Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Conformational effects in the photochemistry of tetrahydro-1,4-naphthoquinones Jennings, Barry Michael 1975

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Notice for Google Chrome users:
If you are having trouble viewing or searching the PDF with Google Chrome, please download it here instead.

Item Metadata

Download

Media
831-UBC_1975_A1 J45_5.pdf [ 7.56MB ]
Metadata
JSON: 831-1.0061060.json
JSON-LD: 831-1.0061060-ld.json
RDF/XML (Pretty): 831-1.0061060-rdf.xml
RDF/JSON: 831-1.0061060-rdf.json
Turtle: 831-1.0061060-turtle.txt
N-Triples: 831-1.0061060-rdf-ntriples.txt
Original Record: 831-1.0061060-source.json
Full Text
831-1.0061060-fulltext.txt
Citation
831-1.0061060.ris

Full Text

CONFORMATIONAL EFFECTS IN THE PHOTOCHEMISTRY OF TETRAHYDRO-1,4-NAPHTHOQUINONES by BARRY MICHAEL JENNINGS B.Sc. (Hon.). U n i v e r s i t y of Calgary, 1970 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 September, 1975 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my writ ten pe rm i ss i on . Department of The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date £W A , l 9 7 £ - i i -ABSTRACT The photochemistry of a v a r i e t y of tetrahydro-1,4-naphthoquinones (structure 1) has been investigated. These were synthesized by D i e l s - A l d e r r e a c t i o n of corresponding _p_-quinones and acyclic-1,3-dienes. 0 I Three substituent-dependent types of reactions were observed: (1) for adducts possessing hydrogen substituents at C^ a and Cg & (bridgehead p o s i t i o n ) , the prevalent process was one of abstraction of a 3-hydrogen atom from C c (or equivalently, C c) by excited j o carbonyl oxygen. In general, three product types were then observed, derived from carbon-carbon bond formation (proceeded i n two instances by conformational r o t a t i o n about the C. - C Q bond) i n the b i s -4a oa a l l y l i c r a d i c a l so produced. Placing a methyl or phenyl substituent at renders the 3-hydrogens non-equivalent, and abstraction occurs i n accord with expectations based on the formation of the more stable b i r a d i c a l intermediate. In adducts possessing bridgehead substituents, r o t a t i o n about the C. - C„ bond i n the b i r a d i c a l i s suppressed and only a s i n g l e 4a 8a r J product type (enone alcohol) i s formed, which possesses the same r e l a t i v e conformation as the b i r a d i c a l and s t a r t i n g adduct. In the - i i i -case where the bridgehead substituents are carboxymethyl, however, secondary photolysis i n benzene s o l u t i o n occurs, g i v i n g r i s e to a product where the bridgehead substituents are nearly e c l i p s e d . (2) For the adduct possessing exo-methyl substituents at p o s i t i o n s 5 and 8 as w e l l as methyls at the bridgehead p o s i t i o n s and at and Cgj 3-hydrogen ab s t r a c t i o n was p a r t i a l l y suppressed i n favor of a process t e n t a t i v e l y concluded to involve y~hydrogen a b s t r a c t i o n by excited enone carbon, g i v i n g r i s e to a product, the formation of which again requires l i t t l e conformational change i n the b i r a d i c a l . (3) For adducts possessing endo-methyl substituents at C c and C D _) o as w e l l as bridgehead substituents, a novel oxetane product was observed, formally the r e s u l t of a c y c l o a d d i t i o n r e a c t i o n i n v o l v i n g the remote double bond and one of the carbonyl groups. The oxetane derived from the duroquinone adduct was found to be p h o t o l a b i l e , g i v i n g back s t a r t i n g m a terial and, eventually, a q u a n t i t a t i v e conversion to a novel cage diketone. The r e a c t i v i t y d i f f e r e n c e s f o r these systems, as w e l l as f o r those previously studied i n our laboratory, are i n t e r p r e t e d as being due to the e f f e c t s of substituents on the energy b a r r i e r to conformational isomerization i n the b i r a d i c a l intermediates. F i n a l l y , the p o t e n t i a l u t i l i t y of these photochemical reactions f o r the synthesis of unusual r i n g systems i s noted. - i v -TABLE OF CONTENTS Page INTRODUCTION \ 1 1. General 1 2. Photochemistry of Diels-Alder Adducts 7 3. Objectives of Present Research 31 RESULTS AND DISCUSSION . .. 34 1. Diels-Alder Adducts of Mono-substituted jcv-Benzo-quinones with 2,3-Dimethyl-l,3-butadiene 34 A. 4a3,5,8,8aB-tetrahydro-2,6,7-trimethyl-l,4-naphthoquinone (95) ... 35 B. 6,7-Dimethyl-2-phenyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (96) 46 C. Discussion of Photochemistry of 95 and ... 53 2. Diels-Alder Adduct of 2,3-Dimethyl-_p_-Benzoquinone with 2,3-Dimethyl-l,3-butadiene (97) 55 3. Diels-Alder Adducts with Bridgehead Substituents. 61 A. 4a3,8a3-Dicyano-6,7-dimethyl-4a,5,8,8a-tetra-r hydro-1,4-naphthoquinone (98) 63 B. 2,3-Dichloro-4a3,8a3-dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (99). 68 C. 4a3s8a3-Dicarbomethoxy-6,7-dimethyl-4a,5,8,8a -tetrahydro-1,4-naphthoquinone (100) 71 - V -Page A. Diels-Alder Adducts of Some Substituted j>-Benzoquinones with Hexa-2,4-diene 78 A. Diels-Alder }Adducts of Duroquinone with trans,trans-hexa-2,4-diene (101 and 102) 79 a) Photolysis of 2,3,4a3,53,S3,8a3-hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (101) 81 b) Photolysis of 2,3,4a6,5a,8a,8a6-hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (102) . 87 B. 4a3,8a3-Dicyano-5a,8a-d imethyl-4a,5,8, 8a-tetrahydro-l,4-naphthoquinone (103). 96 5. Discussion 99 EXPERIMENTAL 140 BIBLIOGRAPHY 181 APPENDIX 192 - vi -LIST OF FIGURES Page Figure 1 > „... 5 2 12 3 38 4 .. 39 5 .. 41 6 43 7 48 8 51 9 ; 57 10 , 59 11 . 62 12 .. 65 13 66 14 70 15 72 16 73 17 82 18 83 19 84 20 89 21 90 22 94 23 97 24 123 25 122 26 126 27 127 28 128 29 136 30 138 - v i i -LIST OF SCHEMES Page Scheme 1 .'....«, 4 2 * 6 3 9 4 10 5 10 6 13 7 16 8 16 9 : 17 10 19 11 20 12 22 13 23 14 34 15 44 16 45 17 52 18 56 19 60 20 63 21 68 22 68 23 71 24 74 25 75 26 77 27 80 28 86 29 87 30 93 31 96 32 102 33 103 34 105 35 107 36 107 37 I l l 38 114 39 117 40 120 41 133 - v i i i -LIST OF TABLES Page Table I 29 I I 36 I I I 46 IV 62 V 106 VI 112 VII 113 VIII 115 IX 116 X 119 XI 122 XII 130 - ix -ACKNOWLEDGEMENT I wish, f i r s t of a l l , to thank Dr. John R. Scheffer f o r h i s advice, support, and encouragement during the course of my studies at U.B.C. I t was a p r i v i l e g e and pleasure to work f o r a man who couples a p r o f e s s i o n a l a t t i t u d e towards his work with a personal i n t e r e s t i n h i s students. I also wish to. thank the f a c u l t y and graduate students of the Chemistry Department, and e s p e c i a l l y my co-workers i n , l a b 346, whose frie n d s h i p s made my stay at U.B.C. most enjoyable. Furthermore, I wish to thank my wife, Susan, f o r her excellent typing of t h i s thesis and f o r her patience during i t s preparation. I also express my thanks to my father, E.W. Jennings, f o r the excellent job of mounting the many diagrams. F i n a l l y , I express my gratitude to the U n i v e r s i t y of B.C. f o r f i n a n c i a l support i n the form of a Teaching A s s i s t a n t s h i p . - 1 -INTRODUCTION 1. General Photochemistry, which deals with chemical reactions that are dependent on the action of v i s i b l e or u l t r a v i o l e t l i g h t , has been an area of intense a c t i v i t y i n the past twenty years. However, pr i o r to that, the f i e l d received only li m i t e d attention, with most studies being concerned with gas-phase reactions. Solution photochemistry was neglected, largely because the techniques now available to resolve the complex mixtures of products often encountered had not yet been developed. As w e l l , investigators were handicapped by the u n a v a i l a b i l i t y of adequate a r t i f i c i a l sources of l i g h t . As one author noted, "... with the sun as the chief source of ra d i a t i o n , progress i n the f i e l d often depended on the weather!" 1 This s i t u a t i o n started to change dramatically i n the l a t e 1950's, when i t was rea l i z e d that photochemistry offered p o t e n t i a l access to unusual, and therefore i n t e r e s t i n g , r i n g systems which would be very d i f f i c u l t , i f not impossible, to synthesize by other methods. Isomerization of the norbornadiene derivative to the corresponding quadricyclene 1_ (eq. I ) 2 and photoconversion of carvone 3_ to carvone-camphor 4^  (eq. 2 ) 3 were two of the e a r l i e s t examples of ju s t t h i s point. A short time l a t e r , Eaton and Cole published 1* t h e i r c l a s s i c a l synthesis of cubane 1_ i n which the key intermediate J> was obtained hv (eq. 1) hv (eq. 2) by photolysis of the re a d i l y available cyclopentadienone dimer _5 (eq. 3). I t was not long u n t i l the photochemical method became accepted as a key t o o l i n the synthesis of highly strained p o l y c y c l i c Br hv Br • Br few steps \ J (eq. 3) - 3 -r i n g systems? Just as q u i c k l y , i n v e s t i g a t o r s began to explore the nature of the a c t u a l photochemical processes themselves, to the point that, at the present time, the f i e l d has expanded tremendously i n t o one of wide and v a r i e d areas of research. Testimony to t h i s f a c t are the thousands of research papers published annually on a l l aspects of photochemistry, mechanistic as w e l l as s y n t h e t i c . One important f a c t o r which may a f f e c t the outcome of a photochemical r e a c t i o n i s the m u l t i p l i c i t y of the excited state from which the r e a c t i o n o r i g i n a t e s . On e l e c t r o n i c e x c i t a t i o n , two p o s s i b l e spin configurations may r e s u l t . I f a l l spins remain paired, as they were i n the ground s t a t e , then a s i n g l e t excited state i s produced. On the other hand, i f e x c i t a t i o n i s accompanied by a s p i n i n v e r s i o n process, a t r i p l e t s t ate i s obtained. D i r e c t e x c i t a t i o n from a ground state s i n g l e t to an excited t r i p l e t s t a t e i s a quantum mechanically forbidden process; population of excited t r i p l e t states must occur v i a a secondary process, e i t h e r intermolecular energy t r a n s f e r ( c a l l e d s e n s i t i z a t i o n ) or intramolecular intersystem crossing from the s i n g l e t excited s t a t e . Likewise, d e a c t i v a t i o n from the excited t r i p l e t s t ate to the ground state s i n g l e t i s forbidden; hence the excited t r i p l e t s t ate of a molecule i s s u b s t a n t i a l l y longer-l i v e d than the excited s i n g l e t s t a t e , and for t h i s reason the majority of observed photochemical reactions occur from the t r i p l e t s t a t e . However, a number of s i n g l e t state reactions are known, - 4 -and these may or may not give r i s e to products d i f f e r e n t from those origi n a t i n g from a t r i p l e t state. An example i n which sin g l e t s and t r i p l e t s lead to di f f e r e n t products i s found i n the photochemistry of 3,Y~ u n s a turated ketones, represented i n Scheme l . 