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Photochemistry of Diels-Alder adducts Gayler, Rudolf Erich 1973

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\ PHOTOCHEMISTRY OF DIELS-ALDER ADDUCTS BY RUDOLF ERICH GAYLER d i p l . Chem. ETH, Zur i c h , 1968 M.Sc, U.B.C., Vancouver, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of CHEMISTRY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1973 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada ABSTRACT The photochemistry of a v a r i e t y of Di e l s - A l d e r adducts of general structure I has been inve s t i g a t e d . The adducts chosen for study were those formed between the dienophiles p-benzoquinone, 1,4-naphthoquinone, and duroquinone and the dienes 2,3-dimethylbutadiene, trans,trans-2,4-hexadiene, 2-methylbutadiene, and 1,3-pentadiene. Three substituent-dependent photochemical reaction types were observed: (1) For adducts with C a and/or C.a methyl groups, y -hydrogen J o a b s t r a c t i o n was preferred and led to the novel r i n g system I I . (2) For adducts lacking these y-hydrogen atoms, an unusual new re a c t i o n course pr e v a i l e d . This consisted of g-hydrogen atom ab s t r a c t i o n from (or equivalently C g) to give the d i r a d i c a l I I I . Closure of t h i s d i a l l y l i c d i r a d i c a l i n three of the possible four ways (1,6-bonding, 3,8-bonding and 3,6-bonding) and subsequent k e t o n i z a t i o n gave the observed products of general structure IV, V and VI resp e c t i v e l y , although not a l l three products were observed i n each case. The r e l a t i v e amounts of these products were strongly solvent dependent. A methyl group at C, dir e c t e d o the g-hydrogen ab s t r a c t i o n to the C_ p o s i t i o n i n accord with expectations o based on r a d i c a l s t a b i l i t y . This same o v e r a l l r e a c t i v i t y obtained for the corresponding naphthoquinone D i e l s - A l d e r adducts. (3) F i n a l l y , f o r the duroquinone-2,3-dimethylbutadiene adduct an unusual cyclobutanone-con-t a i n i n g photoproduct VII was observed i n a d d i t i o n to those r e s u l t i n g from g-hydrogen ab s t r a c t i o n . Based on deuterium l a b e l i n g studies, t h i s product was suggested to a r i s e v i a d i r e c t C hydrogen abstra c t i o n by the C_ enone o J carbon atom followed by 2,8 bonding. Photoproducts of the type IV,VI and VII undergo novel thermal rearrangements f o r which mechanisms are proposed. In a d d i t i o n ene-dione - i i i -VII undergoes a p a r t i c u l a r l y i n t r i g u i n g base-catalyzed rearrangement which i s formally the r e s u l t of a 1,2-carbanionLc s h i f t . In summary, the photochemical reactions described demonstrate i n t e r e s t i n g v a r i a t i o n s on the f a m i l i a r y~hydrogen abstra c t i o n process, show the f e a s i b i l i t y and preliminary scope of excited state g-hydrogen abs t r a c t i o n processes (heretofore v i r t u a l l y unknown), and appear to provide a general method f o r the synthesis of t r i c y c l i c r i n g systems of the type II and V which are c l o s e l y r e l a t e d to c e r t a i n n a t u r a l l y occurring sesquiterpenes. VII - i v -TABLE OF CONTENTS Page INTRODUCTION 1 A. General 1 B. Photochemistry of D i e l s - A l d e r Adducts of Dienes with p_-Benzoquinone 5 C. Survey of Photochemical Intramolecular g-Hydrogen Abstractions by Carbonyl Oxygen 17 D. Objectives of Present Research 23 RESULTS AND DISCUSSION 28 A. Diel s - A l d e r Adduct of trans,trans-2,4-Hexadiene and p_-Benzoquinone (62) 28 B. Diels-Alder Adduct of p_-Benzoquinone and 1,3-Pentadiene (64) 3 6 C. Diel s - A l d e r Adduct of Isoprene and p_-Benzoquinone (63) 45 D. Diels-Alder Adducts of 1,4-Naphthoquinone with 2,3-Dimethyl-l,3-butadiene and with Isoprene (66 and 65) 57 E. 5-tert-Butylcyclohex-2-ene-l,4-dione (71) 62 F. Diel s - A l d e r Adduct of Duroquinone and 2,3-Dimethyl-1,3-butadiene (73) 6 8 1. Synthesis and Photolysis 68 2. 1,3,4,6,8,9-Hexamethyl-5-hydroxytricyclo-[4.4.0.05'9]deca-3,7-dien-2-one (145) 69 (a) Structure 69 (b) Thermolysis 72 - V -Page 3 10 3. 1,3,4,6,8,9-Hexamethyltricyclot4.4.0.0y' ]dec-8-ene-2,5-dione (146) 7 5 (a) Structure 7^ (b) Thermolysis 7 6 (c) Base-Catalyzed Rearrangement 7^ 4. Mechanism of the Photolysis of Adduct _73 83 EXPERIMENTAL 101 APPENDIX 1 2 6 BIBLIOGRAPHY 127 - v i -LIST OF SCHEMES, TABLES AND FIGURES Page Scheme 1 7 2 8 3 12 4 16 5 17 6 30 7 38 8 54 9 56 10 57 11 61 12 . . 63 13 67 14 68 15 70 16 79 17 80 18 '. 81 19 82 20 84 21 85 22 87 Table 1 27 2 31 3 42-43 4 46 5 55 6 93 F i g . 1 3 2 15 3 47 4 49 5 50 6 53 7 58 8 • 60 9 71 10 73 11 75 12 77 13 . 98 14 98 - v i i -ACKNOWLEDGEMENT My sincere thanks go f i r s t of a l l to Dr. J.R. Scheffer f o r h i s continual advice and encouragement during my studies at U.B.C. I t was a pleasure to work f o r somebody who gave h i s time so f r e e l y and who showed not only p r o f e s s i o n a l but al s o personal i n t e r e s t i n h i s students. Secondly, I would l i k e to thank my fri e n d s and coworkers Kuldip Bhandari, Brian B o i r e , Barry Jennings, Pete K n i t t e l , John Louwerens, Mel Lungle, May Ngan, Dennis Ouchi, and l a s t but not l e a s t Rocky Wostradowski f o r t h e i r wonderful company. Furthermore, I would l i k e to thank my wife Barbara f or her excellent i l l u s t r a t i n g work i n t h i s t h e s i s . I am further indebted to many s t a f f members of t h i s Department, i n p a r t i c u l a r to Diane Johnson f o r her e f f i c i e n t typing. Last but not leas t I would l i k e to express my gratitude to the Univ e r s i t y f o r a Teaching A s s i s t a n t s h i p and a Graduate Fellowship. v i i i -To Barbara - 1 -INTRODUCTION A. General The vast expansion of photochemistry i n the l a s t two decades demonstrates the growing i n t e r e s t of chemists i n various f i e l d s towards t h i s f r u i t f u l and f a s c i n a t i n g area. Many r e s u l t s have been integrated as standard chemical procedures mainly i n synthetic organic chemistry. In organic photochemistry s p e c i f i c parts of the molecules (called chromophores) are excited with u l t r a v i o l e t l i g h t c r e a t i n g highly energetic species which react along pathways mostly i n a c c e s s i b l e to ground state molecules. The wavelengths used i n i r r a d i a t i o n experiments i n conventional organic photochemistry vary between 200 and 400 nm. Within t h i s range molecules containing ir-bonds are excited to species with energies of approximately 70 to 140 kcal/mole. Since s i n g l e carbon-carbon and carbon-hydrogen bonds do not absorb i n t h i s region of the spectrum, i t i s pos s i b l e to tr a n s f e r energy to s p e c i f i c parts of organic molecules and thereby b r i n g about reactions induced by the l i g h t absorbing group (chromophore). A further s e l e c t i v i t y can be achieved between the d i f f e r e n t chromophores of a molecule with the aid of f i l t e r s which allow only c e r t a i n energy ranges of l i g h t to pass through. - 2 -The chromophores of the molecules investigated i n t h i s work were various conjugated carbonyl groups. The u l t r a v i o l e t spectrum of a carbonyl group shows two d i s t i n c t absorptions. In ketones and aldehydes one of them usu a l l y appears somewhere between 200 and 250 nm and has a high e x t i n c t i o n c o e f f i c i e n t 0\>10,000). It i s due to the promotion of a iT-electron to i t s antibonding o r b i t a l IT and i s given the term IT—IT . The other band i s due to e x c i t a t i o n of an el e c t r o n i n a non-bonding ft o r b i t a l on oxygen to the Tr - o r b i t a l of the carbonyl group. These absorptions occur between 270 and 350 nm, depending on s u b s t i t u t i o n and the degree of conjugation.''" Their e x t i n c t i o n c o e f f i c i e n t s are very low (10-100) as they are space forbidden t r a n s i t i o n s . One of the * outstanding features of the n-Tr excited s i n g l e t state of ketones i s the high e f f i c i e n c y of intersystem crossing to t r i p l e t s t a t e s . These have r e l a t i v e l y long l i f e t i m e s due to the spin forbiddeness of t h e i r ft return to the ground s t a t e . The n-Tr e x c i t a t i o n can be represented as 2 i n F i g . 1. An el e c t r o n from the non-bonding p - o r b i t a l of oxygen i s * excited to the u o r b i t a l . Regarding the p i c t o r i a l representation i n F i g . 1 i t has to be remembered that the i r - o r b i t a l s drawn on carbon ft and oxygen are to represent both IT and TT o r b i t a l s i n order to accommodate three e l e c t r o n s . Promotion of the non-bonding e l e c t r o n leaves behind a s i n g l y occupied n - o r b i t a l on oxygen much l i k e the one of an alkoxy ft r a d i c a l . Hence the n-fr t r i p l e t state of ketones behaves i n many 3 regards l i k e an alkoxy r a d i c a l . Much l i k e the l a t t e r i t i s a powerful hydrogen ab s t r a c t i n g species. Some of the most common photochemical reactions of ketones are i l l u s t r a t e d i n eq 1-6. - 3 -: 0 yy hv n—JT 01 y c y Figure 1 . Two and three dimensional representation of the carbonyl group i n i t s ground state (I) and n - r r " excited state (II and I I I ) . o represents s p n hybrid electrons c o a x i a l with sigma C-0 bond; y's, p electrons; • ,7r-systen electrons. - 4 -0 II , 1 / C \ N 2 RH OH I R1 / 9^ R2 •R (eq 3) The Norrish Type I reaction (eq 1) i s favored i n cases where the 2 4 r a d i c a l *R i s a very stable one. The Norrish Type II r e a c t i o n (eq 2) i s a very e f f i c i e n t reaction i n the case of a r y l - a l k y l ketones."* Polar solvents render the f i r s t step of t h i s r e a c t i o n i r r e v e r s i b l e through hydrogen bonding to the hydroxyl group formed. The r a t i o of products formed v i a the two paths a_ and b_ depends on subtle s t e r i c e f f e c t s . ^ Equation 3 shows the photoreduction of a ketone which i s favored i n proton donating solvents such as isopropanol. Equations 4 and 5 delineate cycloaddition reactions to o l e f i n s . The intramolecular version of these two reactions i s also commonly observed. Just one example of many known rearrangement reactions i s shown i n equation 6. B. Photochemistry of Die l s - A l d e r Adducts of Dienes with p_-Benzoquinone In 1964 Cookson and coworkers^ reported the study of some D i e l s -Alder adducts of p_-benzoquinone. They found that the cyclopentadiene adduct 1_ underwent cycloaddition to the cage product An analogous (eq 7) 1 product was obtained with the 1,3-cyclohexadiene adduct. However, i r r a d i a t i o n of the 1,3-butadiene adduct 3^was reported to give besides tar a dimer to which structure 4_ was t e n t a t i v e l y assigned. 0 0 0 (eq 8) 3 4 Interest i n the divergent behavior of t h i s l a t t e r r e a c t i o n led to a r e i n v e s t i g a t i o n i n t h i s laboratory by Scheffer, Wostradowski and Bhandari. In t h e i r study the unusual t r i c y c l i c products 5_ and 6^  were found when - 6 -adduct 3^  was i r r r a d i a t e d through a f i l t e r transmitting l i g h t of X » 3 4 0 nm. (eq 9) benzene 1 : 7 tert-butanol 5 : 1 Structure _5 was unambiguously assigned on the basis of an X-ray a n a l y s i s . Ene-dione 6^  was found to interconvert thermally at 2 0 0 ° to ene-dione 5_. The proposed mechanism for the formation of the two photoproducts of adduct _3 i s i l l u s t r a t e d i n Scheme 1 . The reaction was thought to proceed v i a a novel hydrogen a b s t r a c t i o n by the carbonyl oxygen through a five-membered r i n g t r a n s i t i o n state to give a b i a l l y l i c b i r a d i c a l ]_. Bonding at d i f f e r e n t termini of the a l l y l i c r a d i c a l s accounts for the formation of enols J3 and SL Subsequent ketonization y i e l d s the two photoproducts _5 and 6_. No cycloaddition product analogous to cage product 2^  had been observed. Two facts seemed to account for the d i f f e r e n c e i n behavior of adducts 1_ and 3 :^ F i r s t l y , models show that i n adduct _1 and i n the analogous cyclohexadiene adduct the two o l e f i n i c double bonds are held r i g i d l y i n proximity to each other by means of the bridge between carbons - 7 -Scheme 1 0 0 6 5 5 and 8. Hence c y c l o a d d i t i o n i s a very favorable process i n t h i s molecule. In contrast to t h i s , compound _3 has a f a i r l y mobile i s o l a t e d double bond. The second reason i s the unfavorable formation of a bridgehead r a d i c a l at or Cg i n adduct _1, should a 6-hydrogen a b s t r a c t i o n mechanism be operating as the one postulated i n Scheme 1 for adduct 3^ . The y i e l d s of photoproducts 5_ and 6_ were quite low (ca. 10%, combined y i e l d ) . This was considerably improved i n the photolysi s of the adduct of 2,3-dimethyl-l,3-butadiene and p_-benzoquinone (10)1^ The photochemical behavior of the l a t t e r i s shown i n Scheme 2 . Two of the Scheme 2 hv A > 340 nm 10 I s o l a t e d Y i e l d s i n benzene tra c e t e r t - b u t y l a l c o h o l 80% 12 35% tr a c e n^ w 3,8-bonding 1 1 1 • • enoi of 11_ 3,6-bonding e n o l q £ ^ 1,6-bonding 13 14 (*,* = •,• or +,-) 15 copacamphor t _ 9 _ products observed, 11 and 1_2_, were analogous to the ones formed i n the photoly s i s of the unsubstituted adduct 3_. An i n t e r e s t i n g feature of structure 11_ as w e l l as 5_ i s that the same r i n g system i s found i n several n a t u r a l l y occurring sesquiterpenes such as copacamphene ^a and sativene ( 1 6 ) . ^ The a d d i t i o n a l new product 13_ formed i n the photolysis of 1_0 i n benzene can a r i s e m e c h a n i s t i c a l l y through the same type of intermediate 14 as postulated i n the unsubstituted case. The a l l y l i c r a d i c a l (or c a t i o n , see below) i s now s t a b i l i z e d by a methyl group at the terminal p o s i t i o n (C, i n 14). The s i g n i f i c a n t increase i n product formation i n the D — substituted case might be due to t h i s s t a b i l i z a t i o n of the intermediate 14. Further support f o r the formation of intermediate 14_ comes from the phot o l y s i s of a l c o h o l 13_ i n tert-butanol and i n benzene under i d e n t i c a l conditions as i n the i r r a d i a t i o n of the adduct 1_0_ ( c f . eq 10a and b) . Cleavage of the C,.-CQ bond probably gives the same intermediate \ - 10 -14 since the a l c o h o l shows the same product solvent dependence as adduct 10. The reaction of a l c o h o l 13_ leading to 12 could a^  p r i o r i be considered as an allowed concerted [1,3]-sigmatropic s h i f t of from C,. to which would not involve a d i s c r e t e intermediate such as 14. However, there i s some precedence f o r the nonconcertedness of the 1,3 s h i f t of the Y-carbon of an a, (3-unsaturated ketone. C a r g i l l and 9 coworkers found that photolysis of ketone 17_ gave a mixture or equal amounts of isomers 18a and 18b. This r e s u l t strongly suggests the formation of a b i r a d i c a l intermediate. 