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It: Initllf.5’.§5|l‘lv. -‘ ..1Lnunre.iy [fig 1. ’1’ (I . 1.5". u all 1‘. v” 33:50.". (4.1.2.0.. .710): . . V .‘E‘ . 4......»115. .t..dn..v}u..v1. ”.1 Illr . . 223.54% v. 73423 Ml7 MlCHlGAN 8 UNIVERSITY LIBRARIES \lllllllll l. lllll \ lllll 3 1293 00590 7534 ll“ LIBRARY Michigan State University This is to certify that the thesis entitled PFDTO CHEMISTRY OF ACYLPHENYL 0L EFINIC ESTERS presented by Fenton Ransom Heirtzler has been accepted towards fulfillment of the requirements for Master of Science Chemistry degree in GDMM v or profes or , _. ____‘._ ..5_r__ ‘_._4___ \ _—.. -fifl Date m WV]: I??? 0-7639 MSU is an Affirmative Action/Equal Opportunity Institution PLACE N RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before due due. DATE DUE DATE DUE DATE DUE L______+__ l—T‘T: a . g; MSU I8 An Afflrmdive ActioNEquel OppOttunity lnflitutlon WWW—craft ‘— PHOTOCHEMISTRY 0F ACYLPHENYL OLEFINIC ESTERS By Fenton Ransom Heirtzler A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Chemistry 1989 3544‘ C} ABSTRACT PHOTOCHEMISTRY 0F ACYLPHENYL OLEFINIC ESTERS by Fenton Ransom Heirtzler The triplet lifetimes and quantum yields for Type II cleavage of 4'-va1eryl alkenyl benzoates and 4'-butyry1phenyl alkenoates were determined by Stern-Volmer kinetics relative to those of A'-valeryl methyl benzoate and 4'-butyrylphenyl acetate in benzene and 4:1 - methanolzbenzene, respectively. Intramolecular charge transfer quenching by the tethered olefin of the alkyl phenone «,«* triplet state with rate constant, kCT- 1.3 x 107: 3 x 106 5'1 was shown to contribute significantly to triplet decay processes of 4'-butyry1phenyl 3-butenoate. The absence of similar phenomena from the 4'-va1eryl -allyl-, -3-butenyl- and -3-methyl-2-butenyl benzoate and 4'-butyrylphenyl 4-pentenoate esters was attributed to poor overlap geometry of the photosubstrate -olefines and -aromatic rings. Preparative irradiations of 4'-acetyl -allyl- and -3-butenyl- benzoate, 4'-acetylphenyl 3-butenoate and S'-acety1-2'-methoxy -a11yl- and -3-butenyl benzoate gave only unidentified materials from polymerisation and photoreduction. * The 3n,n configuration of 4'—valerylphenyl acetate in benzene was * estimated to be preferred over the 3x,« one by ca. 0.6 kcal/mol. No photo-Fries type products were detected in the photolyses of the acetate esters . ACKNOWLEDGEMENTS The author wishes to thank Professor Peter J. Wagner for seeing him through this degree. His concern for the author's future education is deeply appreciated. Recognition is due to the friends, both within and outside of the Wagner group, who made the author's sojourn here more bearable, in particular L---. Her patience and faith were astounding. Financial support, in the form of Department of Chemistry Teaching Assistantships, a Quill Fellowship and National Science Foundation Research Assistantships administered by Professor Wagner, is also acknowledged. iv To my Family Table of Contents Chapter Page List of Tables ----------------------------------------------------- x List of Figures ---------------------------------------------------- xiii INTRODUCTION ------------------------------------------------------- 1 I. FUNDAMENTALS ------------------------------------------------- 1 A. Formation of the Triplet State ---------------------------- l B. Basic Photophysics of Triplet Ketones --------------------- 2 II. TYPE II PHOTOREACTIVITY ------------------------------------- 3 A. Hechanism ------------------------------------------------- 3 B. Aliphatic Substituents ------------------------------------ 5 C. Aromatic Substituents ------------------------------------- 6 D. Triplet Equilibrium --------------------------------------- 9 E. Solvent Effects ------------------------------------------- 11 III. QUENCHING -------------------------------------------------- 12 A. Energy Transfer ------------------------------------------- 12 B. Charge Transfer ------------------------------------------- 13 C. .Extent of Electron Transfer ------------------------------- 13 D. Intramolecular Charge Transfer ---------------------------- 15 E. Regioelectronic Quenching --------------------------------- 17 IV. INTRAMOLECULAR TRIPLET AROMATIC PHOTOCYCLOADDITION ---------- 21 A. Acylphenyl Alkenyl Ethers --------------------------------- 21 B. Literature Precedents ------------------------------------- 24 vi v. KINETIC FORMULATIONS ----------------------------------------- 31 A. Quantum Yields- and -Efficiencies ------------------------- 32 B. Lifetimes ------------------------------------------------- 33 C. Stern-Volmer Kinetics ------------------------------------- 34 VI. RESEARCH GOALS ---------------------------------------------- 34 RESULTS ------------------------------------------------------------ 36 I. COMPOUNDS STUDIED -------------------------------------------- 36 II. SYNTHESIS --------------------------------------------------- 37 III. PHOTOLYSIS ------------------------------------------------- 40 A. Photokinetic- and Quantum Yield- Experiments -------------- 40 1. Photoproduct Identification ---------------------------- 40 2. Stern-Volmer Quenching Plots --------------------------- 41 3. Quantum Yields ----------------------------------------- 41 4. Limiting Quantum Yield --------------------------------- 45 5. Maximised Quantum Yield -------------------------------- 47 6. Crotonate Ester Quenching ------------------------------ 49 B. Preparative Irradiations ---------------------------------- 51 IV. DERIVED PHOTOKINETIC PARAMETERS ----------------------------- 52 A. Triplet Lifetimes ----------------------------------------- 52 B. Rate constants for Acetophenone Formation ----------------- 53 C. 4’-Butyrylphenyl 3-Butenoate Rate Parameters -------------- 55 1. Bimolecular- and Intrinsic- Decay ---------------------- 55 2. Intramolecular Quenching Rate Constant ----------------- 55 3. Intramolecular Quenching Quantum Efficiency ------------ 56 4. Ground State Quenching --------------------------------- 57 V. TRIPLET ENERGIES --------------------------------------------- S8 vii VI. MOLECULAR MECHANICS CALCULATIONS ---------------------------- 59 DISCUSSION --------------------------------------------------------- 63 I. ACYL ALKENYL BENZOATE ESTERS --------------------------------- 63 A. Photokinetic Parameters ----------------------------------- 63 B. Preparative Irradiations ---------------------------------- 63 C. Lack of «,n* Photoreactivity ------------------------------ 64 II. 4'-BUTYRYLPHENYL ALKENOATE ESTERS --------------------------- 66 A. Intramolecular Quenching ---------------------------------- 66 B. Quenching Geometry ---------------------------------------- 66 C. EXperimental Complications -------------------------------- 69 l. Instability of 3-Butenoate Esters ---------------------- 69 2. 4'-Acy1phenyl 3-Butenoate Analysis Conditions ---------- 70 III. h'—ACYLPHENYL ACETATE ESTERS ------------------------------- 71 A. Lowest Triplet State -------------------------------------- 71 B. Absence of [1,3] - Type Migration ------------------------- 75 IV. CONCLUSION -------------------------------------------------- 77 A. Summary --------------------------------------------------- 77 B. Reccomendations ------------------------------------------- 77 EXPERIMENTAL ------------------------------------------------------- 81 I. PURIFICATION AND PREPARATION OF CHEMICALS -------------------- 81 A. Solvents and Additives ------------------------------------ 81 B. Internal Standards ---------------------------------------- 82 C. Quenchers ------------------------------------------------- 83 D. Ketones --------------------------------------------------- 83 II. PHOTOLYSIS PROCEDURES -------------------------------------- 110 A. Glassware ------------------------------------------------ 110 viii B. Preparation of Solutions --------------------------------- 110 C. Degassing ------------------------------------------------ 111 D. Irradiation ---------------------------------------------- 111 E. Analysis ------------------------------------------------- 111 F. Techniques for 4’-Acylphenyl 3-Butenoate Esters ---------- 112 III. TECHNIQUES AND CALCULATIONS ------------------------------- 113 A. Stern-Volmer Quenching ----------------------------------- 113 B. Reciprocal Quantum Yield Versus Ketone Concentration ----113 C. Quantum Yield Versus Additive Concentration -------------- 114 D. Photoproduct Concentration ------------------------------- 114 E. Quantum Yields ------------------------------------------- 116 IV. SPECTRA -------------------------- E -------------------------- 117 A. Proton NMR Spectra --------------------------------------- 117 B. Carbon NMR Spectra --------------------------------------- 117 C. Ultraviolett-Visible Spectra ----------------------------- 117 D. Infrared Spectra ----------------------------------------- 118 E. Mass Spectra --------------------------------------------- 118 F. Phosphorescent Spectra ----------------------------------- 118 V. NMR TUBE IRRADIATIONS --------------------------------------- 119 A. Sample Preparation --------------------------------------- 119 B. Sample Irradiation and Monitoring ------------------------ 119 C. Individual Runs ------------------------------------------ 120 VI. MOLECULAR MECHANICS CALCULATIONS --------------------------- 121 APPENDIX ---------------------------------------------------------- 123 REFERENCES-------—-----------------------------------------------4144 ix List of Tables Table Page 1 Photochemical Parameters for Quenching of Alkenyl 4'-Valery1 Benzoate Esters with 2,5-Dimethyl-2,4- Hexadiene in Benzene --------------------------------------- 45 2 Quantum Yield- and Photokinetic- Parameters for Quenching of 4'-Butyry1phenyl Alkenoate Esters with 2,5-Dimethyl-2,4- Hexadiene in 4:1 - MethanolzBenzene ------------------------ 47 3 Quantum Yield- and Photokinetic- Parameters for Quenching of 4'-Va1ery1phenyl Acetate -------------------------------- 49 4 Summary of Results of Irradiations of Acetophenones Through Pyrex Filter in 250 MHz Proton NMR Experiments ----- S2 5 Reciprocal Triplet Lifetimes of 4'-Valery1 Alkenyl Benzoate Esters ----------------------------------------------------- 53 6 Rate Constants for Acetophenone Formation and Reciprocal Triplet Lifetimes of 4'-Butyry1pheny1 Alkenoate Esters ----- 54 7 Rate Constants for Acetophenone Formation and Reciprocal Triplet Lifetimes of 4'-Acylphenyl Acetate Esters ---------- S4 8 Miscellaneous Parameters from 4'-Butyry1pheny1 3-Butenoate Experiments ------------------------------------------------ S8 9 Triplet Energies of 4'-Va1erylpheny1 Acetate in Different Solvent Classes at 77°K ------------------------------------ 59 10 ll 12 13 14 15 16 l7 l8 Dependence of STRAIN ENERGIES, Intramolecular Aromatic- Olefin Distances and Tether Geometry on Ester Dihedral Angle B to the Phenyl Ring in 4'-Acetyl Allyl Benzoate ----- 60 Dependence of STRAIN ENERGIES, Intramolecular Aromatic - Olefin Distances and Tether Geometry on Ester Dihdral Angle B to Phenyl Ring in 4'-Acetylphenyl 3-Butenoate ------------ 61 Comparison of Phosphorescence «,«* Energies of 4-Valerylphenyl Acetate to n,«* and «,r* Triplet Energies of Several Aryl Alkyl Ketones in Non-Polar Solvent ---------------------------------------------------- 75 Gas Chromatographic- and HPLC- Photoproduct Response Factors -------------------------------------------------- 115 Quenching of Acetophenone Formation from 4'-Valeryl Allyl Benzoate with 2,5-Dimethyl-2,4-Hexadiene in Benzene ------- 123 Quantum Yield of Acetophenone Formation from 4'-Va1ery1 Prenyl Benzoate in Benzene------f ------------------------- 125 Quenching of Acetophenone Formation from 4'-Va1ery1 3-Butenyl Benzoate with 2,5-Dimethyl-2,4-Hexadiene in Benzene --------------------------------------------------- 126 Quenching of Acetophenone Formation from 4'—Va1erylphenyl Acetate with 2,5-Dimethyl-2,4-Hexadiene in Benzene -------- 128 Dependence of Quantum Yield of Acetophenone Formation from 4'-Valery1pheny1 Acetate on Concentration of Pyridine in Benzene --------------------------------------------------- 130 xi 19 20 21 22 23 24 Quenching of Acetophenone Formation from 4'-Va1erylphenyl Acetate with 2,S-Dimethyl-Z,4-Hexadiene in 4:1 - Methanol: Benzene --------------------------------------------------- 131 Quenching of Acetophenone Formation from 4'-Butyry1phenyl Acetate with 2,S-Dimethyl-Z,4-Hexadiene in 4:1 - Methanol: Benzene --------------------------------------------------- 133 Quenching of Acetophenone Formation from 4'-Butyrylphenyl 3-Butenoate with 2,5-Dimethyl-2,4-Hexadiene in 4:1 - Methanol: Benzene ----------------------------------------- 135 Dependence of Quantum Yield of Acetophenone from 4'-Butyrylphenyl 3-Butenoate on Photosubstrate Concentration in 4:1 - MethanolzBenzene ------------------- 137 Quenching of Acetophenone Formation from 4'-Va1ery1pheny1 Acetate with Methyl Crotonate in 4:1 - Methanol: Benzene--l40 Quenching of Acetophenone Formation from 4'-Butyry1phenyl 4-Pentenoate with 2,5-Dimethyl-2,4-Hexadiene in 4:1 - Methanol: Benzene ----------------------------------------- 142 xii Figure List of Figures Page Jablonski Energy Diagram for Phenyl Ketones ---------------- 3 Type II Photchemical Processes of Phenyl Alkyl Ketones ----- 5 Resonance Contributors to Phenyl Ketone n,«* and «,n* Triplet States --------------------------------------------- 7 Influence of Aromatic Substituents on n,«* and «,w* Triplet Energy Levels -------------------------------------- 8 Mechanism of Charge Transfer Quenching of n,x* Triplet State of Ketones by Alkenes -------------------------------- 14 Stern-Volmer Plot for Quenching of Acetophenone Formation from 4'-Valeryl Alkenyl Benzoate Esters with 2,5-Dimethyl- 2,4-Hexadiene in Benzene ----------------------------------- 42 Stern-Volmer Plot for Quenching of Acetophenone Formation from 4'-Butyrylphenyl Alkenoate Esters in 4:1 - Methanol: Benzene ---------------------------------------------------- 43 Stern-Volmer Plot for Quenching of Acetophenone Formation from 4'-Acylpheny1 Acetate Esters in 4:1 - Methanol: Benzene ---------------------------------------------------- 44 xiii 10 ll 12 l3 l4 Dependence of Reciprocal Quantum Yield of Acetophenone Formation from 4’-Butyry1phenyl 3-Butenoate on Ketone Concentration in 4:1 - Methanol:Benzene -------------------- 46 Dependence of Quantum Yield of Acetophenone Formation from 4'-Valerylphenyl Acetate on Concentration of Pyridine in Benzene ---------------------------------------------------- 48 Stern-Volmer Plot for Quenching of Acetophenone Formation from 4'-Valerylphenyl Acetate with Methyl Crotonate and 2,5-Dimethyl-2,4-Hexadiene in 4:1 - Methanol:Benzene ------- SO Conformation of 4'-Acety1 Allyl Benzoate Defined for Dihedral Angles a- 0°, fi- 180° and 1- 180° ----------------- 62 Conformation of 4'-Acetylphenyl 3-Butenoate Defined for Dihedral Angles a- 0’, B- 180° and 1- 180° ----------------- 62 Minimised Energy Molecular Mechanics Geometries of 4'-Acetylphenyl 3-Butenoate for Phenyl Oxygen - Ester Carbonyl Bond trans Coplanar- and l70°-from-Coplanar- Conformations .............................................. 