6 SCHEME 1 0 0 The singl e t state gives a product a r i s i n g from a 1,3-acyl migration, while the t r i p l e t state leads to cyclopropane ri n g formation. By f a r the most frequently encountered chromophore (or part of the molecule which absorbs l i g h t ) i s the carbonyl group. The u l t r a v i o l e t spectrum of a simple a l i p h a t i c ketone features two d i s t i n c t absorptions. The f i r s t , and more intense, band arises out of e x c i t a t i o n of an electron from the carbonyl TT o r b i t a l to i t s antibonding TT o r b i t a l , * and i s termed a TT - TT t r a n s i t i o n . I t i s usually found i n the region from 200 - 250 nm and has a high (1,000 - 100,000) e x t i n c t i o n c o e f f i c i e n t . The second absorption band i s due to the e x c i t a t i o n of an e l e c t r o n from the non-bonding JD o r b i t a l on oxygen to the carbonyl IT o r b i t a l . C a l l e d the n - IT t r a n s i t i o n , i t i s generally found from 270 - 400 nm, depending on the degree of conjugation present i n the molecule, and has a low e x t i n c t i o n c o e f f i c i e n t (10 - 100) because it- i s a space forbidden t r a n s i t i o n . One important feature of the n - IT s i n g l e t excited state i s i t s high e f f i c i e n c y of intersystem crossing to the t r i p l e t excited s t a t e . This l a t t e r -5 -3 state possesses a r e l a t i v e l y long l i f e t i m e (10 - 10 sec) - 9 - 5 compared to that of the s i n g l e t state (10 - 10 sec) from which i t o r i g i n a t e d . Again, t h i s i s due to the spin (quantum mechanical) forbiddeness of the T^ **- S q process. Figure l 7 gives * a three-dimensional representation of the n - IT t r a n s i t i o n . An fa # 3 b «5> * * Figure 1. A representation of the n - TT t r a n s i t i o n , •.IT system electrons; o, electrons i n an sp o r b i t a l c o - a x i a l to the C-0 bond; y, electrons i n the p o r b i t a l of oxygen; =.'•:-.= F TT bond electrons; anti^bonding o r b i t a l s . « * e l e c t r o n i n the non-bonding £^ o r b i t a l i s excited to the TT o r b i t a l , l e a v i n g behind an o r b i t a l on oxygen which i s e l e c t r o n d e f i c i e n t . - 6 -A behavioral similarity to an alkoxy radical may thus be expected, 8 * and is in fact observed; the n - TT excited state, l i k e the alkoxy radical, is a powerful hydrogen atom abstracting species. A frequently encountered photochemical reaction of ketones arising from the n - TT excited state i s the Norrish II reaction, depicted in Scheme 2. I n i t i a l n - TT excitation i s followed by hydrogen atom abstraction through a six-membered transition state SCHEME 2. to give a biradical, which may then suffer bond closure to give a cyclobutanol or fission to give a ketone and olefin. - 7 -2. Photochemistry of D i e l s - A l d e r Adducts. In 1964, Cookson and co-workers reported 1°the r e s u l t s of a study of the photochemistry of some D i e l s - A l d e r adducts of p-benzoquinone. The adduct with cyclopentadiene j5 (n = 1) was found to isomerize to i t s corresponding cage, compound 9_ (n = 1) i n high y i e l d (eq. 4). 8 (n=0,l,2) 9 (n=0,l,2) S i m i l a r l y the adduct with cyclohexa-1,3-diene j$ (n = 2), and as reported l a t e r J x t h e adduct with cyclobutadiene _8 (n = 0), formed the corresponding cage compounds 9_ (n = 2 and 0 r e s p e c t i v e l y ) on i r r a d i a t i o n . S u p r i s i n g l y , the success of t h i s r e a c t i o n depended on the presence of a bridge or bond j o i n i n g carbon atoms 5 and 8; the 1,3-butadiene-benzoquinone adduct 10 was reported to y i e l d tar and i l l - d e f i n e d products of t e n t a t i v e s t r u c t u r e _11_, postulated to a r i s e from intermolecular a,3-unsaturated double bond dimerization. (eq. 5) - 8 -In 1971, Scheffer and co-workers 1Reinvestigated the photochemistry of 10_ and found that, on selective n - TT e x c i t a t i o n , i n addition to extensive polymer formation, two novel t r i c y c l i c products _12_ and 13 were formed i n 10% o v e r a l l y i e l d (eq. 6). The structure of 12 was (eq. 6) Product Ratios i n : Benzene 1 7 tert-Butanol 5 1 unequivocally determined by X-ray analysis \ "*while structure 13 was assigned on the basis of i t s spectral data and quantitative thermal conversion to 12. The suggested mechanism for the reaction i s shown i n Scheme 3. * I n i t i a l n - ir e x c i t a t i o n of _10_, followed by 8-hydrogen abstraction through a five-membered t r a n s i t i o n state gave the resonance s t a b i l i z e d b i r a d i c a l _1A, which then underwent bond formation to the enol form3 of 12 and J_3 (15 and Ij5, respectively). This mechanism also implied that adducts f a i l e d to undergo th i s reaction due to the bridgehead SCHEME 3. nature of the b i r a d i c a l species which would r e s u l t from the 8-hydrogen abs t r a c t i o n process. The analogous 2 , 3-dimethyl-l, 3-butadiene-jJ-benzoquinone adduct _17 was also s t u d i e d l 5 Photolysis of J_7_ afforded three products 18-20 i n v a s t l y improved y i e l d s , as shown i n Scheme 4. Ene-diones 18 and _19_ were analogous to J_2_ and _13_, r e s p e c t i v e l y , while enone alc o h o l 20_ represented a novel s t r u c t u r e . These r e s u l t s provided - 10 -SCHEME 4. Isolated Y i e l d s i n : Benzene trace 35% 22% tert-Butanol 80% trace trace a d d i t i o n a l evidence f o r the mechanism postulated i n Scheme 3; 3-hydrogen a b s t r a c t i o n by carbonyl oxygen would give r i s e to b i r a d i c a l 21 (Scheme 5), which could then form bonds between various ends of SCHEME 5. - l i -the b l s - a l l y l i c system to give 2XJ d i r e c t l y , and the enol forms 22 and 23. The intermediacy of enol _22_ (and hence of JJ3) was supported by the observation that photolysis of _17_ in tert-butanol-0-d gave isomer _1J3 with one deuterium substituted e x c l u s i v e l y i n the exo-4 p o s i t i o n (92% incorporation from mass spectrum) (eq. 7). The (eq. 7) 18 same product was obtained by mild base catalyzed deuterium exchange of p r o t i o ketone 1_8. This p r e f e r e n t i a l exchange of the exo-proton has precedent i n the work of T i d w e l l 1 6 a n d Werstiuk* 7 In a study of some bi c y cl o (2.2.1] heptanones, the enhancement of the exchange rate i n compound 25_ over that i n 2_4 (Figure 2) was a t t r i b u t e d to the c o n t r i b u t i o n of the homoenolate species 2 6 \ 7 a - 12 -R e l a t i v e Rates of Exchange I —H 24 exo ^endo Ref. Figure 2. 5.89 x 10 9.07 x 10' 17b r2 -5 2.0 4.6 x 10 17a -2 R e l a t i v e hydrogen exchange rates i n some bicyclo[2.2. l] heptanones. While t h i s evidence was compelling f o r the intermediacy of enol 22, i t was not f o r enol 23, due to the low y i e l d of 19_ i n tert-butanol. To v e r i f y the intermediacy of 23, a study of the tetradeuterated adduct 2_7 was undertaken. Photolysis i n anhydrous benzene (eq. 8) y i e l d e d the corresponding tetradeuterated ene-dione 28_, analogous to 19. D D 0 hv (eq. 8) Mass spectroscopy showed a l o s s of only 8.4% deuterium, which corresponded to a 66% deuterium i n c o r p o r a t i o n at the p o s i t i o n (nmr spectrum), assuming that no los s of deuterium had occurred - 13 -at other p o s i t i o n s . This strongly supported the intermediacy of enol 23_ (and also 1 6 ) . The photoproducts 1 8 - 2 0 were found to be i n t e r r e l a t e d by a s e r i e s of thermal and photochemical rearrangements, shown i n Scheme 6 , which also served to corroborate t h e i r s t r u c t u r e s . The thermal SCHEME 6 . benzene conversion of _19_ ( l i k e that of 13^ 1 2 ) c o n s t i t u t e d a [ l , 3 ] s u p r a f a c i a l sigmatropic rearrangement, formally forbidden by Woodward-Hoffmann r u l e s 1 8 a n d therefore was l i k e l y non-concerted 2 0 On the other hand, the photoconversion of 2 0 ^ 1S_ and the thermal conversion of 2 0 -*• 1 8 were examples of allowed [ l , 3 J and [ 3 , 3 ] sigmatropic rearrangements r e s p e c t i v e l y . Whether they were i n f a c t concerted was uncertain; a r e a c t i o n analogous to the 2 ! 0 19_ transformation had been shown 1 9 to be n o n - s t e r e o s p e c i f i c , i e . non-concerted (eq. 9). The formation of equal amounts of ^ 0 and _31 was i n t e r p r e t e d i n terms of the b i r a d i c a l intermediate 32_ which underwent bond r o t a t i o n p r i o r to product f o r m a t i o n l 9 a The photochemical - 14 -29 hv + (eq. 9) 32 transformation of /20 -»- _18, formally a [3,3] s u p r a f a c i a l sigmatropic rearrangement, i s also not allowed by the Woodward-Hoffmann r u l e s l 8 ' 2 0 Schaffner and co-workers 2 1have observed a s i m i l a r type rearrangement i n the photolysis of _33 (eq. 10). 