17 18a 1 : 1 18b The formation of ene-dione 1JL from a l c o h o l ]_3_ i s formally a [3,3]-s u p r a f a c i a l sigmatropic rearrangement which i s , however, not allowed 12 photochemically. Therefore an intermediate such as 14_ seems very l i k e l y to occur. Schaffner and Fuchs"^ have also observed a photochemical rearrangement which was formally a [3,3] sigmatropic s h i f t (see eq 10c). - 11 -The p o s s i b i l i t y that products 1_1 and 1_2 from the pho t o l y s i s of adduct JLO would be formed e x c l u s i v e l y as secondary photoproducts of a l c o h o l 13 was ruled out by a k i n e t i c a n a l y s i s which showed no induction period f o r the appearance of the two ene-dione products. The reason for the marked solvent dependence of product formation i s not w e l l e s t a b l i s h e d . One p o s s i b l e explanation involves demotion of the intermediate b i r a d i c a l to a solvated z w i t t e r i o n 21_ inr.analogy to the formation of such species i n the photochemistry of cyclohexa-2 dienones as postulated by Zimmerman and coworkers (Scheme 3). - 12 -There i s , of course, a major d i f f e r e n c e between zwittericns 21 and 26 i n that i n Zimmerman's intermediate the z w i t t e r i o n foros a conjugated system which i s not the case i n Zl. P r e f e r e n t i a l bond formation i n the l a t t e r might be expected to occur at the solvent s t a b i l i z e d C D p o s i t i o n to give product 11. o In the photolysis of adduct 1(3 i n benzene the intermediate zwitterion or b i r a d i c a l 1_4 would not be solvated as w e l l . Bond formation at C D would give a more substituted double bond than bond formation at o C c. However, the two major products obtained (eq 11) arose from r i n g - 13 -(eq 11) 0 14 12 13 closure at Cg. Both ene-dione 12^ and alcohol 13_ so formed were thermodynamically les s stable than ene-dione _11 as r e f l e c t e d i n t h e i r thermal conversions to give ene-dione 11_. The analogous thermal reaction took place as well with the unsubstituted photoproduct 6K It i s therefore not only the presence of a more substituted double bond which makes ene-diones 5_ and JUL thermodynamically more s t a b l e . It i s possible that i n the benzene photolysis k i n e t i c c o n t r o l leads to the thermodynamically les s stable products 12 and 13 since they might resemble intermediate 14_ more c l o s e l y i n structure than does ene-dione JUL ( c f . Hammond's principle"'""'') and would therefore have a lower a c t i v a t i o n energy. As mentioned, the r e l a t i v e s t a b i l i t i e s of the photoproducts of adduct 10 followed from an i n v e s t i g a t i o n of t h e i r thermal properties (eq 12). (eq 12) 13 11 12 - 14 -Both the photoproducts JL3 and 12 were thermally converted into ene-dione JL1. The r e a c t i o n of 1_3_ can be (but does not have to be) regarded 12 formally as an allowed [3,3]-suprafacial sigmatropic rearrangement. The thermal r e a c t i o n of 3_2_ i s a forbidden [1,3]-suprafacial sigmatropic 13 s h i f t which may or may not be concerted. The l a t t e r r e a c t i o n occurred as w e l l i n the unsubstituted adduct. There too the benzene photolys i s l e d to the thermodynamically les s stable product. Further i n s i g h t into the mechanism was achieved by proving the intermediacy of enol 28_. Photolysis of adduct 10_ i n tert-butanol-O-d led to ene-dione 29_ deuterated i n the exo-position at the expected s i t e . The same product was also obtained by base-catalyzed deuterium exchange of the protio-ketone jJL. The evident formation of enol 28_ rules out an a l t e r n a t i v e mechanism which would y i e l d intermediate 30 v i a C R-hydrogen a b s t r a c t i o n by C 0 through a five-membered c y c l i c - 15 -t r a n s i t i o n s t a t e . Subsequent r i n g closure between and Cg also would have given 11. The f a c i l e deuterium exchange of the exo proton i n ene-dione 11 has precedence i n a study of the base-catalyzed 14 deuterium exchange i n some bicyclo[2.2,l]heptanones. The enhanced rate of exchange of compound 32_ compared to _31_ was ascribed to the s t a b i l i z a t i o n of the enolate by homoconjugation with the second carbonyl group (structure 33). r e f . 14 r e f . 14 Figure 2. A f u r t h e r i n v e s t i g a t i o n of the mechanism of the photolysis of | Diels-Alder adduct 10_, was c a r r i e d out to e s t a b l i s h the B-hydrogen abstraction and enol formation. The tetradeuterated adduct 34_ was i r r a d i a t e d i n benzene and tert-butanol to give deuterated ene-diones 39 and 37. In the photolysis i n tert-butanol the intermediate enol exchanges deuterium f o r hydrogen and the product contains only 3.0 D. In benzene 60% D was found at C,. The remainder was probably exchanged f o r hydrogen due to some moisture present i n benzene. This experiment established that the enol i s also an intermediate for the product formed i n benzene. - 17 -C. Survey of Photochemical Intramolecular g-Hydrogen Abstractions by  Carbonyl Oxygen P r i o r to the in v e s t i g a t i o n s i n our laboratory only a few w e l l investigated cases of photochemical g-hydrogen abstractions had been reported, two of them by Padwa and c o w o r k e r s . O n e of these two c l o s e l y r e l a t e d reactions involves trans-N-tert-butyl-2-phenyl-3-benzoyl a z i r i d i n e 4^ ) as shown i n Scheme 5."^ The g-proton abstract i o n occurs i n the step going from 41 to 42. Scheme 5 - 18 -The analogy with the benzoquinone adduct J_0_ i s not quite adequate since i n 4_1 the oxygen bears a negative charge whereas i n 10 i t i s the excited state of the carbonyl group which leads to hydrogen atom a b s t r a c t i o n . The e a r l i e s t reported suggestion of a 8-hydrogen ab s t r a c t i o n i s one by Leermakers and V e s l e y1 7 i n 1963. They proposed that i n the 48 49 photolysis of pyruvic acid (46, eq 14) 3-hydrogen ab s t r a c t i o n would lead to a hydroxy carbene _48 which could react with another carbene to give a c y l o i n 47_ v i a 49. However, no other evidence f o r the formation of a carbene was obtained. 18 In 1972 } a f t e r the present thesis was begun, Agosta and coworkers published a s e r i e s of i n t r i g u i n g reactions i n v o l v i n g g-hydrogen a b s t r a c t i o n . Several a-methylene ketones were i r r a d i a t e d to give the two types of products shown i n eq 16-19. The general mechanism fo r the formation of the cyclopropyl ketones (eq 20) involves a b s t r a c t i o n 50 - 19 -31% (eq 16) 24% u -V-hv 57 u 23% (eq 17) 31% 52 17% (eq 18) 38% 53 64% (eq 19) .9 I OH 54 OH R (eq 20) 55 - 20 -of the 3-hydrogen to give a very stable b i r a d i c a l 54. This species was compared by the authors to trimethylene (55), a ground state t r i p l e t species with a t h e o r e t i c a l l y estimated d e r e a l i z a t i o n energy of 34 kcal/mole. For reasons not yet c l e a r , the cyclohexyl substituted ketone _53 does not give any product derived from 3-hydrogen a b s t r a c t i o n . The c y c l o b u t y l ketones were formed v i a y-hydrogen abstraction as shown i n eq 21. Another possible example of a 3-hydrogen abstract i o n process was 19 reported by Jeger and coworkers i n 1971. Photolysis of s t e r o i d 5_6 afforded cyclopropanol 5_7. The mechanism f o r t h i s r e a c t i o n i s by no means c l e a r . On the basis of previous examples and from model considerations one would have expected a y-hydrogen abstraction from the (eq 21) 56 57 (eq 22) C^g methyl group to form a cyclobutanol product as i n the photolysis of 5_8 and many analogous compounds. The authors proposed that a c e r t a i n a c t i v a t i o n of the a l l y l i c C D hydrogen and/or a favorable non-o planar s p a t i a l arrangement of the excited carbonyl group might favor CgH abstraction vs. attack at the methyl group. However, models show that the C Q hydrogen i s not close to the non-bonding, i . e . o abstracting o r b i t a l of the excited carbonyl group. Another example of a cyclopropanol formation v i a B-hydrogen 20 abstracti o n was reported by Roth and E l Raie. Amino ketone 60_ gave dioxane hv,Pyrex (eq 24) CH 3 CH 3 60 61 - 22 -cyclopropanol 61 i n 80% y i e l d . I f other dialkylamino groups are substituted for the morpholine no analogous re a c t i o n takes p l a c e . The mechanism f o r the cyclopropanol formation might involve an intermediate formed by e l e c t r o n t r a n s f e r from nitrogen to oxygen as i n the case of the previously mentioned benzoyl a z i r i d i n e s . - 23 -D. Objectives of Present Research Previous i n v e s t i g a t i o n s i n t h i s laboratory had shown (see Introduction) that a l k y l s u b s t i t u t i o n of the i s o l a t e d double bond i n adduct JL0_ led to much higher y i e l d s of t r i c y c l i c photoproducts and 0 Y 6' 0 possibly influenced the s i t e of bond formation (at p o s i t i o n 3 or y i n structure 10). In the previously investigated 2,3-dimethylbutadiene adduct JLO, the two 6-positions (6 and 3' i n structure 10) were equivalent on symmetry grounds. By introducing only one substituent at the i s o l a t e d o l e f i n i c bond the 3 and 3' p o s i t i o n s would be rendered d i f f e r e n t and hydrogen abstract i o n at one s i t e might become favored over the other. For t h i s reason and also i n order to expand the knowledge about the e f f e c t of substituents and hence about the mechanism of the r e a c t i o n , the photochemistry of compounds 62-66 was i n v e s t i g a t e d . More s p e c i f i c reasons f o r the choice of these compounds are given i n the d i s c u s s i o n . - 24 -Naphthoquinone adducts 65_ and J56 were investigated to expand the scope of the reaction with the use of an aromatic chromophore. In the case of the benzoquinone adducts the proposed intermediate 14. has two s i t e s on the enone side for bond formation (C^ and C^). In contrast to t h i s , bond formation i n intermediate § ] _ from the carbon analogous to i n 14 would destroy the benzene resonance, and such products were expected to be less favorable. - 25 -14 67 Another point of i n t e r e s t was to test whether a monocyclic ene-1,4-dione system such as 68_ would undergo s i m i l a r reactions as the b i c y c l i c system of the Diels-Alder adducts. If so, t h i s kind of system would open up a new route to bicyclo[2.2.2]-hexa-2,5-diones. For t h i s purpose tert-butylcyclohexenedione 71 was i n v e s t i g a t e d . F i n a l l y , the photochemical behavior of the D i e l s - A l d e r adduct (73) of duroquinone and 2,3-dimethylbutadiene was i n v e s t i g a t e d . This 73 was prompted by observations i n the l i t e r a t u r e that highly substituted quinones and D i e l s - A l d e r adducts thereof undergo photochemical reactions which are d i f f e r e n t from t h e i r less substituted analogues. A s t r i k i n g d i f f e r e n c e was found i n the reactions of several 2 2 ~" ^  A quinones with o l e f i n i c compounds ** (Table 1). The products formed were e i t h e r oxetanes or cyclobutanes or a mixture of both as shown i n Table 1. Exclusive oxetane formation was found with p_-benzoquinone. One methyl group on each double bond led to a mixture of products. Two methyl groups on the same double bond (76 and 77) gave e x c l u s i v e l y cyclobutanes. This was also the case i n the dimethyl substituted cyclohex-2-ene-l,4-dione J7_8_ which has the same chromophore as the duroquinone adduct 73. 25 21 Bryce Smith, B a r l t r o p , and t h e i r coworkers have suggested that the d i f f e r e n t modes of a d d i t i o n may r e f l e c t d i f f e r e n t excited s t a t e s , * i n p a r t i c u l a r oxetane formation may occur from an n - T r state and cyclobutane formation from a T T — r r s t a t e . The l a t t e r was supported .'by the f i n d i n g that ene-dione J78 showed phosphorescence from i t s T T - T T - 27 -* t r i p l e t s t a t e . Since TT-TT t r i p l e t s of carbonyl groups do not abstract 26 hydrogen, i t was w e l l i n l i n e with t h i s that 78, when photolyzed i n isopropanol, did not y i e l d any products r e s u l t i n g from hydrogen 22 abstracti o n from the solvent-. Table 1 oxetane cyclobutane 0 0 - 28 -RESULTS AND DISCUSSION A. Diels-Alder Adduct of trans,trans-2,4-Hexadiene and p_-Benzoquinone It had been found that the adduct of 2,3-dimethylbutadiene with p_-benzoquinone gave improved y i e l d s of photoproducts compared to the adduct with butadiene i t s e l f ( c f . i n t r o d u c t i o n ) . This e f f e c t might have been due to the s t a b i l i z a t i o n of the a l l y l i c r a d i c a l formed a f t e r i n i t i a l hydrogen abstraction by the carbonyl oxygen (14). This 27 s t a b i l i z a t i o n i s supported by thermochemical measurements of the heat of formation of r a d i c a l s . The 1-methylallyl r a d i c a l was found to be 2.5 k c a l more stable than the unsubstituted a l l y l r a d i c a l . It was reasoned that the same kind of s t a b i l i z a t i o n should be favourable for the formation of intermediate _79 from the 5,8-dimethyl adduct 62^ . It was of i n t e r e s t to see i f , and i f so, how the methyl group i n 62^  would influence the r a t i o of bond formation at Cg v s . Cg. Adduct 28 62 was synthesized according to the method of Euler and coworkers. - 29 -A mixture of £ - b e n z o q u i n o n e and excess trans,trans-2,4-hexadiene kept at 60° for 30 min gave adduct 62_. The stereochemistry of 62_ i s assumed to be the one shown on the basis of the generally preferred endo-29 add i t i o n of the diene. Adduct (32 also contained two methyl groups i n proximity to the carbonyl functions. Hence a second possible pathway, that of y-hydrogen a b s t r a c t i o n , was introduced i n t h i s molecule. As i t turned out, the l a t t e r pathway was the only one observed. Photolysis of jj_2 i n benzene gave ene-dione 80 i s o l a t e d i n 26% y i e l d by column chromatography. The reaction presumably proceeded through a b i r a d i c a l intermediate j?l_ which upon r i n g closure to the enol 82_ ketonized to the observed product 80_. The stereochemistry of the methyl group i n 80_ i s assumed to be the one shown on the basis of the proposed mechanism. The formation of 8 £ also supports the stereo-chemistry of adduct J52. If the methyl groups i n adduct j62 would have been syn to the bridgehead hydrogens the formation of product 80_ would not have been p o s s i b l e . - 30 -Scheme 6 Structure 8 £ was supported f i r s t of a l l by the s p e c t r a l data. The carbonyl absorption i n the i r spectrum appeared at 5.78 u, i n d i c a t i v e of six-membered r i n g ketones. S i g n i f i c a n t features of the nmr spectrum were the m u l t i p l e t of the two v i n y l hydrogens at A.1-4.6 T and the doublet due to the C ^ Q methyl group at 8.7 T (J = 7 Hz). The u l t r a v i o l e t spectrum showed a band at 291 nm (e 56) i n methanol. The p o s i t i o n and the low e x t i n c t i o n c o e f f i c i e n t of t h i s band are consistent with the presence of a saturated ketone. Further s t r u c t u r a l support was provided by a hydrogen deuterium exchange experiment. Ene-dione 80_, dissolved i n deuterochloroform, was - 31 -treated with an aqueous a l k a l i n e deuterium oxide s o l u t i o n . A slew (2 weeks) exchange of two hydrogens took place as observed i n the nmr spectrum to give 83_. No s t e r e o s e l e c t i v i t y was found as i n the deuterium exchange of photoproduct 1_1_ ( c f . introduction) . This had given exo-deuterated 29. This d i f f e r e n c e agrees w e l l with the rate found for the base-catalyzed deuterium exchange of ketone 84_ compared with those of ketone 85 and diketone _3_3 (Table 2) . The l a t t e r two show marked preference f o r exchange of the exo hydrogen. The formation of _29_ was also much f a s t e r than that of S3_ under s i m i l a r c o n d i t i o n s . This i s r e f l e c t e d i n the very f a s t rate of exo hydrogen exchange of _33 which i s s i m i l a r i n structure to _11 (rate enhancement due to homoenolate formation, see Figure 2). Table 2 o Si 85 0 33 exo 5.48 x 10 -2 0 2.0 k = 7.88 x 10 Reference 27 k . 7.62 x 10 endo 14 -5 4.6 x 10 14 -2 k = second order rate constant for NaOD catalyzed D-exchange i n dioxane-D20 at 2 5 ° . - 32 -Further evidence for structure J30 was obtained by i t s hydrogenation to the saturated dione 86. A s t r i k i n g feature i n the nmr spectrum of 86_ was the pentuplet due to the methine at 7.34 T . The coupling i s due to the four neighboring hydrogens which i n the hydrogenated product form equal angles with the methine. This i s not the case i n photoproduct 80_ where deviations of the dihedral angles between the methine and i t s v i c i n a l hydrogens are probably due to the s t r a i n induced by the presence of the double bond. 8 80 86 87 Base-catalyzed deuterium exchange of 86_ gave J[7. The methine now appeared as a broadened t r i p l e t . The broadening i s due to the 31 H,D coupling which may be calculated (J = 6.55 x J ) to be H, H H, D approximately 0.5 Hz. In order to obtain more evidence for the suggested mechanism and i n p a r t i c u l a r for the formation of the intermediate en o l , adduct 62_ was photolyzed i n tert-butanol-O-d. As i n the case of the photolysis of the 2,3-dimethylbutadiene adduct 10 incorporation of deuterium was expected i f an intermediate enol was formed. Photoproduct {$8 showed 0.3 D incorporation (mass spectrum). The nmr spectrum indicated a decrease i n the i n t e g r a l of the same area that was affected by base-- 33 -catalyzed deuterium exchange of 80. The low deuterium content of only 30% might have been due to hydrogen exchange reactions on the alumina column used for the i s o l a t i o n of the product. The exclusiveness of Y-hydrogen abstract i o n may be explained on the basis of the preferred conformation of the molecule and the proximity of the Y-hydrogens and the n - o r b i t a l on oxygen. One of the leas t stable conformations would be 89_ i n which the methyl groups are strongly i n t e r a c t i n g i n a bows p r i t - f l a g p o l e - l i k e 32 fashion. This boat conformation of the cyclohexene r i n g would o however allow the 3-hydrogens to be moderately close (2.8 A to oxygen centre) to the oxygen n - o r b i t a l . Of the two boat conformations of the cyclohexene r i n g , 90_ would be more stable than 89. In 90_ the methyl groups are i n a pseudo-equatorial p o s i t i o n and very close to the oxygen. Another very favorable conformation i s the quasi-chair conformation 33 91. Inspection of molecular models of 9J3 and £ 1 shows that the o methyl hydrogens are much closer ( t h e o r e t i c a l l y as close as 0.9 A) to o oxygen than the B-hydrogens (3.2 A i n _91_ f o r the pseudo-equatorial o hydrogen, 4.0 A i n 90). - 34 -(eq 29) In the unsubstituted adduct J3 where g-hydrogen abstraction does occur there are two stereochemically d i f f e r e n t p a i r s of B-hydrogens. One p a i r i s syn to the bridgehead hydrogens, the other a n t i . In a favorable conformat ion l i k e 92 only one of the anti—hydrogens i s close 0 to one of the oxygens (approximately 2.2 A). The syn-hydrogens cannot - 35 -be brought any c l o s e r than about 2.6 A i n any conformation. Models show also that a b s t r a c t i o n of the anti-hydrogen produces an o r b i t a l on the B-carbon with a good overlap with the ir-systen of the adjacent double bond. Abstraction of a syn-hydrogen would n e c e s s a r i l y occur from a conformation i n which the carbon-hydrogen bond i s almost perpendicular to the neighboring T r - o r b i t a l . Further evidence against syn-hydrogen abstraction was found i n the behaviour of the 1,4-diphenylbutadiene adduct 9_3. K. B h a n d a r i ^ i n t h i s laboratory found that t h i s compound was photocheciically i n e r t . This i s despite the fa c t that the B-hydrogens are benz y l i c and hence very re a c t i v e towards hydrogen atom abstraction.