 0.0593b a[Ketone] = 1.91 x 10'3 M; [AP] = 0.109 M, 313 nm. b[o-P] in Actinometer = 0.172 M; I = 8.99 x 10'3 ein 1'1. 298 Table 76. Sensitization of Trans-Cis Isomerization of trans- Stilbene with p—Benzyloxybenzophenone in Benzene at 25°C.a qu = 110 M‘1 GC Analysis: 6' 20% SE-30 on Chrom G ¢1so= 0.97 180°C -1 -1 [t-S] ’ M Scorr ¢t-S 0.“1/¢t_s 55.0 0.118 0.265 1.55 27.6 0.0771 0.395 1.19 36.6 0.0862 0.289 1.92 18.9 0.0999 0.333 1.23 13.8 0.0388 0.397 1.18 AP 0.0613b a[Ketone] = 0.0935 M; [BP] = 0.103 M, 366 nm. b[t-S] in Actinometer = 0.0595 M; I = 8.13 x 10‘3 ein l 299 Table 77. Sensitization of Trans-Cis Isomerization of trans- Stilbene with ggBenzyloxybenZOphenone in Benzene at 25°C.3 qu = 106 M'1 GC Analysis: 6' 20% SE-30 on Chrom 0 °iso= 0.92 180°C -1 -1 ' [t-S] ’ M BCOI’I‘ ¢C-t 0.“1/¢C_t 93.5 0.173 0.203 2.02 96.7 0 109 0.256 1.60 31.2 0.080 0.282 1.96 23.9 0.0639 0.300 1.37 15.6 0.0972 0.332 1.23 11.7 0.0382 0.359 1.19 BPl 0.170b BP2 0.0599b a[Ketone] = 0.0392 M; [BP] = 0.109 M, 366 nm. b[t-S] in BPl = 0.0219 M; [t-S] in BP] = 0.0692 M; I = 9.12 x 10‘3 ein 1'1. 250 Table 78. Determination of kq for prenzyloxyacetophenone and 2,5—Dimethyl-2,“-hexadiene in Benzene at 27°C by Laser Flash Spectroscopy.a kq = 2.91 x 109M‘1s'l A = 920 nm [01, 10’3M k, 1053-1 0.0 2.19 0.0279 ' 2.35 0.0558 2.29 0.111 2.35 0.166 2.95 0.275 3.06 a[Ketone] = 0.01“ M; TT = “69 nsec (920 nm); TT = “38 nsec (390 nm). Table 79. Determination of kq for prenzyloxyacetophenone and 2,5-Dimethyl-2,9-hexadiene in Benzene at 27°C by Laser Flash Spectroscopy. kq = 1.91 x 109N'1s“l [Q], 10'3M k, 106s"1 0.0 2.23 0.0700 3.12 0.1“0 3.75 0.209 9.15 0.397 5.22 0.517 6.92 0.859 13.80 1.18 18.90 251 Table 80. Determination of kq for ggBenzyloxybenzophenone and 2,5-Dimethyl-2,“—hexadiene at 27°C in Benzene by Laser Flash Spectroscopy.a kq = 1.99 x 109M"1s'l A = 550 nm. [0], 10‘2M k, 106 s’1 0.0 18.2 1.90 19.9 2.79 22.6 9.17 23.7 6.93 31.20 10.30 37.6 a[Ketone] = 0.008 M; TT = 56.2 nsec = 550 nm IT = “8.7 nsec = 390 nm Table 81. Determination of kq for prenzyloxyvalerophenone with 2,5-Dimethyl-2,“-hexadiene in Benzene at 27°C by Laser Flash Spectroscopy.a kq = 2.99 x 109M"1s"l l = 380 nm [0], 10'3M k, 105s'l 0.0 19.8 0.138 15.6 0.276 16.0 0.“15 16.“ 0.686 16.9 a[Ketone] = 0.0128 M; TT = 79.7 nsec (380 nm); TT = 86.1 nsec (“20 nm). 