53 xiv I N'Tf R (3 D I] C if I C) N I, EQNQAMENTALS WWW; The absorption of a suitable photon of light by a molecule promotes an electron from a r- or nonbonding- orbital to an antibonding orbital. The electronically excited molecule can exist in either the singlet state, where the promoted electron is spin-paired with that remaining in the original half-vacant orbital, or in the triplet state, where the electrons are spin-unpaired. In the case of aromatic ketones, the upper vibrational level of a n,x* singlet excited state is initally formed. This then rapidly deactivates to its lowest vibrational levell with a unimolecular rate constant of ca. 1012 3-1, whereupon it predominantly undergoes intersystem crossing to either a n,«* or «,«* triplet state. Fluorescence is not a major phenomenonz. Because intersystem crossing is formally spin;forbidden, the magnitude of its rate constant, kisc depends on the size of the singlet-triplet energy gap and the nature of 1 * 3 * 1 * 3 * the triplet state. For n,« -> n,« and n,w -> «,1 transitions, k as 108 and 1011 3'1 isc follows quickly. In the event of intersystem crossing to an upper , respective1y3. Vibrational relaxation again 1 electronically excited triplet state, population of the lower triplet occurs through internal conversion4, kic l“““"§§§§i§§§ T W:1E: 2 kIc i T 1 hv products Figure l. Jablonski Energy Diagram for Phenyl Ketones A process common to the triplet state of many ketones posessing aliphatic hydrogen atom located 1 to the carbonyl group is the Norrish Type II cleavage reaction. It was first noted in 1934 by Norrish and Appleyard7, who detected the formation of acetone and propene during the gas phase photodecomposition of 2-hexanone. It is now known to proceed through a n,«* triplet state for phenyl ketonesa. In the n,n* triplet state, a carbonyl oxygen n-orbital electron is promoted to a n* antibonding aromatic orbital. An electron deficient "hole" in the n-orbital electron density is thereby created. The carbonyl oxygen consequently reacts as an electrophilic species, typically abstracting hydrogen atoms from extra- and intra- molecular sources. In the former case, bimolecular photoreduction by solvents or additives containing labile hydrogen atoms to form benzpinacol-type products occursg. In the latter instance, spatially accessible aliphatic hydrogen atoms elsewhere on the molecule, but often on the position 7 to the ketone carbonyl of a C or longer n-alkyl chain, are 3 abstracted to form a hydroxy-l,4-biradica110 with rate constant kH. The intermediacy of this biradical has been indicated by spectroscopic11 and trapping studieSIOb. It cleaves to the corresponding acetophenone enol and alkene according to kc and to a lesser extent cyclizes, key to 1 form a l-phenylcyclobutanol derivative. Reverse hydrogen abstraction . IOC to reform the ground state starting ketone, krev also occurs Experimentally, the gverall rate constant for formation of cleavage products, k (vide infra) is usually measured. II The addition of regulated amounts of Lewis bases such as methanol, Eggs-butanol, p-dioxan or pyridine impedes reverse hydrogen transfer through hydrogen bonding to the hydroxyl group of the biradicallz. The quantum efficiency of acetophenone and cyclobutanol formation are thus maximised at some certain concentration of Lewis baselZ-lé. =_r:.: 321E: 1...“... 3n,“ _ (R l. hv + 2. ISC l OH O [:JLWAF I ‘~ 1.9 X, 80 O R l/ X Figure 2. Type II Photoprocesses of Phenyl Alkyl Ketones B. h t’ t' uen s The reactivity of the triplet ketone responds to resonance- and inductive- (de)stabilising groups adjacent to the alkyl radical site like that in simple radicalsls. Good linear correlation is thus found in Hammett plots of relative rate constants of appropriately substituted butyrophenone and valerophenone derivatives versus a inductive substituent constantsl6. Resonance electron -donating and -accepting substituents are also accounted for. The extensive amount of work carried out on the Type II process allows it to serve as a "clock" against which the rates of other processes can be 17,18 compared . C. Aromatic Substituents The effect of ring substituents on the reactivity of triplet phenyl alkyl ketones is far more complicated, however. Relatively energetically proximate to the reactive n,n* triplet is a «,n* triplet state4’19-22. Its electronic configuration is a result of the promotion of an aromatic « electron to a carbonyl 1* orbital, increasing the carbonyl electron density. Consequently, Type II reactivity from phenyl alkyl ketones having «,«* lowest triplet states is expected to be greatly decreased. Therefore, the effects of ring substituents on the electron deficient character of the carbonyl oxygen and the relative ordering of the energies of the two triplet states must both be consideredZI. The classical resonance forms which are thought to contribute significantly to each excited state are depicted in Figure 3. Valerophenone derivatives ring-substituted with electron- withdrawing substituents, like 9-, m- and p— F and CF3, g-CN, m- and p- 3 and p-C(O)R (R- alkyl) show kn~ 1 x 108 s'1 in 21,23,24 25,26 COZCH3, g-OCF benzene like 9- and ca. 4 x 107 3-1. For electron-donating substituents 2- CH3, 9-, m- and p-OCHS, p_-SCH3 and p-C6H5, kIIs '02 '0! ct»: . 3 .1. 11,! 0 :o:— -o: .901.” on I + 3 i “I * * Figure 3. Resonance Contributors to Phenyl Ketone n,« and «,n Triplet States Additionally, the 9- and p-chlorovalerophenones show decreased values for k while that of the meta isomer is closer to that of II’ valerophenone itself16’21. However, attempted Hammett correlations of kII values for these 0 compounds relative to kI for valerophenone versus 0 parameters reveal I regions of two different slopes- one for the mggg- and Egg;- inductively withdrawing groups and the other for resonance donating groupsZI. Rate constants for conjugating, electron withdrawing substituents like p-COZCHB, p-CN, and m- and p- C(O)R deviate widely from either line23 According to classical precedent, this suggests the operation of at least two diffent mechanism527 for hydrogen abstraction. It is 'well established that inductively electron withdrawing substituents stabilise the n,«* triplet state over the w,n* triplet state by ca. 3.0 to 6.0 keel/mole, relative to valerophenone, where this advantage is ca. 3.0 kcal/moleZI. Introduction of donating substituents to the phenyl ring simultaneously destabilises the n,n* triplet state and lowers the energy of the n,n* triplet24. The latter is thought to stem from splitting of the n,n* triplet state with the charge-transfer state and/or La spectroscopic states. The consequences of this effect range from rendering the triplet states of the methylvalerophenones approximately isoenergetic up to favouring the «,x* triplet state of p- thiomethyoxyvalerophenone by ca. 10 kcal/mol over the n,n* oneZl. The Q- and 2 -Cl and p-carbomethoxyvalerophenones provide a mixed case, wherein the conjugative stabilization the n,«* triplet state is partially offset by their inductive propensity toward hydrogen abstraction. This later notion is reinforced by the m -C1, -CN and -C02CH3 substituents preclude any stabilisation through orbital mixing23; derivatives, where these electron withdrawing, non-conjugating * their lowest energy triplet is n,n in nature. 3 i a n’x 3a,: ---'--.. I’,/”””’ 3 * -Z' '——: \ n, X / 3n, 1’ 31!, I \‘ ‘ e \ 3 ‘ it, it electron X= H. m:n°CH3 819011011 acceptors donors 7‘: * Figure 4. Influence of Aromatic Substituents on n,« and n,n Energy Levels D. Triplet Equilibrium A rationale to explain the Type II reactivity of n,«* lowest triplet phenyl ketones is still necessary, however. Similarly, electron donor substituted acetophenones, benzophenones and acetylnaphthalenes (n,x* lowest triplet) are moderately reactive to photoreduction26 It was postulated by Wagner 17 years ago that the reactivity of «,n* lowest triplet phenyl ketones stemmed from a thermodynamic equilibrium between the unreactive n,«* (T1) and reactive n,«* (T2) statesZI. Thus, in theory the observed rate constant for hydrogen abstraction is proprotional to the partial rates from each triplet state. The equilibrium population of the states in turn depends on the E between the two states according to a energy difference AE- En a- x I Boltzmann distribution function, Equation 1, where Xi are the fractional populations of each state and R and T have their usual definitions. For AEZ ca. 3 kcal/mol, or alternately assuming that the non-electrophillic nature of the «,n* T1 states must render their intrinsic, "pure" rate of hydrogen abstraction insignificant relative to that of T Equation 2, where krn is the rate constant for 2! * obsd unadulterated n,n reactivity and kr , the experimentally observed one, therefore describes the predicted rate dependence. Values of krn can in turn be estimated, for example, by comparison to the photoreactivities of similarly substituted benzophenone528 with known * n,a lowest triplet states.29 10 (1) (2) The validity of this theory was initally demonstrated by comparison of the Type II reactivities of series of anisoyl alkyl ketones (T1- * * 3x,a ) and phenyl alkyl ketones (Tl- 3n,« )28. Approximately the same relative change in photoreactivity as a function of substitution at the 1 carbon was observed between each series. The condition of exclusive n,a* reactivity instead of, say, reactivity arising from the mixing of zero-order 3n,n* and 3«,n state326b was also supported by measurements of activation energies for the photoreduction of definite Tl- 3n,n and 3n,« acetophenones30 According to quantum mechanical- and kinetic- formulations, the detection of significant activation energies precluded that alternate theory from the current case, and the fact that the activation energies * * of the 3«,n T ketones were noteably higher than those of the 3n,n l * ones implied that thermal equilibration to 3n,« T2 was a prerequisite for reactivity. This latter caveat was understandable because now, * barring direct 3x,« '1‘1 reactivity, the TZ-T1 energy gap and the actual activation energy must both be surmounted for reaction to occur. Other, more recent cases where decreased reaction rates have been * * quantitatively related to the 3n,w - 3w,x energy gap include the 28.30 photoreduction of acetophenones and the a-photocleavage of aryl 11 alkyl ketones31. It is also thought to account for the differences in excited state deactivation32- and yet other Type II photocleavage33- rates. The rate constant for formation of Type II cleavage products from 2-carbomethoxyvalerophenone, 1.2 x 108 5-1 in benzene, has also been used to provide an estimate of the T1 - T2 energy gap in this chromophore, 0.3 kcal/mole. This agrees reasonably with the spectroscopically determined value23. Thus, the consequences of equilibrating ketone triplet states appear to be general. 5. Solvent Effegts Polar solvents also destabilise the n,n*, triplet state of phenyl ketones relative to the ground state by hydrogen bonding to the carbonyl n-orbital electrons. The «,«* triplet state is simultaneously stabilised through a related phenomenonzoa. Decreased phosphorescence rates, indicative of the longer-lived n,n* triplet state, have also been observed in polar mediazoa. Combined with the solvent effect on biradical revertibility, the net effect is mixed. Phenyl ketones with n,x* lowest triplets show increased quantum yields with Lewis base concentration until a plateau near 1.0 is reached. However, in pure polar solvent312'14’21 ,their kII (an d kH) values drop by ca. 50%. * Those ketones having «,x lowest triplets show greatly decreased hydrogen abstraction rates, and their quantum yields are maximised at much lower Lewis base concentrations. A drastic decrease in quantum yields beyond this concentration then occursl4 12 I11. QUENCHING Quenching can be defined as the the deactivation of an excited state, mitigated by collision with another molecule, the quencher. Triplet aryl ketones are commonly quenched by energy- and/or charge- transfer processes. A. Energy [raggfer Energy transfer (E.T.) occurs via a HOMO-HOMO/LUMO-LUMO (or vice versa) electron exchange mechanism. The long lifetimes of triplet species relative to singlet ones make this a common process4. It is most significant when the ketone triplet energy (for phenyl alkyl ketones, ca. 60 - 75 kcal/molZI) is greater than that of the quencher. It is characterised by experimental rate constants which are proportional to the size of the triplet energy difference until a maximum is reached. Geometrical constraints on the donor-acceptor orbital overlap and the efficiency of E. T. within the close-contact pair usually keep the rates below the diffusional limit34 in less 9 'ls'l. diffz 1° 5 kcal/mol35) and molecular oxygen (ET- 23 kcal/mol35) olefins are viscous solvents; k Conjugated butadienes (ET- ca. 60 commonly encountered E. T. quenchers4 13 B. Charge Transfer Charge transfer (C. T.) quenching occurs by a "half" exchange- for phenyl ketones, this amounts to a one-electron photoreduction, commonly by an electron-rich alkene. This process predominates when the triplet energy of the charge acceptor, E is higher than that of an electron- T rich donor4’36; for phenyl ketones, this corresponds to ETZ ca. 74 kcal/mol37. Kinetic behaviour contrasts that in E. T. quenching in several ways. Firstly, rate constants are in the ca. 105 to 108 M-ls-1 range37. More significantly, an increase in the rate with decrease of ketone triplet energy and inefficient product formation have been interpreted in terms of the mildly exothermic formation of an inital complex with charge-transfer character36'38. The lack of stereospecificity in oxetane photoproducts and the reisolation of isomerised alkenes suggest that the C. T. complex decomposes to a 1,4- biradical intermediate39. Amines40’41 and sulfides4l’42 also quench via C. T. complex formationgb, by virtue of their lone pair electrons. Quenching by conjugated butadienes may even proceed to a small extent through a C.T. mechanism37 C. e set 0 ansfer When AGET’ the free energy change for electron transfer, drops below -5 kcal/mol, and if C.T. complex formation is not hindered by bulky substituents on the quencher37, electron transfer becomes rate- limiting and the rate constant for triplet C.T quenching, kCT can be 14 :5 ‘9 O 29;E::g) -_-”‘R"L * Figure 5. Mechanism of Charge Transfer Quenching of n,« Triplet State of Ketones by Alkenes directly related to the thermodynamic properties of the C. T. couple through Equation 3, the Guttenplan-Cohen modification of Rehm and Weller's relationship43 for singlet electron transfer quenchingdla. 3 + - 1n(kCT) z AG z E(D/D ) - A E00 - E(A /A) - TAS (3) ET Here, AsEoo and E(A-/A) are the zero-point triplet energy and ground state reduction potential respectively, of the ketone, E(D/D+) is the oxidation potential of the charge donor and TAS the entropic contribution to electron transfer. Since E(D/D+) is equal to the donor ionisation potential, IP plus a relatively constant electrostatic D factor, the relationship can be reformulated more convienently as Equation 4. 3 108(kCT) z IPD - A E00 - E(A /A) + constant (4) 15 Thus, plots of log(kCT) versus IPD for various quenchers and a given ketone triplet34, or log(kCT) versus -A3Eoo+ E(A-/A) for the triplet energies of various ketones and a single quencherélb should both show reasonable linear correllation. The former instance has been demonstrated by the studies of Guttenplan and Cohen on the quenching of benzophenone and fluorenone photoreduction by aromatic and aliphatic donors (including some a1kenes41), as well as similar work by Wagner on the quenching of Type II photoreaction by alkenes37 and the photoreduction of trifluoroacetophenone by aromatics44. The latter type of correllation was verified by Guttenplan and Cohen's studies on the quenching of ketone photoreduction by triethylamine4l An increase in solvent polarity has been found to drastically increase the C. T. quenching rate constants for those ketones having x,«* lowest energy triplets41b. However, comparison of the slopes of these and other plots to those from singlet exciplex formation leads to the conclusion that only partial electron transfer is posible in triplet exciplexes.4la’44. D. tramo ar Char e Transfer uenchin In these kinds of studies, the excited state- and quenching chromophores are separated by a chain of non-transmitting atoms. The difference in reciprocal triplet lifetimes between these species and suitable model systems provides a relative measure of the rate constant for intramolecular C.T. quenching, k Physical contact, manifested CT' through the geometrical- and spatial- requirements of the separating '16 tether, can thereby be proven. Information on the intrinsic quenching abilities in the absence of diffusional constraints can also be obtained. For example, the triplet lifetimes of phenyl alkyl ketones a, 7 and 8-substituted with tertiary amino functions have been shown to depend on the carbonyl-amine separation45. A minimum lifetime and a maximum C.T. quenching rate constant, kCT- 7.2 x 109 5-1 were seen45b for 1-substituted ketone, l. A ca. 1.0 a concentration of triethylamine in benzene was necessary to quench valerophenone itself45 to the same extent. That this reflected a through-space, and not a through-bond phenomenon was demonstrated by Wagner and Scheve in their studies on the h-benzoylpiperidines, 2. Here, the conformational rigidity of the piperidine ring prevented intramolecular quenching of the benzoyl triplet state46 Also, in the gig- and trans- isomers of compound ;, intramolecular quenching rate constants of 1.5 x 1010 5-1 for each were determined through measurements of quantum yields for isomerisation of the double bond47 and triplet lifetimes. In compound 3, the quantum yield for 17 formation of Type II photoproducts in benzene was only ca. 0.6% of that for butyrophenonel6, which together with its triplet lifetime implied an intramolecular quenching rate constant of 8 x 108 3.1. The efficiency of these processes was attested to by the isolation of products from the decomposition of unstable oxetane adducts Q and the fact that the quenching rates could not be nearly duplicated on a bimolecular level47. O O ZR 1R 0 H p. H 3 4. ~i'R-CH3,2R-Hor ‘R- H.2R- can, . e oe ect on c uenchin substrates can be devised in which the C.T. quenching moiety enjoys access to different parts of the chromophore. Thus, the extent of quenching can be related to the degree and type of localisation in the excited state. A classic example is Turro's studies on the quenching of the n,«* singlet states of alkylated norcamphor derivatives, g by electron ~attracting and -donating alkeneség. Here, the rate of quenching by trans-l,2-dicyanoethylene was shown to be dependent on alkyl substitution which blocked access to the areas above and below the carbonyl plane, while quenching by gig-l,2-dimethoxyethylene was 18 limited by those alkyl groups which hindered approach from the sides of the carbonyl group. 