33 0 hv [3,3] (eq. 10) The o r i g i n of the dramatic solvent e f f e c t on the product d i s t r i b u t i o n i n both adducts H) and _17 was not at a l l c l e a r . The p o s s i b i l i t y that _18 and 1_9_ were secondary products of 20. w a s r u l e d out by time-dependence studies. One suggestion 1 5invoked the formation of the z w i t t e r i o n i c 2 2 intermediate 35_, s t a b i l i z e d i n t e r t - b u t a n o l by hydrogen bonding and s o l v a t i o n of the p o s i t i v e charge at Cg. P r e f e r e n t i a l 3,8 bonding, w i t h subsequent formation of JL8, would be expected to occur as was observed. In benzene, t h e r e f o r e , the r e a c t i o n could be i n t e r p r e t e d as proceeding through e i t h e r a b i r a d i c a l or z w i t t e r i o n i c in termedia te , fo l lowed by p r e f e r e n t i a l bond formation at the i n d u c t i v e l y s t a b i l i z e d p o s i t i o n . However, the products so formed (19 and 20) are thermodynamically u n s t a b l e , e x e m p l i f i e d by t h e i r thermal conversion to _18 (also 13 ->• 12). G a y l e r 2 3 advanced the a l t e r n a t e suggest ion that i n benzene, the p h o t o l y s i s i s k i n e t i c a l l y c o n t r o l l e d due to the p o s s i b l y c l o s e r resemblance of _19 and 20. to the s t r u c t u r e of the intermediate b i r a d i c a l 2_1; and thus t h e i r formation would have a lower a c t i v a t i o n energy (Hammond p r i n c i p l e 2 **). In an extension of t h i s work, the unsymmetrical adduct 36 (p_-benzoquinone with isoprene) was i n v e s t i g a t e d 2 3 ' 2 5 t o determine the r e g i o s e l e c t i v i t y of the B-hydrogen a b s t r a c t i o n p r o c e s s . C o n s i d e r a t i o n of the i n f l u e n c e of a methyl group on a l l y l r a d i c a l s t a b i l i t y suggested that the formation of b i r a d i c a l 37. (Scheme 7, path a) would be favored over 38 (path b). Since an a l l y l r a d i c a l ' s highest SCHEME 7. OH occupied molecular o r b i t a l has a node at the c e n t r a l carbon atom, a methyl substituent there, as i n 38, would have l i t t l e e f f e c t , whereas a methyl substituent on a terminal carbon, as i n _37 would be expected to have a pronounced influence on the s t a b i l i t y of the r a d i c a l . This was found to be the case. P h o t o l y s i s of 36_ i n e i t h e r benzene or tert-butanol gave the products shown i n Scheme 8, i n the SCHEME 8. Re l a t i v e Ratios i n : Benzene 5 3 2 tert-Butanol - 7 1 - 17 -indicated r e l a t i v e r a t i o s . In both solvent systems studied, the products r e s u l t i n g from abstraction at the 8-position (ie. 3[9_ and 40) predominated over 4_1_, the product of 8'-abstraction. Related to the s t a b i l i z i n g effect of a methyl substituent was the photochemistry of the p-benzoquinone-trans,trans-2,4-hexadiene adduct 4_2.- 8-Hydrogen abstraction from either carbon atom 5 or 8 would again y i e l d a b i r a d i c a l with a methyl substituent at the terminal end of one of the a l l y l systems, such as 43 (Scheme 9)* which would s t a b i l i z e the species. This was not observed, however. SCHEME 9. Photolysis i n benzene or tert-butanol led to a single photoproduct, assigned structure 4_4 on the basis of spectroscopic data and deuterium - 1 8 -exchange studies. The mechanism for formation of 4_4 involved y-hydrogen abstraction from the C C or C 0 methyl group to give b i r a d i c a l 5 o 4 5 , which then underwent bonding to give enol 4_6_ (the intermediacy of which was again v e r i f i e d by photolysis i n tert-butanol-O-d) and subsequent ketonization to 4 4 . The stereochemistry at C , . and Cg i n adduct 4 2 and at C ^ Q i n 4 4 was assumed, based on the spectra and the mechanism of formation of 4_4_; the epimeric form 4 7 could not give structure 4 4 . In a p a r a l l e l study, adduct 4_8 was investigated to determine the extent to which Y~hydrogen a b s t r a c t i o n could compete with g-hydrogen a b s t r a c t i o n . Photolysis of 4_8 i n benzene or t e r t -butanol gave products 4_9_ and _50 i n a r e l a t i v e r a t i o of 7 : 1 (eq. 1 1 ) . (eq. 1 1 ) Thus, despite the f a c t that B-abstraction should have been favored e l e c t r o n i c a l l y , the product a r i s i n g from the s t a t i s t i c a l l y favored process of y~hydrogen a b s t r a c t i o n was formed p r e f e r e n t i a l l y . I t was i n t e r e s t i n g to note that i n neither 4_2_ nor 4J3 was there observed any product r e s u l t i n g from a b s t r a c t i o n of the t e r t i a r y B -( a l l y l i c ) hydrogen. This was also the case i n the p h o t o l y s i s o f - 19 -adduct 5l_, in which the 8-hydrogens are tertiary, a l l y l i c and benzylic, and therefore in theory readily abstractablef 5 Irradiation of 5l_ under a variety of conditions led to no detectable change. A possible reason PK 0 hv ^ N.R. 3> for these observations was advanced, based on conformational analysis. The butadiene-/p_-benzoquinone ring system was described 2 5in terms o f five more or less well defined conformeirs A-E, as shown i n Scheme 10 . SCHEME 10. - 20 -9 7 r Also shown are " a c c e s s i b l e " $-hydrogen to oxygen distances (those greater than 3.5 8 were not considered). When X = H, and Y = CH^ (as i n 42) or Ph (as i n 51), only i n conformers A and B are the B-hydrogens a c c e s s i b l e ; however, these conformations are d e s t a b i l i z e d by Y - Y ( i e . Me - Me, 4_2_, or Ph - Ph, 51) non-bonded i n t e r a c t i o n of a bowsprit-f l a g p o l e - l i k e n a t u r e 2 8 As w e l l , B-hydrogen a b s t r a c t i o n i n e i t h e r conformer • A or B would break a C-H bond nearly orthogonal to the double bond j> o r b i t a l s , thereby minimizing i n c i p i e n t a l l y l r a d i c a l s t a b i l i t y . Thus, i t was reasoned 2 3' 2 5 y-hydrogen a b s t r a c t i o n from methyl occurred, p o s s i b l y from conformer C, where the methyl hydrogens can be as close as 0 . 9 X from oxygen 2 3although conformers D and E also possess methyls with favorable hydrogen-to-oxygen distances (1.4 A*)25 F i n a l l y , to determine the e f f e c t s of methyl substituents at other p o s i t i o n s i n the b a s i c r i n g system ( c f . , compound 10), the adduct of duroquinone with 2,3-dimethyl-l,3-butadiene j>2_ was s t u d i e d 2 3 ' 2 5 Photolysis i n a v a r i e t y of solvents l e d to products 53_ - 55 i n the r e l a t i v e amounts shown i n Scheme 11. Ene-dione 54 represents a previously Benzene 0.5 1 -tert-Butanol 1.1 1 -A c e t o n i t r i l e 4 1 -Methanol 13 1 2 1:1 Dioxane - Water 30 1 6 - 2 1 -unobserved product s t r u c t u r e , whose str u c t u r e was deduced from i t s s p e c t r a l properties and from i t s two step conversion back to adduct 5J£ as shown i n equation 12. The thermal transformation _54 -*• _56 represents 0 (eq. 12) a novel example of a retro-ene r e a c t i o n 2 9 ( a r r o w s ) , although a l e s s concerted mechanism i s also p o s s i b l e . The presence of the new structure 54 also suggested the p o s s i b i l i t y that _53 may have had a novel structure as w e l l ; however, x-ray analysis 3"supported the structure 53 given i n Scheme 11. This product was thus analogous to compound 20, and as such, was found to thermally convert to _55, analogous to the 20 _18 transformation (Scheme 6). The s t r u c t u r e of _55 was assigned on the basis of i t s s p e c t r a l s i m i l a r i t i e s to compound 18. To explain the divergent photochemical behavior of adduct 52 two p o s s i b l e mechanisms were considered (Scheme 1 2 ) 2 3 ' 2 5 The f i r s t (path A) involves an i n i t i a l 8-hydrogen a b s t r a c t i o n by carbonyl oxygen to give b i r a d i c a l 57_ (which very l i k e l y explains the formation of j>3 and 55) , followed by a p r o t o t r o p i c s h i f t 3 1 to give _58. Bonding between carbon atoms 2 and 8 and k e t o n i z a t i o n then gives 54. The a l t e r n a t i v e mechanism (path B) c a l l s f o r an i n i t i a l y-hydrogen a b s t r a c t i o n - 22 -SCHEME 12. OH 0 54 by enone carbon atom 3, giving b i r a d i c a l ^0, which gives 54 d i r e c t l y upon bond formation. The two pathways to photoproduct 5 4 are t h e o r e t i c a l l y distinguishable since path A requires the intermediate enol 5 9 . Photolysis of j>2_ i n tert-butanol-0-d or dioxane-D20 ( 1 : 1 ) 2 3 ' 2 5 y i e l d e d isomer 5 4 i n which there was no deuterium incorporation; however, product J55_ isolated i n the l a t t e r >instance contained exactly one deuterium atom i n the CL - 23 -p o s i t i o n (mass spectrum, nmr). Thus path A was t e n t a t i v e l y ruled out i n favor of B for the formation of 54. P r i o r to these i n v e s t i g a t i o n s by Scheffer. et a l , v i r t u a l l y no examples of 8-hydrogen ab s t r a c t i o n had been reported? 2 Shortly a f t e r these r e s u l t s were known, Agosta and co-workers published a report i n which a- s e r i e s of a-methylene ketones formed products r e s u l t i n g from B-hydrogen a b s t r a c t i o n (63 and 66) as w e l l as those from the more f a m i l i a r yhydrogen ab s t r a c t i o n (Norrish II) process (62 and 65), These r e s u l t s are summarized i n Scheme 13. The formation of 63 SCHEME 13. 61 62 63 V 67 68 69 - 24 -and 66_ was attributed to the intermediacy of a b i r a d i c a l such as 68 ( a r i s i n g from the B-hydrogen abstraction process), which i s formally a derivative of trimethylene methane (69), 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 3**delocalization energy of 34 k c a l . mole. 1 I t i s int e r e s t i n g here to note that the observed photoreactions of adducts 10 and JL7_ also require a capacity f o r extensive s t a b i l i z a t i o n of t h e i r b i r a d i c a l intermediates and 21 respectively. Compound 7_0, lacking the ene-dione double bond present i n _17_, underwent no detectable reaction, even a f t e r prolonged periods of i r r a d i a t i o n 3 5 The process of y-hydrogen abstraction by enone carbon, on the 3 £ other hand, has ample l i t e r a t u r e precedent. Herz and Nair reported one of the e a r l i e s t examples (eq. 13) i n which the proposed reactive state was the TT - TT , rather than the n - u , based on the phosphorescence spectrum of 7_1. Electron r i c h substituents such as methoxyl are known 3 7 - 25 -* to lower the energy of the TT - TT t r i p l e t s t a t e , r e l a t i v e to that of * * the n — TT t r i p l e t s t a t e . In the case of the TT — TT state was the t r i p l e t with the lower energy. * As has been mentioned previously, the n - TT excited state i s a powerful hydrogen atom abstracting species, and a b s t r a c t i o n by the oxygen of a carbonyl group, e s p e c i a l l y from the a - p o s i t i o n of p r o t i c solvents ( i e . isopropanol), i s u s u a l l y a t t r i b u t e d to t h i s s t a t e . Conversely, the lack of such a b s t r a c t i o n (photoreduction) i n t r i p l e t s t a te reactions i s u s u a l l y taken as a strong i n d i c a t i o n of an unreactive t r i p l e t TT - TT state. Schaffner and co-workers have suggested that hydrogen a b s t r a c t i o n by the (3-carbon of an a,3-unsaturated ketone i s t y p i c a l of TT — TT t r i p l e t s . Another example of hydrogen a b s t r a c t i o n by enone carbon was provided by Nakanishi and co-workers? 