252 Table 82. Determination of kq for 2,2'-Dibenzyloxybenzo- phenone with 2,5-Dimethyl-2,“—hexadiene in Ben- zene at 27°C by Laser Flash Spectroscopy.a 6 lS-l kq = 8.27 x 10 M- A = 570 nm [Q], 10‘3M k, 106s'l 0.00 19.0 6.99 18.3 19.0 27.6 27.9 35-2 91.7 “8.9 = 66.9 nsec (570 nm); .1 = a[Ketone] = “.68 x 1073M; T 72.8 nsec (570 nm). TT Table 83. Determination of kq for 2,6-Dimethoxybenzophenone with 2,5-Dimethyl-2,“-hexadiene in Benzene at 27°C by Laser Flash Spectroscopy.a kq = 3.26 x 109M"1s"l A = 920 nm [Q], 10‘3M k, 106s'l 0.00 0.733 0.0696 0.958 0.138 1.19 0.395 1.89 0.686 2.87 1.02 3.99 1.36 5.23 a[Ketone] = 0.0125 M; TT = 1916 nsec (“20 nm); TT = 1901 nsec (685 nm). 253 Table 8“. Determination of kq for geMethoxybenzophenone with 2,5-Dimethy1-2,9-hexadiene in Benzene at 27°C by Laser Flash Spectroscopy.a kq = 6.77 x 109M‘1s"l A = 520 nm [Q], 10‘3 M k, 106s‘l 0.00 1.28 0.0692 1.60 0.138 2.30 0.395 3.5“ 0.686 6.67 1.02 7.79 a[Ketone] = 0.005 M; rT = 783.2 nm (520 nm); (“00 nm); = 961.3 nm (380 nm); TT = 1262 nm TT TT = 1003 nm (390 nm). Table 85. Determination of kq for ngethoxybenzophenone and 2,5-Dimethyl-2,“-Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. kq = 8.29 x 109M"1s‘l A = 700 nm. [Q], 10"3 M k, 106s“l 0.0 8.26 0.699 12.10 1.39 18.90 2.09 25.30 a[Ketone] = 0.005 M; Tl 206.1 nsec - A = 520 nm. = 121.1 nsec - A = 700 nm; T2 = 25H Table 86. Determination of kq for 2,6-Dimethoxybenzophenone and 2,5-Dimethy1-2,u-Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. kg = u.86 x 109M'1s'l x = 680 nm [Q], 10‘3 M k, 106s'l 0.00 6.U9 0.0662 8.02 0.3“5 8.46 0.686 9.09 1.02 11.20 1.69 13.80 3.30 22.00 T1 = 15H.1 nsec A = 680 nm; [Ketone] = 0.0128 M. Table 87. Determination of kq for 2,2'-Dibenzy1oxybenzo- phenone and 2,5-Dimethy1-2,U-Hexadiene in Methanol at 27°C by Laser Flash SpectrOSCOpy. kg = 5.37 x 109M'ls.'l A = 700 nm [0], 10'3 M R, 1063‘1 0.00 7.86 0.699 11.30 1.u0 1“.50 2.79 23.80 T1 = 127.3 nsec A = 700 nm; T2 = 191.6 nsec A = 570 nm [Ketone] = 0.004 M. 255 Table 88. Determination of kq for ggBenzyloxy-S-Methyl- benzophenone and 2,5-Dimethy1-2,“-Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. kq = 6.6“ x 109M‘1s."l A = 700 nm [Q], 10‘3 M k, 106s“1 0.00 “.12 0.1“ 5.u0 0.279 6.5“ 0.“17 7.32 0.693 8.79 T1 = 2“2.7 nsec A = 700 nm [Ketone] = 0.005 M Table 89. Determination of kq for o—BenzyloxybenZOphenone and 2,5-Dimethy1-2,“-Hexadiene in Methanol at 27°C by Laser Flash SpectroSCOpy. kq = 5.78 x 109M’1s'l A = 650 nm [Q], 10'3 M R, 1063‘1 0.00 20.3 1.