~* - 36 -Ph 0 hv.X > 340 nm no reaction Ph 0 93 B. Diel s - A l d e r Adduct of p_-Benzoquinone and 1,3-Pentadiene (64) This adduct featured both y-hydrogens and an a n t i g-hydrogen l i a b l e to photochemical a b s t r a c t i o n . I f both types of hydrogens were abstracted the product d i s t r i b u t i o n would provide a means of e s t a b l i s h i n g the competition between g- and yhydrogen a b s t r a c t i o n . Adduct 64_ was synthesized from piperylene and p_-benzoquinone. D i s t i l l a t i o n of the crude product gave a yellow o i l . The corresponding nmr spectrum showed two groups of v i n y l hydrogens with v i r t u a l l y i d e n t i c a l 0 0 (eq 30) 64 - 37 -chemical s h i f t s as the v i n y l hydrogens i n the 5,8-dimethyl adduct 62. The bridgehead hydrogens are m u l t i p l e t s centered at T 6.8 as i n adduct 62. The methyl group appears as a doublet at T 9.1 (J * 7 Hz). The stereochemistry of 64^  was assigned as shown i n eq 30 on the basis of the same arguments used for adduct 62. The l i q u i d adduct (v4_ could not be 34 c r y s t a l l i z e d although Grob and Wicki claimed that t h i s compound had a melting point of 1 4 6 - 1 4 7°. However, t h e i r structure proof was based on elemental analysis and on conversion of the product i n t o the dimethoxy d e r i v a t i v e 94-. This l a t t e r step would have been j u s t as successful with hydroquinone 95_ as the reactant. The l a t t e r could e a s i l y be formed by aromatization of adduct 64. (eq 31) 64 94 Indeed, G.Bendz also obtained a yellow o i l from the reaction of piperylene and £ - b e n z o q u i n o n e which upon d i s t i l l a t i o n or attempted c r y s t a l l i z a t i o n was always converted into the corresponding hydro-quinone 95. The melting point of the l a t t e r ( 1 4 4 - 1 4 5°) was i n good agreement with the one claimed by Grob and Wicki for adduct (>4. In t h i s work though, the crude reaction product could be p u r i f i e d by d i s t i l l a t i o n to give 80% of the desired product 64_. The corresponding hydroquinone was only present i n higher b o i l i n g f r a c t i o n s . - . - 38 -Photolysis of monomethyl adduct j>4_ i n benzene or tert-butanol led to the formation of two major products 96^  and 97 i n a time independent r a t i o of about 7:1 ( c f . Scheme 7). The products were c o l l e c t e d by g l p c . The conditions and y i e l d s were not optimized since the main purpose was to e s t a b l i s h the mechanism of the reaction and the structure of the products. The major product, 96, was obtained as a c r y s t a l l i n e compound. Its i r spectrum showed one carbonyl peak at 5.79 y. Scheme 7 100 101 - 39 -The nmr spectrum was very s i m i l a r to that of the photoproduct 80_ from the photolysis of adduct 62^ The s i g n a l at highest f i e l d i n £ 6 i s due to the saturated methylenes. The pattern of t h i s m u l t i p l e t i s v i r t u a l l y i d e n t i c a l to the analogous m u l t i p l e t i n ene-dione 80. The s i g n a l due to the two v i n y l hydrogens i s also very s i m i l a r i n the two compounds. The minor product 97 was i s o l a t e d as a c o l o r l e s s l i q u i d . The carbonyl peaks appeared at 5.67 u f o r the 5-membered r i n g carbonyl group and at 5.79 y f o r the six-membered one. The nmr spectrum was s i m i l a r to the analogous unsubstituted photoproduct §_. The two v i n y l hydrogens appear as two broadened t r i p l e t s with a coupling constant of 8 Hz. The s p l i t t i n g i s due i n each case to approximately equal coupling constants with the two neighboring hydrogens. The assignment of the l o w - f i e l d s i g n a l to the C 0 v i n y l was based on the comparison of o the chemical s h i f t s of the v i n y l hydrogens of 97_ and 114. In the l a t t e r compound the i d e n t i f i c a t i o n of the two v i n y l hydrogens was evident from the s p l i t t i n g pattern (for d e t a i l s see discussion of 114). The methyl group i n 97_ appears as a doublet with a coupling constant of 8 Hz and i t s stereochemistry i s assumed to be as drawn on the basis of the proposed mechanism (Scheme 7), 114 ° - 40 -The mechanisms f o r the formation of the two photoproducts are outlined i n Scheme 7. Abstraction of a y-hydrogen of the methyl group gives r i s e to a product analogous to that observed i n the photolysis of the 5,8-dimethyl substituted adduct 62. Abstraction of a 8-hydrogen occurs only at the non-substituted Cg p o s i t i o n to give intermediate 100. A s t r i k i n g feature of t h i s intermediate i s that i t apparently closes only between the and p o s i t i o n s independent of the solvent used. There i s no obvious reason which could account f o r the lack of bond formation between the C~ and C Q p o s i t i o n s which was observed i n J o the unsubstituted and 6,7-dimethyl substituted adducts and 10. The y-hydrogen abstract i o n process i s preferred over the B-hydrogen abstraction mode by a f a c t o r of about 7. The Cg B-hydrogen abstracted i s probably a n t i to the bridgehead hydrogen since abstraction of the syn-hydrogen at the more substituted and hence p o t e n t i a l l y favored s i t e of abstraction at C^ does not occur. However, abstraction of t h i s t e r t i a r y hydrogen at the C^ p o s i t i o n would require a conformation (structure 102) i n which the methyl group occupies a r e l a t i v e l y unfavorable pseudo-axial p o s i t i o n . 102 - 41 -The order of preference for the hydrogen abstraction i s also consistent with the distances between the respective hydrogen and the abstracting carbonyl oxygens as shown i n structure 103 (distances 33 measured on Prentice H a l l Molecular Models ) . This d i s t a n c e - r e a c t i v i t y c o r r e l a t i o n i s of i n t e r e s t i f compared to other molecules as shown i n Table 3. In two cases (106 and 109) hydrogen abstrac t i o n involves the 2.6 A 2.0 A 103 carbonyl carbon. There seems to be a cutoff point for hydrogen o abstraction at 2.2 A with the exception of 110 which abstracts over a o distance of 2.7 A. In t h i s case a very stable intermediate 111 i s 18 formed which, as Agosta and coworkers point out, i s formally a d e r i v a t i v e of trimethylene methane (55) with an estimated d e r e a l i z a t i o n energy of 34 kcal/mole. Agosta's group also found competitive (3- and OH 111 Vs 55 Table 3 - 42 -Distance of hydrogen Occurrence of from abstracting center H-abstraction (measured i n A units on P r e n t i c e - H a l l Molecular Models)33 Q 104a 104b 1.1 (planar e c l i p s e d conformation) 1.8 (non-planar, staggered conformation) yes 0 Ph 105 1.7 yes 36 106 2.0 (planar conformation) yes 37 2.0 yes 0 107 Ph 2.2 yes 36 0 , 108 2.2 (planar conformation) 2.6 (non-planar conformation) no 109 2.5 (planar conformation) no 37 - A3 -Y-hydrogen abstraction w i t h i n the same molecule. In 5_1 and some other 18 molecules B-hydrogen abstraction was even more favorable than Y-hydrogen abstracti o n (cf eq 32). These distances measured on simple models of 0 + (eq 32) 51 31% 23% - 44 -course neglect a great number of factors since bond lengths and angles vary with structure and are d i f f e r e n t i n the excited s t a t e . A l s o , favorable o r b i t a l overlap along the reaction coordinate, or formation of a very stable intermediate may reduce the importance of the distance between the abstracted hydrogen and the abstracting oxygen. Furthermore r i g i d structures such as 105 may abstract hydrogen more e a s i l y than f l e x i b l e s t r u c t u r e s . This entropy f a c t o r i s r e f l e c t e d i n the d i f f e r e n t r e a c t i v i t i e s found i n the photolyses of phenylketone 105 and of valerophenone. The l a t t e r , having an oxygen-hydrogen distance of o o t h e o r e t i c a l l y 1.1 A (or 1.8 A i n a staggered conformation, c f . 104a and 104b), reacted 50 times slower than the r i g i d phenylketone 105 ° 36 (Table 4) which had an oxygen hydrogen distance of 1.7 A. The D i e l s - A l d e r adducts investigated i n t h i s laboratory possess oxygen-hydrogen distances which appear within a range favoring hydrogen abstraction as exemplified with adduct _3 i n Table 3. - 45 -C. D i e l s - A l d e r Adduct of Isoprene and p_-Benzoquinone (63) The photochemistry of adduct 6_3 was investigated to further elucidate the e f f e c t of substituents on y i e l d and product d i s t r i b u t i o n . 28 It was synthesized according to the method of Euler and coworkers by r e f l u x i n g isoprene and p_-benzoquinone f o r 1 hr i n benzene. High 63 y i e l d s (y 80%) i n the photolysis of the 6,7-dimethyl substituted adduct 10 compared to the low y i e l d s (^  10%) i n the unsubstituted case were possibly due to the s t a b i l i z a t i o n of the intermediate b i r a d i c a l or z w i t t e r i o n by one of the methyl groups at the terminal p o s i t i o n of the a l l y l i c r a d i c a l or cation formed ( c f . 14). The methyl group i n adduct 63_ introduces an asymmetry i n the molecule. The 3- and 3'-hydrogens are no longer equivalent and t h e i r a b s t r a c t i o n leads to two d i f f e r e n t intermediates 112 and 113. Intermediate HO HO 0 14 112 113 - 46 -112 i s s t a b i l i z e d by the terminal methyl group. In intermediate 113 the methyl group i s substituted at the c e n t r a l p o s i t i o n of an a l l y l i c system and probably has no s t a b i l i z i n g e f f e c t . In the case of an a l l y l i c cation the formal charge of the c e n t r a l carbon atom was 38 calculated by the Pople method to be -0.12 (+0.56 at the terminal p o s i t i o n s ) . Due to t h i s small charge the e f f e c t of a substituent at the c e n t r a l p o s i t i o n would probably be n e g l i g i b l e . In the case of an a l l y l i c r a d i c a l the highest occupied MO has a node at the c e n t r a l carbon and hence a substituent at t h i s p o s i t i o n would have l i t t l e e f f e c t on the s t a b i l i t y of the r a d i c a l . On the basis of these substituent e f f e c t s the pathway v i a intermediate 112 was expected to predominate over that v i a 113. Photolysis of adduct 6_3 i n benzene or i n tert-butanol gave the products shown i n Table 4. Table 4 0 - 47 -The products were i s o l a t e d by gas chromatography. Ene-dione 114 had the two c h a r a c t e r i s t i c carbonyl peaks f o r five-mesbered and s i x -membered rings at 5.6 8 and 5.80 u, r e s p e c t i v e l y . The nmr spectrum (Figure 3) showed the C 0 v i n y l hydrogen as the lowest s i g n a l at T 3.69 o Figure 3 It was coupled to the neighboring v i n y l hydrogen (J = 8 Hz) and also very weakly ( 1 Hz) to the a l l y l i c C, methine. At T 4.11 the C_ o / v i n y l hydrogen appeared as a p a i r of doublets. It was coupled with the C„ hydrogen (8 Hz) and the C, methine (6 Hz). The l a t t e r appeared as a broad t r i p l e t at T 6.63. This t r i p l e t i s due to approximately equal coupling constants 6 Hz) with the and hydrogens. Compound 1_2 with an a d d i t i o n a l methyl group at C 0 showed a s i m i l a r t r i p l e t at T 6.72 o (see appendix). - 48 -The s i g n a l due to 4-exo-proton consisted of thepair of doublets at T 6.80. The coupling constant with the endo proton i s 18 Hz; t h i s large value i s probably due to the ir-contribution of the adjacent carbonyl group. This e f f e c t i s generally large i f the two methylene protons 31 l i e to one side (to the l e f t i n 117) of the i r - o r b i t a l . A model of 117 shows t h i s to be the case. The model also i n d i c a t e s that the 117 exo-proton i s approximately perpendicular to the bridgehead proton. Thus the observed coupling constant i s only 2 Hz. The endo-proton shows a corresponding coupling of 4.5 Hz with the proton. It appears u p f i e l d at T 7.65 and i s , of course, coupled to the exo-proton with the same coupling constant of 18 Hz. The C ^ Q methylene protons give r i s e to a doublet (J = 1.5 Hz) at T 8.34. They seem to be magnetically equivalent and couple only with the methine. The methyl group appears as a s i n g l e t at x 8.60. The and protons show mul t i p l e t s of s i m i l a r appearance and at s i m i l a r chemical s h i f t s as the corresponding protons i n the dimethyl product 12_ (see appendix). The u l t r a v i o l e t spectrum of compound 114 indicates the presence of a t3, y-unsaturated ketone by i t s increased e x t i n c t i o n c o e f f i c i e n t of * 39 300 for the n - T r t r a n s i t i o n at 296 nm. The structure of ene-dione 115 was indicated by a s i n g l e carbonyl peak i n the i r spectrum at 5.72 u. The nmr spectrum (Figure 4) showed one v i n y l hydrogen as a m u l t i p l e t at T 4.33-4.49. The exo-proton 31 appears at x 7.56 (calculated value ) . I t i s coupled to the endo-proton with a coupling constant of 18 Hz and to the bridgehead methine with a coupling constant of 4 Hz. The endo-proton i s almost perpendicular to the methine and i s s p l i t into a doublet (J = 18 Hz) by the exo-proton. A small s p l i t t i n g of 1 Hz i s superimposed on t h i s doublet. The exo-proton could be s e l e c t i v e l y exchanged for deuterium (see introduction) by t r e a t i n g a chloroform s o l u t i o n of ene-dione 115 with deuterium oxide and a small amount of potassium hydroxide. The - 50 -s i g n a l due to the exo-proton disappeared and that of the endo-proton was converted i n t o a t r i p l e t ( J = 2.6 Hz) due to hydrogen-deuterium coupling. In add i t i o n deuteration caused the methine m u l t i p l e t to be transformed i n t o a broad s i n g l e t . In the proteo ketone the methyl group gave r i s e to a broadened s i n g l e t at x 8.35. The remaining protons appeared as m u l t i p l e t s and could not be assigned i n d i v i d u a l l y . Ene-dione 116 showed two carbonyl bonds i n the i r spectrum at 5.70 and 5.84 u. In nmr spectrum (Figure 5) the v i n y l hydrogen appeared as a Figure 5 p a i r of pentuplets at T 4.47. The pentuplet i s due to a l l y l i c coupling (J = 1.5 Hz) with the three methyl protons and the C Q methine. The - 51 -p a i r a r i s e s from coupling (J = 6 Hz) with the methine. The l a t t e r gives r i s e to the broadened t r i p l e t (T 6.67) common to a l l of the compounds investigated having t h i s t r i c y c l i c r i n g system (cf. 12 (appendix) and 114). The a l l y l i c methyl group forms a doublet at T 8.06. It couples with the v i n y l proton (J = 1.5 Hz). The s i g n a l at highest f i e l d , a broad doublet (J = 12 Hz) i s due to the methylenes. I r r a d i a t i o n of the v i n y l hydrogen converted the C, methine t r i p l e t i n t o a doublet and the methyl doublet i n t o a s i n g l e t . The uv spectrum of 116 showed * an enhanced e x t i n c t i o n c o e f f i c i e n t of 330 f o r the n-rr t r a n s i t i o n at 39 295 nm, c h a r a c t e r i s t i c of f3 ,y-unsaturated ketones. During the i n i t i a l stages of the i r r a d i a t i o n of adduct 6J3 a fourth minor photoproduct was observed. However, i t photolyzed further and could only be i s o l a t e d i n very small amounts. The uv spectrum of t h i s material showed a band at 240 nm (e 10,000) and one at 335 nm (e 50). This spectrum while not allowing any assignment, i s nevertheless compatible with the spectrum expected f or alcohol 118 or 119, products l i k e l y to be formed i n analogy to alcohol L3_ formed i n the photolysis of the 6,7-dimethyl adduct 10. 