6. lR-SR-alkylorfi This is understandable, since in a C.T. mechanism, dicyanoethylene must * quench through the half-filled x orbital above or below the carbonyl plane, and dimethoxyethylene should interact by means of the half- vacant oxygen n-orbital in the plane. Thus, quenching rates by trans- 1,2-dicyanoethy1ene were least for those photosubstrates where 2R, 4R or 5R- CH3 (IR and 3R- H or CH3) and quenching by gig-1,2- dimethoxyethane was slowest for photosubstrates where 3R or SR- CH3 (1R, 2R and 4R- H or CH3). In a significant intramolecular case, Winnik measured the phosphorescent lifetimes, r for a series of w-alkenoxy p- P * O . benzoylbenzoate esters, 1 having n,« lowest triplet excited states in acetic acid as a function of tether length49. A moderate drop in 1 relative to 4-carbomethoxybenzophenone was P! observed498 from n- 6 (kCT- 1.3 x 104 5.1) up to n- 8 5 -1 (kCT- 2.3 x 10 s ); thereafter 1 decreased rapidly until n- 12 (kCT- P 7.9 x 105) after correction for bimolecular quenching by the ground state ketone49b. Simple molecular models demonstrate that n- 8 19 corresponds to the smallest chain length at which the olefinic moiety can come within ca. 1 A of the ketone carbonyl and still maintain the trans-coplanar ester conformation; contact with the aromatic ring is insufficientég. Winnik has pointed out that this and the sharp drop in phosphorescent lifetime with tether length implied that the alkene must be well within the sum of the van der Waal radi for itself and the carbonyl for effective quenching to occur. Up to n- 12, quenching is enhanced by an increase in the number of proximate olefin-ketone carbonyl conformations. Beyond this chain length, the entropy of the total number of conformations available to the flexible w-alkenyl chains gradually overcomes the number of favourable quenching interactionsagb. Alternately, the absence of strong intramolecular quenching of the phosphorescence of the 2-(N,N-dimethylamino)ethyl p-benzoylbenzoate ester, g in CClA has been attributed by Wagner and Siebert to the inaccessibility of the tethered amine to the n,w* lowest triplet state5o. It is interesting to note that although much slower than the rate constant for intermolecular quenching of benzophenone with 9 M—ls-l triethylamine in benzene51, 2.3 x 10 , the rate of 20 intramolecular quenching here, 1 x 105 s.1 was still comparable to that observed in Winnik's esters. This apparent anomaly reflected the greater reducing ability of tertiary amines than primary olifinessz On the other hand, C.T. quenching studies on the Type II photoelimination of w-(N,N-dia1kylamino)alkyl p-valerylbenzoate esters 2 in acetonitrile50 showed much greater rates, kCT- 5.1 x 108 and 6.6 x 108 3-1 for n- 2 and 3, respectively, against 1.6 x1010 M'ls.l for quenching of the methyl ester homologue with triethylamine. This contrast was thought to be a consequence of the locality of the O N(CH O ‘9; 3)2 8. R' (36115: n‘ 2 2. R= “C4119;n- 2, 3 h'-acylbenzoate chromophore's «,«* lowest triplet state on the aromatic ring, within reach of the tethered amine. A further endorsement of this concept was provided by the mgga isomer of g (n- 2), which had a n,«* lowest triplet state and showed a triplet lifetime compareable to that of its methyl ester homologue50. 21 IV INTRAMOLECULAR TRIPLET AROMATIC PHOTOCYCLOADDITION 1 A. Ac 1 hen Aiken 1 thers The Type II photokinetics of the n,«* lowest triplet state of the acylphenyl alkenyl ethers, 19 were also recently examined by Wagner and Nahm for evidence of intramolecular C.T. interactionsSB. The simple para-3-buteny1 ether and its Egghg isomer (both R- nCaflg) showed values of 8.9 x 107 and 3.3 x 107 5-1, respectively. Compared to intramolecular C.T. quenching of n,n* triplet states by olefines, the magnitude of this effect was between those of the benzophenone alkenyl esters49, l and the fl-vinyl phenyl ketonesé7, 3 and 3. This may have been a consequence of the intrinsically different C.T. quenching efficiencies of n,«* and w,«* triplet states and/or the limitations imposed by tether length and geometry and distance from the quenched chromophore. Further light was shed on the nature of the lowest triplet state in the alkenyl ethers by the much lower quenching rates exhibited by the * mega isomer of IQ. Although posessing a n,n lowest triplet state, in 22 analogy to m-methoxyphenyl alkyl ketones 21, charge-separated resonance hybrids are excluded from its triplet state. This, and the great H3CO , H3CO . enhancement in C.T. rate constants upon alkyl substitution in the double bond of the paga isomer, implied that this process was aided by the development of a partial positive charge in the 4'-aromatic position of the excited state. Other kinetic phenomena made definite predictions about the quenching mechanism. First, the rates of C. T. quenching in the garg- ether and of gig —> trans isomerisation of the double bond in the p- gig-3-hexenyl ether (R- nCal-lg) far exceeded those for Type II photoelimination in the methyl ether homologue. In analogy to the reversible addition of olefins to n,«* ketone triplet states 39’54, this was thought to imply the formation of a spiro-cyclopentyl 1,4- biradical intermediate 1;, from the C. T. complex. Like the intermolecular54 and intramolecular47 [2+2] photocycloaddition leading to oxetane formation54, closure of the biradical was found to give initialy bicyclo[4.2.0]octa-2,4-diene type product553a, 12. Analogous reactivity was exhibited by the ortho ether353b, as well as homologues of 2 and ortho-g which were 23 substituted with methyl groups on the double bond53. The combination of biradical revertibility and a kinetically predominant quenching mechanism made for low quantum yields but good (ca. 70%) chemical yields. 3 O kcr c. T. [M l—’ _" R o . complex i 11 l. hv 2. ISC O hv A O R With few exceptions, however, the inital cycloadducts were unstable to ring-opening via 3,3-sigmatropic rearrangement55, giving the corresponding cyclodcta-l,3,5-trienes 1;, as also seen in simpler all- carbon ring system356. Absorption of a second photon of light then initiated a [2+2] electrocyclic ring closure, which produced exo-l- '24 acetyl-S-oxabicyclo[7.2.O.04’8]undec-2,ll-dienes, lg. These compounds were themselves unstable to the octatrienes, and thermally reverted to those compounds via a supposedly non-concerted process. The various 4-pentenyl ethers of the ortho- and para- isomers also formed compareable cycloadducts, but with much lower quenching rates. No similar photoproducts were detected from the meta 3-butenyl ethers. 5. Literature {recedents Since this Thesis concerns some aspects of the generality of this unusual reaction, a diversion to compare conceptually related reactions is warranted. Kinetically, the previously discussed C.T. quenching and photocycloaddition resembles the inter- or intra- molecular reaction of triplet excited cyclic enones with olefins; both proceed by rapid C. T. complex formation followed by stepwise, reversible bond formation to 57a produce fused cyclobutanes through a 1,4-biradical intermediate or return to the ground state photosubstrate. O - . o . + —' —> or ——' L‘ “<- ‘] ll 0 ' ' CT .,- I '— L 25 The inital formation of an ipsg bound biradical in the 4'-acylphenyl ethers --p§;a to the acyl moiety-- is also thought to be in accord with molecular orbital calculations58 predicting large LUMO coefficients, and spectroscopic evidence59 of high (triplet) electron density on the para position of conjugatively electron-accepting benzenoids. These predictions were also bourne out by Paquette's studies on the di-n-methane rearrangement of benzanorbornadienes Egg;- substituted with similar groups, I; 608. The rate-determining step of this reaction is thought to be the formation of a biradical from attack of the fused aromatic position onto the vinyl group61. Thus, in principle, two regioisomers might be expected from irradiation of 1;- however, only 16 was formed, via attack of the aromatic « bond electrons from the position para to the conjugatively electron accepting group. A predicted preference58 for the opposite regioselectivity from analogous photosubstrates substituted with conjugatively electron-donating groups has also been experimentally confirmed60b. xQA>< 1“ ‘5 <25 xQA> x- C(O)CH3, CN, oozczns, No2 Also supporting this same sort of excited state electronic distribution is one of the few other examples of photocycloaddition of an alkene onto a «,«* triplet aromatic. In 1985, Dbpp documented the efficient formation of thermally unstable 1,4-cycloadducts, 11 between l-acylnaphthalenes and a-morpholinoacrylonitrile62. However, this olefin was highly activated, and the addition mechanism is not entirely clear. '1' ON ’ T slow R O 1112- H, CH,,ph Formation of orgho photocycloadducts between olefines and singlet excited benzene derivatives is also possible under certain 27 circumstances, although generalisations in reaction ~outcome and -mechanism are difficult63. The grghg mode is usually favoured when the aromatic is conjugatively electron withdrawing64a. Electron- donating olefins are also known to yield exclusively ggthg 64b,c photocyloadducts with benzene , and with aromatics having dual donor-acceptor properties64d. The mechanism for their formation appears to involve ground state complexes whose geometry can be partially correlated with the electronic properties of the olefin64b. Because orbital symmetry rules for singlet benzene forbid a concerted mechanism648 as well as because the quantum yields for cycloaddition increase with solvent polarity64b, it is thought to occur by stepwise bond formation through a C. T. complex. However, in the absence of appropriate substituents which polarise the aromatic ring electron density, great regioselectivity is not observed64a-C. One case in point is the work of Gilbert and co-workers on the irradiation of g-methoxy -benzonitrile and -methyl- benzoate lg in neat ethyl vinyl ether64d. The rearranged products from cycloaddition, 12 and 29, formed through a rearrangement like that of the acylphenyl alkenyl ethers, were isolated in high chemical yield. X x 0c €sz OCH3 2H5 X 1" . + E “3sz OCH3 OCH3 18, X- (:N, C0201, 12 2Q 28 The gara and para isomers of the -CN homologue also underwent compareable photocycloadditions, but with less regioselectivity; adducts resulting from addition of the ethoxy end of the enol to the -CN bearing aromatic carbon were also formed in compareable amounts64d. Addition of other alkenes to the methoxybenzonitriles gave cycloadducts from the ortho- (both regioisomers), meta— (vide infra) and other additon modes65 The p-(3-butenyl)benzonitrile ;; also undergoes smoothly the intramolecular version of this reaction to form the expected biphotonic product 22 upon prolonged irradiation6 The arrha isomer of 2; also reacted, as did the p-carbomethoxy homologue of the nitrile, albeit at reduced rates. The lack of reactivity from the meta isomer here may have reflected geometrical, and not electronic limitations on the singlet C. T. complex or biradical66. Alkenes can also undergo aara photocycloaddition to singlet benzene. This pathway predominates for olefines and benzene derivatives having similar electron affinities63. It has been shown to proceed probaly through a symmetry-allowed, essentially concerted 29 process; excited state exciplexes, not ground state C.T. complexes are possibly implicated64d. The initally formed tricyclo[3.3.0.02’8 ]oct-3- ene type systems, 2; have found wide use in Natural Product Synthesis67 + I E . Finally, a comparison of the effects of tether -length and -constitution on the relative efficiencies of photocycloaddition and C. T. quenching is necessary. Wagner and Nahm described a maximum of C. T. quenching- and photocycloaddition- quantum yields for three-atom separation of the double bond from the acylphenyl chromophore53. No quenching was observed for chain lengths greater than four atoms. These systems showed a strong preference for formation of a five-membered ring biradical intermediate. This trend has also been documented through the "rule of five" in intramolecular enone-olefin 57b c . . ’ as seen below for the stereoselective reactions photocycloaddition of 25 and g; , the quantum yields for intramolecular aara photocycloaddition of w-phenyl-l-alkenes64, the stereospecificity of oxetane formation from the 1,6-unsaturated phenyl ketonesé7 (cf. compound 5) and intramolecular naphthonitrile-alkene singlet exciplex formation68. It is also parallelled by ground state radical698- and 30 O O aleiill‘O”‘\gfi’ III” (D’“\~/‘§§. M 25 11V hv V .O o lo 0 carbonium69b- cyclisation studies. It should be noted, however, that interactions requiring chain lengths greater than five atoms were seen in Winnik's w-alkenyl esters, in Siebert's w-amino esters,in 6-dialkylaminobutyrophenone, and are not impossible in enone photocycloaddition57b. As well, excimer formation and self- photodimerisation of >four-atom linked bis-anthracenyl singlet substrates has been observed70. Intramolecular photocycloaddition in the acylphenyl alkenyl ether, as well as in the singlet arrha and mara cases occurs efficiently 66’71 (substituent through either an all-carbon- or ether- tether effects on the nature of the lowest excited state notwithstanding). The introduction of an ester function into the longer tethers of the w-amino valerophenone estersso but especially in Winnik's compounds was not detrimental to their quenching abilities. In singlet meta cycloaddition substrates, however, the presence of ester functions in 31 O 0 II II Ph(CH2,n-Oc—CH=CH2 Ph(CH2)n—CO-CH=CH2 26.n9 1,20r13 ZL,nP 1,20r3 the tether adjacent to the olefin such as in lé or 21 drastically lowers reactivity55. On the other hand, enone photocycloadditions have been implemented through a variety of tether linkages, including a conformationally restraining one like seen for 2&72. V O ION The following is a cursory description of the relations which will be used to derive the Type II steady state kinetic parameters used in this Thesis. 