9 Photolysis of taxinine diacetate _7_3 i n a v a r i e t y of solvents y i e l d e d the transannularly c y c l i z e d product _74 (eq. 14). In t h i s instance, the a b s t r a c t i o n H H - 26 -was by the a-carbon atom; s e n s i t i z a t i o n and quenching experiments indicated a r e a c t i v e t r i p l e t state. In addition, the high quantum y i e l d i n polar solvents (0.091 i n dioxane; 0.078 i n tert-butanol) r e l a t i v e to that i n benzene (0.031) led the authors to conclude that the r e a c t i v e t r i p l e t was a TT - TT state. A d d i t i o n a l evidence for t h i s conclusion was the observation that photolysis of 7_3 i n isopropanol resulted i n no hydrogen a b s t r a c t i o n from solvent. Agosta and co-workers' + 0 - 1* 2have studied the photochemistry of a number of a,8-unsaturated cj'clopentenone systems, represented by equations 15 - 17. I t was postulated i n each case that the products arose v i a a hydrogen abstra c t i o n by the 6-carbon atom, followed by e i t h e r secondary hydrogen a b s t r a c t i o n to give o l e f i n s , or bonding between the ends of the b i r a d i c a l intermediates. With reference to equations 16 and 17, i t was noted that the carbonyl moiety need not be a part of the cyclopentene r i n g . As these reactions 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 , they were thought to o r i g i n a t e from a t r i p l e t excited state? 3' Returning to the case of compound 5J2, there was also some precedent for the involvement of a rr - Tf t r i p l e t state. Depending on the degree of s u b s t i t u t i o n , a s t r i k i n g d i f f e r e n c e i n products was observed i n the photoreaction of a v a r i e t y of jo-benzoquinones with - 2 7 -olefins. With no substituent present (ie. £-benzoquinone, 75) the sole product formed"*"*was the oxetane 76 (eq. 18), the result of a 2 + 2 cycloaddition of ole f i n to the carbonyl group. With methyl I i - 28 -0 + hv 0 (eq. 19) O 77 78 79 substituents present, i n addition to oxetane formation, the competitive process of 2 + 2 cycloaddition of o l e f i n to the ene-dione double, bond was observed, y i e l d i n g cyclobutanes, as i n the case of 77 (eq. 19)'j In certain instances, exclusive cyclobutane formation was observed. These r e s u l t s are summarized i n Table i l * 6 I t was te n t a t i v e l y concluded h 7that the d i f f e r e n t products were formed from d i f f e r e n t excited states: n - TT giving oxetanes and 77 — TT leading to cyclobutanes. However, a study by Pappas and Portnoy1* 8suggested that t h i s may not be the case. Using 1,4-naphthoquinone as a model, no dependence of the product r a t i o on solvent was observed which argued against the p a r t i c i p a t i o n of different excited states. In the case of compounds JK) and j H , i t had been suggested that exclusive cyclobutane formation originated from a TT — TT excited state, lowered i n energy by the electron releasing effect of the methoxyl substituent? 7 However, Portnoy and Pappas1*8 showed that 6-methoxy?-l,4-naphthoquinone (85), which they reasoned should also show an enhanced r a t i o of cyclobutane formation due to the a b i l i t y of the methoxyl group to s t a b i l i z e a TT - TT t r i p l e t at p o s i t i o n 2, yielded v i r t u a l l y the same product r a t i o as the * - 29 -TABLE I. PHOTOREACTIVITY OF _p_-QUINONES WITH OLEFINS. A. Exclusive Oxetane Formation. 0 B. Concurrent Oxetane and Cyclobutane Formation. 0 0 0 C. Exclusive Cyclobutane Formation. 87 88 89 90 0 D. No Addition. 0 - 30 unsubstituted analog 83. These res u l t s were interpreted as indicating that the presence of the methoxyl was important only when i t was situated on the double bond p a r t i c i p a t i n g i n the reaction. Furthermore, i t was concluded 1* 8that the effects of the methoxyl (or methyl) group were, a) to l o c a l i z e e x c i t a t i o n i n the adjacent double bond, and b) to s t a b i l i z e an intermediate complex or r a d i c a l species. Only i n the * case of _93, was the TT — TT state implicated, being responsible for the observed lack of r e a c t i v i t y . A v i a b l e alternate explanation for the r e a c t i v i t y of _52 was advanced based on conformational a n a l y s i s 2 3 ' 2 5 0 f the f i v e conformers A - E i n Scheme 10, i t was suggested that conformer C ( i e . structure 94) would be favored by the bridgehead methyl substituents since only i n t h i s conformation are they not eclipsed. As a r e s u l t the J2 o r b i t a l situated on carbon atom 3 approaches r e l a t i v e l y closely to the inner C Q a l l y l i c hydrogen and thus the y-hydrogen abstraction process o i s f a c i l i t a t e d . Similar reasoning might then account for the results observed i n the cases of compounds 71^ B and 73 3 9namely, hydrogen abstraction by carbon i s favored by the proximity of the Tr-orbital and the hydrogen i n these r i g i d structures. - 31 -3. Objectives of Present Research I t had been demonstrated previously (see Introduction) that e l i m i n a t i n g the symmetry of the parent 4a,5,8,8a-tetrahydronaphthoquinone r i n g system (cf. compound 10) by p l a c i n g a lone substituent at Cg introduces a r e g i o s e l e c t i v i t y to the process of B-hydrogen abstraction; the observed photoproducts (Scheme 8) show p r e f e r e n t i a l formation of the more stable b i r a d i c a l species, r e s u l t i n g from 8 rather than 8' a b s t r a c t i o n (compound 36). I t was also of i n t e r e s t to determine i f p l a c i n g a substituent on the ene-dione double bond could bring about such a r e g i o s e l e c t i v e product d i s t r i b u t i o n . To t h i s end, adducts 95 and 96^ were investigated. Again, the lone substituent destroys 36 0 molecular symmetry i n /9_5 and 96., rendering the processes of 8 and 8' a b s t r a c t i o n nonequivalent. There was i n a d d i t i o n , the p o s s i b i l i t y that a phenyl or methyl substituent so positioned would a l t e r the photochemistry from that observed thus f a r i n these systems (cf.,the Pappas argument 1* 8regarding the e f f e c t of methyl and methoxyl sub s t i t u e n t s ) . - 32 -The o r i g i n of the "/-hydrogen ab s t r a c t i o n by enone carbon i n compound _52 was s t i l l unclear. As already mentioned, two fa c t o r s could influence the observed formation of 54; a) the presence of the two methyl groups on the ene-dione * * chromophore causes a r e v e r s a l of close l y i n g n - TT and TT — TT excited states; thus a b s t r a c t i o n by carbon may have ori g i n a t e d from an excited TT - TT s t a t e , much i n l i n e with the proposals of Barltrop and Schaffner? 8 b) the r e a c t i o n proceeds under the infl u e n c e of conformational c o n t r o l ; hydrogen a b s t r a c t i o n by carbon i s favored by conformer C (Scheme 10) which brings the enone carbon atom and the a l l y l i c a bstractable hydrogen into proximity. To obtain a d d i t i o n a l information i n regard to these a l t e r n a t i v e s , compounds 9_7 - 100 were investigated. Adduct 97 possesses the same 0 O o o 99 100, E=C0„Me 4. - 33 -chromophore and therefore should also possess s i m i l a r electronic properties as compound 52, while compounds 9_8 - 1 0 0 place substituents at the bridgehead positions and should help to determine the extent of the influence of conformational control on the photorearrangement. Additional d e t a i l s w i l l be provided i n the Results and Discussion section. F i n a l l y , to extend the scope of the photoreaction of the substituted r i n g system, compounds 101 - 1G3 were investigated. Compounds 1 02 and 1 03 are more highly substituted analogues of adduct 42., while compound 1 0 1 , i n addition to being the C,./Ca epimer of 1 0 2 , i s 101 R -Me, R2=H analogous to adduct _52. Again more s p e c i f i c reasons for t h i s study are deferred to the next section. - 34 -RESULTS AND DISCUSSION 1. Diels-Alder Adducts of Mono-substituted _p_-Benzoquinones with 2,3-Dimethyl-l,3-butadiene. I t had been demonstrated i n t h i s laboratory that the product d i s t r i b u t i o n r e s u l t i n g from i r r a d i a t i o n of the isoprene-_p_-benzoquinone Diels-Alder adduct 3_6 r e f l e c t s the s t a b i l i z i n g effect of the lone methyl substituent on the formation of the two possible b i s - a l l y l i c r a d i c a l intermediates (cf. Introduction). To determine the e f f e c t , i f any, a substituent on the ene-dione double bond of the tetrahydro-naphthoquinone rin g system would have on the r e g i o s e l e c t i v i t y of the 3-hydrogen abstraction process, adducts 95_ and 96 were investigated. Once again, abstraction of the 8-hydrogen from carbon-atom 5 (Scheme 14) SCHEME 14. - 35 -would give a d i f f e r e n t b i r a d i c a l intermediate (104) than would a b s t r a c t i o n from C Q (105); the r a t i o s of products should again o r e f l e c t the s t a b i l i z i n g influence of the C^-substituent. A. 4a3,5,8,8a3-Tetrahydro-2,6,7-trimethyl-1,4-naphthoquinone (95) . Adduct 9_5 was synthesized by the method of Bergmann and Bergmann1*9 (eq. 20). A mixture of methyl-p_-benzoquinone and 2,3-dimethyl-l,3-butadiene was heated i n a sealed tube at 110°, r e s u l t i n g i n a 77% y i e l d of adduct 95. O P h o t o l y s i s of d i l u t e benzene or t e r t - b u t y l a l cohol solutions (2 mg/ml) of _95_ led to the formation of f i v e products 106-110 (eq. 21) i n the r e l a t i v e r a t i o s i n d i c a t e d i n Table I I . The photoreaction 95 0 + 0 108 (eq. 21) 0 TABLE I I . Relative r a t i o s of Products from Photolysis of 95. Solvent Benzene tert-Butanol could be monitored by glpc, which indicated that a l l of 106-110 were primary photoproducts i n that no induction period for the formation of any product was observed. However, the r e l a t i v e r a t i o s of the products, as determined by cutting out and weighing peaks from the glpc chart paper, were found to vary s l i g h t l y during the course of the reaction i n d i c a t i n g that some interconversion among the photoproducts was occurring. Thus the values reported i n Table I I represent those at the conclusion of the photolysis when no measureable (glpc) amount of 95_ remained. Products were isolated by preparative glpc; y i e l d s and conditions were not optimized as the main purpose of the experiment was mechanistic i n nature. A l l products were shown to be isomeric with 9_5 by t h e i r mass spectra and elemental analyses. Enone alcohols 106 and 109 both display carbonyl stretching bands at 5.93u i n t h e i r i r spectra, along with small hydroxyl bands at 2.80y. The most noticeable differences i n t h e i r nmr spectra 106 107 108 109 110 3.8 1 2.6 3.4 1 9 . 6 - 3 1 - 3 7 -(figure 3) are the r e l a t i v e chemical s h i f t s of the signals due to the protons and methyl groups situated on the unsaturated carbonyl portion of the molecule. In 106, the C. v i n y l proton resonance i s > 4 located at T3.61, downfield from the proton signal i n 109 (T4.29), S i m i l a r l y , the C^, v i n y l methyl signal i n 109 comes at lower f i e l d (T8.06) than the C 3 methyl of 106 (T8.22). These s h i f t s are brought about by the polarization 5"present i n an a,8-unsaturated carbonyl moiety (depicted schematically i n structure 111) , which results i n a deshielding of the H proton which i s bonded to the 8 carbon atom. As one might expect, t h i s H 6+ 5-R — C = C H - C = 0 8 a | i i i R deshielding effect i s less pronounced i n the case of methyl groups, as they are insulated to a degree by the carbon-carbon bond. The remainder of the spectra are quite s i m i l a r (Figure 3). The v i n y l proton gives r i s e to the multiplet occurring at T4.40. The broadened doublet at approximately T7 i s assigned to the C, methine. 6 As w i l l be seen, t h i s i s a c h a r a c t e r i s t i c signal of the enone alcohol - 38 -Figure 3. NMR Spectra of Enone Alcohols 106 and 1 0 9 . structure with a proton bonded at carbon C,. The hydroxy1 proton o gives r i s e to a singl e t at approximately T7.6, superimposed on a multiplet attributed to the methine. The C^Q methylenes give r i s e to resonances i n the region from T8.4 - 8.6. The structure of ene-dione 107 was indicated by i t s single sharp carbonyl band at 5.70u i n the i r spectrum, c h a r a c t e r i s t i c of a five-membered r i n g c y c l i c ketone? 1 The nmr spectrum of 107 (figure 4) showed no signal below x7. A narrow multiplet at T7.40 I • I Figure 4. NMR Spectrum of Ene-dione 107. was assigned to the C, methine. The C. exo-proton appears as a double 6 4 - 40 -doublet at T7.83 (calculated s h i f t 5 2 ) coupled to the endo-protori (J=18Hz) and (weakly) to the C & methine (J=lHz). The endo-proton showed a doublet at T7.97 ( c a l c u l a t e d 5 2 ) . The C g and C g methyls give r i s e to broad sin g l e t s at T8.28 and 8.38. The sharp singl e t at T8.84 i s assigned to the methyl, thus comfinning the assigned structure for 107. The i n t e r a c t i o n between the exo-proton and methine was v e r i f i e d by the collapse of the multiplet at T7.40 to a broad doublet on exchange of the exo-proton with deuterium. Similar long range couplings are f a i r l y common; for example, they are observed i n 112, though i n t h i s s p e c i f i c case, a carbonyl carbon i s not S 3 J = 0.5Hz involved. They are usually very weak (0 - 2Hz) and appear when the inte r a c t i n g protons are arranged i n the "W" configuration shown i n 113 5 0. Molecular models reveal that the C. exo- and C. protons i n 4 o diketone 107 assume ju s t t h i s configuration. 113 The above-mentioned exchange of the exo-proton with deuterium-was brought about by treating a solution of 107, i n an nmr tube with - 41 -a 2N s o l u t i o n of potassium hydroxide i n deuterium oxide. A f t e r p e r i o d i c shaking over a period of eight hours, the nmr spectrum was retaken ( f i g u r e 4), which shows, by the t o t a l disappearance of the double doublet at T7.79, the s e l e c t i v e exchange of the exo-proton. In a d d i t i o n to the noted change i n the proton resonance, the o doublet at Tl.91 (due to endo-proton) collapses to a broad t r i p l e t . No other change i s observed i n the nmr spectrum. Product 110 features a s i n g l e i r carbonyl band at 5.72u. I t s nmr spectrum ( f i g u r e 5) shows, i n ad d i t i o n to v i n y l methyl s i g n a l s T — r - 1 — ' — 1 — H r ' i ' i — 1 1 • i 1 ' r — 1 — T Figure 5. NMR Spectrum of Ene-dione 110. at T8.34 and T8.47, a doublet at T8.95, assigned to the methyl and coupled to the'C. proton with a coupling constant of 7.5Hz. This - 42 -doublet again distinguishes structure 110 from that of dione 107. While the proton resonance can not be discerned, the remainder of the spectrum closely resembles that of ene-dione 185** Ene-dione 108 exhibits an i r spectrum with two carbonyl bands at 5.68 and 5.80u, analogous to the i r of ene-dione 19J 5 > 2 5which indicates the presence of a five-membered and a six-membered c y c l i c ketone 5 1 The u l t r a v i o l e t spectrum also supports structure 108 by showing absorptions at 294 nm (e 481) and 307 nm (e 426). Such enhanced extinction c o e f f i c i e n t s have been found 5 5to be c h a r a c t e r i s t i c of most 8>Y -unsaturated ketones, such as 108, and have also been observed previously i n the uv spectra of analogous products _13_ and The nmr spectrum, shown i n figure 6, features a broad doublet at T4.42 (J=7Hz) due to the v i n y l proton which i s coupled to the Cr methine. The double doublet at lb.11 i s attributed to the C, proton, 6 b coupled to the v i n y l and to the methine (J=8Hz). The exo and endo-protons each display doublets with mutual coupling constants of • 17.5Hz, and appear at T7.14 and T8.15 respectively. The Cg v i n y l methyl shows a si n g l e t at T8.12, while the C^ and C^ methyls give r i s e to sharp singlets at T8.73 and T9.02. The presence of these t e r t i a r y methyl singlets thus rules out the alter n a t i v e structure 114 for t h i s product, - 43 -Figure 6. NMR Spectrum of Ene-dione 108. which would give r i s e to singlet and doublet resonances for the methyl groups (compare again 107 and 110). Ad d i t i o n a l evidence for the structures of products 106-110 was obtained from an interesting series of thermal and photochemical rearrangements, shown i n Scheme 15. Thus, sealed tube thermolysis - 44 -SCHEME 15. of 106 at 200° gave 107, while thermolysis of 109 under i d e n t i c a l conditions gave 110. Both transformations represent formally allowed [3,3] suprafacial sigmatropic rearrangements\ 8although a stepwise mechanism i s also possible. Sealed tube thermolysis of 108 gave a high y i e l d of 107, a formally d i s a l l o w e d 1 8 [l ,3] suprafacial sigmatropic rearrangement 2 0 The formation of 108 on photolysis of 106 represents an allowed [l,3] sigmatropic rearrangement, although the work of C a r g i l l 1 9 ( c f . compound 29) presents an example where such a transformation i n nonconcerted. On the other hand, the 106 h^ 107 and 1 0 9 ^ 1 10 conversions are formally disallowed photochemical [3,3] rearrangementsJ 8 an analogous transformation, that of 33 to _34_ has been observed by Schaffner and - 4 5 -co-workers 2 1(see Introduction). The res u l t s thus p a r a l l e l those obtained for the dimethyl products derived from adduct _17_ (see Introduction). Once again, l i k e compound _L8, ene-diones 107 and 110, which feature the same ring system as compound _18, appear to be the thermodynamically most stable. The mechanism for the formation of products 106-110 from 9 5 very l i k e l y involves i n i t i a l 3-hydrogen abstraction from either C c or C D, with formation of b i r a d i c a l intermediates 115 and 116 J o respectively (Scheme 16). Subsequent bond formation (and ketonization SCHEME 16. 116 0 115 A,7-hoiVrHnf> 106 s - h o n d - i n g , kp.tonizatiQii» 107 \ 2,7 -hond-ing t ketonisatipn > 108 1 1 6 1 , 6 - b n n d - t n g y 109 a - b r m d i n g y kpfon-j z a t l o n > 110 - 4 6 -i n the cases of 107, 108 and 110) would then account for the observed products. As w e l l , the product d i s t r i b u t i o n suggests the p r e f e r e n t i a l formation of intermediate 115. This i s shown i n Table I I I . TABLE I I I . Relative Ratios of Products A r i s i n g from Intermediates 115 and 116. Solvent 115 116 Benzene 2.2 1 tert-Butanol 2.6 1 The reason why ene-dione 114, which could be formed by 3,6-bonding i n 116 (eq. 22), i s not observed i s not r e a d i l y apparent. No doubt (eq. 22) (not formed) related to t h i s i s the fact that enone-alcohol 109, on photolysis i n benzene, did not rearrange to 116 nor to any other product. Such behavior i s observed only for 109; enone alcohols 106 and /20 r e a d i l y photoisomerize i n benzene to the corresponding compounds 108 and 19. B. 6,7-Dimethyl-2-phenyl-4a3,5,8,8a3-tetrahydro-1,4-naphthoquinone (96). The synthesis of adduct /96 was performed i n a manner s i m i l a r to that of 95^, a f t e r the method of Bergmann and Bergmann^9a mixture of phenyl-j)-benzoquinone and 2,3-dimethyl-l,3-butadiene was thermolyzed - 47 -i n a sealed Pyrex tube for one hour at 100°C (eq. 23). 