118 119 13 - 52 -Further support f o r the structure of the photoproducts was found i n the thermolysis of 114 and 116. In analogy to the previously found thermal re a c t i o n of ene-diones of the type shown i n eq 34 ( c f . introduction) photoproduct 114 gave q u a n t i t a t i v e l y 115 which was i d e n t i c a l with 115 i s o l a t e d before as a photoproduct of J53. Ene-dione 116 also reacted to give the new ene-dione 120 i n 95% y i e l d . The i r R R (eq 34) (R = H or CH_) (eq 35) (eq 36) 116 120 - 53 -spectrum of 120 showed a s i n g l e carbonyl peak at 5.70 y. In the nmr spectrum (Figure 6) the v i n y l hydrogen appeared as a complex m u l t i p l e t . The and C 3 protons, both m u l t i p l e t s at T 7.16-7.27 and T 6.80-6.90 r e s p e c t i v e l y , were assigned on the basis of the Figure 6 7.0 ao <io -c s i m i l a r i t y of t h e i r chemical s h i f t s and shapes with the analogous protons i n the 8,9-dimethyl substituted product 1 1 ^ ( c f . appendix). The endo-proton of 120 was again found as a doublet with a coupling constant of 18 Hz ( c f . spectrum of 115). Here too a small doublet (J = 1 Hz) was superimposed on the main doublet. F i n a l l y the methyl group appeared as a narrow m u l t i p l e t at T 8.23. - 54 -The mechanism leading to the photoproducts very l i k e l y involves a b s t r a c t i o n of a 6-hydrogen at the C c or the C Q p o s i t i o n to give j o intermediates 112 and 113, Ring closure of these intermediates gives r i s e to enols which upon ketonization form the products observed. Intermediate 112 i s s t a b i l i z e d by a terminal methyl group and as a r e s u l t the products a r i s i n g v i a t h i s intermediate predominate i n benzene (4:1) as w e l l as i n tert-butanol (7:1) over the product formed from intermediate 113. Scheme 8 - 55 -The type of r i n g system formed (A or B, Table 5) depends on the solvent used. As i n the photolyses of benzoquinone adducts with butadiene and 2,3-dimethylbutadiene, benzene favors r i n g system B and tert-butanol r i n g system A. Thermal reactions of photoproducts with r i n g system B going to products with structure A suggest again the greater thermodynamic s t a b i l i t y of the A-type system. Table 5 Ratio of Products Formed v i a 112 v s . v i a 113 Ratio of Ring Systems A:B benzene 4:1 3:8 tert-butanol 7:1 7:1 A B - 56 -A f a c t not well understood Is that ene-dione 120 i s not formed i n tert-butanol from intermediate .113 although t h i s solvent usually favors the copacamphor-type t i n g system A. Some subtle e f f e c t s seem Scheme 9 113 OH t-BuOH 120 116 to govern t h i s s e l e c t i v i t y as i n the case of the adduct of 1,3-penta-diene and benzoquinone where photolysis i n both benzene and t e r t -butanol gave predominantly the product with B-type s t r u c t u r e . O v e r a l l , however, the photolysis of the isoprene adduct Jp_3 established the d i r e c t i n g e f f e c t of a methyl substituent i n 'this type of Diel s - A l d e r adduct. - 57 -D. D i e l s - A l d e r Adducts of 1,4-Naphthoquinone with 2,3-Dimethyl-l,3- butadiene and with Isoprene The reason f or the i n v e s t i g a t i o n of these two compounds was discussed i n the i n t r o d u c t i o n . Adduct 66_ was synthesized according to + EtOH r e f l u x , 20 hr (eq 37) 40 the procedure of A l l e n and B e l l as shown i n eq 37. Photolysis of adduct 66_ i n benzene gave al c o h o l 121 which was i s o l a t e d by column chromatography as a c r y s t a l l i n e compound i n 43% y i e l d . Scheme 10 122 - 58 -The i r spectrum showed an OH band at 2.80 u and a carbonyl band at 5.91 u« In the nmr spectrum ( F i g . 7) the methine appears as a doublet at x 6.75. It i s only coupled to the v i n y l proton and not to the methine since the dihedral angle with the l a t t e r i s close to 9 0 ° . The methine i s s p l i t into a p a i r of doublets with coupling constants of about 8 and 3 Hz. Inspection of a model shows that the methine and the C ^ Q endo hydrogen are nearly eclipsed whereas the exo-hydrogen forms an angle with the proton of about 1 1 0° . Hence, on the basis of the 31 Karplus r e l a t i o n s h i p , the 3 Hz coupling i s l i k e l y due to the exo-hydrogen and the 8 Hz coupling due to the endo-hydrogen. The l a t t e r appears as a p a i r of^doublets at T 8.45 (calculated v a l u e ^ ) . It i s coupled (13 Hz) Figure 7 -r 4.2+ 5 9 -to the exo-hydrogen and to the methine ( 8 Hz). The exo-hydrogen at T 8 . 6 6 i s analogously s p l i t by the endo-hydrogen (J = 1 3 Hz) and with the methine (J = 3 Hz). I r r a d i a t i o n of the methine leads to an AB quartet due to the C ^ Q methylenes with a coupling constant of 1 3 Hz. The Cg methyl protons appear as a doublet at T 8 . 1 4 . Their small s p l i t t i n g of 1 . 5 Hz i s due to a l l y l i c coupling with the v i n y l hydrogen. I r r a d i a t i o n of the v i n y l s i g n a l leads to collapse of the methyl doublet to a s i n g l e t . Also c o l l a p s i n g i n t o a s i n g l e t i s the s i g n a l due to the C, methine. D The formation of alcohol 1 2 1 very l i k e l y proceeds again through an intermediate ( 1 2 2 ) formed by abs t r a c t i o n of a g-hydrogen. Bonding between C^ and Cg leads to the observed product. Bonding from the C ^ Q 3 p o s i t i o n which was observed i n the analogous benzoquinone adduct 1J3 did not occur, presumably because the benzene resonance would have been destroyed thereby. I r r a d i a t i o n of adduct 66^  i n tert-butanol using the same f i l t e r did not y i e l d the alcohol but led to a host of products. These could not be i s o l a t e d i n pure form but the nmr spectra of some of the enriched f r a c t i o n s were i n d i c a t i v e of structures such as 1 2 3 and 1 2 4 which can 4 1 e a s i l y be formed by a i r oxidation of hydroquinone 1 2 5 . The l a t t e r i n - 60 -turn i s probably formed during the photolysis since hydroquinones are always formed i n various amounts i n the photolyses of the investigated Die l s - A l d e r adducts. Alcohol 121 was found to be thermally very stable up to 2 4 5° . Adduct 65_ was synthesized from isoprene and 1,4-naphthoquinone as shown i n Scheme 11. It was o r i g i n a l l y assumed that t h i s molecule would be an appropriate model to test the e f f e c t of the methyl group since only two products seemed l i k e l y to be formed upon B-hydrogen a b s t r a c t i o n . The two intermediates so formed d i f f e r i n the p o s i t i o n of the methyl group on the a l l y l i c r a d i c a l . The methyl group at the 33 terminal p o s i t i o n i n intermediate 127 makes i t more stable than 126. Figure 8 _J I I I . I : I I I I I I I I I I I I I I I I I I I 1 I I I I I I I 1 I I I I I I I I I I I I 1 I J i i i i I i i i i I I i i i I i i i i 1 i i i i I i i -i i T i i i i I i i i i T r 8.0 7.0 6.0 S.0 4.0 3.0 2.0 1.0 0 MANUAL , AUIO : ' SAMPU: REMARKS: - 61 -Scheme 11 - 62 -Indeed, the alcohol 129,formed from the more stable intermediate, was e x c l u s i v e l y observed i n the photolysis of adduct 65_ i n t e r t - b u t a n o l . It was i s o l a t e d i n low y i e l d by glpc as a c o l o r l e s s l i q u i d . Structure 129 was indicated by the following s p e c t r a l data: The i r spectrum (CCl^) showed a carbonyl peak at 5.86 u. The nmr spectrum (Figure 8) i s very s i m i l a r to that of the alcohol formed from the 2,3-dimethyl butadiene-1,4-naphthoquinone adduct. Interesting points are the C, methine o appearing as a m u l t i p l e t between x 6.6 and 6.8, the methine as a p a i r of doublets at x 7.6 coupled to the C ^ Q exo and endo-hydrogens with coupling constants of 8 and 3 Hz r e s p e c t i v e l y . The same values were found for alcohol 121. The methyl group appeared as a s i n g l e t at x 8.9. The si g n a l s due to the C ^ Q methylenes were not separated w e l l enough on the 60 MHz spectrum to allow a d e t a i l e d a n a l y s i s . Thin layer chromatography showed the presence of many other products i n the photolysate but these could e i t h e r not be i s o l a t e d i n pure form or e l s e they were unstable. The r e s u l t of t h i s photolysis was further evidence f o r the d i r e c t i n g e f f e c t of the methyl group. However, due to the low y i e l d of the i s o l a t e d alcohol t h i s experiment i s l e s s compelling than the one with the analogous benzoquinone-isoprene Diels-Alder adduct. E. 5-tert-Butyl-cyclohex-2-ene-l,4-dione (71) Cyclohexendione 7_1_ was investigated on the assumption that i t might photolyze to y i e l d the b i c y c l i c dione 7_2 (eq 38). This was an extension of the previously observed reaction of 62^  (eq 39) which had given the analogous product 80 . i n general terms one can express t h i s type of - 63 -reaction as shown i n eq 40 where RH can also be part of the ketone molecule substituted on e i t h e r side of the carbonyl group. Some reactions of t h i s type are i l l u s t r a t e d i n eq 41 to eq 44. The reactions i n eq 42 and eq 44 were reported a f t e r the present i n v e s t i g a t i o n was begun.. On the basis of these reactions i t seemed conceivable that tert-butylcyclohexendione would undergo the anti c i p a t e d r e a c t i o n . This would have been an a t t r a c t i v e synthesis f or bicyclo[2.2.2]cctane ri n g systems. The synthesis of t h i s compound i s outlined i n Scheme 12. A l l the 4 steps are described i n the l i t e r a t u r e and give y i e l d s of 80% or b e t t e r . Scheme 12 - 64 -- 65 -- 66 -Quinone _71 i s a low melting compound (mp 3 5 - 3 7°) which enolizes r e a d i l y i n s o l u t i o n and on s i l i c a gel to the corresponding tert-butylhydro-quinone 136. Photolysis of quinone 71^  i n tert-butanol or benzene gave p_-hydro-quinone and not the desired b i c y c l i c dione 72. The hydroquinone i s almost c e r t a i n l y formed v i a a Norrish Type II reaction as shown i n Scheme 13. It i s not quite c l e a r why _71 should not have yielded some dione 7_2_ on the basis of the reaction observed with adduct ([2 (eq 39). The presence of the t e r t - b u t y l group i n 7_1 might induce too much s t e r i c s t r a i n f o r a c y c l i z a t i o n process to occur. In a somewhat analogous compound, g,g-dimethylbutyrophenone, the e l i m i n a t i o n r e a c t i o n was 47 unusually predominating over cyclobutanol formation (only 3%). 46 A report by Smith and Agosta which appeared a f t e r t h i s project was completed showed that i n an analogous cyclohexenone system the formation of a bicyclo[2.2.2joctane r i n g system i s not a favorable pathway (Scheme 14). However, i n the analogous cyclopentenone d e r i v a t i v e t h i s pathway i s the major one observed ( c f . eq 43). Scheme 13 - 68 -Scheme 14 hv,X > 330 nm t-BuOH,14 days 141 142 144, 4% 143, 23% F. Diels-Alder Adduct of Duroqulnone and 2,3-Dimethylbutadiene 1. Synthesis and Photolysis This highly substituted adduct was synthesized according to the 48 method of A n s e l l and coworkers (eq 45). Addition of a few c r y s t a l s of X 197°,23 hr - i hydroquinone (trace) 67% (eq 45) 73 - 6 9 -hydroquinone prevented polymerization processes. In the absence o f hydroquinone the reaction r e s u l t s i n an i n t r a c t a b l e gum. As outlined i n the i n t r o d u c t i o n , adduct _73 was investigated * because i t was conceivable that i t might react from i t s TT-TT t r i p l e t state and would therefore not lead to hydrogen abstractions t y p i c a l of ketone n-Tr t r i p l e t s . Moreover, due to the bridgehead methyl groups no e n o l i z a t i o n to the hydroquinone was po s s i b l e and hence good y i e l d s of photoproducts could be expected. Photolysis of adduct 73 i n solvents of various p o l a r i t i e s gave products 145, 146 and 147 (Scheme 15) i n d i f f e r e n t r a t i o s . The y i e l d s of photoproducts were high. Column chromatography o f a run i n benzene led to i s o l a t i o n of 46% ene-dione 146 and 22.6% o f alcohol 145. 2. 1,3,4,6,8,9-Hexamethyl-5-hydroxytricyclo[4.4.0.0']deca- 3,7-dien-2-one. (a) Structure Alcohol 145 was i s o l a t e d i n the form of c o l o r l e s s c r y s t a l s . The a,g-unsaturated carbonyl group gave r i s e to a peak at 5.98 y i n the i r spectrum. The nmr spectrum (Figure 9) shows three v i n y l i c methyl groups between T 8.1 and 8.3. Three other methyl groups appears as sharp s i n g l e t s at high f i e l d . The two C ^ Q methylenes give r i s e to a p a i r of doublets at x 8.43 and 9.04 (J = 12.5 Hz). The l a t t e r s i g n a l i s probably due to the exo-hydrogen which i s situated above the i T - o r b i t a l s of the carbonyl group and the 3,4-double bond. A strong - 70 -Scheme 15 0 0 73 hv I X > 340 nm 0 145 146 Relative Ratios benzene 0.5 1.0 t-BuOH 1.1 1.0 CH3CN 4.0 1.0 MeOH 13 1 dioxane-H o0 30 1 Figure 9 absorption at 251 nm (e = 7420) i s consistent with the presence of an a,S-unsaturated ketone. An a l t e r n a t i v e structure 148 for the alcohol had to be considered. It has the i d e n t i c a l ring-system as ene-dione 146 i s o l a t e d i n the (eq 46) 148 - 72 -same photolysis and would have been mechanistically f e a s i b l e (see discussion of mechanism). On the basis of s p e c t r a l data alone i t was impossible to rigorously r u l e out structure 148. Hence, the alcohol was submitted to an X-ray a n a l y s i s . This was performed by 49 Professor J . Trotter and Dr. C A . Bear of t h i s department to whom the author would l i k e to express h i s thanks. The r e s u l t s of the X-ray analysis c l e a r l y confirmed structure 145. (b) Thermolysis On the basis of structure 145 f o r the alcohol the thermal reaction of the l a t t e r can be r a t i o n a l i z e d i n a straightforward manner. Thermo-l y s i s of the alcohol i n a sealed tube gave o r i g i n a l adduct 7_3 and ene-dione 147 (eq 47). 0 (eq 47) 73, 53% Ene-dione 147 was characterized by a carbonyl peak at 5.72 u i n i t s i r spectrum. The s i g n a l at lowest f i e l d i n the nmr spectrum (Figure 10), a broad s i n g l e t , i s due to the a l l y l i c methine. The methine appears as a quartet ( J = 7 Hz) at T 7.99. The stereochemistry of th i s hydrogen i s probably exo since hydrogen-deuterium exchange took place r e a d i l y i n a two phase system of carbon t e t r a c h l o r i d e and - 73 -Figure 10 a l k a l i n e deuterium oxide. The analogous dimethyl substituted ene-dione J.1 was found to undergo p r e f e r e n t i a l exo_-deuterium exchange ( c f . eq 15). The s p e c t r a l data of the ene-dione 147 i s o l a t e d i n the photolysis of adduct _7_3 i n very polar solvents were i d e n t i c a l with the data of 147 obtained by thermolysis of alcohol 145. The formation of 147 has precedence i n the thermolysis of 1_3 which gave the analogous product 11_ (eq 14) i n what can be considered formally as a [3,3]-suprafracial sigmatropic s h i f t of the C^-C^ bond. T h e o r e t i c a l l y the C c-C, bond could also undergo a [3,3]-sigmatropic s h i f t . The s e l e c t i v e reaction i n v o l v i n g the C -C Q bond might p a r t i a l l y - 74 -o o be accounted f o r by i t s larger bond length (1.563 A v s . 1.547 A for the 49 C,--C, bond ) . A r a d i c a l mechanism leading to 147 cannot be ruled out. J o Formation of the o r i g i n a l adduct 7_3 from alcohol 145 i s an example of an oxy-retro-ene reaction (eq 48). ( I n t e r e s t i n g l y , the forward reaction leading to alcohol 145 may be c a l l e d a photochemical oxy-ene reaction ). For yt&-unsaturated alcohols this type of reaction i s quite c o m m o n . E q u a t i o n 49 shows such an example. In addi t i o n to the r e t r o -ene reaction both alcohol 145 and alcohol 149 can undergo a competitive [3,3]-sigmatropic s h i f t . The retro-ene r e a c t i o n of 145 might also proceed through a b i r a d i c a l intermediate. As i n the [3,3]-sigmatropic s h i f t of 145 the retro-ene r e a c t i o n could i n p r i n c i p l e involve cleavage of the C c-C c bond. However, only the probably weaker (vide J D supra) C,--CQ bond was broken. 149 - 75 -3. 