32 A. Quanrum -Yie1ds and -Efficiencies The quantum yield of a photochemical process, é is the ratio of molecules which can undergo that process to the total number of photons absorbed by the concerned photosubstrate73. In terms of photoproduct concentration [P] and light intensity absorbed, Ia, ¢ is defined in Equation 6. Experimentally, Ia may be determined from the Beer-Lambert o - [P]/Ia (6) law74. Kinetically, quantum yields are described in terms of the product of the individual quantum efficiencies, ¢i of each step along the pathway leading to the final, detectable species. The ¢i are defined as the productive fraction of net unimolecular decomposition rates from each intermediate state. Thus, the observed quantum yield for formation of Type II cleavage protoproducts from a phenyl alkyl ketone, é is defined in Equation 7 II as the product of ¢isc’ ¢H and P, the quantum efficiencies of singlet -> triplet intersystem crossing, hydrogen abstraction, and partitioning of the resulting 1,4-biradical towards cleavage products. ¢II a ¢ISC ' ¢H . P (7) In spite of the number of independent unknowns, Equation 7 is easily evaluated. First, ¢ - 1.0 for phenyl alkyl ketonesz. Also, ISC 33 in the presence of a Lewis base, return of the 1,4-biradical to the ground state photosubstrate is blockedl6, and so P reduces to kcl/(kcl + kc ), a relatively constant term for constant substitution at the 7 positionloc. Now the maximised quantum yiels for cleavage product formation, ¢MAX is represented by Equation 8. éMAX ' ¢H ' kcl/(kcl + kcy) , (8) §l__Lifs£iass The intrinsic lifetime of a transient species, 1, is defined as the reciprocal of the sum of the rate constants for all intramolecular processes accessible to it73, Equation 9. For phenyl alkyl ketones l/r - z kd (9) capeable of hydrogen abstraction, 2 kd includes kir“ kH’ kCT etc. The intrinsic lfetime of such a photosubstrate is then related to ¢H and kH’ the actual rate constant for hydrogen abstraction from the triplet state, through Equation 10. Substitution of Equation 10 into Equation ¢H - kH - r (10) 8 and defining the experimentally determined rate constant for formation of cleavage products, kII- kH - kcl/(kC1 + kcy)’ then yields Equation 11, which, with knowledge of 1, provides an experimentally 34 accessible rate constant for Type II photocleavage reactivity13’l6. O - k - r (11) C. fitera-Volaar Kinetics The lifetime of an excited state can be experimentally determined by monitoring the effects of a state specific quencher, Q, on the extent of a respectively state specific photoprocess according to the 73,75 Stern-Volmer equation For phenyl alkyl ketones undergoing Type II cleavage8'13, this amounts to Equation 12, where Q is the quantum o°/o - 1 + kq ~ [Q] - r (12) yield in the presence of a known concentration of quencher, Q and @0- Q . Evaluation of r then follows from the slope of a plot of Qo/Q II 76,77 versus [Q] and kq for a quencher quenching at or near the diffusional limit34. V R S G A In this Thesis, the Type II photokinetics of compounds analogous to Siebert's 4'—valeryl benzoate esters, but bearing terminal olefinic tethers, were initally studied for evidence of intramolecular C.T. quenching. Irradiations of some of the corresponding h'-acetyl 35 benzoate esters were also examined for photocycloadducts comparable to those from the 4'-acylphenyl alkenyl ethers. The results of those experiments prompted the scrutiny of two other classes of keto-esters: Firstly, the photokinetics of w-alkenoate esters of 4'-acylphenols, wherein the "direction" of the tethering ester moiety was "reversed", were studied. The triplet lifetimes of these photosubstrates were compared to those of the yet-unmeasured h'-acylphenyl acetate esters. Thus, information on the effects of yet another aromatic substituent on Type II reactivity was obtained as a bonus. Secondly, the possiblity of photocycloadducts from acetophenones having both a para-methoxy group, to favour a n,n* lowest triplet state, and a meta benzoate-linked tether was investigated. R 13 S I] L I? S I COMPOUNDS STUDIED The Type II photokinetic- and quantum yield— parameters of the 4'-valeryl ally1-, 3-methyl-2-butenyl- (prenyl-) and 3-butenyl- benzoates 22a, 39a and 31b in benzene were measured. Also examined in this regard were the 4'-butyrylphenyl -3-butenoate and -4-pentenoate esters, 32b and 33b, in 4:1-methanol: benzene. o 2|? ~ 06% one 19 n R O n O O mn-1;‘R-CH,;’R-H mums-ca, 221:. n- 1; ‘R- "can; ’12- H 321:. n- 1; R- "c3111 m n- 1; 'R- “C4H9; 2R- CH, 33]). n- 2; R- "C3111 3n. n- 2; 'R- cn,; 211-. H 111:. n- 2; 'R- "c411,; ’R- H Irradiations of the corresponding acetophenone derivatives, 29a, 31a and 32a, as well as the 5'-acetyl-2'-methoxy -allyl- and -3-butenyl benzoate esters 33a and 32a were also followed by 1H NMR spectroscopy. 36 37 OCH3 CH3 0% O O n 35:. n- 1 35:. n- 2 II. SXEIEESIS Methyl rraaa-crotonate was prepared by Fisher esterification78 of an excess of crotonic acid with methanol in the presence of a catalytic amount of sulfuric acid79. The benzoate and alkenoate ester photosubstrates and calibration standards 22 - 3; were obtained from the corresponding carboxylic acids and alcohols. Their structural identities were confirmed by their 1H- and 13C- NMR-, IR- and mass- spectra. All compounds were of greater than 98% purity by gas chromatography, except where noted. The h'-acylbenzoic acids were prepared by displacement of fluoride by cyanide from the 4'-acylfluorobenzene580 followed by basic hydrolysis, according to the overall method used by Siebertgl. In the case of 4'-acetybenzonitrile, basic hydrolysis gave an unacceptably low yield of 4'-acetylbenzoic acid, and so the hydrolysis was carried out under acidic conditionsgz. The physical properties of the benzoic acids were identical to those reported earlier81’82. 38 The 4'-acy1 allyl benzoates 22 were obtained from reaction of the 4'-acylbenzoyl chlorides with allyl alcohol83. The acid chloride technique effected partial positional isomerisation of the double bond in the 4'-acyl prenyl benzoates 19, and so they were prepared in gas chromatographically pure condition from the 4'-acyl potassium benzoates and diethylprenylsulfonium tetrafluoroborateg4 using a modification of the procedure of Julia85 The 4'-acyl 3-butenyl benzoates 3; were also unsuited for preparation via the acid chlorides; they were obtained instead from the 4'-acyl potassium benzoates and excess 4-bromo-l—butene in 1:1- hexamethylphosphoric triamidezethan0186. The bromoalkene was prepared by an established mean587 The 4'-acy1phenyl esters were obtained from the appropriate 4'- acylphenols and carboxylic acids or anhydrides. The 4'-acetylphenol was commercially available, while the other 4'-acylphenols were formed in one step from butyric or valeric acid, phenol and polyphosphoric acid according to a procedure adapted from the literature88. Their spectroscopic and physical properties agreed with those already reported89. The acetate esters were prepared by Schotten-Baumen esterification of the phenols with acetic anhydride in cold sodium hydroxide solutiongo. Physical- and/or spectroscopic- properties of the acetate 91'92, when reported. esters agreed with those in the literature The 3-butenoate and A-pentenoate esters a; and ii as well as 4'-acetylphenyl rraaa-crotonate (vide infra) were prepared by coupling the appropriate 4'-acylphenols and alkenoic acids with 39 dicyclohexylcarbodiimide and 4'-N,N-dimethylaminopyridine93. The 3-butenoic acid was commercially available and h-pentenoic acid was prepared by a known procedure94 The spectral properties of the 3-butenoate esters (1H- and 13C- NMR, IR) agreed with their anticipated structures and after simple work-up showed them to be of greater than 98% purity, the major impurity being their trans-crotonate isomers. The relative amounts of each isomer were initally assayed from the ratio of signal areas in their 1H NMR spectra attributable to protons unique to the 3-butenoate and rraaa-crotonate95 residues, at 63.29 (doublet of triplets, 2H, -C(O)CBZCH-CH2) and 61.96 (doublet of doublets, 3H, -C(O)CH-CHCH3), respectively. The esters were not stable under gas chromatographic conditions (15 m DB-l column; column temperature- 150°) and all attempts to remove these impurities (flash chromatography from silica- and neutral alumina, ultra high vacuum distillation from silanized glassware, Dials-Alder reaction with cyclopentadiene) were fruitless. They were relatively stable as neat oils at ca. 0° in silanized glassware. The proportion of crotonate ester of 32a increased rapidly in the 4:1-methanolzbenzene photolysis solutions- to ca. 4% within four hours at room temperature (generally the time required to prepare and degas the photolysis solutions) or ca. 50% overnight. However, control experiments indicated that no further isomerisation of photosubstrate 12b or photoproduct 32a occurred under the actual conditions (ca. 0°) and time frame (ca. 2 h) of the irradiations. The amount of 32_- crotonate in the photolysis solutions was assayed by reverse phase HPLC 40 (UV detection at 250 nm; solvent gradient program (% acetonitrile in water; flow rate- 1.0 ml/min.): 36%, then at 15 min. to 50%, then at 22 min. to 36%). The 4'-acetylphenyl rraaa-crotonate eluted at 10.5 min, 0.6 min after 32a. Therefore, the peak at 27.2 min. which increased with time in area at the expense of the area of the peak from 32a at 26.0 min. was assumed to arise from figb-crotonate. See "Photolysis"/ "Results” and "Photolysis Procedures"/ "Experimental" Sections for further details. The 4'-butyrylphenyl a-pentenoate esters i; were stable compounds and were obtained without complication. The alkenyl esters of 5'-acetyl-2'-methoxybenzoic acid 33a and fiéa were synthesized by coupling the carboxylic acid and appropriate alcohol with dicyclohexylcarbodiimide and 4'-N,N-dimethyl- aminopyridine93. The 5'-acetyl-2'-methoxybenzoic acid was prepared by a known procedure from acetyl salicylic acid96'97. 111, PHOTOLY§IS A u t 'eld Ex e 'ments 1. Photoproduct Identification All acetophenone photoproducts were identified by comparison of their gas chromatographic- or HPLC- retention times to those of authentic samples. The identity of the 4'-butyryl- and 4'-valeryl- phenyl acetate photoproduct was also confirmed by analogy to the 41 earlier characterisation of the 4'-butyrylphenyl acetate photoproduct by Pittslg. 2. Stern-Volmer Quenching Plots Degassed and vacuum-sealed benzene or 4:1-methanolzbenzene solutions containing 0.03 5 ketone and varying amounts of 2,5-dimethyl- hexa-2,4-diene (DMHD) or methyl trans-crotonate quenchers were irradiated at 313 nm in a merry-go-round apparatus to 2 - 12% conversion. Linear Stern-Volmer plots of ¢°/¢ versus quencher concentration were derived from the ratio of concentrations of acetophenone photoproduct measured for each solution. The slope of these plots was equal to qu, where kq was the rate of quenching of the 76’77. The values collected in triplet ketone and r is its lifetime Tables 1 - 3 were taken from runs agreeing to within ca. 10% of each other and their Stern-Volmer plots for typical runs are summarised on Figures 6 - 8 and 11. The line calculated from similar data for A'- carbomethoxyvalerophenone reported by Siebert‘23’8l is included in Figure 6 for comparison. 3. Quantum Yields The quantum yields for the formation of the acetophenone photoproducts were measured by the irradiation of degassed benzene solutions containing 0.1 u valerophenone actinometer in parallel with 0.03 M ketone photosubstrate16. Conversion of valerophenone was kept 42 ‘ e 10‘ // C 0 (1)/(D . 2.0 ‘ /' O . . / / / 1.0 I r I I 01!” 0.010 0.020 0.030 0.040 UDHflEEL.hd ‘Figure 6. Stern-Volmer Plot for Quenching of Acetophenone Formation from 4'-Va1ery1 Alkenyl Benzoate Esters with 2,5-Dimethy1- 2,4-Hexadiene in Benzene. Data for line equation of 4'-carbomethoxyvalerophenone from Doctoral Dissertation of E. Siebert included for comparison. Legend: allyl ester: open circle; 3-butenyl ester: closed circle; methyl ester: no marks. 43 3.0 - 0 (1)/(D . 2.0 - I I I ‘ A AI 1' I 1.0 V I f I t I ' I 0.0000 0.0010 0.0020 0.0030 0.0040 [13120131. M Figure 7. Stern-Volmer Plot for Quenching of Acetophenone Formation from 4'-Butyry1pheny1 Alkenoate Esters with 2,5-Dimethyl- 2,4-Hexadiene in 4:1 - Methanol:Benzene. Legend: 3-butenoate ester: closed square; 4-pentenoate ester: open triangle; acetate ester: open circle. 44 4.0 - 3.0 . o 1 mo . 1 . II II 2.0 - II II . I II II 1.0 i I ' I ' I ' I I ‘ I 0.0000 0.0025 0.0050 0.0075 0.0100 0.0125 [DIENE], M Figure 8. Stern-Volmer Plot for Quenching of Acetophenone Formation from 4'-Acylphenyl Acetate Esters with 2,5-Dimethyl-2,4- Hexsdiene in 4:1 - Methanol:Benzene. Legend: 4'-butyrylphenyl acetate: open square; 4'-valerylphenyl acetate: closed circle. 45 to ca. 3% or lower. Quantum yields are reported with Stern-Volmer data in Tables 1 - 3. Table l. Photokinetic Parameters for Quenching of Alkenyl 4'-Valerylbenzoate Esters with 2,5-Dimethy1-2,4-Hexadiene in Benzene Photosubstrate Alkenyl moiety @11 qu,fl'l a p-COZCH3VP CH3 0.19 42 29b Chch-CH2 0.18:0.03 55:3 30b CHZCH-CH(CH3)2 0.25:0.01 ---- 31b (CH2)2CH-CH2 0.181i0.001 61:1 a: para-carbomethoxyvalerophenone; data taken from Doctoral Dissertation of E. Siebert. 4. Limiting Quantum Yield . 13,50 The intercept of the plot of 1/II versus concentration of 4'—butyrylphenyl 3-butenoate, shown in Figure 9, was taken as l/éLIM’ where ¢LIM was defined as the quantum yield for Type II photoelimination in the absence of intermolecular quenching50’53a. This quantity is listed in Table 2. 46 13.0 ‘ 12.0 " 11.0 ‘ 1/ triplet intersystem crossing quantum yiele. The [1,3] rearrangement of B,1-unsaturated ketones has also been proposed to occur from an upper triplet statelll. Consequently, the 4'-acylphenyl acetate photosubstrates were especially suited to further probing this question. The lack of «,«* (or other triplet state) ~mitigated photo-Fries rearrangement is perhaps best demonstrated by the approximately unitary quantum yield for Type II cleavage of 4'-valerylphenyl acetate. This point is further emphasised by the fact that polar solvents are known to favour the formation of intramolecular photo-Fries type productsloga- the increased Type II quantum yield for this ketone upon changing from benzene to 4:1-methanol:benzene is contrary to this expectation. Also in opposition is the known enhancement in polar solvents of triplet state reactivity toward homolytic bond cleavagellz. As well, in both of the acetate ester post-photolysis solutions the only high retention time peaks visible on the gas chromatographic traces were attributed to photosubstrate, photoproduct, internal standard and two small, broad, closely eluting peaks presumeablyloa from cyclobutanols. This is significant, because rate constants for dissociation of singlet excited polyatomic molecules113 have been 12 -1’ ca. 2 estimated to be at least 10 s 10 5-1 faster than that of singlet -> triplet intersystem crossing for phenyl alkyl ketonesz 77 Thus, even any possibility of singlet photo-Fries reactivity from the current chromophores appears to be ruled out. IV, Copplusion This Work showed that limited intramolecular C.T. quenching of the «,n* triplet state through the aromatic ring of 4'-acylphenyl w-alkenoate, but not 4'-acy1 w-alkenyl benzoate esters, is possible. This difference stems from the propensity toward physical contact possible between the tethered olefin and the aromatic ring of the chromophore and apparently not the extent of charge transfer polarisation intrinsic to the lowest triplet state of each. The photokinetic- and spectroscopic— properties of the 4'-acylphenyl acetate chromophores parallel those of other phenyl nalkyl ketones which posess the «,«* lowest energy triplet configuration, but suggest that this electronic configuration is only slightly preferred over the n,x* one. Together these conclusions imply that intramolecular C.T. quenching through the aromatic ring of weakly dominant «,«* triplets by tethered olefines is possible. There are many phenyl alkyl ketone-based, aromatic-tethered photosubstrates which, ad hoc, could give rise to C.T. quenching and/or 78 intramolecular cycloaddition products. The esters studied in this Thesis give more realistic estimates of which cases might be fruitfully explored. The compounds described below are ordered in their pertinence to this Work and the ease of their preparation. As well, molecular mechanics calculations might be suggested to evaluate geometrical considerations before a given compound is studied. Other 4'-Acyl Alkenyl Benzoates. Winnik's conclusions on the relative abilities of benzoate-tethered w-alkenes to contact the aromatic ring as a function of chain length suggest that the Type II kinetics of 4'—valeryl benzoates having 5-hexeny1 and 6-heptenyl ester tethers be examined. Although photocyloproducts might not be formed, insight on the susceptibility of the 4'-acyl benzoate chromophore (E E x- 0.3 kcal/mol)23 toward intramolecular quenching by alkenes n,t- «, could be obtained. 