100° 1 hour sealed tube The photochemical reaction of 9j6 was monitored by observing changes i n the i r spectrum of the reaction mixture as the reaction progressed. This showed a rapid change i n the region below 6.5]i on i r r a d i a t i o n i n either benzene or tert-butanol, accompanied by the appearance and growth of a carbonyl band at 5.70u, at the expense of the s t a r t i n g material carbonyl at 5.93]i u n t i l the 5.70y absorption remained the lone v i s i b l e carbonyl band. Workup by column chromatography was accompanied by extensive decomposition as indicated by a band of black material which remained at the top of the column. However, the i s o l a t i o n of a single photoproduct was achieved i n about 30 -35% y i e l d . This product was assigned the structure 117 on the basis of spectral data (eq. 24). * o - • (eq- 2 4 ) Ene-dione 117, i n addition to displaying an i r spectrum featuring a 5.70y carbonyl band, exhibits the nmr spectrum shown i n figure 7. - 48 -Figure 7. NMR Spectrum of Ene-dione 117. The double doublet at T7.06 ( c a l c u l a t e d 5 2 ) i s assigned to the exo-proton, coupled to the endo-proton (J=18Hz) and weakly to the methine (J=1.5Hz). The endo si g n a l occurs a f x7.62 ( c a l c u l a t e d 5 2 ) ; also as a doublet (J=18Hz). V i n y l methyls appear at T8.32 and T8.69. The nmr spectrum thus favors structure 1_17 over that of 118, a possible a l t e r n a t i v e for the photoproduct. No signal appears at lower f i e l d than T6.88, except for the phenyl protons (singlet at T 2 . 6 4 ) . This would not be expected for structure 118. The C. proton i n 118 i s a to a carbonyl, t e r t i a r y and benzylic, and thus should appear at a lower f i e l d 5 0 t h a n the benzylic a-methylene protons i n dibenzyl ketone 119, which show a resonance at T6.3 5 6 0 II Ph - CH 2 - C - CH 2 - Ph 119 Further support for structure 117 was found when a solution of 117 was treated with a 1.2N deuterium oxide solution of potassium hydroxide i n an nmr tube. As was the case previously with ene-diones 18 and 107, the exo-proton was s e l e c t i v e l y exchanged for deuterium. The r e s u l t i n g changes i n the nmr spectrum (figure 7) are the disappearance of the double doublet at T7.06 and a collapse of the doublet at T7.62 (C^ endo) to a broad s i n g l e t . I t was possible to i s o l a t e a second photoproduct, i n addition to 117, from the photolysis of 96 i n benzene i f the reaction was interrupted when the i n t e n s i t i e s of the i r carbonyl bands at 5.70 and 5.93y were - 50 -about equal. Column chromatography resulted i n a small quantity (< 20%) of an o i l which showed a small hydroxyl absorption i n the i r as w e l l as a 5.93y carbonyl. The v i n y l proton region (T3-4.5) i n the nmr spectrum resembled that of the mixture of enone alcohols 106 and 109, and i t was tentatively concluded that a mixture of isomeric enone alcohols 120 and 121 was present i n a r a t i o of about 6:1 based .on the nmr integration of the v i n y l proton signals. 120 121 Rechromatography of the mixture, which was again accompanied by decomposition, resulted i n only p a r t i a l separation; 120 and 121 were is o l a t e d as crude so l i d s i n very low y i e l d . The main difference i n the nmr spectra of 120 and 121 (figure 8) i s , as i n the case of 106 and 109, the r e l a t i v e p osition of the C^ v i n y l (T3.20) i n 120 and the C 3 v i n y l (T4.03) i n 121. Again, the deshielding effect previously discussed for a,B-unsaturated ketones i s responsible for the downfield p o s i t i o n of the v i n y l resonance i n 120 (cf.structure 111). The lack of s u f f i c i e n t material prevented further study of compounds 120 and 121. • The formation of 117, 120 and 121 can be explained by the $-hydrogea - 51 -Figure 8. NMR Spectra of Enone Alcohols 120 and 1 2 1 . abstraction mechanism shown i n Scheme 17, involving b i r a d i c a l i n t e r -mediate 122, i n the case of 117 and 120, and the species 123 i n the case of 121. The formation of 117 from 122 was shown to involve the SCHEME 17. O 117 intermediacy of enol 124 by the observation that photolysis of adduct 96 i n tert-butanol-0-d led to deuterio-117 (92% incorporation of deuterium, calculated from mass spectrum - see Appendix for calculations). The nmr spectrum of deutereo-117 was i d e n t i c a l to that of the product of the base-catalyzed J)^0 exchange reaction and showed that the deuterium was located exclusively at the C^ exo-position. While no quantitative information i s av a i l a b l e , i t i s obvious that the photochemistry of 96_ proceeds almost exclusively v i a b i r a d i c a l 122, although the low yie l d s of products obtained detract somewhat from t h i s conclusion. Furthermore, i t seems that some - 53 -subtle effects are operating i n t h i s instance since the major product in benzene i s 117 and not 125, which possesses the ring structure found i n products emerging from photolysis of several Diels-Alder adducts i n benzene, such as 1_9 and 108. At no time was the presence of 125 detected. C. Discussion of Photochemistry of 9_5 and 96. Of the two b i r a d i c a l s 104 and 105 (shown i n Scheme 14) which would r e s u l t from a 3-hydrogen abstraction from C c and C Q, respectively 5 o i n adduct 9_5 or 9_6, i t was anticipated that 104, i n which the substituent occupies the terminal p o s i t i o n of the a l l y l r a d i c a l and thus exerts a s t a b i l i z i n g influence, would be formed i n preference to 105, where the substituent i s situated at the central carbon of the a l l y l system. The highest occupied molecular o r b i t a l of an a l l y l r a d i c a l has a node at the central carbon atom; Hence a substituent located there would be expected to have very l i t t l e s t a b i l i z i n g (or d e s t a b i l i z i n g ) effect on the species. On the other hand, i t has been shown through thermochemical measurements 5 7that the 1—methylallyl r a d i c a l i s more stable than an unsubstituted a l l y l r a d i c a l by 2.5 kcal.mole. - 54 -The photochemistry of 9_5, l i k e J36 (Introduction), i s found to be i n accord with these considerations. The data shown i n Table III reveals that products a r i s i n g from b i r a d i c a l 114, Scheme 16 ( i e . 104, R=Me), are preferred by at least a two-to-one r a t i o over those formed from 115 ( i e . 1_05, R=Me). An even greater preference for species 104 i s observed i n the photochemistry of /9_6_, where only traces of material originating from 105 could be detected. This r e s u l t i s i n accord with the expected greater s t a b i l i z i n g influence of a phenyl group substituted at an a l l y l r a d i c a l terminus, as i n 104, R=Ph, due to the extensive d e r e a l i z a t i o n of electron density into the aromatic r i n g . No thermochemical data are available for the 1-phenylallyl r a d i c a l ; however, i t i s known that increasing the d e r e a l i z a t i o n of electron density results i n an increase i n r a d i c a l s t a b i l i t y . For example, pentadienyl r a d i c a l (126) i s more stable 5than 1-methylallyl r a d i c a l by 2.5 kcal mole.* Furthermore, benzyl r a d i c a l (127) i s more The effect of introducing a single substituent on the ene-dione double bond i s l i m i t e d , however, to t h i s observed d i r e c t i n g influence i n product d i s t r i b u t i o n . That the photoproducts formed from 95_ and j>6 stable than methyl r a d i c a l by 15 kcal mole. -1 126 127 - 55 -possess the same basic r i n g systems as do products 18-20, derived from the unsubstituted adduct 17_, suggests that a s i n g l e substituent does not alt e r , the excited state energies of the tetrahydronaphthoquinone r i n g system, as proposed for substituted p_-benzoquinones by B a r l t r o p 4 7 (see i n t r o d u c t i o n ) . 2. D i e l s - A l d e r Adduct of 2,3-Dimethyl-j>-benzoquinone with 2,3-Dimethyl-l,3-butadiene (97). I t was noted i n the Introduction that the divergent photochemical r e a c t i v i t y of adduct 52_ might be due to the presence of the two methyl groups on the ene-dione chromophore of the molecule which al t e r e d or reversed the energies of the r e a c t i v e excited states involved ( i e . n — TT vs TT - TT ). To test t h i s hypothesis, adduct 97_, which possesses the same dimethyl substituents on the chromophore as did 52, was investigated. Formation of compound 128 from 97_, a process analogous to the 52 -»- _54 conversion, would serve to confirm such an e f f e c t . Adduct 97_, 4a$,5,8,8a8-tetrahydro-2,3,6,7-tetramethy 1-1,4-naphthoquinone, was synthesized, using the method of Fieser and Chang as summarized i n Scheme 18. The o x i d a t i o n 5 9 o f 2,3-dimethylaniline to quinone 129 was performed using " a c t i v e " manganese dioxide, which - 56 -SCHEME 18. 