1,3,4,6,8,9-Hexamethyltricyclo[4.4.0.0 ' ]dec-8-ene-2,5-dione (146) (a) Structure Photoproduct 146, a c o l o r l e s s l i q u i d , showed two carbonyl peaks i n the i r spectrum at 5.67 u and 5.85 y. The former indicates the presence 31 of a four-membered r i n g ketone. The nmr spectrum (Figure 11) reveals Figure.11 - 76 -three t e r t i a r y methyl groups as sharp s i n g l e t s between T 8.78 and 9.03. Two v i n y l i c methyl groups appear as m u l t i p l e t s at T 8.25-8.40. The methyl i s s p l i t by the adjacent methine i n t o a doublet at T 8.95 with J • 7.5 Hz. The proton correspondingly appears as a clean quartet at T 7.57 with the same coupling constant. The remaining and C ^ Q protons form a m u l t i p l e t at T 7.90-8.10. The stereochemistry of the methyl group i s assumed to be the one shown on the basis of the proposed mechanism (Scheme 20). Further support for structure 146 was found i n i t s thermal and base catalyzed rearrangements. Thermolysis of ene-dione 146 i n a sealed tube gave i n almost quantitative y i e l d an isomer (150) of the o r i g i n a l adduct T3. The s i m i l a r i t y between 150 and _73 i s r e f l e c t e d i n 4 the uv spectrum which shows bands at 247 nm (e 1.2 x 10 ) and 356 nm (b) Thermolysis 0 0 16 hr 192° (eq 51) 0 0 146 150,92% 73,90% - 77 -(e 84) for 150 and for 73^ a maximum at 251 nm (e 1.1 x 10^) and a featureless absorption from 280 to 400 nm having an e x t i n c t i o n c o e f f i c i e n t of 103 at 356 nm. In the i r spectrum of 150 a carbonyl band appeared at 5.99 y (5.98 y for 73). The nmr spectrum of 150 (Figure 12) shows the Figure 12 and C 2 methyls as a mu l t i p l e t at T 8.03-8.13. The two bridgehead methyls appear as s i n g l e t s at T 8.84 and 9.00. The Cj methyl i s s p l i t i nto a doublet at T 8.98 (J = 7.5 Hz). I r r a d i a t i o n of the v i n y l hydrogen leads to a collapse of the Cg methyl m u l t i p l e t into a doublet (J = 0.7 Hz) and to a simp l i f ication of the mu l t i p l e t caused by the Cg and C 7 protons. I r r a d i a t i o n of the C g v i n y l methyl group converts the v i n y l hydrogen i n t o a broad doublet (J = 1.5 Hz), probably due to a l l y l i c coupling with the C 7 methine. - 78 -The f a c i l e isomer!zation of 150 to the o r i g i n a l adduct 7_3 with boron t r i f l u o r i d e further supports i t s s t r u c t u r e . The reaction with a saturated s o l u t i o n of boron t r i f l u o r i d e i n methylene chloride was very f a s t . The isomerization with the less r e a c t i v e boron t r i f l u o r i d e etherate i n r e f l u x i n g dioxane was much slower (10% conversion a f t e r 1.5 days). The mechanism for the formation of 150 can be considered as a retro-ene r e a c t i o n " ^ ( c f . arrows i n eq 51). The s t e r i c requirements for t h i s reaction are we l l met i n 150 since the hydrogen (stereochemistry follows from mechanism, Scheme 20) i s located d i r e c t l y above the ir-o r b i t a l of the i s o l a t e d double bond to which i t i s to be tr a n s f e r r e d . The d r i v i n g force f o r the reaction i s probably enhanced by the r e l i e f of s t r a i n of the cyclobutanone r i n g and the formation of a highly conjugated chromophore. The r e l i e f of the s t r a i n i n the 4-membered ring i s probably larger than the r e l i e f of s t r a i n i n alcohol 145. This i s r e f l e c t e d i n the fa c t that i t takes higher temperatures ( 2 8 0°) to promote the reaction of the alcohol than i t takes f o r ene-dione 1 4 6 ( 1 9 0° ) . (c) Base-Catalyzed Rearrangement Ene-dione 146 was refluxed i n a water-dioxane s o l u t i o n to which a speck of s o l i d potassium hydroxide had been added. The product i s o l a t e d a f t e r n e u t r a l i z a t i o n and extraction of the aqueous mixture was ene-dione 147 previously i s o l a t e d from the thermolysis of alcohol 145. This product i s formally the r e s u l t of a 1,2-carbanionic s h i f t of enolate 151 to give enolate 152. Scheme 16 For t h i s r e a c t i o n to be concerted, the s h i f t has to be e i t h e r s u p r a f a c i a l 12 with i n v e r s i o n or a n t a r a f a c i a l with retention at the migrating s i t e . These requirements cannot be met i n t h i s s t e r i c a l l y constrained molecule. Another mechanism would involve the formation of the - 80 -intermediary anion 153 which could undergo ring-closure i n a Michael type 1,4-addition as indicated with arrows i n Scheme 16. However, such an anion as 153 would be expected to be protonated i n an aqueous medium and would therefore lead to o r i g i n a l adduct 7_3 which was not observed. A t h i r d a l t e r n a t i v e would involve a reaction sequence outl i n e d i n Scheme 17. The various structures do not ne c e s s a r i l y represent true intermediates as the reaction might be concerted. However, i f anion 154 were an intermediate i t would very l i k e l y be protonated i n an aqueous medium such as was used. Scheme 17 147 - 81 -The mechanism described above has precedents i n the rearrangement 51 of some y~diketones reported by Yates and Betts. As shown i n Scheme 18 two consecutive anionic 1,2-phenyl s h i f t s give r i s e to the product with the wrong l a b e l l i n g . The a l t e r n a t i v e mechanism instead, as shown i n Scheme 19, leads to the c o r r e c t l y l a b e l l e d product. I t should be noted that i n p r o t i c media the anion .162 i s protonated and undergoes cleavage Scheme 18 Ph Ph Ph 155 CMe3 N a ° C H 3 ether Ph Ph Ph 0 156 CMe, 0 Ph Ph 0 157 CMe, 1,2 P h - s h i f t 0 Ph 0 ^ CMe, Ph H Ph 158 Ph Ph Ph 0 160 CMe, 1) 1,2 Ph - s h i f t 2) protonation Ph 0 Ph t Ph 159 0 CMe, * - 1 3 c - 82 -Scheme 19 0 Ph Ph 0 Ph Ph CMe„ U V . C M e3 Ph Ph 164 0 Ph P h ^ > T >T P h ' 1? 161 0 0 0 n© 157 0 © 0 0 0 u w u NaOCH ^ N ^ V c M e — P h^ AY^( > _ p h e t h e r el^ 163 162 NaOCH Ph Ph 3 r i 0 MeOH 0 0 0 0 CMe. P h ^ > < ^ * > ^ 3 Ph- T - C M E 3 CHPh2 165 1 0 CMe, Ph Ph 0 I 1 CHPh2 ChPh2 166,5% 167,83% CHPh0 ChPh. 156 -„ 2 2 - 83 -to give ketones 166 and 167. The analogous anion 159 i n Scheme 17 i s probably not formed or i s very s h o r t - l i v e d since the r e a c t i o n i s c a r r i e d out i n an aqueous medium. 4. Mechanism of the Photolysis of Adduct 7_3 The formation of photoproducts 145 and 147 (see Scheme 20) can be accounted for by the same mechanism postulated f o r the analogous products observed p r e v i o u s l y , i . e . v i a i n i t i a l 8-hydrogen abstract i o n by oxygen. This leads to intermediate 168a which can close i n two ways to give e i t h e r alcohol 145 or the enol form of ene-dione 147. It was an a_ p r i o r i p o s s i b i l i t y that ene-dione 147 was a photoproduct of alcohol 145 since the analogous dimethyl substituted alcohol 13_ gave the r e l a t e d ene-dione 11 on p h o t o l y s i s . However, the l a t t e r was also a primary photoproduct of adduct 10_ as determined by a k i n e t i c a n a l y s i s . ^ In order to resolve t h i s point i n the present case, equal amounts of adduct 7_3 and alcohol 145 were i r r a d i a t e d stimultaneously under i d e n t i c a l conditions. A f t e r complete conversion of adduct 7_3 the alcohol was s t i l l v i r t u a l l y unaltered. Prolonged photolysis led to destruction of the alcohol i n both samples, and no s i g n i f i c a n t new peaks could be detected by g l p c Hence ene-dione 147 i s a primary photoproduct. Ene-dione 146 can be formed i n at l e a s t two d i f f e r e n t ways, path A and path B i n Scheme 20. Path A s t a r t s out with the common intermediate 168a formed by 3-hydrogen a b s t r a c t i o n . A subsequent hydrogen s h i f t of the hydroxyl hydrogen gives r i s e to intermediate 168b which can close to y i e l d enol 170. Ketonization of the l a t t e r affords the i s o l a t e d ene-dione 146. - 84 -Scheme 20 147 145 73 path B ill y-H a b s t r a c t i o n by carbon - 85 -The a l t e r n a t i v e pathway B involves y-hydrogen abstract i o n by a 8-carbon of the a,$-unsaturated chromophore to give intermediate 171. Ring closure of the l a t t e r affords ene-dione 146 d i r e c t l y without the formation of an enol i n contrast to path A. The hydrogen s h i f t i n path A leading to intermediate 168h has 52 53 some analogy i n the work of Orlando et a l . and of F a r i d . Photolysis of tert-butyl-p-benzoquinone i n dimethoxyethane gave the products shown i n Scheme 21. Hydrogen abstraction leads to the semi-quinone Scheme 21 174 175 176 b i r a d i c a l 174. The l a t t e r was proposed to tautomerize to b i r a d i c a l 175. This step bears some analogy to the hydrogen s h i f t i n path A (Scheme 20) from 168a to 168b. However, intermediate 174 probably - 86 -has a better chance to undergo a hydrogen s h i f t since i t very l i k e l y has a longer l i f e t i m e than 168a which i s not a stable semi-quinone r a d i c a l . The a l t e r n a t i v e pathway B f o r the formation of ene-dione 146 i s not unprecedented at a l l . One of the e a r l i e s t observed reactions involving hydrogen abstraction by a 8-carbon of an a,6-unsaturated 54 ketone was reported by Herz and Nair (eq 52). The reac t i v e state involved i n the formation of 178 i s probably a T T - T T t r i p l e t since the * phosphorescence spectrum of 177 was i n d i c a t i v e of a ir—ir s t a t e . The methoxy group i s known to lower the T T - T T t r i p l e t energy r e l a t i v e to * 26 the n-TT t r i p l e t l e v e l due to i t s e l e c t r o n - r e l e a s i n g e f f e c t . In the case of enone 177 the 7T-TT t r i p l e t i s of even lower energy than A the n-TT t r i p l e t . This l e v e l r e v e r s a l can also be brought about by polar solvents * * i n molecules with close l y i n g i r— I T and n—rr t r i p l e t s t a t e s . This i s - 87 -i l l u s t r a t e d with an i n v e s t i g a t i o n by B e l l u s , Kearns, and Schaffner of the photochemistry of octalone 179. The solvent dependence and quenching studies which allowed s e l e c t i v e quenching of the upper t r i p l e t Scheme 22 ,£0 179 T * n-Tr TT-TT i n alcohol. "XX) 180 \ \ A s XX) 181 i n benzene-toluene 0 182 Ph BuOH benzene toluene 80% 14% 3% 11% 45% 2% 40% - 88 -state when the energy of the quencher was between the two t r i p l e t energy l e v e l s led to the c o r r e l a t i o n of energy l e v e l s i l l u s t r a t e d i n Scheme 22. In alcohol the TT-TT t r i p l e t i s lower i n energy than the * n-Tr t r i p l e t and leads predominantly to rearrangement y i e l d i n g ketone 180. In the nonpolar solvent benzene intermolecular y-hydrogen abstraction by the carbonyl oxygen takes place leading to f3 ,y-unsaturated ketone 181. In toluene the major product i s formed by hydrogen abstrac-t i o n from toluene, a good hydrogen donating solvent (eq 53). The + CH3-Ph - C D + -CH Ph (eq 53) 179 183 .f (Ph'A^Ph) 182 reactions occurs v i a a TT-TT t r i p l e t . The l a t t e r i s higher i n energy than the n-Tr t r i p l e t i n benzene. However, the energy l e v e l s are very close and hence i t becomes pos s i b l e that the reaction from the higher t r i p l e t l e v e l i s dominating. * In summary polar solvents can bring about a r e v e r s a l of n-Tr and TT-TT t r i p l e t states i n molecules where the two l e v e l s are close i n - 89 -A energy. It should be added here that i n the case of c l o s e - l y i n g n-TT A and TT-TT t r i p l e t states v i b r o n i c coupling leads to mixed states with A A 56 n-TT and TT-TT character. Hydrogen abstract i o n by oxj'gen i s commonly accepted to be t y p i c a l A 55 of n - T r t r i p l e t s of carbonyl fun c t i o n s . Schaffner and coworkers suggest that hydrogen ab s t r a c t i o n by the 8-carbon of an a,8-unsaturated ketone i s A . t y p i c a l of TT-TT t r i p l e t s . The lack of hydrogen abstract i o n m t r i p l e t reactions from p r o t i c solvents such as isopropanol i s usually taken • • * ... 26 as a strong i n d i c a t i o n of an unreactive TT-TT t r i p l e t . Another r e a c t i o n i n v o l v i n g hydrogen a b s t r a c t i o n by a carbon atom was reported by Nakanishi and coworkers. ""^ Photolysis of taxinine diacetate 184 i n various solvents led to a transannular c y c l i z a t i o n (eq 54). The three dimensional structure (186) of 184 shows that the a l l y l i c hydrogen has .to be abstracted by the ct- Carbon of the chromophore. Abstraction by the oxygen i s s t e r i c a l l y impossible. An intermolecular hydrogen a b s t r a c t i o n was ruled out on the basis of k i n e t i c experiments and because the a l l y l i c hydrogen was protected by the cage-like molecule from external attack. It should be noted that i n the r e a c t i o n studied by Herz and Nair i t was the 8-carbon and not the a-carbon performing the hydrogen a b s t r a c t i o n . The r e a c t i o n of 184 could be s e n s i t i z e d with acetophenone as w e l l as quenched with piperylene thus suggesting a t r i p l e t as the r e a c t i v e s t a t e . Furthermore the high quantum y i e l d s i n polar solvents A (0.091 i n dioxane, 0.078 i n tert-butanol) which s t a b i l i z e TT-TT t r i p l e t states (vide supra), as compared to the lower quantum y i e l d i n benzene (0.031) led to the conclusion that the r e a c t i o n probably occurred from - 90 -! (eq 54) '•» OAc 186 a TT-TT t r i p l e t s t a t e . This was also supported by a photolysis of 184 i n isopropanol which did not give any products a r i s i n g from hydrogen ab s t r a c t i o n from the solvent. As mentioned, t h i s i s usually ft i taken as an i n d i c a t i o n of a lowest TT-TT t r i p l e t state ( c f . Schaffner s study ) . - 91 -58 Recently Agosta and coworkers have demonstrated hydrogen abstraction reactions by the B-carbon atoms of a v a r i e t y of cy c l o -pentenones. For example, consider the photolysis of cyclopentenone 187 as i l l u s t r a t e d i n eq 55. Hydrogen abstract i o n by the B-carbon - 92 -i s suggested to occur through a six-membered t r a n s i t i o n state giving b i r a d i c a l 191. Ring closure affords the minor b i c y c l i c product 190. Hydrogen ab s t r a c t i o n by the a-carbon i n b i r a d i c a l 191 y i e l d s the two major products 188 and 189. 59 A s i m i l a r r e a c t i o n was found with a s e r i e s of cyclopentenones of type 192 i n which the carbonyl group was not part of the r i n g (see eq 56). Both reactions i l l u s t r a t e d i n eq 55 and 56 could be s e n s i t i z e d and quenched with no change i n product r a t i o s and were therefore thought to proceed v i a t r i p l e t s t a t e s . In review, these hydrogen abstractions by 8-carbon have been suggested to occur from TT-TT t r i p l e t s t a t e s . With regard to the r e a c t i v e state of adduct 7_3 there i s some precedence for the l i k e l i h o o d of a TT-TT t r i p l e t s t a t e . This was mentioned b r i e f l y i n the i n t r o d u c t i o n . I t was stated there that benzoquinones and cyclohex-2-ene-l,4-diones which are substituted with two methyl groups on the carbon-carbon double bond undergo cycloadditions to o l e f i n s to give e x c l u s i v e l y cyclobutanes A This had been t e n t a t i v e l y a t t r i b u t e d to a r e a c t i o n from a TT-TT t r i p l e t 21 s t a t e . A more complete l i s t of the r e a c t i v i t i e s of c e r t a i n quinones and ene-1,4-diones i s given i n Table 6. 