“0 31.7 2079 390)" “.17 ““.5 T1 = ““.7 nsec A = 730 nm T2 = “9.3 nsec A = 650 nsec [Ketone] = 0.005 M. 256 Table 90. Determination of k for geBenzyloxyacetophenone and 2,5-Dimethy1-2,“-Hexadiene in Methanol at 27°C by Laser Flash Spectros00py. kq = 9.38 x 109M'1s‘l A = 390 nm [Q], 10'3M k, 106s"l 0.00 1.70 0.0838 1.99 0.112 2.89 0.167 3.“3 0.277 “.17 0.“l“ 5.“9 T = 587.9 nsec A = 390 nm T2 = 557.6 nsec A = “90 nm 1 [Ketone] = 0.01 M. Table 91. Determination of kg for geBenzyloxyvalerophenone and 2,5-Dimethy1-2,“-Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy. kq = 5.32 x 109M'ls'l A = “00 nm [0], 10‘ M k, 106s‘l 0.00 “.07 0.1“0 “.88 0.279 5.73 0.“l7 6.25 0.693 9.05 r = 2“5.5 nsec A = “00 nm [Ketone] = 0.021 M. 257 Table 92. Determination of kq for 2-Keto-[2,2]-Paracyclo- phane and 2,5-Dimethy1-2,“-hexadiene in Benzene at 27°C by Laser Flash Spectroscopy.a kg = 1.72 x 109M'ls'l A = 380 nm [Q], 10'3 M k, 1065-1 0.00 0.57 l.“0 2,39 2.80 “.“2 5.6 10.10~ a[Ketone] = 0.0157 M; TT = 1120 nsec (550 nm) TT = 1766 nsec (380 nm). Table 93. Determination of kg for 2-Keto-[2,2]-Paracyclo- phane and Methyl Naphthalene in Benzene at 27°C with Laser Flash Spectroscopy.a kg = 1.“5 x 109M'1sfl [Q], 10’3 M R, 1065'1 0.0 0.“0u 7.20 1.55 1“.“0 2.57 21.60 3.55 a[Ketone] = 0.0157 M. 258 Table 9“. Determination of kq for 2-Keto-[2,2]-Paracyclo- phane with Methyl Naphthalene in Benzene at 25°C by Laser Flash Spectroscopy.a kq = 1.56 x 109M‘1s‘1 [Q], 10"3 M k, 105s‘l 0.0 0.909 0.0719 0.“87 0.1““ 0.771 0.358 1.15 0.713 1.51 1.06 1.87 1.90 2.79 a[Ketone] = 0.0157 M. Table 95. Determination of k for 2-Keto-[2,2]-Paracyc1o- phane and 1,3—Cy01800tadiene in Benzene at 27°C by Laser Flash Spectroscopy.a kq = 1.u7 x 1080143"1 A = 550 nm [Q], 10"3 M k, 106s"l 0.0 0.618 0.298 0.639 0.59“ 0.702 0.889 0.7“0 1.“8 0.779 2.20 0.903 2.92 0.979 3.63 1.06 “.60 1.36 a[Ketone] = 0.0157 M. 259 Table 96. Determination of kq for 2-Keto-[2,2]-Paracyclo— phane and 2,5-Dimethy1-2,“—Hexadiene in Methanol at 27°C by Laser Flash Spectroscopy.a kg = 2.63 x 109M"ls‘l [Q], 10'3 M k, 1063‘1 0.0 0.470 0.1u0 0.676 0.3“8 1.15 0.693 2.06 1.03 3.11 1.37 3.92 a[Ketone] = 0.02 M. Table 97. Determination of kq for 2-Keto-[2,2]-Paracyc1o— phane and 1,3-Cyclooctadiene in Methanol at 27°C by Laser Flash Spectroscopy.a kg = 1.33 x 108M‘1s‘l [Q], 10‘3 M k, 106s‘l 0.0 0.508 0.297 0.u20 0.7“1 0.