129 97 was prepared j u s t p r i o r to use by the method of Attenburrow, et a l 6 0 Refluxing .an ethanolic solution of 129 and diene overnight yielded the desired adduct 97. The photolysis of 97_ i n benzene was monitored by glpc which showed the formation of a single photoproduct which proved to be in e r t to prolonged i r r a d i a t i o n . Column chromatography resulted i n a 25% y i a l d c f a colorless c r y s t a l l i n e isomer of 97_ (mass spectrum, elemental analysis) which was assigned structure 130 on the basis of i t s spectral properties which were s i m i l a r to those of enone alcohol 20. (eq. 25) 130 Compound 130 exhibits an i r (KBr) spectrum with a hydroxyl band .. at 2.94y and an a,3-unsaturated carbonyl stretch at 6.05y (KBr). The nmr spectrum of 130 (figure 9) features a single v i n y l resonance at T4.42 - 57 -(C^ proton) and a singlet at T7.70 which disappears upon addition of deuterium oxide, indicating i t i s due to the hydroxyl proton. Three v i n y l methyls appear at T8.16, 8.25 and 8.30, while the lone t e r t i a r y methyl (at C^) comes at T8.93. The doublet at x7.13, again c h a r a c t e r i s t i c of the enone alcohol structure (cf. nmr of 106 and 109), i s assigned to the C. methine, while the multiplet at T7.84 i s attributed to 6 the methine. The methylenes are nearly magnetically equivalent, as indicated by th e i r resonances at T8.59 and 8.65. Figure 9 shows the nmr spectrum of deuterated 130. Figure 9. NMR Spectrum of 130. I r r a d i a t i o n of 97_ i n tert-butanol led to i n i t i a l formation of 130 plus a second minor photoproduct 131, as detected by glpc. In this - 5 8 -instance, however, enone alcohol 130 suffered a secondary photochemical transformation to 131, coincident with the reaction of 9_7, u n t i l the 131:130 r a t i o was 2:1 when no glpc detectable quantity of 97_ remained. In a separate experiment, i r r a d i a t i o n of 130 i n tert-butanol resulted i n complete transformation to 131. tert-butanol The structure of photoproduct 131 was indicated by i t s i r carbonyl band at 5.74y, indicating a five-menbered ri n g ketone, and by i t s nmr spectrum, shown i n figure 10. The Cg and C^  v i n y l methyl signals come at T8.25 and 8.40, while the C^ t e r t i a r y methyl shows a singlet at T8.85. The doublet (J=7Hz) at T9.09 i s attributed to the C^ methyl coupled to the C^ methine which should appear as a quartet and i s partly v i s i b l e at T7.73, coupled to the C^ methyl (J=7Hz). The small coupling superimposed on t h i s quartet i s l i k e l y due to long range coupling to the C, methine, as was the case with o the analogous ene-dione 107. The signal at T7.24 i s assigned to the C^ methine. The remaining protons form a complex multiplet i n the T7.5 - 7.8 region. Reaction of a CDCl^ solution of 131 with a 1.2N deuterium oxide - 59 -Figure 10. NMR Spectrum of Ene-dione 131. solution of potassium hydroxide led to the exchange of the proton for deuterium, which suggested that the proton"was i n the exo configuration (see Introduction). The reaction was very slow however, requiring two weeks for complete exchange of the proton to occur at 25°. In addition to the disappearance of the T7.73 si g n a l (C^ proton), other nmr changes noted (figure 10) were the collapse of the doublet at T9.09 to a broad s i n g l e t , and a s i m p l i f i c a t i o n « of the s i g n a l at x7.24 (C- methine). This l a t t e r observation once o again v e r i f i e d the existence of C A - long range coupling. - 60 -The mechanism for the formation of 130 and 131 i s given i n Scheme 19, and involves an i n i t i a l 8-hydrogen abstraction from either C,. or C Q to give the b i s - a l l y l i c r a d i c a l intermediate 132. In benzene 8 SCHEME 19. 1,6-bonding > benzene or tert-butano 130 3,8-bonding hv. tert-butanol ketonization > 131 1,6-bonding then leads to direct formation of 130. In tert-butanol, i n addition to formation of 130, a bond closure between positions 3 and 8 l i k e l y leads to enol 133 which then ketonizes to give 131. As w e l l , the 130 -+ 131 conversion i n tert-butanol i s observed, the formal r e s u l t of a photochemical [3,3] sigmatropic rearrangement, which i s t h e o r e t i c a l l y forbidden on the basis of o r b i t a l symmetry considerations\ 8 - 6 1 -The fact that compound 131 i s formed i n the photolysis of 97, and not 128, suggests that i n the case of adduct _52, ene-dione double bond substitution alone does not account for the photochemical formation of 54. 3. Diels-Alder Adducts with Bridgehead Substituents. On the basis of the results obtained for adduct 9_7, i t was next of interest to determine the role of substituents bonded to carbon atoms C. and C„ of the tetrahydronaphthoquinone ri n g system 4a oa (i e . the bridgehead p o s i t i o n s ) , and thus to test the second hypothesis advanced for the photochemical r e a c t i v i t y of 52: v i z . , the theory based on the conformational effect (see Introduction) of these substituents. To t h i s end, the photochemistry of adducts 98-100 was investigated. The choice of these adducts was determined by t h e i r ease of synthesis and 0 99 Rj = CN; R 2 = Cl 134 Rx = Me; R 2 = H by the r e l a t i v e s t e r i c bulk or si z e of R^ . The s i z e of a given substituent was takenas i t s A v a l u e ^ l a i e . , i t s effect on the equilibrium constant K for the process shown i n figure 11, that of cyclohexane chair inversion. Table IV l i s t s the conformational free energy Figure 11. Cyclohexane Chair Inversion. differences (AG°) ^ 1 Corresponding to the constant K. To a f i r s t TABLE IV. Conformational Free Energy Differences. Group (X) -AG° (kcal mole" ) H 0 CN 0.15 - 0.25 CO Me 1.1 Me 1.5 - 2.1 approximation these values were regarded as in d i c a t i v e of the r e l a t i v e preference for the Diels-Alder adducts bearing substituent X at the bridgehead positions to assume the twist conformation (conformer CJ, Scheme 10) i n preference to the other four conformers (see Introduction, Scheme 10). Adducts J38, j?9, 100 and 134 thus formed a series of compounds to test t h i s e f f e c t . As i t turned out, compound 134 was unavailable for study due to d i f f i c u l t i e s encountered i n i t s attempted synthesis. - 63 -A. 4a3,8a8-Dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-l,4-naphthoquinone (98). Adduct 9J3 was synthesized as outlined i n Scheme 20, The oxidation of 2,3-dicyanohydroquinone was accomplished using a SCHEME 20. 135 98 variant of the method reported by Brook 6 2 Nitrogen dioxide was f i r s t condensed into a f l a s k at -196°C, then added dropwise to a rapidly s t i r r e d suspension of dicyanohydroquinone i n carbon tetrachloride. The oxidation to 135 was complete i n t h i r t y minutes, and the y i e l d of 135 was quantitative. The Diels-Alder reaction was performed i n the manner of A n s e l l , et a l 6 3 a n d resulted i n a 75% y i e l d of adduct 98 as large, pale yellow prisms. The course of the photolysis of 9j8 was followed by observing the disappearance of the peak due to s t a r t i n g material ( i e . 98) on glpc. In benzene so l u t i o n , 98^ reacted upon i r r a d i a t i o n to give a complex mixture of many products (as indicated by t i c ) , none of which could be isolated i n amounts s u f f i c i e n t for characterization. - 64 -Photolysis i n tert-butanol s o l u t i o n , however, resulted in.the formation of two products 3.36 and 137, which were separated by column chromatography. The f i r s t was obtained as a c o l o r l e s s c r y s t a l l i n e s o l i d i n 50% y i e l d and was i d e n t i f i e d as the isomeric (mass spectrum, elemental analysis) enone alcohol 136 on the basis of i t s s p e c t r a l s i m i l a r i t i e s to compound 20. Product 136 ex h i b i t s a s o l i d s t a t e (KBr) i r spectrum featuring hydroxyl (2.90u), cyano (4.41y) and carbonyl (5.87y) bands. In the case of the carbonyl s t r e t c h , the band p o s i t i o n i s s l i g h t l y s h i f t e d to lower wavelength than normally encountered for the a,B-unsaturated carbonyl band i n enone alcohols of s i m i l a r structure (cf. 20, carbonyl at 5.90y). This may be a t t r i b u t e d to the inductive e f f e c t 5 1 of the cyano groups present. This i s i l l u s t r a t e d by the 0.06y s h i f t to lower wavelength of the carbonyl band i n compound 139 as compared to that i n 138^ ** CH 3 C0 2CH 2CH 3 CN-CH 2C0 2CH 2CH 138, v c = Q = 5.77y 139, v c = Q = 5.71y The nmr spectrum of 136 features an AB system for the v i n y l protons, as shown i n fig u r e 12. As i n the cases of compounds 106 - 65 -Figure 12. NMR Spectrum of Enone Alcohol 136. and 109, p o l a r i z a t i o n i n the a,8-unsaturated carbonyl portion of the molecule r e s u l t s i n the observed chemical s h i f t s of the C, (T2.99) and (T3.69) protons. The mutual coupling constant i s 10Hz. The multiplet at T4.07 i s assigned to the v i n y l , while a broad singl e t at T7.19, which disappeared on adding deuterium oxide, i s attributed to the hydroxyl proton. One of the C^Q methylenes shows a doublet (J=13Hz) around T7.7; the other i s masked by the acetone-d^ solvent resonances. The Cg v i n y l methyl comes at T8.03, a narrow doublet (J=1.5Hz) coupled weakly to the C 7 v i n y l v i a a l l y l i c c o u p l i n g 5 0 - 66 -while the Cg methyl shows a sharp singlet at T8.73. The second photoproduct 137, isolated as a colorless o i l , proved to be a secondary photoproduct of 136, as demonstrated by the complete conversion of 136 to 137 upon i r r a d i a t i o n i n tert-butanol. The i r spectrum of 137 shows a cyano band at 4.42y and two carbonyl bands at 5.65y and 5.80y, possibly i n d i c a t i n g the presence of a five-membered ring ketone (inductive effect of cyano group!) and an ester carbonyl 5 1 The nmr spectrum shown i n figure 13 features a sharp single t at Figure 13. NMR Spectrum of 137. - 67 -T 8.53, p o s s i b l y due to the protons from a t e r t - b u t y l e s t e r 6 5 Two v i n y l methyls appear as small m u l t i p l e t s at T8.29 and 8.38. No other s i g n a l s could be assigned with any c e r t a i n t y . Support f o r the proposal that 137 was a t e r t - b u t y l ester derived from 136 came i n the mass spectrum of 137 which showed a parent ion" at 314 amu i n d i c a t i n g that one molecule of tert-butanol, the solvent, had been incorporated into the molecular formula. Several attempts to p u r i f y 137 or to form d e r i v a t i v e s met with f a i l u r e . As a r e s u l t , a structure could not be proposed f o r t h i s molecule. I t seems, however, that 137 i s not s i m i l a r to any product thus f a r encountered and, while i n t e r e s t i n g i n i t s own r i g h t , does not shed any a d d i t i o n a l information on the r o l e of bridgehead substituents i n D i e l s - A l d e r adduct photochemistry. For t h i s reason, compound 137 was set aside. The photochemistry of 98_ was also investigated using a c e t o n i t r i l e and methanol as solvents. In e i t h e r case, the only product obtained was enone alcohol 136. The formation of enone a l c o h o l 136 i s l i k e l y due to i n i t i a l 3-hydrogen a b s t r a c t i o n , leading to b i r a d i c a l species 140 (Scheme 21), which then s u f f e r s 1,6 bond closure to give 136 d i r e c t l y . Secondary photol y s i s of 136 gradually leads to 137 . - 68 -SCHEME 21. 