2'-A1kenyl-4'—Acetyl Methyl Benzoates. The alter ego of the 5'-acetyl-2'-methoxy alkenyl benzoates, the compounds 22 would combine the favourable geometry of the 4'-acy1pheny1 alkenyl ethers with the electronic configuration of the 4'-acy1 benzoates. The isolation of [2+2] photocycloadducts from their irradiation would confirm the proposed geometrical limitations on C.T. quenching. Ortho-Acyl Benzoate Esters. The «,n* triplet state of p-carbomethoxyvalerophenone is estimated to be stabilised over the n,x* one by ca. 0.7 kcal/mol more than the para isomer23, suggesting that * compounds 21 might show greater promise of C.T. quenching of the «,r triplet state respectively. 79 o COZCH3 09“ 00:5 n O n O 3.6 31 n- 2, 3 R‘ C113, "C4519 n- l, 2 4'-Butyry1phenyl Methyl- and Vinyl- Carbonates. The presence of two oxygen atoms to reduce the electron deficiency of the tether carbonyl of 22 should improve the preference for the w,n* lowest triplet state through charge transfer polarisation. Whether this would result in C.T. quenching and photocycloaddition in 22 would depend on the preference of the vinyl carbonate for a trans-coplanar conformation. 0 OCH 0 O . 1r 3 . 1r V" Cens O nC4H9 0 O 0 38 39. 4'-Acyl N,N-Dialkenyl Benzamides. The trana-coplanar lowest energy conformation of the 4'-acyl alkenyl benzoatesloz does not favour contact between the olefin and the aromatic ring. This problem would be alieviated in the 4'-acy1 dialkenyl benzamide series, 52. The sp2 80 geometry around the amide nitrogen114 would force one of the tethers to be proximate to the ring. 4'-Butyrylphenyl 4-Methyl-3-Pentenoate. The photokinetics of a; should demonstrate greater C.T. quenching than of the 3-butenoate ester, by virtue of the greater electron-donating ability of the more highly substituted tether37’53a. Photocycloadducts may also be possible. 0 R n 2 11Q11, 0 0 o 50 4.1 E )C P 13 R I 14 E 11 T [A L I, EURIFICATION AND PREPARATION OFfCHEMICALS A. vents d A itives Benzene. Baker Reagent Grade benzene was purified in 4 1 lots by stirring repeatedly for periods of ca. 1 day with 150 ml concentrated HZSO4 untill no discolouration was apparent in the acid layer. It was then washed 3 times each successively, with water, saturated NaHCO3 solution, water and saturated NaCl solution. After drying over MgSOa, followed by refluxing over P it was distilled through a 0.9 m 205' heated glass column packed with glass helicies at a rate of ca. 100 ml/h. The central cut, ca. 70% of the total distillate volume, was collectedal. Methanol. To 4 1 of Baker Reagent Grade methanol was added ca. 10 g of freshly cut sodium metal. After refluxing overnight, it was fractionated through a 30 cm Vigreux column. The central cut, ca. 60% of the total distillate volume, was collected. Pyridine. A 500 ml volume of Fisher Reagent Grade pyridine was refluxed for 2 days over 7 g BaO and fractionally distilled twice 81 82 through a 30 cm column packed with copper mesh. In each case, the central 70% of the total distillate volume was collected. Reverse Phase HPLC Solvents. a) Ultraviolett-HPLC grade methanol and acetonitrile were passed through a 0.45 p mesh Nylon-66 filter prior to use. b) Distilled water was refluxed overnight as a 0.012 M NaOH - 0.0012 M KMnO solution and fractionated through a 1.5 m glass Vigreux 4 column. The central 50% of the total volume was collected and immediately stored as an 10% -acetonitrile or -methanol solution. B. laternal Standards Hexadecane. Aldrich 99% pure hexadecane was used as recieved. Ethyl benzoate. Ethyl benzoate was available in 100% pure condition from a previous studyIlj. Propyl benzoate. nPropyl benzoate was available in 100% pure condition from a previous study116. Butyl benzoate. nButyl benzoate was available in >99 5% pure condition from a previous study116. Heptyl benzoate. nHeptyl benzoate was available in >99.3% pure condition from a previous study116. Octyl benzoate. nOctyl benzoate was available in 100% pure condition from a previous study117. 83 C. Qaanchers 2,5-Dimethyl-hexa-2,4-diene. Aldrich 99% pure 2,5-dimethyl-2,4- hexadiene was allowed to sublime in the refrigerator. Methyl trans-crotonate. A mixture of 80 g (0.93 mol) of crotonic acid and 30 ml absolute methanol (0.73 mol) was refluxed for 24 h with 2.2 ml concentrated H2804 78’79 two fractional distillations, 31% of the ester, bp= ll6.5-ll6.9°C (lit. 119°/768 mm Hg)79. 1H NMR (0001 under Fisher conditions78 to give, after 60 MHz): 67.03 (dq, 1H, J - 7.3; 3; c- 14 Hz, ab), 5.88 (dq, 1H, Jca- 2; JC ba Jb = 8 Hz, HC), 3.81 (s, 3H, Hd), 2.93 (dd, 3H, Jac- 2; J b ab- 3 Hz, Ha)' IR (CH2C12): 3054, 3016, 2950, 2910, 2836, 1722, 1662, 1434, 1308, 1206, 1176 cm.1 4'-Fluorovalerophenone. This compound was prepared by Friedel-Crafts acylation of fluorobenzenego. To a mechanically stirred mixture of 89 ml fluorobenzene (0.89 mol) and 104 g anhydrous A1Cl3 (0.78 mol) in 100 ml nitromethane at 0° was added 50 m1 valeryl chloride (0.42 mol) over 5 min. The mixture was gradually warmed to room temperature with 84 stirring over 1 h and then heated to a gentle reflux for 10 h. At the end of that time the hot mixture was cautiously poured into 100 ml 12% HCl and cracked ice. This mixture was extracted repeatedly into ether and the combined organic phase was washed with l N NaOH until the aqueous phase was colourless. After washing with water and brine and finally drying over MgSO removal of the solvent left 65 g of a brown 49 oil. Distillation of that material at 60-90°/0.l-l.0 mm Hg (lit. 95°/0.l6 mm Hg)81 gave a yellow liquid which was recrystallised from methanol in the refrigerator to give 37 g (49%) of a low-melting solid, pure by GC analysis. 1H NMR (60 MHz; CDC13): 67.95 (dd, 2H, Jca- 5.0; Jcb- 8.0 Hz, Hc), 7.10 (t, 2H, Jbaz ch- 10.0 Hz, Hb), 2.93 (t, 2H, Jde- 7.0 Hz, Hd), 1.2-1.9 (complex, 4H, Hd; He), 0.93 (t, 3H, er- 6.0 Hz, Hf). IR (CCla): 2966, 2942, 2881, 1792, 1606, 1460, 1413, 1225, 1212, 1186, 844 em‘l. EI-MS: m/z- 181 (M+1+), 180 (M+'), 151, 138, 123 (base), 95. 4'-Acety1benzonitrile Prepared according to Siebert's procedure81 in 40% yield by the treatment of 4’-fluoroacetophenone with 1.08 equivalents sodium cyanide in refluxing dimethylsulfoxide after crude distillation (bp- 90-120°C/ca. 0.8 mm Hg) and recrystallisation from hexane, mp- 52-54° (lit. 54-56°)118. 1H NMR (60 MHz, CDC13); 68.10 (d, 2H, J a- 8.0 Hz, Hb), 7.90 (d, 2H, Ja - 8.0 Hz, Ha)’ 2.72 (s, 3H, Hc)° b b IR (CCla): 2244, 1704, 1617, 1440, 1413, 1370, 1302, 1270, 855 cm.1 EI-MS: m/z- 145 (M+'), 130 (base), 102, 75. NC 4'-Valery1benzonitrile. Prepared according to Siebert's proceduregl by the treatment of 4'-fluorovalerophenone with 1.15 equivalents of sodium cyanide in boiling dimethylsulfoxide in 59% yield after crude distillation (bp- 129-159°/0.8-0.9 mm Hg) and recrystallisation from hexane, mp- 34-35° (lit. 32-33°)81. 1H NMR (60 MHz; CDC13): 68.12 (d, 2H, J a- 5.0 Hz, Hb), 7.83 (d, 2H, Ja - 5.0 Hz, Ha) 3.01 (t, 2H, JC - d - 6.0 Hz, e b b 8.0 Hz, Hc), 1.25-2.00 (complex, 4H, H He), 0.98 (t, 3H, J d; f 4)‘ 2965, 2937, 2879, 2236, 1694, 1471, 1412, 1214, 1022, EI-MS: m/z- 187 (M+'), 154, 145, 130 (base), 102. H IR (CCl 1 £)° 859 cm- 4'-Acetylbenzoic acid. According to a procedure adapted from the literaturesz, 25 g of 4'-acetylbenzonitrile (0.172 mol) was heated to reflux for 15 h in 50 ml concentrated HCl, 150 ml glacial acetic acid and 30 ml water while monitoring by thin layer chromatography. At the end of that time, the solvent was removed by distillation, and the residual yellow oil was redissolved in 750 ml saturated NaHCO3 and 2.25 1 water. The aqueous solution was washed with ethyl ether, and the ether extracts discarded. The product was then precipitated from the bicarbonate solution by the careful addition of 2 N HCl, and recrystallised from copious amounts of water to give 14.9 g (53% yield) of fine white needles, mp- 206-208°C (lit. 205-206°)82. 1H NMR (60 MHz; acetone-d6): 68.03 (s, 5H, Ha; Hb; HC), 2.60 (s, 3H, Hd). IR (KBr pellet): 3067, 2567, 1712, 1677, 1437, 1300, 947, 861 cm'l. EI-MS: m/z- 164 (M+°), 149 (base peak), 121. 87 How: 4'-Valerylbenzoic acid. The acylbenzoic acid was prepared by the procedure used by Siebertgl. A solution of 18 g 4'-valerylbenzonitri1e (0.096 mol) in 63 ml 30% aqueous potassium hydroxide and 18 m1 ethanol was heated to reflux for 24 h. At the end of that time, the solution was rendered neutral by the addition of 6 N HCl. After cooling, the resulting precipitate was collected by suction filtration and washed with water to give 18.3 g (70%) of a tan solid, mp- 154 5-156 6° (11:. 155-157°)81. In NMR (60 MHz; 00c13): 68.08 (s, 4H, ab; HC), ca. 5.7 (broad s, 1H, Ha)’ 3.07 (t, 2H, J - 7.0 Hz, Hd), 1.1-2.l (complex, de - 6.0 Hz, Hg). IR (CHC13): 2547, 2677, 1 4H, He; Hf), 0.93 (t, 3H, J8f 1647, 1467, 1367, 917, 861 em' EI-MS: m/z- 206 (MI'), 189, 177, 164, 161, 149 (base peak). 4'-Acetyl allyl benzoate. In a procedure modified from Mills83, 0.89 ml SOCl2 (0.012 mol) was added through a septum to a stirred, ice-cold solution of 2.00 g 4'-acetylbenzoic acid (0.012 mol) and 1.1 ml pyridine (0.014 mol) in 40 ml benzene under N The resulting mixture 2. was heated to reflux for 4 h, whereupon a red colour developed. The solution was decanted from a gummy precipitate, and the precipitate was in turn washed 3 times with benzene. The volume of the combined organic solution was reduced to ca. 10 ml by distillation at reduced pressure, cooled and added dropwise to a cooled, stirred solution of 0.95 ml allyl alcohol (0.0140 mol) and 1.1 m1 pyridine in 25 ml petroleum ether under N After stirring an additional 30 min at 0°, 2. the solution was warmed to room temperature and stirred overnight. At the end of that time, the reaction mixture was suction filtered, and the filtrate was diluted with benzene and sequentially extracted 3 times each with aqueous 1% Na2CO3 and water. After drying with MgSO4 and removing the solvent, this afforded a red oil, which was purified by column chromatography (Davisil 60; 30:70-EtOAc: hexanes) to give 1.30 g of a orangish oil (52% yield). 1H NMR (300 MHz; C0013): 68.11 (d, 2H, Jedf 8.7 Hz, He), 7.97 (d, 2H, J e- 8.7 Hz, Hd), 6.02 (m, 1H, d - 17.2 Hz, H ), 5.27 (dt, 1H, J , - a a Hb), 5.39 (dt, 1H, J - 1.6; J ac a c b - 10.4 Hz, Ha,), 4.92 (broad t, 2H, JC 13 1.5; J - 5.7 Hz, HC), 2.71 (s, b C NMR: 6199.1, 166.8, 141.7, 135.3, 133.2, 131.2, 129.5, a'b 3H, Hf). 119.9, 67.1, 27.8. IR (CCla): 3097, 2957, 1730, 1697, 1659, 1115, 797 cm-1. EI-MS: 204 (M+ ), 183, 147 (base peak). UV-VIS (heptane): Amax- 245, 285 nm. 4'-Valery1 allyl benzoate. Prepared as was 4'-acetyl allyl benzoateg3 passage through Activity-1 basic alumina removed red colour completely. (57% yield) 1H NMR (300 MHz; CDC13): 68.11 (d, 2H, Je - 8.5 Hz, He), d e- 8.5 Hz, Hd), 6.06 (m, 1H, Hb), 5.42 (dq, 1H, Ja z a! 7.97 (d, 2H, Jd - 17.2 Hz, H ), 5.28 (dq, 1H, J , 2 J , z 1.3; J , - 10.4 a a a a c a b - 5.7 Hz, Hc)’ 2.95 (t, 2H, Jacz 1.5; Jab Hz, H ,), 4.81 (dt, 2H, J z J ,z 1.4; J a ca ca cb Jfg- 7.4 Hz, Hf), 1.69 (quin, 2H, Jgfz Jgi- 7.7 Hz, Hg)’ 1.38 (sex, 2H, 13 Jig: Jij- 7.4 Hz, Hi)' 0.92 (t, 3H, in- 7.3 Hz, Hj). C NMR: 6200.1, 165.5, 140.4, 133.7, 132.0, 129.8, 127.9, 118.5, 65.7, 38.8, 25.8, 22.0, 13.5. IR (CClA): 2960, 2939, 2880, 1695, 1657, 1106, 800 cm 1. EI-MS: m/z- 247, 246 (M+'), 217, 204, 189 (base peak). 90 Diethyl 3-methy1-2-butenyl sulfonium tetrafluoroborate. 1. Preparation of anhydrous hydrofluoroboric acid ethrate84a. To 36.9 ml of dry ice-acetone-cooled boron trifluoride ethrate (0.300 mol) was added 6.0 m1 cooled, liquified, anhydrous hydrogen fluoride (0.30 mol). The resulting pale orange liquid was stored under argon in a polyethylene vessel in a freezer and was generally used within 12 hours of its preparation. 2. Preparation of the sulfonium salt. In a modification of a procedure of Julia84b, 48.5 g hydrofluoroboric acid ethrate (0.30 mol) was added in several portions to a stirred solution of 27.3 ml 3-methy1-2-buteny1 alcohol (prenyl alcohol; 0.267 mol) and 58.4 ml diethyl sulfide (0.542 mol) in 45 m1 CH2C12. The resulting solution was stirred at 0° for several hours and then at RT for ca. 18 h, whereupon two phases had formed. The lower phase was isolated, diluted with 100 m1 CH2C12, dried with MgSOA, leaving an orange oil after rotary evaporation of the solvent. The oil was triturated 4 times with extremely dry ether, and the remaining white solid was recrystallised from 1:1 absolute ethanolzethyl ether to give, after drying overnight in a vacuum dessicator (P205), 53.3 g of crystals (81% yield), mp- 1 41.5-43.0 °C. H NMR (60 MHz, CDC13) 65.30 (broad t, 1H, J - 8.0 Hz, dc Hd), 4.04 (d, 2H, ch- 8.0 Hz, HC), 3.34 (q, 4H, Jbaa 9.0 Hz, Hb), 1.92 (s, 6H, He), 1.56 (t, 6H, Ja l b- 11.0 Hz, Ha). IR (CH2C12): 1664, 3070, 691, 1065 cm. EI-MS: m/z- 165 (3.3% relative intensity), 152 (7.5%), 130 (13.9%). Compare to dimethyl geranyl sulfonium tetrafluoroborateaéb, mp- 48-53°; 1H NMR: 65.40 (t, 2H, J- 8.0 Hz), 4.17 (d, 2H, J- 8.0 Hz), 2.92 (s, 6H), 1.85 (s, 3H). 91 ./’I BF4 _- 4'-Acetyl prenyl benzoate. A mixture of 3.50 g 4'—acetylbenzoic acid (0.0213 mol), 7.88 g diethyl prenyl sulfonium tetrafluoroborate (0.0320 mol) and 1.47 g oven-dried K CO3 (0.0212 equivalents) in 250 m1 2 anhydrous CH2012 was stirred under a CaCl2 guard tube for 4 day585. The reaction mixture was extracted 3 times with 70 m1 5% NaHCO, 4 times with water, dried with MgSO and the passed rapidly through a short 4 plug of Activity-1 basic alumina. After removal of the solvent, the product was purified by column chromatography (Davisil-60; 10:90- EtOAczhexanes elutant) to give 1.12 g of a light yellow oil (23% yield), which could be recrystallised with some difficulty from hexane to give white crystals, mp- 36.6-37.7 °C. 1H NMR (300MHz, CDC13): 68.09 (d, 2H, Jed. 7.5 Hz, He), 7.96 (d, 2H, J - 7.5 Hz, Hd), 5.44 (m, de 1H, Hb), 4.81 (d, 2H, Jcb - 7.0 Hz, He), 2.60 (s, 3H, Hf), 1.76 (s, 3H, Ha)” 1.74 (s, 3H, Ha,). 13C NMR: 6198.0, 166.1, 140.3, 139.8, 134.5, 130.0, 128.3, 118.5, 62.2, 26.6, 25.6, 17.9. IR (CHC13): 3060, 2991, 1. EI-MS: m/z- 232 (M+'), 217, 199, 165, 147 -1 1691, 1719, 1423, 841 cm- (base peak). UV-VIS (heptane): Amaxz 285 nm, e z 17 000 A-n'l cm 285 The 5% bicarbonate wash was treated with dilute acid to recover 1.96 g 4'-acety1benzoic acid (56%) by filtration. The yield of product was possibly improved by addition of 2 equivalents of K2C03, although 92 it was not affected by an increase in reaction time past 3 days, nor by an increase of the equivalents of sulfonium salt past 1.0. 4'-Va1ery1 prenyl benzoate. In a manner similar to that used in the preparation of 4'-acety1 prenyl benzoate85, this compound was prepared as fine white needles of mp- 37.2-38.3°C in 29% yield. 1H NMR (300MHz, - 8.7 Hz, He), 7.95 (d, 2H, J CDC13): 68.08 (d, 2H, Je e- 8-7 HZ. Hd)’ d d 5.43 (m, 18, Hb), 4.80 (d, 2H, Jcb- 7.3 Hz, HC), 2.95 (c, 28, Jfga 7.4 Hz, Hf), 1.76 (s, 3H, Ha), 1.74 (s, 3H, Ha')’ 1.68 (quin, 2H, Jgfz Jgi- 7.3 Hz, 8 ), 1.37 (sex, 28, J z J..- 7.2 Hz, H.), 0.91 (c, 38, J..- 8 18 1J 1 J1 7.3 Hz, 81). 13c NMR: 6200.4, 166 1, 140.4, 139.8, 134.2, 130.0, 128.0, 118.5, 62.2, 38.5, 26.0, 25.6, 22.2, 17.9, 13.61 IR (CHC13): 2965, 1727, 1696, 1273, 1104, 830 cm‘l. EI-MS (25 eV): m/z- 232, 217, 207, 189, 164, 162, 149. An additional 1.03 g starting material (31%) was recovered by acidification of the 5% bicarbonate wash and filtration. 