21 * The suggestion by Barltrop and Hesp that i t might be the TT-TT * t r i p l e t state which leads to C=C a d d i t i o n and the n-TT t r i p l e t state which leads to C=0 a d d i t i o n was contraindicated by a study of Pappas and P o r t n o y . ^ In the view of Barltrop and Hesp the cases of compounds undergoing both C=0 and C=C a d d i t i o n would involve competitive A A reactions from n-TT and TT-TT t r i p l e t s t a t e s . Assuming the l a t t e r Table 6 A. Exclusive C=0 Addition 0 B. Concurrent Additions to C=0 and C=C 0 0 0 C. Exclusive C=C Addition - 94 -explanation to hold true and also that d e a c t i v a t i o n processes compete with photoaddition, Pappas and Portnoy stated that the r a t i o of products a r i s i n g from C=0 and C=C ad d i t i o n should be dependent on the concentration of the alkene or alkyne added. However, using 1,4-naphthoquinone as a model they d i d not f i n d any concentration dependence i n the photochemical add i t i o n to diphenylacetylene. Furthermore there was no solvent e f f e c t observed i n the same rea c t i o n which argues against the involvement of two d i f f e r e n t excited s t a t e s . In the case of the exclusive C=C additions of methoxy-p_-benzo-64 64 quinone and of 2-methoxy-l,4-naphthoquinone i t was a t t r a c t i v e to * suggest that t h i s resulted from the lowering of the TT-TT t r i p l e t l e v e l 26 due to the e l e c t r o n r e l e a s i n g e f f e c t of the methoxy group. However, Pappas and P o r t n o y ^ found that 6-methoxy-l,4-naphthoquinone gave v i r t u a l l y the same r a t i o of C=0 v s . O C addi t i o n products as did the unsubstituted 1,4-naphthoquinone. T h e o r e t i c a l l y a methoxy group at p o s i t i o n 6 should have s t a b i l i z e d the TT-TT t r i p l e t equally as such a group at p o s i t i o n 2. However, the experimental r e s u l t s suggest that the methoxy substituent d i r e c t s the mode of additon only i f i t s p o s i t i o n i s on the C=C bond involved i n the c y c l o a d d i t i o n . Pappas and P o r t n o y ^ suggested that the e f f e c t of the methoxy group (or an acetoxy or methyl group) i s (a) to " l o c a l i z e " e x c i t a t i o n i n the adjacent C=C bond and (b) to s t a b i l i z e an intermediate complex or b i r a d i c a l species. * 60 The presence of a TT-TT t r i p l e t state was suggested by Pappas and Portnoy to be responsible f o r the complete lack of photoaddition of 6,7-dimethoxy-1,4-naphthoquinone to diphenyl or dimethylacetylene. In the case of the duroquinone adduct 7_3 the mechanism i n v o l v i n g hydrogen abstraction by carbon i s d i f f e r e n t from the abstraction of - 95 -hydrogen by oxygen i n that there i s no e n o l i c intermediate such as 170 formed ( c f . Scheme 20). The presence of enols has been proven i n the 170 photolysis of adducts 10_ and 6i2 by the incorporation of a deuterium atom when they were i r r a d i a t e d i n tert-butanol-O-d. Photolysis of adduct _7_3 i n deuterated tert-butanol led to no incorporation of deuterium (mass spectrum) i n the ene-dione 146 i s o l a t e d . This strongly suggested that no enol was formed. However, the reaction.of the bulky tert-butanol at the s t e r i c a l l y hindered p o s i t i o n might not have been p o s s i b l e . The a l t e r n a t i v e mechanism for the enol to ketonize would be through an intramolecular 1,3-shift of the hydroxy hydrogen. It has been found, however, that enols ketonize i n a bimolecular r e a c t i o n . ^ Nevertheless the photolysis was repeated i n a mixture of dioxane and deuterium oxide. The l a t t e r was chosen because i t was expected to be small enough to be able to approach the hindered p o s i t i o n . However, here again there was no deuterium incorporated i n ene-dione 146. I n t e r e s t i n g l y , the ene-dione 147 formed at the same time i n t h i s very polar medium was found to be deuterated. This was expected on the - 96 -168a ' 169 147-d basis of the mechanism in v o l v i n g 3 _hydrogen abstract i o n (eq 57 ) . An acid catalyzed generation of enol 170 i n dioxane/deuterium oxide was also attempted i n order to see whether the enol could be formed and deuterated independently. However, i n a s o l u t i o n which was 0.05 M i n deuterium chloride no exchange took place i n 11 days at 6 0 ° . Under the same conditions the t e r t i a r y hydrogen of 2-methylcyclohexanone exchanged i n less than 1 h r . Higher temperatures ( 1 0 0° ) or higher acid concentration (1 M) led to decomposition of ene-dione 146 in t o numerous products. From these observations i t follows that a c i d -catalyzed e n o l i z a t i o n of 146 i s not a very f a c i l e r e a c t i o n . S t e r i c hindrance to exchange i s u n l i k e l y since i n the base-catalyzed r e a c t i o n the enolate i s formed r e a d i l y . Although acid-catalyzed exchange reactions are much slower than base-catalyzed r e a c t i o n s , the l a t t e r i s probably accelerated by a homoenolate formation (much as i n Figure 3) which i s also a good s t a r t i n g point f or the mechanism proposed f o r the base-catalyzed rearrangement (Scheme 17 ) . Despite the f a i l u r e to incorporate deuterium into ene-dione 146 by acid c a t a l y s i s , the i r r a d i a t i o n experiments i n deuterated solvents - 97 -are very much i n favor of a hydrogen abstrac t i o n by carbon. Whether t h i s occurs from a TT-TT t r i p l e t state i s not c e r t a i n f o r two reasons. F i r s t l y a look at uv spectrum ( F i g . 14 ) of adduct 7_3 shows that the * n-TT band overlaps with another band. Similar bands were found by Cookson 66 and coworkers i n a great number of D i e l s - A l d e r adducts of p_-benzo-quinone and various c y c l i c conjugated dienes. These bands were assigned by Cookson to charge transfer states a r i s i n g from i n t e r a c t i o n of the o l e f i n i c double bond with the chromophore. The wavelength of these t r a n s i t i o n s was found to increase with decreasing i o n i z a t i o n p o t e n t i a l of the o l e f i n i c bond. The compounds i n Figure 14 show much more A overlap of the charge-transfer band with the n-ir band than the bands i n Figure 13. This can l i k e l y be c o r r e l a t e d with the lower i o n i z a t i o n p o t e n t i a l s of the tetrasubstituted o l e f i n i c bonds i n the compounds of Figure 14 compared to the le s s substituted o l e f i n i c bonds i n the molecules of Figure 13. Considering these f a c t s , i t i s t h e o r e t i c a l l y p o s s i b l e that even with a f i l t e r absorbing a l l the l i g h t of X s< 340 nm, reactions might occur from charge-transfer s t a t e s . Even i f the e x c i t a t i o n i s to an A n-TT s i n g l e t s t a t e , intersystem crossing could lead to a charge-transfer t r i p l e t s t a t e . A Further evidence against the involvement of a TT-TT t r i p l e t state i n the photolysis of adduct 204 was obtained i n an i n v e s t i g a t i o n by Jennings^7 i n t h i s laboratory. Photolysis of adduct 204 did not give r i s e to a product formed v i a hydrogen abstrac t i o n by carbon although the ene-dione part of the molecule was i d e n t i c a l with adduct 73. Therefore i t i s apparently not the e l e c t r o n i c e f f e c t of the two methyl - 99 -0 benzene hv 0 0 204 205 groups on the enone double bond, which brings about the novel hydrogen abstraction observed i n adduct 73. Another reason f or t h i s a b s t r a c t i o n might be the presence of a conformation f a c i l i t a t i n g t h i s process. The conformation of adduct 7_3 could very w e l l be d i f f e r e n t from the rest of the Diels-Alder adducts studied, due to the presence of the two bridgehead methyl groups. Far more than hydrogen these two methyl groups would prefer a conformation i n which they are staggered. Such a conformation i s shown i n structure 206. In t h i s conformer one of the C a hydrogens can be e a s i l y H CH 0 s 3\ X CH 206 - 100 -abstracted by the n - o r b i t a l of the oxygen and at the same time one of the C,. hydrogens i s close to the Tr-orbital at Q^' Abstraction of the C,. hydrogen by and r i n g closure between C,. and leads to the observed product 146.. The hydrogen abstractions by carbon observed by Nakanishi"^ and 54 by Herz and Nair might also be favored by the proximity of the T f - o r b i t a l and the hydrogen i n these r i g i d s t r u c t u r e s . - 101 -EXPERIMENTAL General Infrared ( i r ) spectra were recorded on a Perkin-Elmer Model 137 spectrometer using sodium chloride c e l l s . Nuclear magnetic resonance (nmr) spectra were recorded by Ms. P h y l l i s Watson, Mr. Roland Burton, and Mr. Evert Koster of t h i s department on the following spectrometers: Varian Model T-60, HA-100 and XL-100. TMS was used as an i n t e r n a l standard i n a l l cases. U l t r a v i o l e t (uv) spectra were recorded on a Unicam Model SP 800 B spectrophotometer using methanol as solvent unless otherwise i n d i c a t e d . Mass spectra were obtained on Atlas CH-4-B and AEI-MS-902 spectrometers, operated by Mr. George D. Gunn and Mr. Brian Stevenson of t h i s department. Melting points were determined on a Fisher-Johns melting point block and are a l l uncorrected. Microanalyses were performed by Mr. P. Borda of t h i s department. For gas l i q u i d p a r t i t i o n chromatography (glpc) a Varian Aerograph Model 90 P and Varian Aerograph Autoprep Model A 700 were used. Both were connected to Honeywell E l e c t r o n i k 15 s t r i p chart recorders. The following columns were used ( a l l on 60/80 Chromosorb W as s o l i d support): 20% DEGS, 5' x 1/4" (column A); 30% DEGS, 5' x 1/4" (column B); 30% DEGS, 10' x 1/4" (column C); 5% DEGS, 20' x 3/8" (column D); 20% SE-30, 5' x 1/4" (Column E); 10% FFAP, 5' x 1/4" (column F ) . In - 102 -the text the column type i s followed by the column temperature, the c a r r i e r gas flow r a t e , and the retention time (t i n min) of the compound i n question. For column chromatography S i l i c a Gel (less than 0.08 mm) from E. Merck AG was used under 5-10 p s i nitrogen pressure. Thin layer chromatography ( t i c ) plates were prepared with S i l i c a Gel G or GF 2 5^ for TLC acc. to Stahl (10-40 u) and developed i n iodine chambers. The alumina used for f i l t r a t i o n s was Woelm, n e u t r a l , a c t i v i t y grade 1. Photolyses were performed by means of a 450 W medium pressure Hanovia type L lamp placed i n a water cooled quartz immersion w e l l , or with a Westinghouse 275 W sunlamp. I r r a d i a t i o n s with the Corning glass f i l t e r No. 7380 (transmitting l i g h t of X » ; 340 nm, referred to as the 340 nm f i l t e r ) were performed with reaction vessel and f i l t e r at a distance of approximately 6" from the lamp. The f i l t e r was constantly cooled by an a i r stream. Solutions to be i r r a d i a t e d were degassed at lea s t 15 min p r i o r to photolysis with L grade nitrogen or argon. The solvents used were reagent grade and usually d i s t i l l e d . The following compounds were used repeatedly: 1,4-naphthoquinone (K & K Laboratories, I n c . ) , 2,3-dimethyl-l,3-butadiene (Aldrich) , p_-benzoquinone (Eastman, p r a c t i c a l grade). - 103 -5a, 8a -Dlmethyl-4ag ,5,8,8af3 -tetrahydro-1,4-naphthoquinone (62) _— In a modified procedure of Euler et a l . a s l u r r y of 3.093 g (28.6 mmol) of p_-benzoquinone and 5.577 g (67.9 mmol) of trans,trans-2,4-hexadiene (Aldrich) was s t i r r e d magnetically at 60° i n a f l a s k equipped with a condenser. A f t e r 15 min the benzoquinone had di s s o l v e d . The heating was continued f o r another 15 min and subsequently the dark brown s o l u t i o n was allowed to cool to room temperature. The s t i r r i n g was continued for 3 h r . Removal of the excess diene under vacuum and r e c r y s t a l l i z a t i o n of the r e s u l t i n g c r y s t a l -l i n e product from petroleum ether ( 6 8° ) gave 3.138 g (16.5 mmol, 58%) of l i g h t - y e l l o w c r y s t a l s of 62, mp 57.0-57.5° ( l i t .2 8 5 8 - 5 9 . 5° ) . R e c r y s t a l l i z a t i o n of the mother l i q u o r y i e l d e d another 1.694 g (8.9 mmol, 31%) of 62^ , mp 5 1 - 5 3° . The pure product had the following s p e c t r a l c h a r a c t e r i s t i c s : i r (CCl^) 5.94 (broad, C=0) y; nmr (CCl^) x 3.4 ( s , 2, v i n y l H at C 2 and C 3 ) , 4.4 ( s , 2, v i n y l H at Cfi and C ? ) , 6.8 (m, 2, C A &H and C g aH), 7.2-7.8 (m, 2, C5H and C gH), 8.9 (d, 6, J - 7 Hz, methyl); n—rr uv max (benzene) 371 nm (e 68). Photolysis of Tetrahydronaphthoquinone j62 A s o l u t i o n of 997 mg (5.52 mmol) of 62_ i n 400 ml benzene was i r r a d i a t e d with the sunlamp through the 340 nm f i l t e r . The re a c t i o n was monitored by observing the disappearance of the 371 nm peak of 62_ i n the uv spectrum. A f t e r 121 hr t h i s peak had disappeared and t i c (alumina, chloroform) and glpc (column B, 1 7 0° , 150 ml/min) showed one major product (t 8.0 min). The i r r a d i a t e d s o l u t i o n was concentrated - 104 -under vacuum and the r e s u l t i n g dark brown o i l chromatographed on a short column (1.4 x 15 cm) of n e u t r a l alumina using chloroform as an eluent. The combined and concentrated f r a c t i o n s containing the major product gave a f t e r c r y s t a l l i z a t i o n of the brown o i l from petroleum ether ( 6 8° ) / e t h e r 274 mg (1.44 mmol, 26%) of 10-methyltricyclo-[4.4.1.3'7.0]undec-8-ene-2,5-dione(80), mp 7 5 . 5 - 7 8 . 5°. Two further r e c r y s t a l l i z a t i o n s y i e l d e d f a i n t l y yellow c r y s t a l s of mp 8 0 . 0 - 8 0 . 5°; i r (CCl^) 5.78 (C=0) y; nmr (CDC13) T 4.1-4.6 (m, 2, v i n y l H), 7.2-7.7 (m, 7), 7.7-8.4 (m, 2, methylene), and 8.7 (d, 3, J = 7 Hz, methyl); uv max (MeOH) 291 nm (e 56); mass spectrum (70 eV) m/e parent 190. Anal. Calcd. f o r C1 2H1 4 ° 2: C > 7 5 , 7 6 ; H» 7'4 2' F o u n d : c» 75.50; H, 7.32. The same major product was obtained i n photolyses using the 450 W Hanovia lamp, and also by u t i l i z i n g petroleum ether ( 6 8° ) as w e l l as t e r t - b u t y l a l c o h o l as solvents. The l a t t e r increased the reaction rate considerably (approximately f i v e times). The i d e n t i t y of the product observed i n these solvents was checked by i r and melting p o i n t . Deuterium Exchange of Ene-dione 80 A s o l u t i o n of 20 mg of 8 £ i n deuterochloroform was shaken i n an nmr tube with deuterium oxide containing a speck of potassium hydroxide. The exchange of the hydrogens took place slowly as was seen by a gradual decrease of the high f i e l d part of the m u l t i p l e t at T 7.2-7.7; a f t e r 2 hr 0.5 H was exchanged, a f t e r 3 days 1.5 H, 9 days I. 9 H, 20 days 2.0 H. - 105 -Hydrogenation of Ene-dione 80 To a s o l u t i o n of 93 mg (0.49 mmol) of 80 i n 25 ml e t h y l acetate, approximately 20 mg of 10% palladium on charcoal was added. Hydrogen uptake at atmospheric pressure was very f a s t (y 30 s e c ) . A f t e r 1 hr no further hydrogen uptake could be detected. The re a c t i o n mixture was f i l t e r e d through C e l i t e to give 92 mg (99%) of 10-methyltricyclo-3 7 [4.4.1. ' .0]undeca-2,5-dione (86) which was r e c r y s t a l l i z e d from petroleum ether ( 3 5 - 6 0° ) to produce c o l o r l e s s c r y s t a l s : mp 8 4 . 5 - 8 5 . 0°; i r (CCl^) 5.80 (C=0) u; nmr (CCl^ and CDC13 mixture) T 7.34 (pentuplet, 1, J = 3 Hz, C 3 methine), 7.50-7.75 (m, 5 ) , 7.80-8.75 (m, 7), 8.82 (d, 3, J = 6.5 Hz, methyl); uv max (MeOH) 293 nm (E 51); mass spectrum (70 eV) m/e parent 192. Anal. Calcd. f o r C1-H.,0o: C, 74.96; H, 8.39. Found: C, 74.86; H, 8.52. Deuterium Exchange of Dione 8_6 A s o l u t i o n of ^6 i n deuterochloroform was shaken p e r i o d i c a l l y i n an nmr tube with deuterium oxide i n which a speck of potassium hydroxide had been d i s s o l v e d . A f t e r 12 days the two hydrogens had been exchanged as seen i n the nmr (CDC13) x 7.31 (broad t , 1, J = 3 Hz, C 3 methine), 7.45-7.75 (m, 3), other parts of spectrum i d e n t i c a l with the proteo-dione 86. - 106 -Photolysis of Tetrahydronaphthoquinone £2_ i n t e r t - B u t y l Alcohol-O-d A s o l u t i o n of 89 mg (0.47 mmol) of 62 i n 7.5 ml t e r t - b u t y l a l c o h o l -0-d was i r r a d i a t e d through the 340 nm f i l t e r . A f t e r 2.5 hr the re a c t i o n was complete as monitored by uv at 371 nm. The r e s u l t i n g s o l u t i o n was concentrated under vacuum and f i l t e r e d through a short column ( ^ 4 x 1 cm) of n e u t r a l alumina using chloroform as an eluent. Concentration of the f i l t r a t e afforded 28 mg of c r y s t a l l i n e material which was r e c r y s t a l l i z e d from ether/petroleum ether ( 6 8° ) to give 14 mg of ene-dione J30 p a r t l y deuterated at C^. The nmr spectrum showed a decrease of approximately 0.5 H i n the same area (around T 7.5) which showed a decrease i n i n t e g r a t i o n upon base-catalyzed deuterium exchange of 80. The mass spectrum (70 eV) featured: m/e 93(100), 190(35.0), 191(18.3). From t h i s i t followed that ca. 0.3 D had been incorporated. 2,3-Dimethyl-l,4,4a,9a-tetrahydroanthraquinone (66) — A procedure of A l l e n and B e l l was followed. A s o l u t i o n of 8.403 g (53.2 mmol) of 1,4-naphthoquinone and 10.342 g (126 mmol) of 2,3-dimethyl-l,3-butadiene i n 50 ml of 95% ethanol was refluxed for 20 hr . On cooling i n a r e f r i g e r a t o r a c r y s t a l l i n e p r e c i p i t a t e was formed. F i l t r a t i o n and r e c r y s t a l l i z a t i o n from acetone afforded 6.9 g (28.8 mmol, 40 54%) of c o l o r l e s s c r y s t a l s of 66, mp 147°. ( l i t . 1 5 0 ° ) , i r (CHC13) 5.91 (C=0) y; nmr (CDC13) x 1.8-2.4 '(m, 4, aromatic H), 6.5-6.8 (m, 2, C. H and C. H), 7.2-8.2 (broad ms 4, a l l y l i c H), 8.4 (s, 6, methyls); 4a 9a uv max (MeOH) 250 (e 1.08 x 104, TT-TT*), 296 (e 1.85 x 1 0 3 ) , 302, 3 shoulder (e 1.85 x 10 ) , 340 nm shoulder (e 150). - 107 -Photolysis of Anthraquinone 6§_ A s o l u t i o n of 1.002 g (4.17 mmol) of 66_ i n 400 ml benzene was i r r a d i a t e d through the 340 nm f i l t e r f o r 15 h r . The re a c t i o n mixture was concentrated under vacuum and chromatographed on 100 g of S i l i c a Gel using 5% acetone/chloroform as an eluent. From t h i s column 410 mg of 66_ were recovered and 257 mg (43%, based on recovered s t a r t i n g material) 5 9 of 3,4-benzo-8,9-dimethyltricyclo[4.4.0.0 ' ]dec-7-ene-5-ol-2-one (121) were i s o l a t e d . R e c r y s t a l l i z a t i o n of the l a t t e r from ether/petroleum ether ( 6 8° ) gave c o l o r l e s s c r y s t a l s , mp 1 2 6° ; sublimed material ( 1 0 0 ° , 0.02 mm), mp 12 6 . 