“9“ 1.08 0.598 2.20 0.721 2.92 0.853 a[Ketone] = 0.02 M. 260 Table 98. Arrhenius Data for kq from 2-Keto-[2,2]-Para- cyclophane and 2,5-Dimethy1-2,“-Hexadiene in Methanol. E = 1.818 0.280 kcal/mole a log A = 10.69 0.25 T, °K 1/T, 10'3 °K‘1 k, 109M‘1s‘l Log k 330.0 3.03 2.56 9.408 265.1 3.77 1.59 9.202 240.2 4.16 1.23 9.090 211.9 4.72 0.645 8.809 193.8 5.16 0.390 8.591 304.2 3.29 2.63 . 9.420 Table 99. Arrhenius Data for kq from 2-Keto-[2,2]-Paracyclo- phane and 1,3-Cyclooctadiene in Methanol. E3 = 1.19“ i 0.099 kcal/mole log A = 9.1“ i 0.09 1 8 -l -l T °K l/T, 10‘3 °K’ k, 10 M s log K 194.1 5.15 0.631 7.800 210.0 4.76 0.819 7.913 234.4 4.27 1.03 8.014 256.3 3.90 1.27 8.104 273.2 3.66 1.“9 8.17“ 328.8 3.05 2.33 8.368 261 Table 100. Arrhenius Data for 1‘1 phenone in Benzene. Ea = 3.08“ i 0.257 kcal/mole log A = 9.09 i 0.23 for 2,6-Dimethoxybenzo- T °K 1/T, 10‘3 °K‘l k, 106s'l log k 300.1 3.33 6.23 6.795 195.7 5.11 0.461 5.664 218.3 “.58 0.96“ 5.98“ 2“9.7 “.01 2.16 6.335 279.1 3.58 4.62 6.665 318.0 3.15 10.70 7.029 1 Table 101. Arrhenius Data for 1' from 2,6-Dimethoxybenzo- phenone in Chlorobenzene. E = 2.26 i 0.733 kcal/mole 10g A = 8.81 a 0.54 T °K l/T, 10'3 °K‘1 k, 107s"l log k 300.9 3.32 1.81 7.258 261.3 3.83 0.734 6.866 268.2 , 3.73 0.913 6.961 327.1 3.06 1.96 7.292 351.1 2.85 2.23 7.3“8 262 Table 102. Arrhenius Data for ogMethoxybenzophenone in Chlorobenzene. Ea = “.168 : 0.6“7 kcal/mole 10g A = 9.21 z 0.51 T, °K 1/T, 10'3 °K'l k, 106s‘1 log k 298.7 3.35 1.“9 6.173 239.1 4.18 0.292 5.465 254.7 3.93 0.357 5.553 273.“ 3.66 0.680 5.833 317.0 3.16 1.83 6.263 335.6 2.98 3.61 6.558 Table 103. Arrhenius Data for o—Methoxybenzophenone in Methanol. Ea = 3.0“9 : 0.1“8 kcal/mole 10g A = 9.06 1 0.13 -1 6 T, °K 1/T, 10‘3 °K k, 10 s‘ 16g R 299.1 3.3“ 7.01 6.8“6 195.9 5.11 0.452 5.655 216.6 “.62 0.9““ 5.975 250.6 3.99 2.65 6.423 27“.2 3.65 3.68 6.566 317-9 3.15 9.10 6.959 334.5 2.99 12.00 7.079 263 Table 10“. Arrhenius Data for ggBenzyloxybenzophenone in Chlorobenzene. Ea = 2.815 t 0.759 kcal/mole log A = 9.20 a 0.59 T, °K 1/T, 10"3 °K‘l k, 107s."l log k 300.9 3.32 1.81 7.258 237.4 4.21 0.313 6.496 261.3 3.83 0.73“ 6.866 268.2 3.73 0.913 6.961 327.1 3.06 1.96 7.292 351.1 2.85 2.23 7.348 Table 105. Arrhenius Data for ngenzyloxybenzophenone in Methanol. Ea = 3.57 1 0.285 kcal/mole log A = 9.63 i 0.26 T, °K l/T, 10‘3 OK‘1 k, 106s‘1 log k 300.9 3.32 10.90 7.037 191.7 5.22 0.341 5.533 210.7 4.75 0.728 5.862 236.8 “.22 2.1“ 6.330 256.4 3.90 4.59 6.662 270.1 3.70 0.569 6.755 326.6 3.06 14.20 7.152 26“ Table 106. Arrhenius Data for o- Benzyloxyacetophenone in Chlorobenzene. E3 = 3.662 1 0.601 kcal/mole log A = 9.03 i 0.