93 4-Bromo-1-butene. CAUTION: Due to the high toxicity of the hexamethylphosphoric triamidellg (HMPA) used in this procedure, the entire reaction and work-up were conducted in a well-ventilated hood, the interior surfaces of which were lined with 2-3 layers of paper towels. Rubber gloves, safety goggles and a disposible lab coat were worn. Dirty glassware was rinsed with water or acetone, and the washings were isolated in a bottle. Solid waste was contained in double-lined plastic bags. A11 waste materials were removed and disposed of by qualified personel. The bromoalkene was prepared according to the general procedure of Kraus and Landgrebe87 for w-bromo-l-alkenes. A 3-necked flask outfitted with a dropping funnel, stillhead/condenser and magnetic stirrer was charged with 140 m1 1,4-dibromobutane (1.17 mol) and afterwards heated to 195-205° on an oil bath. To this was added 185 m1 HMPA (1.06 mol) at a rate of ca. 1-2 drops/sec. Distillation of the crude product into a dry ice-acetone cooled recieving flask (bp- 80- 110‘) began ca. 10 min. after starting the addition of HMPA. It was redistilled, bp- 94-96° (11c. 98-100°)87 to give 89.0 g (56% yield) of a clear liquid. 1H NMR (60 MHz, CDC13): 65.73 (m, 1H, HC), 5.13 (d, 94 1H, J - 14.0 Hz, Hd), 5.00 (broad s, 1H, H ), 3.47 (t, 2H, Ja - 10.0 dc d' b Hz, Ha), 2.65 (q, 2H, Jbaz chz 8.0 Hz, Hb). 4'-Acety1 3-buteny1 benzoate. CAUTION: This procedure also called for the use of HMPA. See preparation 4-bromo-l-butene for precautions. Following a proceedure developed by Pfeffer86, to a mixture of 0.82 g 4'-acetylbenzoic acid (0.0050 mol) and 0.30 g pulverised, anhydrous KOH (0.0053 mol) in 20 m1 anhydrous 1:1- HMPAzethanol was added 1.02 ml 4-bromo-l-butene (0.010 mol). After heating to reflux under a CaCl2 guard tube for 2 days, the reaction mixture was treated with an another 1.02 ml 4-bromo-1-butene and refluxed for a further 2 days. The progress of the reaction was monitored by t.l.c.; it could also be followed visually by the disappearance of undissolved 4'-acety1 potassium benzoate. Other experiments not presented in this Thesis showed that this type of reaction could also be implemented using the same number of equivalents of dimethyltetrahydropyrimidione instead of HMPA. The reaction mixture was then poured into 50 ml water and normalised by the addition of 1 fl HCl. The aqueous solution was extracted 4 times with ethyl ether, and the combined organic solution was washed 4 times with 10 ml saturated aqueous NaHCO3, 3 times with water, and 3 times with brine. After drying with MgSO4 and removal of the solvent under reduced pressure, the resulting yellow oil was 95 partially purified by column chromatography (40:60 - EtOAczhexanes) and finally by Kuegelrohr distillation (bpz 110°C /0.02 mm Hg) to give 0.64 g of a clear oil (59% yield). 1H NMR (300 MHz, CDC13): 68.06 (d, 2H, e- 8.0 Hz, H 7.95 (d, 2H, Je - 8.0 Hz, He), 5.86 (m, 1H, Hb), 5.14 f). Jf f (dt, 18, J - 1.6; J - 16.4 82, 8 ), 5.07 (dt, 18, J , z 1.5; J , - ac ab a a c a b 10.3 8z, Ha,), 4.35 (c, 28, Jdc- 6.0 Hz, Hd), 2.58 (s, 3H, Hg), 2.49 13 . (q, 28, Jcb~ ch- 7.4 8z, HC). 0 NMR. 6197.6, 165.7, 140.2, 134.1, 133.9, 129.7, 128.1, 117.4, 64.1, 32.7, 26.4. IR (0014): 3082, 2962, 1742, 1698, 1262, 1277, 832 em'l. EI-MS: m/z- 218 (8+°), 203, 177, 164, 149, 147 (base peak). 4'-Valery1 3-buteny1 benzoate. CAUTION: This procedure also caled for the use of HMPA. See preparation of 4-bromo-1-butene for precautions. A mixture of 3.00 g 4'-valeryl benzoic acid (0.0150 mol) and 0.89 g pulverised KOH (0.0159 mol) in 60 m1 1:1 - HMPAzethanol was treated with 4-bromo-1-butene in a mannor analogous to that used for the preparation of 4'-acety1 3-buteny1 benzoate86. Purification by column chromatography (Davisil 60; 50:50 EtOAczhexanes) gave 2.53 g of a pale yellow 611 (65% yield). 18 NMR (300 MHz 00013): 68.06 (d, 28, J 8 fe- 8. Hz, Hf), 7.95 (d, 2H, Je - 8.8 Hz, He), 5.82 (m, 1H, Hb), 5.13 (dt, 1H, f J - 1.7; J - 17.2 Hz, H ), 5.07 (dt, 1H, J , z 1.4; J , - 10.6 Hz, ac ab a a c a b Ha,), 4.36 (t, 2H, J dcz 6.4 Hz, Hd), 2.94 (t, 2H, Jgi- 7.4 Hz, Hg)’ 2.49 (tq, 2H, Jcaz Jca'z 1.6; chz Jcbz 6.6 Hz, HC), 1.67 (quin, 2H, Jigz Jij- 7.5 Hz, Hi)’ 1.36 (sex, 2H, inz ij- 7.5 Hz, Hj), 0.90 (t, 3H, ka- 7.3 Hz, Hk)' 13C NMR: 6200.3, 140.4, 134.0, 129.9, 128.0, 117.6, 64.2, 38.4, 32.9, 26.0, 22.1, 13.6. IR (0014): 3097, 2907, 1733, 1701, 1280, 1112, 862 em'l. EI-MS: m/z- 218, 214, 203 (base), 189, 164, 161, 149. 4'-Butyrylphenol. A mechanically stirred mixture of 38 g phenol (0.40 mol), 39 g butyric acid (0.40 mol), and 200 g polyphosphoric acid was heated 10 min in a boiling water bath88. The reaction mixture was then cooled in an ice-water bath, and rendered basic to red litmus paper by the careful addition of chilled 10 fl NaOH and NaOH pellets. After diluting to ca. 3 l to dissolve phenoxide salts, the aqueous solution was washed twice with ether and recooled in an ice-water bath. It was then treated with concentrated HCl until the persistence of a deep yellow colour in solution was noted. This solution was extracted repeatedly with ethyl ether (followed by t.l.c.), and the combined organic solution was washed twice each with 10% aqueous NaHCO water, 3 9 and brine. After drying with MgSOa and rotary evaporation of the 97 solvent, the crude product was recrystallised from 3:1 - petroleum etherzbenzene to afford 27.6 g (42% yield) of white crystals, mp- 90.0- 91.0°c (11:. 91°)89. 18 NMR (250 882; c0c13): 68.13 (s, 1H, Ha), 7.97 (d, 28, Jc - 9.0 82, He), 7.02 (d, 28, ch- 9.0 Hz, Hb), 2.94 (c, 28, b Jde- 7.0 Hz, Hd), 1.78 (sex, 2H, Jed: Jef- 7.5 Hz, He), 1'01 (t, 3H, er- 8.0 Hz, Hf). IR (CHZCIZ): 3571, 3333, 3071, 2969, 2938, 2878, 1678, 1607, 1590, 1516, 1414, 1267, 1171, 819 em‘l. EI-MS: m/z- 164 (M+°), 149, 136, 121 (base). 4'-Va1ery1phenol. In a manner similar to that used in the preparation of 4'-hydroxybutyrophenone88, valeric acid, phenol, and polyphosphoric acid were reacted to give, after work-up and recrystallisation, 31% yield of white crystals, mp- 59.8-61 0°C (lit. 62°)77. 18 NMR (60 MHz, cnc13): 68.39 (s, 18, Ha), 8.04 (d, 28, JC - 8.0 Hz, HC), 7.10 (d, 28, b c- 10.0 Hz, Hb), 3.05 (t, 2H, J e- 7.0 Hz, Hd), 1.2- 2.0 (complex, d gf- 6.0 82, Hg). IR (CH2C12): 3572, 3332, 3062, 2962, 2934, 2868, 1672, 1612, 1588, 1270, 1166, 842 em'l. EI-MS: Jb 48, He; Hf), 1.06 (c, 38, J m/z- 220 (8+'), 175, 163, 149, 136, 121 (base). 4'-Acetylpheny1 acetate. Esterification of 8.2 g 4'-acetylphenol (0.060 mol) was accomplished under Schotten-Baumen conditions78. The phenol was treated first with cold 14 fl NaOH (1.5 equivalents) and then with 1.08 g acetic anhydride (1.0 equivalent). Following work-up and recrystallisation from ethanol, this gave 5.30 g (50% yield) of white plates, mp- 50.0-51.5°C (lit. 54°)79. 1H NMR (300 MHz, CDC13): 67.97 (d, 2H, Jc - 8.5 Hz, Hc)’ 7.17 (d, 2H, ch- 8.5 Hz, Hb), 2.67 (s, 3H, b Hd), 2.40 (s, 3H, Ha). 13c NMR: 196.7, 168.5, 154.1, 134.3, 129 5, 121.4, 25.7, 20.2. IR (CCla): 1773, 1697, 1205, 1167, 851 em'l. EI- MS: m/z- 178, 136, 121 (base). UV-VIS (CH3OH): Amax- 247.5 nm; 15 000 A u‘l-em'l. €247.5- 4'-Butyrylpheny1 acetate. Esterification of 8.02 g 4'-butyrylpheno1 (0.050 mol) was accomplished by treatment with 14 fl NaOH followed by acetic anhydridego. Following basic work-up and recrystallisation from 9:1 - petroleum etherzbenzene, this gave 7.45 g (72% yield) of white crystals, mp- 28-29°C. 1H NMR (300 MHz, C0013): 68.20 (d, 2H, Job: 8.6 Hz, Hc), 7.20 (d, 2H, ch- 8.6 Hz, Hb), 2.88 (t, 2H, J e= 7.6 Hz, Hd), d 2.26 (s, 3H, Ha), 1.72 (sex, 2H, Jed: Jef- 7.5 Hz, He)’ 0.95 (t, 3H, 13 e- 6.9 Hz, H C NMR: 6199.3, 169.0, 154.3, 134.7, 129.7, 121.7, Jf f). 40.1, 20.7, 17.3, 13.4. IR (CCla): 2969, 2882, 1773, 1694, 1603, 1372, 1. 1200, 1165, 841 cm- EI-MS: m/z- 164 (8+'), 149, 136, 122, 121 (base), 93. UV-VIS (CH3OH): A - 205; 247 nm, 6 max - 85 A-u-1-cm-l. 5- 14 000; (2&7- 20 14 000; e313 4'-Va1ery1phenyl acetate. Esterification of 8.90 g 4'-va1ery1phenol (0.050 mol) with 14 fl NaOH and acetic anhydride90 followed by slow recrystallisation from petroleum ether-benzene gave 7.22 g of large, white rhombohedral crystals, mp- 26.2-27.1°C (66% yield). 1H NMR (300 MHz, CDC13): 68.02 (d, 2H, Jc - 8.8 Hz, HC), 7.20 (d, 2H, J - 8.8 Hz, b be Hb), 2.83 (t, 2H, J e- 7.4 Hz, Hd), 2.19 (s, 3H, Ha), 1.61 (quin, 2H, d Jedz Jef- 7.5 Hz, He), 1.30 (sex, 2H, erz Jfg- 7.5 Hz, Hf) 0.84 (t, 3H, Jgf- 7.4 Hz, Hg). 13C NMR: 6199.2, 168.8, 154.2, 134 5, 129.5, 121.6, 37.8, 25.9, 21.9, 20.5, 13.4. IR (CC1A): 2963, 2842, 1777, 1694, 1603, 1372, 1198, 1167, 847 em’l. EI-MS (25 eV): m/z- 218 (8+'), 100 7 203 (base), 189, 164, 162, 149, 147 (lit. spectra)9“. UV-VIS (heptane): 1 -l 1 - 204; 246 nm, e - 14 000; e - 12 000; e - 56 A-8' -cm max A 20 246 313 Phosphorescence emission (313 nm excitation, chopper rate- ca. 1 700 c.p.s., 77°K): 2-methy1tetrahydrofuran ([ketone]- 0.000092 u): A0 0- 394 nm, 5:1 - methanolzethanol ([ketone]= 0.00012 M): A0 o- 397 nm. ’ 4'-Acetylphenyl 3-butenoate. The 4'-acety1phenol was esterified with 4'-dimethy1aminopyridine (DMAP) and dicyclohexylcarbodiimide (DCC) according to the procedure of Alexanian93. To a solution of 0.75 g 4'-acety1phenol (0.0055 mol), 0.43 g vinyl acetic acid (0.0050 mol) and 0.030 g DMAP (0.00025 mol) in 15 ml dry CH2C12 under a CaCl2 guard tube was added 1.13 g DCC (0.0055 mol). After stirring at room temperature for ca. 1/2 h, an equal volume of hexane was added and stirring was continued for another 1/2 h. At the end of that time, the reaction mixture was filtered from a white precipitate, and the filtrate was quickly washed three times successively with 5 ml each of 5% aqueous acetic acid, water, 5% aqueous NaHCO water, and then finally once 3 I with brine. After drying with Na2C03 and then rapidly filtering the solution through a ca. 2 cm plug of Activity-1 neutral alumina, the solvent was removed at reduced pressure and room temperature, affording 101 0.61 g of a clear oil (60% yield), contaminated with traces of 4'-acetylphenyl trans-crotonate (vide infra). 1H NMR (300 MHz, CDC13): 67.98 (d, 2H, Jed. 8.9 Hz, He), 7.20 (d, 2H, J e= 8.9 Hz, Hd), 5.95 d (ddt, 18, J - 6.9; J - 10.1; Jba- 17.1 Hz, Hb), 5.22 (dq, 1H, Jaa s bc ba' ' Jae” 1.5; Jab- 17.1 82, Ha), 5.20 (dq, 18, Ja,az Ja,cz 1.3; Ja,b- 10.1 Hz, H ,), 3.29 (dt, 2H, J z J ,z 1.4; J - 6.8 Hz, H ), 2.58 (s, a ca ca cb c 3H, Hf). 13c NMR: 6197.1, 169.5, 154.4, 134.7, 129.9, 129.2, 121.6, 119.4, 38.6, 26.1. IR (CH2C12): 3065, 2938, 1763, 1688, 1601, 1428, -l .' 0 -V =V_ 842 cm . UV-VIS (C8308). Amax- 247.8 nm, e247.8- 13 000 A-8 J{ . The amount of the trans-crotonate isomer present in the product ester was determined by comparison of the integration of its signal in the 1H NMR spectrum at 61.96 93 (vide infra) to that of the 6,7- unsaturated isomer at 63.29. In the initally isolated ester, this was usually below 5.0%. Although relatively stable in the neat in silanized glassware at 0°C, it decomposed rapidly to the crotonate isomer in solution. Therefore, it was used immediately upon isolation. All attempts to completely remove this impurity- silica and alumina chromatography, distillation from silanized glassware washed with dilute ammonium hydroxide, (bp- 80-110°C/0.002 mm Hg), Diels-Alder 102 reaction with cyclopentadiene- only resulted in further isomerisation. Also see ”Photolysis Procedures" for additional considerations. 4'-Acetylpheny1 trans-crotonate. In a procedure similar to the one used for the preparation of 4'-acety1pheny1 3-butenoate93, ££éfl§' crotonic acid and 4'-acetylphenol were coupled to give, after recrystallisation from benzene/hexane, 79% of white crystals, mp- 67.8- 68.4‘C. 1H NMR (300 MHz, CDC13): 67.98 (d, 2H, Jed- 8.0 Hz, He) 7.20 (d, 2H, Jde- 8.0 Hz, Hd), 7.19 (m, 1H, Hb), 6.03 (broad d, 1H, Jcb- 14.7 Hz, Hc)’ 2.58 (s, 3H, Hf), 1.96 (dd, 3H, Jac- 1.7; Jab- 6.9 Hz, Ha)' 13C NMR: 6197.3, 164.4, 154.8, 148.1, 134.7, 130.0, 121.9, 121.8, 32.5, 30.6, 26.3, 26.1, 24.4, 18.0. IR (CH2C12): 3022, 2917, 2822, 1740, 1688, 1167, 1156, 862 cm‘l. EI-MS: m/z= 204 (8+'), 121, 111, 92, 77, 69 (base). UV-VIS (CH3OH): Amax- 248.5 nm; e248.5- 16 000 A-M-1'cm-1. o e d o Mk f ‘xq‘ o 4'-Butyrylphenyl 3-butenoate. In a procedure similar to that used for the preparation of 4'-acety1pheny1 3-butenoate93, a colourless oil was isolated after work-up in 83% yield. 1H NMR (300 MHz, CDC13): 67.95 (d, 2H, Jed. 7.5 Hz, He), 7.15 (d, 2H, J - 6.9; J c de- 7.5 Hz, Hd), 5.98 (ddt, 1H, Jb ba'- 10.2; Jba- 17.2 Hz, Hb), 5.25 (dq, 1H, Jaa'z Jacz 1.3; 103 Jab- 17.2 Hz, Ha), 5.23 (dq, 1H, Ja,az Ja,cz 1.4; Ja'b- 10.2 Hz, Ha')’ 3.22 (dt, 2H, J z J ,z 1.4; J — 6.9 Hz, H ), 2.88 (t, 2H, J - 7.3 ca ca cb c fg Hz, Hf), 1.72 (sex, 2H, Jgfz Jgi- 7.3 Hz, Hg)’ 0.95 (t, 3H, Jig- 7.4 Hz, H1). 13C NMR: 6199.1, 169.5, 154.2, 134.7, 129.6, 129.3, 121.6, 119.4, 40.0, 38.6, 17.2, 13.4. IR (CH2012): 3112, 2969, 1763, 1688, 1603, 1512, 1414, 842 em‘l. EI-MS (25 eV): m/z- 232 (8+'), 204, 189, 164, 147, 136, 121, 68 (base). UV-VIS (CH OH): Amaxg 205; 246.5 nm, 1 -l 3 - 13 000; 14 000; 6 - 120 A~8‘ -cm ‘205 €246.5- 313 o M a! o a C The amount of 4'-butyry1phenyl trans-crotonate initally present, as assayed by 1H NMR spectroscopy immediately after preparation, was compareable to the 4'-acety1phenyl ester case. 4-Pentenoic acid. Grignard reaction of 3-butenyl magnesium bromide with CO2 gas according to a procedure in the literature94 afforded the acid in 35% yield after distillation, bp- 89-91°C/ ~17 mm Hg (lit. 95- 97'/ 15 mm Hg)94 . The reaction was initiated by addition of a catalytic amount of 12. Carbon dioxide gas was generated from dry ice, passed through concentrated HZSO4 and afterwards anhydrous CaCl and 2 9 finally bubbled through the stirred solution overnight. 1H NMR 104 (300MHz, CDC13): 610.1 (broad s, 1H, He), 5.84 (ddt, 1H, J C- 6.2; b Jba'- 10.3; Jba- 17.1 Hz, Hb), 5.09 (dq, 1H, Jacz Jaa'z 1.6; Jab- 17.1 Hz, H ), 5.03 (dq, 1H, J , 2 J , z 1.4; J - 10.3 Hz, H ,), 2.44 (d, a a c a a a a 2H, Jdcz 5.9 Hz, Hd), 2.39 (q, 2H, Jcbz chz 6.3 Hz, HC). IR (CH2C12): 3508, 3090, 3070, 2990, 2934, 2674, 1712, 1642, 1434, 1418, 1288, 1262, 1222 cm-1. EI-MS: m/z- 100 (M+ ), 83, 55 (base). 4'—Acetylphenyl 4-pentenoate. In a procedure like that used for the preparation of 4'-acetylphenyl 3-butenoate93, a colourless oil was isolated in 59% yield after work-up and column chromatography (Davisil 60; 10:90 to 40:60 - ethyl acetatezhexanes). 1H NMR (300MHz, CDC13): 67.93 (d, 2H, J - 7.0 Hz, H ), 7.13 (d, 2H, J = 7.0 Hz, H ), 5.85 e f e e f f (ddt, 18, ch- 6.5; Jba,- 10.3; Jba- 17.1 82, Hb), 5.10 (dq, l8, Jaa,z Jacz 1.6; Jab- 17.1 Hz, Ha), 5.03 (dq, 1H, Ja'az Ja,cz 1.4; Ja'b- 10.3 82, 83,), 2.64 (c, 28, Jdc- 7.0 Hz, Hd), 2.53 (s, 3H, Hg), 2.45 (broad q, 28, J z J - 6.4 82, 8 ). 13c NMR: 6197.1, 171.2, 154.6, 136.2, cb cd c 134.8, 130.0, 121.8, 116.1, 33.3, 28.4, 26.3. IR (CH2C12): 3067, 3011, 2932, 1761, 1688, 1646, 1237, 1208, 863 em'l. EI-MS: m/z- 218 (8+'), 203, 161, 147, 137, 121, 83, 55 (base). UV-VIS (CH3OH): Amax- 248.0 -1 -1 nm, 6248- 14 000 A-fl -cm . 105 4'-Butyrylpheny1 4-pentenoate. Following a proceedure like that used to prepare 4'-acety1pheny1 3-butenoate93, a colourless oil was isolated in 84% yield after work-up and column chromatography (Davisil 60; 10:90 to 40:60 - ethyl acetate: hexanes). 1H NMR (300MHz, CDC13): 67.94 (d, 2H, J e- 8.6 Hz, H 7.13 (d, 2H, Je - 8.6 Hz, He), 5.85 (ddt, 1H, f)’ f - 10.2; Jba- 17.0 82, Hb), 5.10 (dq, 1H, Jaa,z Jacz 1.5 f ch- 6.6; Jba' 82, Ha), 5.04 (dq, 1H, Ja, z J z 1.3; Ja , a 10.2 Hz, H ,), 2.87 (t, a a c a 'b 2H, J - 7.3 Hz, Hg), 2.64 (t, 2H, J - 7.2 Hz, Hd), 2.46 (broad q, 2H, gi chz Jcb 3H, in- 7.4 Hz, H dc - 7.0 Hz, H ), 1.71 (sex, 2H, J. = J..- 7.4 Hz, H.), 0.95 (t, c 1g .13 1 ). 13C NMR: 6199.3, 171.2, 154.4, 136 2, 134 7, J 129.7, 121.8, 116.1, 40.2, 33.3, 28.5, 17.4, 13.5. IR (CH2C12): 3085, 2969, 2938, 2878, 1761, 1688, 1644, 1208, 1167, 1136, 842 em‘l. EI-MS: m/z- 247 (M+l+), 246 (8+'), 218, 203, 165, 147, 136, 121, 83, 55 (base). UV-VIS (CH3OH): Amax- 205; 247 5 nm, e - 88 wad-cm.1 = 16 000; 205 ‘247.5‘ 17 000; e313 100 5'-Acety1-2'-hydroxybenzoic acid. A modification of a known procedure for the Fries rearrangement of acetyl salicylic acid96 was employed to obtain this compound. A suspension of 35 g anhydrous aluminum chloride (0.26 mol) as additional dessicant in dry nitrobenzene (distilled from P20 ) was stirred for 1 h at RT under N To this 5 2' slurry was added an additional 17 g aluminum chloride (0.13 mol) and 15 g acetyl salicylic acid (0.083 mol). After stirring at RT for another hour, the reaction mixture was carefully poured onto cracked ice and 25 ml concentrated HCl. The nitrobenzene was removed by steam distillation, and the crude product was collected by suction filtration. Recrystallisation twice from 40:60 ethanolzwater then gave 7.7 g of white needles (51% yield), mp= 216.5-217.0° (lit. 216-217°)96. 