0 - 1 2 6 . 5°; i r (CHC13) 2.80 (OH), 5.91 (C=0) y; nmr (CDC13) x 1.94-2.72 (m, 4, aromatic H), 4.24 (broad s, 1, v i n y l H), 6.75 (d, 1, J, _ = 3 Hz, C,H), 7.20 ( s h i f t dependent on concentration, broad s, 1, OH), 7.40 (d of d, 1, J , i r i ~ 8 Hz, J . i n ^ 3 Hz, ' ' ' ' l,10endo l,10exo Jl,10endo + Jl,10exo = 1 1 H z' C1H ) » 8'1 4 (d> 3' J = X'5 H z' C8 * * * * * * • 8.45 (d of d, 1, J 1 > 1 0 e n d o - 8 Hz, J 1 0 e n d o > 1 0 e x o - 13 Hz, C ^ ^ H ) , 8.66 (d of d, 1 J . = 3 Hz, J, r t . =13 Hz, C i n H), 8.97 l,10exo 10endo,10exo lOexo (s, 3, Cg methyl); spin decoupling upon i r r a d i a t i o n at x 4.24 leads to collapse of doublet at x 6.75 to a s i n g l e t ; i r r a d i a t i o n at x 7.4 converts C._ , H and Ciri H i n t o an AB quartet, J = 13 Hz); chemical lOendo lOexo s h i f t s f or the C. --methylenes are calculated using 6.—6„ = V ( v / - v i ) ( v i _ v o ) » 1U A D 4- J. j Z 3 3 uv max (MeOH) 247 (e 6.7 x 10 ) , 286 nm (e 1.9 x 10 ) ; mass spectrum (70 eV) m/e parent 240. Anal. Calcd. f o r C 1 6H 1 60 2: C, 79.98; H, 6.71. Found: C, 80.01; H, 6.90. I r r a d i a t i o n of 66 through Pyrex also gave r i s e to the same product which decomposed to numerous products upon prolonged photolysis i n - 108 -benzene. I r r a d i a t i o n s i n _t-butanol lead to many inseparable products and no detectable alcohol 121. 6-Methyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (63) 23 In a modified procedure of Euler et a l . a s o l u t i o n of 4.032 g (37.3 mmol) of _p_-benzoquinone ( r e c r y s t a l l i z e d from ethanol) and 5.0 g (73 mmol) of f r e s h l y d i s t i l l e d isoprene (Eastman Organic Chemicals) i n 25 ml of benzene was allowed to stand overnight and was subsequently refluxed f o r 1 h r . The concentrated mixture was r e c r y s t a l l i z e d from ether/petroleum ether ( 6 8° ) to give 5.140 g (28.2 mmol, 78%) yellow c r y s t a l s of j63, mp 8 1 . 5 - 8 3 . 0°. Five further r e c r y s t a l l i z a t i o n s afforded material of mp 82.0-82.5° ( l i t . 8 5 - 8 6 ° ) ; i r (CHC13) 5.91 (C=0) y; nmr (CDC13) T 2.3 (s, 2, C 2 and C 3 v i n y l H), 4.6 (broad s, 1, v i n y l H), 6.6-7.0 (m, 2, C. H and C_ H), 7.3-8.0 (m, 4, methylene), HSi O c l 8.3 (broad s, 3, methyl); uv max (MeOH) 280 (e 156), 350 nm (e 58). Photolysis of Methyl-tetrahydronaphthoquinone 6J3 i n Benzene A s o l u t i o n of 515 mg (2.93 mmol) of 63_ i n 250 ml benzene was i r r a d i a t e d through the 340 nm f i l t e r . The reaction was followed by monitoring the 350 nm absorption band of 63_. After 15 hr the s t a r t i n g material had reacted completely. On glpc (column B, 1 5 7° , 150 ml/min) the formation of three major products 114, 115 and 116 was observed i n a time independent r a t i o (114:115:116 = 5:3:2, determined from weight of glpc traces; t_. : 114, 20 min; 115, 22 min; 116,30 min). In the R i n i t i a l phase of the photolysis an a d d i t i o n a l minor peak (t 16 min) was observed. However, i t decreased i n the l a t e r stage of the reaction - 109 -and the amount c o l l e c t e d by glpc was too small to allow any c h a r a c t e r i z a t i o n . The major products were c o l l e c t e d by glpc (column C, 145°," 150 ml/min, t D 114, 84 min; 115, 96 min; 116, 126 min) i n the R form of c o l o r l e s s l i q u i d s whose c h a r a c t e r i s t i c s are as follows: 3 9 compound 114, 9-methyltricyclo[4.4.0.0 ' ]dec-7-ene-2,5-dione, i r (CHCl^) 5.68 (C=0), 5.80 (C=0) y; nmr (CDC1_) T 3.69 (d of d, 1, J , . = 1 Hz, j 0 , 0 J , . = 8 Hz, C.H), 4.11 (d of d, 1, J , = 8 Hz, J , , = 6 Hz, C_H), / , o o 1,0 b, I I 6.63 (broad t , 1, J , , J, ^ ~ 6 Hz, C.H), 6.80 (d of d, 1, J . , = ' 1 , 6 6,7 6 4exo,endo 18 Hz, J = 2 Hz, C.H ) , 7.18-7.38 (m, 1, C.H), 7.65 (broad d of d, 4 exo 1 1, J . . = 18 Hz, J , . » 4.5 Hz, C.H , ) , 7.83-7.97 (m, 1, 4endo,exo 3,4endo 4 endo C 3H), 8.34 (broad d, 2, J = 1.5 Hz, C±0 methylenes), 8.60 (s, 3, C g methyl); uv max (MeOH) 296 (e 300), 310 nm, shoulder; mass spectrum (70 eV) m/e parent 176. Anal. Calcd. f or C 1 1 \ 2 ° 2 : C' 7 4'9 8? H> 6-86. Found: C, 74.80; H, 6.79. 3 7 Compound 115, 9-methyltricyclo[4.4.0.0 ' ]dec-8-ene-2,5-dione: i r (CHC13) 5.72 (C=0) u; nmr (CDCl.^) T 4.33-4.49 (symmetric m, 1, v i n y l H), 6.87-6.98 (symm. m, 1, C 3H), 7.12-7.30 (m, 2), 7.42-7.53 (m, 1 ) , 7.56 (d of d, 1, J , , = 18 Hz, J , Hz, C.H ) , 7.60-7.70 4exo,endo 4exo,3 4 exo (m, 2), 7.78 (d of d, 1,' J . , = 18 Hz, J'=l Hz,C.H , ),8.35(broad,s, 4endo,exo 4 endo 3, methyl); uv max (MeOH) 288 nm (e 61); mass spectrum (70 eV) m/e parent 176. Anal, (the sample submitted had been p u r i f i e d by d i s t i l l a t i o n i n the Kugelrohr at 6 4 ° / ~ 0 . 1 mm): Calcd. f or C^H 0 : C, 74.98; H, 6.86. Found: C, 74.75; H, 6.70. - 110 -Deuterium Exchange of 115 A deuterochloroform s o l u t i o n of 115 was shaken with deuterium oxide and a speck of potassium hydroxide and allowed to stand overnight to give 4-exo-deuterated 115; dif f e r e n c e from proteo-115: nmr (CDCl^) T 6.93 (broad s, 1, C 3H), no s i g n a l at T 7.56, 7.80 ( t , 1, J ^ e n d o 4 e x 0 _ ( j 2.6 Hz). Compound 116 (Kugelrohr d i s t i l l e d ( 6 0 - 7 0 ° / 0 . 1 mm) sample f o r 3 9 nmr, mass spectrum and a n a l y s i s ) , 8-methyltricyclo[4.4.0.0 ' ]dec-7-ene-2,5-dione: i r (CHC13) 5.70 (C=0), 5.84 (C=0) y; nmr (CDC13) T 4.47 (d of pentuplets, 1, J = J = 1.5 Hz, J , n = 6 Hz, v i n y l H), /, *-"H3 7, y 6, / 6.67 (broad t , 1, J , , = J , , = 7 Hz, C,H), 6.88-7.75 (m, 6 ) , 8.06 D , / 1 ,0 D (d, 3, J , „ „ = 1.5 Hz, methyl), 8.39 (broad d, J = 12 Hz, C i n methylene); i r r a d i a t i o n of T 4.47 lead to the following changes: T 6.67 (broad d, 1, J , = 7 Hz, C,H), 8.06 ( s , 3, methyl); uv max l,o o (MeOH) 295 (e 330), 305 nm (shoulder); mass spectrum (70 eV) m/e parent 176. Anal. Calcd. f or C1 1H1 2 ° 2: C' 7 4 # 9 8 ; H' 6'8 6' F o u n d : c» 75.08; H, 6.84. The minor photoproduct seen only i n the i n i t i a l stage of the photolysis had: uv max (MeOH) 240 (e 1.0 x 10 ) , 335 nm (e 50). Photolysis of Quinone 6>3> i n t e r t - B u t y l Alcohol Under i d e n t i c a l conditions as i n the photolysis i n benzene a constant buildup of two products was observed on g l p c . The i r and nmr spectra of the two products were i d e n t i c a l with the spectra of products 115 and 116 i n the i r r a d i a t i o n i n benzene. The r a t i o of 115:116 i n t e r t - b u t y l alcohol was 6.6:1 (weight of glpc t r a c e s ) , i - I l l -Thermolysis of Ene-dione 114 A 10 mg sample of 114 was heated i n a sealed Pyrex tube at 168° for 16 h r . The product was dissolved i n chloroform and f i l t e r e d through a short column of neutral alumina. Concentration of the f i l t r a t e under vacuum gave 10 mg of a c o l o r l e s s l i q u i d whose nmr spectrum was i d e n t i c a l with that of 115. Thermolysis of Ene-dione 116 A 15 mg sample of 116 was thermolyzed i n a sealed Pyrex tube at 185° f o r 22 hr. The r e s u l t i n g o i l was dissolved i n chloroform, f i l t e r e d through s i l i c a g e l and concentrated i n vacuo to y i e l d 14 mg of 8-methyltricyclo[4.4.0.03'7]dec-8-ene-2,5-dione (120): i r (CHClg) 5.70 (C=0) y; nmr (CDClg) T 4.62 (m, 1, v i n y l H) , 6.80-6.90 (m, 1, C 3H), 7.16-7.27 (m, 1, C^H), 7.33-7.65 (m, 5 ) , 7.78 (d of d, 1, J . . =18 Hz, J ' = 1 Hz), 8.23 (m, 3, methyl); the following 4endo,exo data are of a sample d i s t i l l e d at 6 0 ° / ^ 0.1 mm to give a c o l o r l e s s l i q u i d : uv max (MeOH) 290 nm (e 80); mass spectrum (70 eV) m/e parent 176. 2-Methy1-1,4,4a,9a-tetrahydroanthraquinone (65) _ Following a procedure of 0. Di e l s et a l . 5.29 g (33.5 mmol) of 1,4-naphthoquinone, 3.5 g (52 mmol) fr e s h l y d i s t i l l e d isoprene (Eastman Organic Chemicals) and 3.5 ml 95% ethanol were kept at 100° i n a sealed Pyrex tube for 4.25 h r . On cooling a c r y s t a l l i n e mass was formed which afforded, a f t e r r e c r y s t a l l i z a t i o n from petroleum ether ( 6 8° ) 41 4.00 g (17.8 mmol, 53%) c o l o r l e s s c r y s t a l s of 65, mp 82.0-82.5° ( l i t . 8 1 ° ) , i r (CHC13) 5.91 (C=0) y; nmr (CDC13) x 1.8-2.4 (m, 4, aromatic H), - 112 -4.6 (m, 1, vinyl H), 6.7 (m, 2, C^H and C^H), 7.2-8.2 (m, 4, methylene), 8.3 (broad d, 3, J = 1.5 Hz, methyl); uv max (MeOH) 250 (e 1.65 x 10 3), 295 (e 1.66 x 103), 302 (e 1.65 x 103), 320-380 nm broad featureless absorption ( e 1 0 2 ) . r 340 nm Photolysis of Quinone 65_ A solution of 315 mg (1.39 mmol) of 65 in 135 ml tert-butyl alcohol and 15 ml benzene was irradiated through the 340 nm fil t e r for 21 hr. Tic showed one major product (R£ 0.5; 10% acetone/chloroform) which was isolated by column chromatography (chloroform) in 80 mg yield. The resulting liquid showed three peaks on glpc (column E), the one with the shortest retention time being the major one. However, after collection of a few fractions on glpc only l i t t l e of the first peak seemed to be left and the peak with longest retention time was now the major one. As a result of this only a l i t t l e of the original major product could be collected. It was obtained as a colorless liquid in 5 9 6 mg yield: 3,4-benzo-9-methyltricyclo[4.4.0.0 ' ]dec-7-ene-5-ol-2-one (129), i r ( C C I 4 ) 5.86 (C=0) y; nmr (CCl^) T 2.0-2.8 (m, 4, aromatic H), 3.6-4.0 .(m, 2, vinyl H), 6.6-6.8 (m, 1, CgH), 7.4 (s, 1, OH, disappears with DjO), 7.6 (pair of d, 1, J l j l 0 e x o % 8 H z ' Jl,10endo ^ 3 Hz, methine), 8.3-8.6 (m, 2, methylene), 8.9 (s, 1, methyl); mass spectrum (70 eV) m/e parent 226. - 113 -Preparation of Fetizon Reagent ( S i l v e r Carbonate on C e l l t e ) 68 The procedure of Fetizon et a l . was followed by adding 30 g of C e l i t e (John Mansville, acid washed) to a mechanically s t i r r e d s o l u t i o n of 34 g (200 mmol) of s i l v e r n i t r a t e i n 200 ml of d i s t i l l e d water. A s o l u t i o n of 30 g (105 mmol) of sodium carbonate (Na^CO^-lOI^O) i n 300 ml d i s t i l l e d water was then added slowly to the homogeneous suspension. A f t e r the addit i o n was complete, s t i r r i n g was continued for a further 10 min. The yellow-green p r e c i p i t a t e was f i l t e r e d and transferred to a round bottom f l a s k wrapped with aluminum f o i l f o r protection of the l i g h t - s e n s i t i v e reagent. The s l u r r y was rotovapped at approximately 60° for 16 hr . The r e s u l t i n g reagent was ca l c u l a t e d to contain 1 mmol of s i l v e r carbonate per 0.57 g. tert-Butyl-p-benzoquinone (137) From a s l u r r y of 45.6 g (80 mmol) of Fetizon reagent i n 380 ml benzene, 30 ml of solvent were d i s t i l l e d o f f to remove traces of water. To the remaining s o l u t i o n 5.82 g (35.0 mmol) of tert-butyl-hydroqulnone (Eastman Organic Chemicals, P r a c t i c a l ) were added and the mixture was refluxed for 2.5 hr (the f l a s k was protected from l i g h t with wrapped aluminum f o i l ) . T i c (15% et h y l acetate/benzene) showed that the reaction was complete. F i l t r a t o n and evaporation of the solvent gave 5.87 g (<99%) of tert-butyl-p-benzoquinone (137) i n the form of orange needles, mp 48-50° ( l i t .4 5 a 5 2 - 5 5 ° ) . - 114 -2-tert-Butyl-4a,5,8,8a-tetrahydro-5,8-methano-l,4-naphthoquinone (138) To a magnetically s t i r r e d s o l u t i o n of 5.8 g (35 mmol) of t e r t -b u t y l - £ - b e n z o q u i n o n e (137), cooled with an i c e bath 0 ° , 7.0 g (106 mmol) of f r e s h l y d i s t i l l e d cyclopentadiene (see below for procedure) was added. A f t e r a further 10 min of s t i r r i n g the i c e bath was removed and the s o l u t i o n was kept at 40° for 2 hr. T i c (15% et h y l acetate/benzene) indicated complete conversion of the s t a r t i n g m a t e r i a l . F i l t r a t i o n and evaporation of the solvent yi e l d e d 7.82 g (34.0 mmol, 97%) of 138 as yellow c r y s t a l s : mp 66-70° ( l i t .4 5 b 8 1 - 8 2 ° ) . 69 D i s t i l l a t i o n of Dicyclopentadiene Commercial dicyclopentadiene (Eastman Organic Chemicals, Technical) was d i s t i l l e d through a column (1 x 10 inc h e s ) , f i l l e d with glass h e l i c e s . The d i s t i l l e d cyclopentadiene (bp 4 1° ) was c o l l e c t e d and stored at dry i c e temperature u n t i l i t was used. 2-tert-Butyl-2,3,4a , 5,8,8a-hexahydro-5,8-methano-l,4-naphthoquinone (139) __ Following a procedure of Chapman et a l . 7.82 g (34.0 mmol) of 138 i n 35 ml of g l a c i a l acetic acid was added slowly over a period of 5 min to a ra p i d l y s t i r r e d suspension of 6.8 g (104 mmol) of zinc dust (Fisher, c e r t i f i e d ) i n 35 ml water. At the end of the addition the temperature had r i s e n to 3 0 ° . Then the mixture turned dark v i o l e t . The color disappeared again as the temperature rose further to 4 4 ° . The reaction mixture was allowed to cool to 33° when 35 ml of water and the same volume of chloroform were added. A f t e r f i l t r a t i o n the organic layer was separated and the aqueous layer extracted once more with an equal amount of chloroform. The combined organic layers were - 115 -washed with a saturated sodium bicarbonate s o l u t i o n u n t i l the aqueous layer turned a l k a l i n e . A f t e r washing the chloroform s o l u t i o n once with water i t was dried over magnesium s u l f a t e and concentrated i n vacuo to give 7.112 g (30.6 mmol, 90%) of s l i g h t l y yellow c r y s t a l s of ene-dione 139, mp 1 1 0 - 1 1 2°. R e c r y s t a l l i z a t i o n from petroleum ether ( 6 8° ) afforded 6.21 g of white needles, mp 113-115° ( l i t .4 7° 1 1 4 - 1 1 5° ) . 5-tert- Butyl-cyclohex-2-ene-l,4-dione (71) A modified procedure of Chapman and coworkers was followed. In a round bottom f l a s k 1.75 g (7.55 mmol) of cyclopentadiene adduct 139 was kept at 190° and atmospheric pressure f o r 15 min. Then the pressure was reduced to 60 mm and the compound allowed to d i s t i l through a short Vigreux column. The l a t t e r consisted of a s i n g l e piece of glass tubing (ca. 30 cm long, 8 mm diameter, bent i n t o V-shape) which was surrounded i n the v e r t i c a l part by a c o i l of Nichrome wire (1 mm diameter) kept at 5 V o l t s . A f t e r 10 min the pressure was further reduced to 12 mm and the d i s t i l l a t i o n continued for 5 min. The d i s t i l l a t e , i n i t i a l l y an o i l , c r y s t a l l i z e d to give 1.05 g (6.31 mmol, 83%) of yellow c r y s t a l s of ene-dione 71, mp 35-37° ( l i t .4 7 c 3 8 - 3 9 ° ) , i r (neat) 5.95 (C=0) u; nmr ( C C 1 4 ) T 3 . 4 (S , 2, v i n y l H), 7.1-7.5 (m, 3, C_ methine and C, methylene), 9.0 (s, 9, t e r t - b u t y l H); uv max j o (MeOH) 362 nm (e 60). Note: Slow d i s t i l l a t i o n leads to extensive aromatization to form tert-butyl-hydroquinone. The l a t t e r was also formed on passing the ene-dione 7_1 through a s i l i c a gel column as w e l l as to a minor extent on - 116 -t i c p l a t e s . R e c r y s t a l l i z a t i o n from petroleum ether ( 6 8° ) leads to lower melting material; t h i s could be due to aromatization to the hydroquinone. 47c According to Chapman et a l . compounds of the type 71 are stable i n d e f i n i t e l y i f kept i n stoppered Pyrex v i a l s i n the dark at 1 0 ° . Photolysis of tert-butyl-cyclohexenedione 71 I r r a d i a t i o n of 99 mg (0.60 mmol) of 71. *n 60 ml benzene through the 340 nm f i l t e r led to complete reaction of _7_1 a f t e r 15 h r . T i c showed one major product (R^ 0.17; 15% ethyl acetate/benzene) which was i s o l a t e d by column chromatography ( s i l i c a g e l ; 20% e t h y l acetate/ benzene). The crude product i s o l a t e d (21 mg, 0.19 mmol, 32%) was r e c r y s t a l l i z e d from benzene to give 14 mg of c o l o r l e s s c r y s t a l s of p_-hydroquinone: mp 169-170° ( l i t .7 0 1 7 0 ° ) , i r (nujol mull) i d e n t i c a l with the spectrum of an authentic sample. Photolysis of 16 i n 15% petroleum ether ( 6 8 ° ) / t e r t - b u t a n o l gave i n 45% y i e l d the same p_-hydroquinone. 