“7 T, °K 1/T, 10'3 °K‘1 R, 1068-1 log k 297.2 3.37 2.38 6.377 239.4 4.18 0.558 5.747 256.8 3.89 0.687 5.837 273.5 3.66 1.05 6.021 318.3 3.1“ 2.96 6.“71 3“1.1 2.93 5.09 6.707 Table 107. Arrhenius Data for o- -Benzyloxyacetophenone in Methanol. Ea = 3.725 1 0.695 kcal/mole 10g A = 8.98 i 0.5“ T, °K l/T, 10.3 °K'l R, 1063-1 log k 295.9 3.38 l.“1 6.1“9 2““.1 “.10 0.“88 5.688 26“.8 3.78 0.761 5.881 281.3 3.56 1.06 6.025 316.5 3.16 2.“2 6.38“ 329.7 3.03 3.87 6.588 265 Table 108. Arrhenius Data for gyBenzyloxyvalerOphenone in Chlorobenzene. Ea = “.77 : 0.“39 kcal/mole 10g A = 10.““ i 0.3“ T, °K 1/T, 10'3 °K‘l k, 10 s‘ log k 297.0 3.37 8.88 6.9“8 237.6 “.21 1.1“ 6.057 256.0 3.91 2.08 6.318 273.1 3.66 3.8“ 6.58“ 318.3 3.14 12.00 7.079 335.3 2.98 23.00 7.362 Table 109. Arrhenius Data for o—Benzyloxyvalerophenone in Methanol. Ea = “.73 i 0.105 kcal/mole log A = 9.96 i 0.08 T, °K 1/T, 10'3 °K'l R, 1063'1 log k 296.“ 3.37 2.99 6.“76 229.5 “.36 0.27“ 5.“38 260.8 3.83 0.924 . 5.966 281.2 3.56 1.88 6.274 317.3 3.15 “.83 6.68“ 331.9 3.01 6.64 6.822 266 Table 110. Arrhenius Data for grBenzyloxy-5-Methy1benzo- phenone in Chlorobenzene. Ea = “.“96 t 0.“5“ kcal/mole 10g A = 10.30 i 0.36 T, °K 1/T, 10"3 °K’1 R, 1065‘1 log k 297.6 3.36 11.30 7.053 236.9 4.22 1.27 6.104 255.9 3.91 2.69 6.430 273.8 3.65 5.61 6.749 317.0 3.16 14.50 7.161 336.1 2.98 21.00 7.322 Table 111. Arrhenius Data for ogBenzyloxy-5-Methylbenzo— phenone in Methanol. E = 3.832 t 0.233 kcal/mole 9.32 i 0.20 T, °K 1/T, 10'3 °K-l R, 1068-1 log k 297.“ 3.36 2.9“ 6.“68 19“.3 5.15 0.108 5.033 221.“ “.52 0.337 5.528 252.8 3.96 0.899 5.95“ 281.2 3.56 1.96 6.292 318.2 3.1“ “.86 6.687 332.1 3.01 7.“1 6.870 267 Table 112. Arrhenius Data for 2,2'-Dibenzyloxybenzophenone in Chlorobenzene. Ea = 3.068 t 0.500 kcal/mole log A = 9.29 i 0.39 l T, °K l/T, 10‘3 °K' k, 10 s‘ 16g k 298.3 3.35 12.70 7.104 239.6 4.17 2.70 6.431 255.6 3.91 4.59 6.662 273.7 3.65 7.51 6.876 316.0 3.17 13.30 7.124 335.5 2.98 l7.“0 7.2“1 268 Table 113. 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