1H NMR (60 MHz, DMSO-d6): 612.30 (broad s, 2H, Ha; Hb), 8.41 (d, 1H, Jedf 2.0 Hz, He), 8.09 (dd, 1H, Jde- 2.0; Jdc- 8.0 Hz, Hd), 7.07 (d, 18, ch- 8.0 82, He), 2.62 (s, 38, Hf). IR (KBr pellet): 3862, 3842, 2902, 2602, 2342, 2322, 1682, 1532, 842, 817 em'l. EI-MS: m/z- 180 (8+'), 165, 162, 147 base). 107 a rfl3fl3 HO 4 5'-Acetyl-2'-methoxybenzoic acid. The title compound was prepared according to the procedure of Kranichfeldt97. To a solution of 2.0 g 5'-acety1-2'~hydroxybenzoic acid (0.0111 mol) in 11.1 g 10% aqueous NaOH (0.0278 mol) was added 3.15 ml dimethylsulfate (0.0333 mol). This mixture was heated under reflux for 1/2 h and then cooled to RT. Treatment with NaOH solution and dimethylsulfate, followed by heating, was repeated two more times. A further 11.1 g of 10% NaOH was then added, and the reaction mixture was heated under reflux an additional 1/2 h. Finally, 0.93 g CaO (0.0166 mol) was added, followed by refluxing for ca. 2.5 h. The cooled mixture was filtered from calcium salts, the filtrate was re-acidified with 2 fl HCl and extracted repeatedly into ether. The combined ethereal extracts were washed with water, then saturated NaCl solution and dried over MgSO4 to give, after evaporation of the solvent under reduced pressure and recrystallisation from 50:50 - ethanolzwater, 1.49 g (70% yield) of white needles, mp- 148.5-150°c (lit. 152°)85. 18 NMR (CHCl3, 60 MHz): 69.20 (broad s, 1H, Ha), 8.62 (d, 1H, Jed- 2.0 Hz, He), 8.12 (dd, 1H, J - 2.0; J 9.0 e d dc' Hz, H 7.14 (d, 1H, ch- 9.0 Hz, Hc), 4.19 (s, 3H, Hb), 2.65 (s, 3H, d). H IR (CH2C12): 3330, 3080, 2956, 2858, 1761, 1690, 1616, 1432, f)' 108 1394, 837 cm-l. EI-MS: m/z- 194 (M+ ), 179 (base peak), 165, 161, 151, 147. “020 FhCO d 5'-Acety1-2'-methoxy allyl benzoate. In a procedure like that used for the preparation of 4'-butyrylphenyl 3-butenoate93, the title compound was obtained in 10% yield after passage through ca. 1.5 cm basic alumina, mp- 43.7-44.7 °C. 1H NMR (300MHz, CDC13): 68.39 (d, 1H, Jgf- 2.0 Hz, H8), 8.10 (dd, 1H, J - 2.0; J e- 8.8 Hz, Hf), 7.08 (d, 1H, fg f - 8.8 Hz, He), 5.98 (m, 1H, Hb), 5.37 (dt, 1H, JaC- 1.6; Jab- 17.3 a,b- 10.4 82, Ha,), 4.77 (d, 28, 13 Jcb- 5.5 Hz, Hc), 3.91 (s, 3H, Hd), 2.51 (s, 3H, Hi)' C NMR: 6196.3, 165.3, 162.9, 133.9, 132.7, 132.2, 129.7, 119 9, 118.4, 111.8, 65.5, Jef Hz, H ), 5.24 (dt, 1H, J , - 1.2; J a a c 56.1, 26.0. IR (CH2C12): 3088, 3024, 2936, 2854, 1738, 1692, 1612, 1562, 1270, 832 cm'l. 81-8s: m/z- 234 (8+'), 219, 205, 193, 179, 177 (base peak). UV-VIS (CH3OH): Xmax - 227.5, 268.0 nm; 6227.53 20 000; -1 -1 6268.0- 15 000 A-n ~cm . -r* 109 0‘ p. 5'—Acety1-2'-methoxy 3-butenyl benzoate. In a procedure like that used for the preparation of 4'-butyrylpheny1 3-butenoate93, this compound was obtained in 75% yield after purification by column chromatography (Davisil-60; 10:90 to 40:60 - EtOAczhexanes) instead of passage through basic alumina. Eventually, a small amount of oily solid with no clear mp formed in the sample. 1H NMR (CDCl 300 MHz): 68.49 (d, 1H, Jig- 3 9 2.4 Hz, Hi)’ 8.09 (dd, 1H, Jgi- 2.4; J - 8.0 Hz, Hg)' 7.07 (d, 1H, gf f8- 8.0 Hz,Hf), 5.99 (m, 18, 8b). 5.29 (d. 1H. Ja 5.23 (d, 1H, Ja’b- 10.4 Hz, Ha,), 4.48 (t, 2H, Jdca 6.6 Hz, Hd), 4.07 13 (s, 3H, He), 2.68 (s, 38, Hj), 2.64 (q, 2H, JC z J = 7.3 Hz, HC). c J - 18.6 Hz, H ), a b b cd NMR: 6196.2, 165.4, 162.7, 134.1, 133.7, 132.5, 129.5, 120.1, 117.3, 111.7, 63.9, 56.0, 32.8, 25.9. IR (CH2C12): 3075, 2944, 2852, 1730, 1684, 1605, 1503, 839 cm‘l. EI-MS: m/z- 248 (8+'), 233, 219, 194, 179, 177 (base), 165, 163, 147. UV-VIS (CHBOH): Amax- ca. 223, 1 -1 268 nm; e - 25 000; e - 16 000 A-8’ :cm 223 268 110 II, PHOTOLYSIS PROCEDURES A. G a sw e Solutions for photolysis were prepared and transferred using "Type A" volumetric glassware and glass syringes with stainless steel needles. Photolyses were carried out in 13 x 100 mm pyrex test tubes which were heated with a natural gas/oxygen torch 3 cm from the top and uniformly drawn out and constricted to a 16 cm length. All glassware used for photokinetic work was especially reserved only for that purpose. It was routinely cleaned by firstly rinsing 3 times with acetone and then boiling 2 - 4 h with a distilled water- Alcanox Detergent solution in a large pyrex jar. After rinsing 5 times with water, it was boiled briefly in clean distilled water. Finally, it was carefully rinsed 5 times and dried at 150°C in an oven reserved exclusively for that purpose. 5. Egggggggigg of Solutions Stock solutions were prepared by directly measuring weights or volumes into volumetric flasks and diluting to the mark. When necessary, further dilutions were implemented using the same technique. Syringes were used to transfer 2.40 ml aliquots to the photolysis tubes. 111 C. Degassing Photolysis tubes were attached to a 10- or 12- port degassing cow through l-holed #OO rubber stoppers, on line to a vacuum pump. The solutions were then gradually frozen over 10- 15 min by immersion in a liquid nitrogen bath and afterwards exposed to the vacuum for 10 min. After again isolating them from the vacuum, they were allowed to thaw at RT. This cycle was repeated a total of 3 times, whereupon the tubes were once again frozen, evacuated and sealed under vacuum by torch. A mechanical vacuum pump was used in all cases except for the 4'-butyrylpheny1 esters, which were sealed under a diffusion pump vacuum . D. Izzadiation Sealed photolysis tubes were irradiated in parallel in a merry-go- round turntable which revolved around a Hanovia 450 W medium pressure mercury lamp and rested in a large water bath. The lamp was inside of a water-cooled quartz jacket, in turn immersed in a 0.002 H K2Cr04-l% 120 R CO solution, which served to isolate the 313 nm emission band . 2 3 E. Analzgis Post-photolysis solutions were analysed using either gas- or high performance liquid- chromatography. 112 In the former case, either a Varian Aerograph-l400 chromatograph equipped with 15 m Megabore DB-l or 30 m Megabore DB-Wax columns, or a Varian-3400 chromatograph outfitted with a 15 m Megabore DB-210 column were used, with He carrier gas (flow rates: DB-l: 25, DB-Wax: 30, DB- 210: 25 ml/min). The chromatographs were connected to Hewlett-Packard —3392A or -3393A integrating recorders. On-column injection and flame ionisation detectors employing H and compressed air were used at all 2 times. Individual G.C. analysis conditions can be found in Table 13 (vide infra) and with the separate experiments in the Appendix. In the later instance, a system composed of a Beckman/Altex 332 Programable Gradient Controller, 2 Beckman 110A Solvent Pumps, a Perkin-Elmer LC 75 Ultraviolett-Visible Detector, a DuPont 860 Column Compartment and an Hewlett-Packard 3380A integrating recorder was used with either Altex-25 cm Ultrasphere-ODS Octyl Reverse Phase or Rainin Dynamax Microsorb-ZS cm Phenyl Reverse Phase columns. E. Iegfigigues £0; 4’-Aczlphenzl 3-Butenoate Esters The instability of these compounds in solution necessitated that the preparation of their photolysis- or calibration- solutions, degassing, irradiation, and analyses be carried out without interruption. The solutions were also kept at 0°C or lower during and after photolysis. Any deviation from these protocol resulted in the partial isomerisation of the photosubstrate and photoproduct. Comparison of pre- and post- irradiation HPLC chromatograms revealed that, within experimental error, no decomposition occurred during 113 photolysis. As an additional precaution, fresh batches of each ester were prepared immediately prior to photolysis or instrument calibration. TECHNI E D CALCULATIONS A. Stern-Volmer Quenching In a typical experiment, a 10 ml stock solution of ketone substrate and appropriate internal standard was prepared and 1 m1 aliquots were pipetted into a series of 5 ml volumetric flasks. To these were added varying amounts of quencher stock solution and the flasks were diluted to the mark. After irradiation, the ratio of photoproduct concentration in an unquenched solution to that in a given quenched solution was equal to the quantum yield ratio. A plot of 00/0 against quencher concentration75 thus yielded a straight line with slope of qu and intercept of 1. e ' ro a u tum Yield Versus Ketone Concentration Varying amounts of a photosubstrate stock solution were added to 1 ml aliquots from an internal standard stock solution and the resulting solutions diluted to 5 ml. In a kinetic paradigm similar to the Stern- Volmer case, a plot of reciprocal quantum yield against ketone concentration gave a straight line with slope equal to k. inter/(krp) and intercept equal to 1/¢ - l/P(l + kd/kr), where ki was the rate LIM nter 114 constant for ground state quenching50’8l by both the a,fi- and 6,7- unsaturated isomers of the ketone and QLIM was the quantum yield for Type II cleavage in the absence of this effect. C. t d Versus Additive Concentration Varying amounts of an additive stock solution were added to 1 ml aliquots from a photosubstrate-internal standard stock solution in 5 m1 volumetric flasks. D. Ehogogrodgct Concentration The concentration of the appropriate acetophenone photoproduct, AP' was determined by comparison of its area on the integrating recorder to that of an internal standard present in the photolysis solution in known concentration. The concentration of the photoproduct is thus described by Equation 17, where Ai's represent the relevent integrator areas and R.F., the response factor, is the area/mole ratio of the [AP'] - (A /A ) x [standard] x R.F. (17) pdct std standard relative to that of the photoproduct. GC- and HPLC- response factors were assayed from solutions of known concentrations under identical analysis conditions. These values on the pertinent experimental equipment are summarised in Table 13. 115 Table 13. Gas Chromatographic- and HPLC- Photoproduct Response Factors Standard/Product (Area/mole)std # Trials (Area/mole)pdct hexadecane/APa 2.20i0.04 3 noctyl benzoate/QCOZallylAPb 1.62:0.03 3 noctyl benzoate/pcozprenylAPc 1.38:0.02 , 1 nheptyl benzoate/ECOZbutenylAPd 1.60:0.02 l nbutyl benzoate/pOAcAPe 1.53:0.04 4 nheptyl benzoate/pOAcAPf 1.62:0.01 l ethyl benzoate/pObutenoateAPg 0.127:0.001 1 npropyl benzoate/pObutenoateAPh 0.118i0.001 1 noctyl benzoate/pOpentenoateAPi 1.72:0.05 4 a: acetophenone (DB-Wax column (110°)). b: 4'-acetyl allyl benzoate (DB-210 00 column; 80° (2 min), then to 150° (50°/min)). C: 4'-acety1 prenyl benzoate (analysis same as pCOzallylAP). d: 4'-acety1 3-butenyl benzoate (DB-210 00 column; 80° (2 min), then to 160° (50°/min)). e: 4'-acetylpheny1 acetate (DB-l GC column (110°)). f: with pOAcVP- benzene Stern-Volmer experiments (DB-210 GC column; 80° (2 min), then to 140° (50°/min)). 8: 4'-acetylpheny1 3-butenoate; Stern-Volmer experiments (ODS-octyl reverse phase HPLC column; CHBOH-HZO mobile phase; 250 nm detection). h: reciprocal quantum yield experiments (phenyl reverse phase HPLC column; CH CN-H 0 mobile phase; 250 nm 3 2 detection). 1: 4'-acetylpheny1 4-pentenoate (DB-l GC column (145°)). 110 E. Quantum Yields The absolute quantum yields for the formation of acetophenone photoproducts at 313 nm, from the photosubstrates studied, AP', were determined by parallel irradiation of valerophenone actinometer solutions in benzene16. The quantum yield of valerophenone under the VP is known to follow the simple dependence on valerophenone concentration described in Equation 1813. current conditions, ¢II 6IIVP - 0.30[vp] + 0.30 (18) The unknown quantum yield, 0 is obtained through Equation 19, where 11’ AP stands for simple acetophenone. The factor (1-TVP)/(1-T), where TVP and T were the optical transmissions of valeropheone and the photosubstrate respectively, is a correction factor allowing for VP , VP ¢II - QII ' [AP l/[AP] ' (l'T )/(1'T) (19) incomplete light absorption by valerophenone or the photosubstrate. The acetophenoen photoproduct under analysis is denoted by AP'. Corrections for this phenomenon were necessary in the quantum yield measurements from the 0 -1 versus [photosubstrate] experiment where II photosubstrate concentration was 0.02 H or lower and all of the quantum yields from the 01 versus [pyridine] experiment. I 117 IV SPECTRA A. oton NMR ectra Spectra of synthetic intermediates were usually recorded with a Varian T-60 Continuous Wave Spectrometer in CDCl previously stored 3 over anhydrous K2C03 with tetramethylsilane reference absorption at 60.0. Photsubstrate spectra were taken with 250 MHz Bruker- or 300 MHz Varian/Gemini- Fourier Transform Spectrometers. In those cases, the 1H-signal from the solvent provided the appropriate reference signal at 67.24. 8. Carbon NMR Spectra Carbon-13 spectra were recorded on the Varian/Gemini Spectrometer in CDC13, referred to the CDCl3 signal at 677.0. C. t v e - V's'ble S ctra Spectra were recorded on a Shimadzu UV-VIS Recording UV-l6 Spectrophotometer in 1 cm quartz Beckman cells. Solvents used were photolysis methanol or Mallinckrodt Specrophotometric Grade nheptane. Background correction was implemented by running a blank of the same cell filled with pure solvent. 118 D. Infrared Spectra Spectra were recorded in a KBr solution cell with spectrograde CCla, CHCl3 or CH2C12 or as KBr pellets on a Perkin-Elmer Model 237 B Grating Spectrometer or a Nicolet IR/42 Fourier Transform Spectrometer controlled by a Dell System 2000 - IBM/30$ Upgrade Unit computer and outputted to a Hewlett-Packard ColorPro Plotter. On the latter instrument, the solution spectra were blanked by the pure solvent. Spectra were calibrated to the 1603 cm-1 absorption of polystyrene121 Mass spectra were recorded on a Finnigan 4000 GC/MS system using the direct inlet mode by Kenneth Rehder or Ernest Oliver. F. Eposphorescence Spectra Phosphorescence spectra were recorded from ca. 10.4 M solutions at 313 nm excitation wavelength at 77°K in 5 mm diameter pyrex NMR tubes. A Perkin-Elmer MPF-44A Fluorescence Spectrometer, scanning at a rate of 120 nm/min and filtered by a chopper rotating at a rate of 1 700 cycles/sec, was outputted to a Hewlett-Packard 3393A integrating recorder. Phosphorescence grade solvents were kindly provided by Dr. J. DeFrancesco. 119 V NMR TUBE IRRADIATIONS A. Sample Prepagation A pyrex WG-XR-SS NMR tube was drawn out and constricted with a torch. Approximately 0.2 m1 of the appropriate concentration of ketone, usually in methanol-d4 containing traces of benzene-d (to 6 lessen the rate of expansion of the solutions upon thawing), was added to this through a syringe. The top of the tube was fitted tightly with the wider end of a small rubber septum and several small, fine needles were inserted partially into the tube through the septum. The top of the septum was pushed into the hole of a rubber stopper on a vacuum cow. Contact with the vacuum line was maintained through the needles. The solutions were then degassed and sealed in vacuum as previously described. B. Sggplg lgradiation and Monitoring Degassed and vacuum-sealed NMR tubes were irradiated directly outside of a Hanovia medium pressure mercury lamp outfitted with a quartz water jacket and a pyrex sleeve. The irradiations were intermittantly stopped and the 1H NMR spectra recorded on the 250 MHz Bruker instrument. 120 C. Individual Runs 4'-Acetyl allyl benzoate/benzene-d A 0.03 M solution was degassed by 6' bubbling with Ar gas and irradiated up to 6.5 h. Spectra recorded throughout the irradiation indicated the appearance of minor signals at 65.88 (dd), 4.44 (dd) and 4.06 (dq) as well as 61.9 (s), 1.55 (d), and 1.52 (d?). The vinyligous and allylic signals of the starting ketone remained essentially unchanged. A large amount of insoluable material was present on top of the solution at the conclusion of the experiment. Analysis of the photolysis solution by analytical t.l.c. revealed only traces of the starting material in addition to large amounts of non- eluting material. 4'-Acetyl allyl benzoate/methanol-d A 0.055 M solution, degassed and 4. sealed under vacuum, was irradiated up to 15 h. Intermittant spectra revealed the gradual disappearance of the acetyl group in the starting material and the appearance of aromatic doublets at 67.29, 7.52, 7.77 and 7.88, as well as other signals at 61.48, 1.52, 1.62 and 2.19. The signals from the allylic tether remained essentially unchanged. A large amount of insoluable material was present at the end of the photolysis. 