5a-Methyl-4a6,5,8,8ag-tetrahydro-l,4-naphthoquinone (64) Piperylene ( A l d r i c h , mixture of isomers) was d i s t i l l e d under 71 72 nitrogen and behind a s h i e l d (EXPLOSION HAZARD ) . It was calculated 20 that 4.0 g of t h i s mixture with n Q = 1.4321 contained 38.3 mmol of the re a c t i v e trans isomer. This amount was added to 3.009 g (27.9 mmol) of p_-benzoquinone ( r e c r y s t a l l i z e d from ethanol) and 4.5 ml benzene. The reaction mixture was kept at 60° for 6 h r . Evaporation of the solvent gave 4.90 g (27.9 mmol, 100%) of a l i g h t brown l i q u i d . D i s t i l l a t i o n of the l a t t e r at 120° through a 10 cm Vigreux column at 0.02 mm gave - 117 -1.23 g (S0%) of 64_, a yellow l i q u i d : i r (neat) 5.88 (C=0), 5.94 (C=0) u; nmr (CC14) x 3.4 ( s , 2, C 2 and C 3 v i n y l H), 4.4 (d, 2, J = 1.5 Hz, C"6 and C ? v i n y l H), 6.8 (m, 2, and C g a methine), 7.0-8.3 (m, 3, C_ methylene and Cc methine), 9.1 (d, 3, J = 7 Hz, methyl); o J uv max (MeOH) 355 (e 60); (hexane) 362 (e 57), 284 nm ( £ 280). 35 Note: G. Bendz also obtained 64_ as a yellow o i l by r e f l u x i n g ( 7 0 - 7 5° ) p_-benzoquinone with piperylene. He reported that d i s t i l l a t i o n of or attempts to c r y s t a l l i z e the yellow o i l converted i t to the corresponding hydroquinone (mp 1 4 4 - 1 4 5° ) . The l a t t e r was also obtained i n t h i s work as part of the higher b o i l i n g f r a c t i o n s ( 1 6 0°/0 . 0 2 mm) i n the d i s t i l l a t i o n of the crude adduct. Photolysis of Adduct 64_ i n t e r t - B u t y l alcohol A s o l u t i o n of 0.75 g (4.3 mmol) of 64_ i n 200 ml t e r t - b u t y l alcohol was i r r a d i a t e d through the 340 nm f i l t e r with a 275 W sunlamp. The reaction was monitored by t i c (15% et h y l acetate/benzene) and by glpc (column A, 1 6 0° , 120 ml/min). Aft e r 12 hr the s t a r t i n g material had completely reacted as shown by t i c . The gas chromatogram showed the formation of two p r o d u c t s , £ 6 and 97_,in a time independent r a t i o 7:1 (weight of glpc trace,t 96,21 min; 97,16 min). The crude concentrated reaction mixture was f i l t e r e d through a short s i l i c a g e l column (10 g) using approximately 200 ml of 15% ethyl acetate/benzene as the eluent. Concentration i n vacuo and c o l l e c t i o n of h a l f of the material on glpc 3 9 (column D, 1 7 0°) gave 4.5 mg (1.2%) of 10-methyltricyclo[4.4.0.0 ' ]dec-3 7 7-ene-2,5-dione (97_) and 41 mg (11%) t r i c y c l o [4.4.0.1 ' ]undec-8-ene-2,5 dione (96). Both had v i r t u a l l y i d e n t i c a l Rf values on t i c . The minor - 118 -product 97, a c o l o r l e s s l i q u i d : i r (CC14) 5.67 (C=0), 5.79 (C=0) u: nmr (CDC13) T 3.3 (broad t; 1, J - 8 Hz, C v i n y l H), 4.1 (broad t, 1, J = 7 Hz, C ? v i n y l H), 6.4-6.8 (m, 1, C& methine), 6.8-8.4 (m, 6 ) , 9.0 (d, 3, J = 8 Hz, CH 3); uv max (MeOH) 296 nm (E 4.4 x 10 2); mass spectrum (70 eV) m/e parent 176. Anal. Calcd. for C ^ H ^ O ^ C, 74.98; H, 6.86; Found: C, 74.72; H, 7.00 (sample had been d i s t i l l e d at 73° and 0.01 mm). The major photoproduct 97_ r e c r y s t a l l i z e d from ether/petroleum ether ( 6 8° ) to give white needles: mp 7 5 - 7 6° , i r (CC14) 5.79 (C=0) p; nmr (CC14) T 4.0-4.6 (m, 2, v i n y l ) , 7.2-7.8 (m, 8 ) , 7.9-8.2 (m, 2, C^^ methylene); uv max (MeOH) 285 nm (E 60); mass spectrum (70 eV) m/e parent 176. Anal. Calcd. f o r C1 1H1 2 ° 2: C' 7 4 , 9 8 ; H' 6*8 6' F o u n d : c» 75.17; H, 7.01. Photolysis of j64 i n Benzene A s o l u t i o n of 0.51 g of 6>4_ i n 200 ml benzene was i r r a d i a t e d under the same conditions as i n the t e r t - b u t y l alcohol run for 50 hr. A polymer-like p r e c i p i t a t e which had been formed was f i l t e r e d o f f (60 mg) and the f i l t r a t e concentrated i n vacuo. The r e s u l t i n g mixture showed on glpc the same r a t i o of products as i n the t e r t - b u t y l alcohol p h o t o l y s i s . The i d e n t i t y of the photoproducts i n both solvents was shown by t h e i r superimposable i r spectra. - 119 -2,3,4a,6,7,8a-Hexamethyl-4a,5,8,8a-tetrahydro-l,4-naphthoquinone (73) _ The procedure of A n s e l l et a l . was followed. A s l u r r y of 1.609 g (9.8 mmol) duroquinone ( A l d r i c h ) , 2.0 g (24 mmol) 2,3-dimethyl-l,3-butadiene ( A l d r i c h ) , and a few c r y s t a l s of hydroquinone were sealed i n a Pyrex tube and thermolyzed at 197° f o r 23 h r . The r e s u l t i n g yellow c r y s t a l l i n e material was r e c r y s t a l l i z e d twice from petroleum ether ( 6 8° ) to give 1.618 g (6.60 mmol, 67%) of f a i n t yellow c r y s t a l s of quinone 73 (mp 1 1 2 - 1 1 3° ) . A further r e c r y s t a l l i z a t i o n gave material of mp 114-48 116° ( l i t . 1 1 5 - 1 1 7° ) ; i r (CHC13) 5.98 (C=0) y; nmr (CDC13) T 7.3-8.4 (m, 4, methylene), 8.0 (s, 6, and C 3 methyl), 8.4 ( s , 6, Cg and C 7 methyl), 8.9 ( s , 6, bridgehead methyls); uv max (MeOH) 251 (e 1.12 x 104) , 280-400 nm, broad featureless absorption ( e 0 / n 146); (hexane) 340 nm 9 247, ^ 290, shoulder ( e O Q n 4.7 x 10 ) , 370 nm, shoulder (E 62). Photolysis of Duroquinone Adduct 73_ i n t e r t - B u t y l Alcohol A s o l u t i o n of 309 mg (1.17 mmol) of adduct 7_3 i n 200 ml 5% benzene/ t e r t - b u t y l alcohol was i r r a d i a t e d for 29 hr through the 340 nm f i l t e r with a 275 W sun lamp. Two products, 146 and 145 were formed as detected by glpc (column A, 1 4 5° , 150 ml/min; t „ 146, 8.5 min; 73, 9.1 min; 145, 10.4 min) and t i c (15% et h y l acetate/benzene; Rf 73, 0.68; 146, 0.62; 145 0.43). The r a t i o of the two products was constant throughout the photolysis(146:145= 47:53 as determined from weight of glpc t r a c e s ) . 3 10 1,3,4,6,8,9-Hexamethyltricyclo[4.4.0.0']dec-8-ene-2,5-dione (146) was i s o l a t e d from glpc as a c o l o r l e s s l i q u i d : i r (CCl^) 5.67 (C=0, 4-membered r i n g ) , 5.85 (C=0), 6-membered ring) y; nmr (CCl^) x 7.57 (q, 1, J = 7.5 Hz, C^ methine), 7.90-8.10 (m, 3, C 1 Q methine and C_, - 120 -methylene), 8.25-8.40 (m, 6, v i n y l methyls), 8.78 (s, 3, methyl), 8.95 ( s , 3, methyl), 8.95 (d, 3, J = 7.5 Hz, methyl), 9.03 ( s , 3, methyl); 9 uv max (MeOH) 246 (E 6.6 x 10 ) , 300 nm (e 70); mass spectrum (70 eV) m/e parent 246. Anal. Calcd. f o r C,-H„ o0„: C, 78.01; H, 9.00. Found: C, 77.80; lo 22 L H, 9.13. 5 9 Compound 145, l,3,4,6,8,9-hexamethyl-5-hydroxytricyclo[4.4.0.0 ' ]deca-3,7-dien-2-one, was c o l l e c t e d from glpc as c o l o r l e s s c r y s t a l s . R e c r y s t a l l i z a t i o n from petroleum ether ( 6 8° ) afforded material of mp 10 1 - 1 0 2°; i r (CC14) 2.69 (OH), 5.98 (C=0) y; nmr (CC14) T 4.62 (m, 1, v i n y l ) , 7.79 (broad s, 1, OH, disappears with D 20), 8.12-8.16 (m, 3, C 3 or C. methyl), 8.20-8.26 (m, 6, C~ or C. methyl and C Q methyl), the 4 J H o l a t t e r m u l t i p l e t collapses to a broad s i n g l e t at 8.23 upon i r r a d i a t i o n at 4.62 , 8.43 (d, 1, J = 12.5 Hz, one of C methylenes), 8.92 ( s , 3, methyl), 9.03 (d, 1, J = 12.5 Hz, one of C Q methylenes), 9.14 (s, 3, 3 methyl), 9.20 ( s , 3, methyl); uv max (MeOH) 251 (e 7.42 x 10 ) , 325 nm (e 58); mass spectrum (70 eV) m/e parent 246. Anal. Calcd. for C. ,H o o0„: C, 78.01; H, 9.00. Found: C, 77.80; ±o 22 2 H, 9.02. X-Ray Structure Determination of Alcohol 145 49 This was c a r r i e d out by Professor J . Trotter and Dr. C A . Bear to whome the author would l i k e to express h i s thanks. Crystals of 145 are t r i c l i n i c , a = 7.832(2), b = 13.797(3), c = o 6.731(1) A, a = 98.21(3), B = 101.36(2), y = 9 2 . 7 1 ( 3 ) ° , Z = 2, space group PT. The structure was determined with Cu Ka s c i n t i l l a t i o n counter data by d i r e c t methods and re f i n e d by f u l l - m a t r i x l e a s t squares, the - 121 -f i n a l R being 0.061 for the 1774 observed r e f l e c t i o n s . Anisotropic thermal factors were used for C and 0; H atoms were re f i n e d i s o t r o p i c a l l y . A number of the bonds involved i n the bridged structure are longer than normal with corresponding deviations from normal values f o r the bond angles. There i s hydrogen bonding between the a l c o h o l i c oxygen and the carbonyl oxygen of the molecule i n the neighboring unit c e l l . A l l other intermolecular contacts correspond to van der Waals i n t e r a c t i o n s . Photolysis of Adduct 7_3 i n Benzene A s o l u t i o n of 803 mg (3.26 mmol) of 73. i n 300 ml benzene was i r r a d i a t e d through the 340 nm f i l t e r f o r 6 h r . Glpc showed products 146 and 145 formed i n a r a t i o of 1.6:1 (from weight of glpc t r a c e s ) . Column chromatography (8% e t h y l acetate/benzene) gave 369 mg (46%) of ene-dione 146 and 182 mg (22.6%) of alcohol 145 ( r a t i o of 146:145. = 2.04:1). Thermolysis of Ene-dione 146 In a sealed Pyrex tube 26 mg of 146 were heated at 192° for 16 hr. The s l i g h t l y brown product was f i l t e r e d through s i l i c a g e l with chloroform to give 24 mg (92%) of a yellow l i q u i d . Glpc showed one peak only (column A, 1 5 0° , 150 ml/min; t „ 150, 7.0 min; 146, 8.5 min). C r y s t a l l i z a -R t i o n from petroleum ether ( 6 8° ) gave yellow c r y s t a l s of 2,3,4a,6,7,8a-hexamethyl-4a,7,8,8a-tetrahydro-1,4-naphthoquinone (150): mp 5 3 . 0 - 5 3 . 5°; i r (CC14) 5.99 (C=0) y; nmr (CCl^) T 4.97 (center of m, 1, v i n y l ) , 7.58-7.93 (m, 2, C , methine and one of C D methylenes), 8.08-8.13 (m, / o 6, C 2 and C 3 methyls), 8.40-8.45 (m, 3, C & methyl), 8.63-8.87 (m, 1, one of Cfi methylenes), 8.84 (s, 3, methyl), 8.98 (d, 3, J = 7.5 Hz, C 7 - 122 -methyl), 9.00 ( s , 3, methyl); i r r a d i a t i o n at 4.97 leads to collapse of C, methyl to a doublet (J = 0.7 Hz) and to a s i m p l i f i c a t i o n of o the m u l t i p l e t at 7.58-7.93; i r r a d i a t i o n of the C, methyl group leads o to a broad doublet (J = 1.5 Hz) of the v i n y l hydrogen; i r r a d i a t i o n of the methyl group gives a s i m p l i f i e d m u l t i p l e t at x 7.58-7.93; uv 4 max (MeOH) 247 (e 1.2 x 10 ) , 356 nm (e 84); mass spectrum (70 eV) m/e parent 246. Anal. Calcd. for C1 6H9 2 ° 2: C' 7 8 , 0 1' H' 9'0 0 , F o u n d : c> 77.99; H, 9.03. Isomerization of 150 with Boron T r i f l u o r i d e A s o l u t i o n of 21 mg of 150 i n 4 ml of methylene c h l o r i d e was saturated with gaseous boron t r i f l u o r i d e u n t i l fumes formed at the o u t l e t of the sealed reaction f l a s k . Shortly before t h i s the s o l u t i o n had turned brown. Aft e r allowing i t to stand for 30 min a few ml of water were added, then s o l i d potassium carbonate to n e u t r a l i z e the mixture. Extraction with chloroform and evaporation of the solvent gave 21 mg of yellow o i l y c r y s t a l s . R e c r y s t a l l i z a t i o n from petroleum ether ( 6 8° ) y i e l d e d 11 mg of yellow c r y s t a l l i n e 7_3. The i r and nmr spectra of the l a t t e r were i d e n t i c a l with the corresponding spectra of the authentic adduct 73. Base-Catalyzed Rearrangement of Ene-Dione 146 A s o l u t i o n of 200 mg ene-dione 146 i n 15 ml 40% water/p_-dioxane (F i s h e r , c e r t i f i e d ) to which a p e l l e t of potassium hydroxide had been added was refluxed overnight under nitrogen. A f t e r a d d i t i o n o f a few - 123 -ml of water and n e u t r a l i z a t i o n with a c e t i c a c i d the mixture was extracted with chloroform. The organic layers were dried over sodium s u l f a t e . Removal of solvent gave a brownish o i l which showed one major carbonyl at 5.73 y i n the i r spectrum (neat). On glpc one major peak was detected and c o l l e c t e d (column F, 1 6 0° , 200 ml/min, t_ 3.0 min) R 3 7 to give a c o l o r l e s s l i q u i d , l,3,4,6,8,9-hexamethyltricyclo[4.4.0.0 ' ]dec-8-ene-2,5-dione (147): i r (CC14) 5.72 u; nmr (CC14) T 7.93 (broad s, 1, C ? methine), 7.99 (q, 1, J = 7 Hz, C"4 methine), 8.05-8.15 (m, 2, C 1 Q methylene), 8.24-8.34 (m, 3, C g methyl), 8.39 (broad s, 3, C g methyl), 8.87 (s, 3, methyl), 9.05 (s, 3, methyl), 9.17 (d, 3, J = 7 Hz, C 4 methyl), 9.28 ( s , 3, methyl); uv max (MeOH) 292 nm (e 70); mass spectrum (70 eV) m/e parent 246. Deuterium exchange of 147 i n the nmr tube (CC14-D20-K0H) led to disappearance of the quartet at T 7.99 and to the formation of a broad s i n g l e t at T 9.17. Anal. Calcd. f o r C-^ H-.O,,: C, 78.01; H, 9.00. Found: C, 77.78; lo LL L H, 8.98. Thermolysis of Alcohol 145 In a sealed Pyrex tube 60 mg of alcohol 145 were thermolyzed at 280° for 2 hr. Column chromatography (8% e t h y l acetate/benzene) gave 12 mg (20%) of adduct 73 (nmr spectrum i d e n t i c a l with authentic 73) and 32 mg (53%) of ene-dione 147. Glpc of the l a t t e r showed a small impurity. The ene-dione 147 was therefore p u r i f i e d by c o l l e c t i o n on glpc (column A, 1 5 0° , 150 ml/min, t 8 min). The i r and nmr spectra of - 124 -the 13 mg of 147 so obtained were i d e n t i c a l with the spectra of 147 i s o l a t e d as the product of the base catalyzed rearrangement of ene-dione 146. Photolysis of Adduct 73 i n t e r t - B u t y l Alcohol-O-d A s o l u t i o n of 109 mg (0.44 mmol) of adduct 73_ i n 8 ml t e r t - b u t y l alcohol-0-d and 1 ml benzene was i r r a d i a t e d through the 340 nm f i l t e r for 40 h r . Column chromatography (8% e t h y l acetate/benzene) gave 21 mg of ene-dione 146 which was not deuterated as judged by i t s nmr and mass spectrum. Photolysis of Adduct 73. i n Deuterium Oxide/p-Dioxane A s o l u t i o n of 91 mg adduct ]3_ i n 7 ml p-dioxane (F i s h e r , refluxed f o r 1 hr with sodium borohydride, then d i s t i l l e d ) and 5 ml deuterium oxide was i r r a d i a t e d through the 340 nm f i l t e r f o r 5.9 h r . Three products A, B, and C were formed i n a r a t i o of 1:6:33 (from weight of glpc t r a c e , column A, 1 7 0° , 60 ml/min, t A, 10.2 min; B, 11.1 min; C, 12.8 min). Part of the photolysate (70 mg) was chromatographed (8% e t h y l acetate/benzene) to give 1.5 mg (2%) of a c o l o r l e s s l i q u i d A, the nmr of which was i d e n t i c a l with non-deuterated ene-dione 146. Compound B (5 mg, 7%) was i d e n t i c a l with the deuterated ene-dione 147 obtained by base catalyzed exchange of 147 ( i d e n t i c a l nmr s p e c t r a ) . The R, and t D values for C corresponded to alcohol 145. The l a t t e r was thermally stable under the conditions used f o r c o l l e c t i o n by g l p c . Note: Ene-dione 147 has the same retention time as adduct 73. - 125 -Photolysis of Adduct 7_3 i n Other Solvents a) i n A c e t o n i t r i l e A s o l u t i o n of 98 mg of adduct 73. i n 100 ml a c e t o n i t r i l e ( F i s h e r , c e r t i f i e d ) was i r r a d i a t e d through the 340 nm f i l t e r f o r 1.4 h r . Glpc analysis (column F, 1 1 8° , 150 ml/min) indicated that a l l s t a r t i n g material had reacted to give a mixture of ene-dione 146 and alcohol 145 i n a r a t i o of 1:4. Further i r r a d i a t i o n to a t o t a l of 4.6 hr did not a l t e r the r a t i o of products. The retention time of ene-dione 146 was i d e n t i c a l with the product observed i n t h i s p h o t o l y s i s . The second product of t h i s i r r a d i a t i o n was c o l l e c t e d and i t s i r spectrum was found to be i d e n t i c a l with the previously i s o l a t e d alcohol 145. b) i n Methanol A s o l u t i o n of 60 mg adduct 73 i n 20 ml methanol was photolyzed as above for 7.4 hr. The products formed were ene-diones 146 and 147, and alcohol 145 i n a r a t i o of 1:2:13 (area of glpc t r a c e s , column A, 1 6 0 ° ) . The product assignment was based on retention times and co-i n j e c t i o n of authentic m a t e r i a l . The r a t i o of products was not s i g n i f i c a n t l y a l t e r e d between 1.6 hr and 7.4 hr i r r a d i a t i o n time. Simultaneous Photolysis of Adduct _7_3 and Alcohol 145 Solutions of 20 mg of adduct 73_ and of alcohol 145, each i n 9 ml of t e r t - b u t y l alcohol plus 1 ml benzene were i r r a d i a t e d simultaneously through the 340 nm f i l t e r . A f t e r 5 hr adduct 73_ had completely reacted while the alcohol was v i r t u a l l y unchanged. Prolonged photoly s i s to a t o t a l of 32 hr l e d to disappearance of the alcohol peak. However, no s i g n i f i c a n t products could be detected by g l p c . - 126 -APPENDIX - 127 -BIBLIOGRAPHY 1. D.C. Neckers, "Mechanistic Organic Photochemistry", Reinhold Publishing Corporation, New York, 1967, p. 28. 2. H.E. Zimmerman, Angew. Chem., I n t . Ed. Engl., j3, 1 (1969). 3. C. Walling and V. Kurkov, J . Amer. Chem. S o c , 88, 4727 (1966); C. Walling and M.J. Gibian, i b i d . , 87, 3361 (1965). 4. N.J. Turro, J.C. Dalton, K. Dawes, G. Farrington, R. Hautala, D. Morton, M. Niemczyk, and N. Schore, Accounts. Chem. Res., 5_, 92 (1972). 5. P.J. Wagner, i b i d . , 4, 168 (1971). 6. R.C. Cookson, E. Crundwell, R.R. H i l l , and J . Hudec, J . Chem. S o c , 3062 (1964). 7. (a) J.R. Scheffer, J . T r o t t e r , R.A. Wostradowski, C.S. Gibbons, and K.S. Bhandari, J . Amer. Chem. 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