4'-Acety1 3-buteny1 benzoate/methanol-d A 0.044 M solution, degassed 4. and sealed under vacuum, was irradiated up to 13 h. Intermittant spectra showed the build up of signals in the 60.2 region, concomittant with the formation of a white, insoluable material. 4'-Acetylphenyl 3-butenoate/methanol-d A 0.03 M solution of freshly 4. prepared 4'-actylpheny1 3-butenoate, degassed and sealed under vacuum, 121 was irradiated for 12 h. Spectra recorded at intervals of 1, 4 and 12 h indicated the replacement of the aromatic peaks in the starting material with peaks at 67.81 (d) and 6.78 (d) along with an increase in the complexity of the peaks in the 65.8-6.0 and 5.0-5.3 regions with irradiation time. Analysis of the photolysis mixture by GC (DB-1 column, column temperature- 120°C) showed only the starting material and slight traces of broad peaks at higher retention times. 5'-Acety1-2'-methoxy allyl benzoate/methanol-d A 0.0029 M solution, 4. degassed and sealed under vacuum, was irradiated up to ca. 100 h. Spectra recorded at 4, 25 and 100 h showed the gradual disappearance of the starting ketone, concomittant with the appearance of miscellaneous peaks in the 60.9 to 2.5 region. An insoluable material was present in solution at the conclusion of the experiment. S'-Acety1-2'-methoxy 3-buteny1 benzoate/methanol-d A 0.0030 M 4. solution, degassed and sealed under vacuum, was irradiated up to 100 h. Spectra recorded at 4 and 25 h showed the gradual disappearance of the starting material, concomittant with the appearance of peaks in the 61.0 to 2.3 region. A film was present on the surface of the solution by the end of the irradiation. V 0 EC ICS CALCULATIONS Molecular mechanics calculations were implemented on a IBM PC/XT computer with an enhanced graphics adapter. The MMX87 program, distributed by Serena Software, Bloomington, Indiana/ 47402 was used. The input files were generated by the STRPI/MIOSTR subroutine and 122 SERENA configuration file and were submitted for processing by the MAKESTM subroutine. Output structures were created by the MIOGRFX subroutine. The MMX87 program featured open shell enhanced PI subroutines and improved torsional constants for esters (relative to the older, MMPI program). As well, it specified only one lone pair of electrons for ester oxygens. The lowest energy conformations of 4'-acetylphenyl 3-butenoate and 4'-acetyl allyl benzoate were determined from restricted HartreeoFoch calculations on their ground state, singlet STRPI/MIOSTR structures. All oxygen atoms and spZ-hybrid carbon atoms were declared P1 atoms and 14- and 12- PI electrons were alotted to each, respectively. The ester twisting calculations were implemented through the introduction of dihedral angle drives about the C-C-O-C dihedral angle of the ester bond 5 to the aromatic ring. The STRPI/MIOSTR input structures were otherwise unchanged from before. The angle drives were specified to rotate from 180° (trans-coplanar) to 0° (pig-coplanar) in 10° increments. Thus, the otherwise lowest energy conformations for a total of 19 structures for each were calculated in the second set of experiments. APPENDIX 123 Table 14. Quenching of Acetophenone Formation from 4'-Valeryl Allyl Benzoate with 2,5-Dimethyl-2,4-Hexadiene in Benzene gun #1,- Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature: ambient column: DB-210; 80° for 2 min, then to 150° at 50°/min; peak width- 2.0. internal standard: n-octyl benzoate [standard]- 0.0031 M 1 qu- 52:2 M @113 0.21 3 3 o 10 x[Q], AP'/standard 10 x[AP'], 0 /¢ M area ratio M 0 0.381 1.90 1.00 2.90 0.287 1.43 1.34 5.80 0.265 1.32 1.45 11.6 0.214 1.07 1.79 20.4 0.173 0.863 2.22 30.6 0.1376 0.686 2.80 40.8 0.1116 0.554 3.47 Actinometer: [VP]- 0.17 M wavelength- 313 nm temperature: ambient internal standard: hexadecane [standard]- 0.020 M 3 3 AP/standard 10 x[AP], 10 x1 area ratio M a 0.706 3.0 8.7 124 Table 14 (cont'd.) Rug #2; Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: see Run #1 internal standard: n-octyl benzoate [standard]- 0.0033 M k r- 5814 8’1 6 = 0.16b q 11 3 3 o 10 x[Q], AP'/standard 10 x[AP'], Q /¢ M area ratio M 0 0.208 1.02 1.00 3.04 0.176 0.862 1.18 6.08 0.134 0.654 1.56 12.16 0.128 0.626 1.63 20.8 0.0929 0.455 2.24 31.1 0.0729 0.357 2.86 Actinometer: [VP]- 0.103 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.010 M 3 3 AP/standard 10 x[AP], 10 x1 area ratio M a 0.0932 6.2 6.2 125 Table 15. Quantum Yield of Acetophenone Formation from 4'-Valery1 Prenyl Benzoate in Benzene Photosubstrate: [ketone]- 0.029 M wavelength- 313 nm temperature- ambient column- DB-210; 80° for 3 min, then to 150° at 50°/min, then hold at 150° for 10 min; peak width- 2.0 until 14 min, then peak width- 32. internal standard: n-octyl benzoate [standard]- 0.0047 M 011- 0.247 AP'/standard 103x[AP'], area ratio M 0.3220 0.0211 Actinometer: [VP]- 0.111 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.010 M AP/standard 103x[AP], 103xIa area ratio M 0.128 2.90 8.70 128 Table 16. Quenching of Acetophenone Formation from 4'-Valeryl 3-Butenyl Benzoate with 2,5-Dimethyl—2,4-Hexadiene in Benzene 888.211 Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: DB-210; 80° for 2 min, then to 160° at 50°/min, then hold at 160° for 8 min; peak width- 2.0 up to 8 min, then peak width- 16. . internal standard: n-octyl benzoate [standard]- 0.0015 M k 1- 60:2 8'1 6 - 0.18 q 11 3 3 o 10 x[Q], AP'/standard 10 x[AP’], ¢ /¢ M area ratio M 0 1.18 2.26 1.00 1.06 1.071 2.05 1.10 2.12 0.975 1.86 1.22 4.23 0.89 1.70 1.33 10.6 0.720 1.38 1.64 21.2 0.519 0.992 2.28 Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.010 M 3 3 AP/standard 10 x[AP], 10 x1 area ratio M a 0.188 4.14 12. Table 16 (cont'd.) Run #2; Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: see Run #1 127 internal standard: n—octyl benzoate [standard]- 0.0015 M k 2- 62:2 8'1 6 - 0.18 q 11 3 3 o 10 x[Q], AP'/standard 10 x[AP'], Q /¢ M area ratio M 0 1.04 2.04 1.00 2.02 0.801 1.56 1.30 4.03 0.771 1.50 1.35 8.06 0.648 1.26 1.60 20.3 0.464 0.905 2.24 Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.0100 M 3 3 AP/standard 10 x[AP], 10 x1a area ratio M 0.170 3.74 11.3 128 Table 17. Quenching of Acetophenone Formation from 4'-Valerylpheny1 Acetate with 2,5-Dimethyl-2,4-Hexadiene in Benzene Rug #1; Photosubstrate: [ketone]- 0.032 M wavelength- 313 nm temperature- ambient column- DB-210; 80° for 2 min, then to 140° at 50°/min, then held at 140° for 15 min; peak width- 2.0. internal standard: n-heptyl benzoate [standard]- 0.0020 M l k r- 7622 8' 6 - 0.269 q 11 3 , 3 , o 10 x[Q], AP /standard 10 x[AP ], 0 /0 M area ratio M 0 0.430 1.41 1.00 2.00 0.356 1.19 1.19 5.99 0.291 0.973 1.45 12.0 0.225 0.753 1.87 16.0 0.192 0.643 2.19 Actinometer: [VP]- 0.11 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.011 M 3 3 AP/standard 10 x[AP], 10 :11a area ratio M 0.073 1.7 5.2 Table 17 (cont'd.) Egg #2 -, Photosubstrate: [ketone]- 0.040 M wavelength- 313 nm temperature- ambient column: see Run #1 129 internal standard: n-heptyl benzoate [standard]- 0.0020 M 1 qu- 77i2 M 611- 0.28 3 3 10 x[Q], AP'/standard 10 x[AP'], 6 /¢ M area ratio M O 0.54 1.8 1.0 4.00 0.3585 1.19 1.51 8.00 0.326 1.08 1.67 12.0 0.259 0.860 2.09 16.0 0.222 0.737 2.44 20.0 0.201 0.667 2.77 36.0 0.140 0.465 3.87 40.0 0.130 0.432 4.17 Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.010 M 3 3 AP/standard 10 x[AP], 10 xIa area ratio M 0.096 2.1 6.4 130 Table 18. Dependence of Quantum Yield of Acetophenone Formation from 4'-Valerylphenyl Acetate on Concentration of Pyridine in Benzene Photosubstrate: [ketone]- 0.031 M wavelength- 313 nm temperature- ambient column: DB-l, 110°; peak width- 0.16. internal standard: n-butyl benzoate [standard]- 0.00120 M 6 °- 0.27 (from Table 17, Run #1) 6 - 0.756 11 MAX [0 8 N], 8 AP'/standard 104x[AP'], 6 6 5 . 11 area ratio M 0.119 0.218 4.00 0.457 0.237 0.285 5.23 0.597 0.356 0.320 5.88 0.670 0.474 0.338 6.21 0.706 0.990 0.3612 6.63 0.756 1.98 0.344 6.32 0.720 2.97 0.322 5.91 0.695 Actinometer: [VP]- 0.077 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.0936 M AP/standard 103x[AP], 103xI a area ratio M 0.0137 2.8 8.7 131 Table 19. Quenching of Acetophenone Formation from 4'-Va1ery1phenyl Acetate with 2,5-Dimethyl-2,4-Hexadiene in 4:1- Methanol:Benzene Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column- see Table 18, Run #1. internal standard: n-butyl benzoate [standard]- 0.0013 M 1 k r- 188:6 8' 6 - 0.82 q 11 4 3 o 10 x[Q], AP'/standard 10 x[AP'], 6 /¢ M area ratio M 0 0.76 1.4 1.0 8.31 0.619 1.18 1.22 16.6 0.537 1.04 1.39 24.9 0.481 0.927 1.55 41.6 0.3938 0.759 1.89 83.1 0.297 0.573 2.51 124.7 0.216 0.417 3.45 Actinometer: [VP]- 0.077 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.0094 M AP/standard 103x[AP], 103xI area ratio M a 0.028 0.57 0.17 132 Table 19, (cont'd.) RM; #2; Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: see Table 18, Run #1. internal standard: n-butyl benzoate [standard]- 0.0017 M 011- 0.86 AP'/standard 103x[AP’], area ratio M 0.62 1.63 Actinometer: [VP]- 0.11 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.010 M AP/standard 103x[AP], 10 xIa area ratio M 0.026 0.59 1.79 ”:1" 133 Table 20. Quenching of Acetophenone Formation from 4'-Butyry1pheny1 Acetate with 2,5-Dimethyl-2,4-Hexadiene in 4:1- Methanol:Benzene Mug #1, -, Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: see Table 18, Run #1. internal standard: n-butyl benzoate [standard]- 0.0016 M k r- 2 3002100 8'1 6 - 0.55 q 11 5 3 o 10 x[Q], [AP']/standard 10 x[AP'], 6 /¢ M area ratio M 0 1.15 2.74 1.00 5.18 0.9584 2.27 1.20 10.4 0.894 2.12 1.29 15.6 0.756 1.79 1.53 20.7 0.705 1.69 1.64 31.1 0.661 1.57 1.75 41.4 0.547 1.30 2.10 51.8 0.524 1.24 2.20 62.2 0.463 1.10 2.49 Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.0092 M AP/standard 103x[AP], 103x1a area ratio M 0.081 1.6 5.0 134 Table 20 (cont'd.) Rug #2; Photosubstrate: [ketone]- 0.033 M wavelength- 313 nm temperature- ambient column: see Table 18, Run #1. internal standard: n-butyl benzoate [standard]- 0.0016 M k r- 2 600:200 5'1 0 - 0.68 q II 4 3 , o 10 x[Q], AP'/standard 10 x[AP ], Q /Q M area ratio M 0 1.241 3.00 1.00 1.15 0.90 2.17 1.38 1.72 0.79 1.9 1.5 2.30 0.597 1.4% 1.68 3.44 0.5456 1.32 1.83 4.59 0.4423 1.07 2.26 Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.0092 M 3 3 AP/standard 10 x[AP], 10 xIa area ratio M 0.071 1.4 4.3 135 Table 21. Quenching of Acetophenone Formation from 4'-Butyry1pheny1 3-Butenoate with 2,5-Dimethy1-2,4-Hexadiene in 4:1- Methanol:Benzene Mug #1; Photosubstrate: [ketone]- 0.030 M (containing 4.1% crotonate isomer) wavelength- 313 nm temperature- 0°C column: Altex-Ultrasphere-ODS octyl reverse phase HPLC column; 4.6 mm diameter x 25 cm length; UV detection at 250 nm; solvent gradient program (%methanol in water; flow rate- l.0 ml/min): 62%, then at 10 min to 90% over 2 min, then at 15 min to 95% over 0.5 min, then at 15.5 min to 62% over 3.5 min, stayed at 62% untill 26 min; 35°C. internal standard: ethyl benzoate [standard]- 0.019 M 1 qu- 390 M ¢II- 0.13 4 4 o 10 x[Q], M AP'/standard 10 x[AP'], ¢ /¢ area ratio M 1.92 0.1838 4.51 1.08 2.87 0.1762 4.32 1.12 3.83 0.175 4.29 1.13 5.75 0.1637 4.01 1.21 7.66 0.1520 3.73 1.31 Actinometer: [VP]- 0.11 M wavelength— 313 nm temperature- 0°C internal standard: hexadecane [standard]- 0.010 M 3 3 AP/standard 10 x[AP], 10 x18 area ratio M 0.053 1.2 3.66 136 Table 21 (cont'd.) Run #2; Photosubstrate: [ketone]- 0.030 M (containing 3.9% crotonate isomer) wavelength- 313 nm temperature- 0°C column: see Run #1 internal standard: ethyl benzoate [standard]- 0.013 M -1 qu- 420 M ¢II- 0.11 4 4 o 10 x[Q], M AP'/standard 10 x[AP'], Q /¢ area ratio M 0.00 0.310 4.96 1.00 4.92 0.2608 4.17 1.19 9.84 0.2087 3.34 1.48 14.8 0.183 2.93 1.70 19.7 0.1622 2.60 1.91 29.5 0.137 2.19 2.26 39.5 0.1166 1.87 2.65 Actinometer: [VP]- 0.11 M wavelength- 313 nm temperature- O’C internal standard: hexadecane [standard]- 0.010 M AP/standard 103x[AP], 103xI a area ratio M 0.063 1.44 4.34 137 Table 22. Dependence of Quantum Yield of Acetophenone Formation from 4'-Butyry1pheny1 Butenoate on Concentration of Photosubstrate in 4:1-Methanol:Benzene Photosubstrate: [ketone]: see following table wavelength- 313 nm temperature- 0°C column: Dynamax Microsorb-phenyl bonded phase 4.6 x 250 mm reverse phase HPLC column; UV detection at 250 nm; solvent gradient program (% acetonitrile in water; flow rate- 1.0 ml/min): 3 min, then at 22 min to 36% over 0.5 min, stayed at 36% untill 28 min; 35°C. internal standard: n-propyl benzoate [standard]- 0.0063 M 6%, then at 15 min to 50% over 0.5 - + a = + '1 a ¢LIM 0.1192_0.0009 slope 62-1 M 4 -1 [Ketone], AP'/standard 10 x[AP'], é o . II II M area ratio M 0.01002 0.8214 5.28 0.104 9.62 0.03008 0.778 5.00 0.0980 10.2 0.04058 0.724 4.65 0.0912 11.0 0.06087 0.6534 4.20 0.0823 12.2 0.08116 0.594 3.82 0.0749 13.4 8: QLIM is ‘11 at infinite dilution, taken from line equation of plot of reciprocal quantum yield versus starting ketone concentration. Actinometer next page 138 Table 22, Run #1 (cont'd.) Actinometer: [VP]- 0.010 M wavelength- 313 nm temperature- 0°C internal standard: hexadecane [standard]- 0.00933 M AP/standard 103x[AP], 103xI a area ratio M 1.6 5.1 0.082 139 Table 22 (cont'd.) Run #2; Photosubstrate: [ketone]: see following table wavelength- 313 nm temperature- 0°C column: see Run #1 internal standard: n-propyl benzoate [standard]- 0.0061 M -1 a - + a - + ¢LIM 0.119_0.001 slope 76-3 M 4 -1 [Ketone], AP'/standard 10 x[AP'], 0 Q II II M area ratio M 0.01018 1.046 7.58 0.102 9.80 0.02036 1.008 7.30 0.0984 10.2 0.03054 0.975 7.06 0.0952 10.5 0.04024 0.908 6.58 0.0887 11.3 0.06035 0.784 5.68 0.0766 13.1 0.08047 0.706 5.12 0.0690 14.5 a . . ¢LIM and slope calculated as in Run #1. Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- 0°C standard- hexadecane [standard]- 0.0032 M AP/standard 103x[AP], 103xI a area ratio M 0.035 0.24 0.74 2 5 1 140 Table 23. Quenching of Acetophenone Formation from 4'-Va1ery1ph§ny1 Acetate with Methyl Crotonate in 4:1-Methanol:Benzene Baa_£1; Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: see Table 18, Run #1. internal standard: n-butyl benzoate [standard]- 0.0013 M k 1- 33:3 5'1 0 - 0.87 q 11 3 3 o 10 x[Q], AP'/standard 10 x[AP'], 0 /0 M area ratio M 0 1.77 3.37 1.00 3.20 1.66 3.31 1.07 5.34 1.495 2.98 1.18 10.7 1.32 2.63 1.34 Actinometer: [VP]- 0.11 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.010 M 3 3 AP/standard 10 x[AP], 10 xIa area ratio M 0.057 1.3 3.9 141 Table 23 (cont'd.) BED—#1.}. Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: see Table 18, Run #1. internal standard: n-butyl benzoate [standard]- 0.0013 M k r- 3312 5'1 q 3 3 o 10 x[Q], AP'/standard 10 x[AP'], 0 /¢ M area ratio M 0 1.11 1.89 1.00 3.04 0.905 1.78 1.07 6.08 0.84 1.6 1.1 15.2 0.708 1.33 1.33 18.2 .0.621 1.21 1.55 30.4 0.478 0.936 2.01 Actinometer: none 142 Table 24. Quenching of Acetophenone Formation from 4'—Butyry1phenyl 4-Pentenoate with 2,5—Dimethy1-2,4-Hexadiene in 4:1- Methanol:Benzene Emil; Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: DB-l; 145° internal standard: n-octyl benzoate [standardl- 0.0010 M k r- 2 300:200 8‘1 8 - 0.37 q II 5 4 o 10 x[Q], AP'/standard 10 x[AP'], ¢ /¢ M area ratio M 0 0.409 7.03 1.00 7:91 0.330 5.67 1.24 15.8 0.2616 4.50 1.56 23.7 0.245 4.21 1.67 31.7 0.206 3.54 1.99 47.5 0.1840 3.17 2.22 63.3 0.167 2.87 2.45 Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.0093 M 3 3 AP/standard 10 x[AP], 10 XIa area ratio M 0.031 0.64 1.93 143 Table 24 (cont'd.) 3211112.; Photosubstrate: [ketone]- 0.030 M wavelength- 313 nm temperature- ambient column: see Run #1 internal standard: n-octyl benzoate [standard]- 0.00090 M 1 k r- 24001100 5' 0 - 0.42 q 11 5 4 o 10 x[Q], AP'/standard 10 x[AP'], 0 /¢ M area ratio M 0 0.579 8.52 1.00 7.40 0.4307 6.67 1.32 22.2 0.380 5.85 1.50 29.6 0.324 5.00 1.76 44.4 0.269 4.14 2.12 59.2 0.228 3.51 2.50 Actinometer: [VP]- 0.10 M wavelength- 313 nm temperature- ambient internal standard: hexadecane [standard]- 0.00316 M 3 3 AP/standard 10 x[AP], 10 x1a area ratio M 0.097 0.67 2.0 BIBLIOGRAPHY 10. 11. 12. 13. 14. 15. 16. 144 B 12 B I. 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