1,6-bonding 137 136 B. 2,3-Dichloro-4a8,8aB-dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (99). In an attempt to possibly further characterize a photoproduct analogous to the unknown photoisomer 137, Diels-Alder adduct 99_ was next studied. I t s synthesis i s shown i n Scheme Z2. Following the procedure of Walker and Waughf62,3-dicyanohydroquinone was oxidized SCHEME 22. - 69 -to 2,3-dichloro-5,6-dicyanoquinone (141) on treatment with concentrated n i t r i c acid. Excess 2,3-dimethyl-l,3-butadiene was then added to a methanolic solution of 141, r e s u l t i n g i n an exothermic reaction and formation of 9_9 after j u s t ten minutes. Photolysis of 9_9 i n benzene again led to a complex mixture of many products ( t i c ) , none of which could be is o l a t e d . I r r a d i a t i o n i n tert-butanol resulted i n a 42% isolated y i e l d of a single photoisomer 142. 142 Enone alcohol 142 i s a colorless c r y s t a l l i n e s o l i d which exhibits an i r spectrum featuring hydroxyl (2.92y), cyano (4.44y), carbonyl (5.90y) and carbon-chlorine (12.45y) stretching bands. I t s nmr spectrum shows a single v i n y l signal at T4.07 due to the proton. The C^Q methylenes give an AB system at T7.47 and T7.81 (calculated v a l u e s 5 2 ) with a coupling constant of 14Hz. The hydroxyl proton which can be exchanged by adding deuterium oxide, shows a s i n g l e t at T7.07. A narrow doublet (J=1.5Hz) at T8.02 i s attributed to the C g methyl, coupled to the v i n y l v i a a l l y l i c coupling. The methyl i s a si n g l e t at T8.67. Figure 14 shows the nmr spectrum of 142-0-d. - 70 -i r~ )0 ;-- r -, 400 i I 300 I I 700 I ' I ' 'I \-r~TT 100 0 hi r Figure 14. NKR Spectrum of Enone Alcohol 142. The formation of 142 l i k e l y involves the B-hydrogen abstrac t i o n mechanism which gives a b i r a d i c a l analogous to 140 (Scheme 21). As no other product except 142 was formed, the ph o t o l y s i s of 99_, l i k e that of j)8, offered very l i t t l e information regarding the influence of bridgehead substituents on molecular conformation. The only c l e a r r e s u l t was that i n t e r t - b u t a n o l , the only product formed i s the isomeric enone al c o h o l . No product incorporating an ene-dione structure such as that present i n LB, _19 or 54 was ever observed. - 71 -C. 4aB,8aB-Dicarbomethoxy-6,7-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (100) . Adduct 100 was synthesized according to the procedure of A n s e l l , et a l 6 7 ' 6 3 w h i c h i s summarized i n Scheme 23. The Diels-Alder reaction SCHEME 23. of 145 with 2,3-dimethyl-l,3-butadiene gave, i n addition to 100, compound 146 as w e l l , which i n part accounted for the low y i e l d (25%) of 200 i n t h i s step ( y i e l d of L46 was 25%). I r r a d i a t i o n of 100 i n benzene solution resulted i n the formation of two products, i d e n t i f i e d as 147 and 148 (eq. 27) i n a combined y i e l d of 65%. (eq. 27) 147 148 0 - 72 -Enone alcohol 147 features i r carbonyl bands at 5.80y (ester) and 5.90y (a,3-unsaturated ketone). The nmr spectrum i s quite sim i l a r to that of the analogous enone alcohols previously reported (for example, 136, figure 12). The and v i n y l s each show a doublet (AB system) with a coupling constant of 10Hz, located ( c a l c u l a t e d 5 2 ) at T3.41 (C^) and T3.78 (C^). The carbomethoxy methyls give r i s e "to a sharp, s i x proton singlet at x6.27. The Cg v i n y l methyl i s seen as a narrow doublet at T8.19 (J=1.5HZ), while the t e r t i a r y methyl i s correlated with a singlet at T8.86. The C^Q methylenes give r i s e to a broad singlet at x8.03, while the hydroxyl hydrogen causes a singlet at T7.22, which disappears on adding deuterium oxide. Figure 15 displays the nmr spectrum of 147 after treatment with Do0. Figure 15. NMR Spectrum of Enone Alcohol 147. - 73 -The uv spectrum of ene-dione 148 features an enhanced e x t i n c t i o n * c o e f f i c i e n t for i t s n - ir absorption (c 165) , c h a r a c t e r i s t i c of a 6 ,Y-unsaturated ketone 5 5such as i s present i n 148. The i r spectrum (KBr) shows a s t r i k i n g carbonyl region with four bands positioned at 5.58, 5.72, 5.78 and 5.86u. The nmr, shown i n fig u r e 16, i s also Figure 16. NMR Spectrum of Ene-dione 148. consistent with structure 148. A m u l t i p l e t at T3.51 i s assigned to the C-j v i n y l proton. The two carbomethoxy methyl signals are seen at T6.22 and 6.26, while the Cg v i n y l methyl gives r i s e to a doublet (J=1.5Hz) at T8.12, and the C g methyl produces a s i n g l e t at x8.75. The chemical s h i f t s of the C, exo and endo-protons are calculated 52 - 74 -to be T7.32 and T7.53, respectively; each features a double doublet with the main coupling of 16Hz due. to the geminal interaction. Superimposed on the exo-proton doublet i s a coupling with the methine (J=5Hz), while the endo doublet i s further s p l i t into two doublets (J=4Hz), again by the proton. The C ^ Q methylenes give r i s e to doublets with a geminal coupling of 14Hz. Their positions are c a l c u l a t e d 5 2 t o be T7.76 and T8.14. Further evidence for structures 147 and 148 was obtained from an i n t e r e s t i n g and novel (at least for these systems) photochemical and thermal i n t e r r e l a t i o n s h i p , shown i n Scheme 24. Thus photolysis of enone alcohol 147 i n benzene gave good yields of 148, i n accord SCHEME 24. with the 20 _19 conversion seen previously (Introduction). Thermolysis of 148, on the other hand, at 185°, led to 50% y i e l d of 147, a r e s u l t not before obtained for t h i s structure. The 147 so obtained was i d e n t i c a l i n every respect'to an authentic sample. None of the expected ene-dione 149 (cf. , _19 ^ 1_8 transformation, Introduction) was detected. - 75 -o 149 E = C02Me A possible explanation for the thermal conversion of 148 to 147 i s shown i n Scheme 25. Thus a keto-enol tautomerization between SCHEME 25. 1,3 s h i f t 147 148 -«- 150 i s possible due to the s t a b i l i z i n g effect (through hydrogen bonding of the enol proton) of the nearby ester carbonyl group. A - 76 -thermal [l,3] s h i f t of the C^-C^ bond from carbon atoms 3 to 5 then brings the double bond into conjugation with the carbonyl group and gives 147 d i r e c t l y . The presence of ester substituents at and C^ . i n 148 i s required to bring about t h i s transformation. Ene-diones 1_3 and _19_, which possess the same r i n g system as 148, but which lack the necessary ester groups, are not thermally transformed to enone alcohol products. Keto-enol tautomerism i s a r e a d i l y observed phenomenon f o r a number of $-ketoesters, such as 151 6 8 In t h i s case, nmr measurements 151 152 have shown that at room temperature, as much, as 7% of 151 e x i s t s as i t s enol form 152. Ene-dione 148 i s not exactly analogous to 151, however, as there are no a-protons present on carbon atom 6. This necessitates the enol's being formed at C^. Nevertheless, such a process should be reasonable i n view of the established intermediacy of an enol i n the formation of compound 19_ (see Introduction), which possesses the same r i n g skeleton as 148. Photolysis of 100 i n tert-butanol led to the formation of product - 77 -147 plus a mixture of several other products, the nmr spectrum of which indicated the r e s u l t of a hydrogen abstraction process from a carbomethoxy methyl group. This mixture was not investigated further. The formation of products 147 and 148 on i r r a d i a t i o n of 100 i n benzene can be explained again by an i n i t i a l 3-hydrogen abstraction by oxygen to give the b i r a d i c a l species 153 (Scheme 26). Bonding SCHEME 26. 147 148 0 as indicated then leads to 147 d i r e c t l y and ( l i k e l y ) to enol 150 which subsequently ketonizes to give 148. - 78 -Once again, no product analogous to 5_4_ was detected i n t h i s system. Further discussion of the photochemistry of 9_8 - 100 w i l l be reserved for section V. 4. Diels-Alder Adducts of some Substituted jv-Benzoquinones with Hexa-2,4-d iene. The process of photochemical 3-hydrogen abstraction has been shown to be a remarkably general one for Diels-Alder adducts of j3-benzoquinones and acyclic-1,3-dienes? 3' 2 5In f a c t , up to the present time, only two examples had been found which did not react v i a t h i s pathway; namely adducts 4_2 and 5_1_. In both cases, the 3-hydrogens on C c and C Q which were deemed "accessible" (Scheme 10) to the j 8 O 42 R = Me 51 R = Ph R 0 carbonyl oxygen had been replaced by substituents, thus blocking t h i s process (see Introduction). I t therefore became of interest to study other compounds analogous to 4j2, i n which the 3-hydrogen abstraction process was expected to be unfavorable, i n order to see i f possibly d i f f e r e n t product structures could be obtained v i a a photochemical pathway. To t h i s end, compounds 102 and 103 were i n i t i a l l y chosen. In addition to the reasons given above, i t was also possible that the series of compounds - 79 -42, 103 and 102 would provide some a d d i t i o n a l information on the e f f e c t of.bridgehead substituents, and thus the study served to p a r a l l e l that of the s i m i l a r series 98_, 99, .100. Just o u t l i n e d . 102 103 An a d d i t i o n a l bonus was provided when, on examining r e a c t i o n conditions for the synthesis of 102, i t was found that adduct 101, the C-/Co diastereomer of 102, was a v a i l a b l e . In this case the B-hydrogens 101 on C c and C 0 were i n theory " a c c e s s i b l e " ; thus 101 was analogous to j o adduct 5_2, i n which the competing processes of hydrogen abstraction by oxygen and by carbon were operating. The p o s s i b i l i t y of a s i m i l a r competition i n the case of 101 was not overlooked. A. D i e l s - A l d e r adducts of Duroquinone with trans,trans-hexa-2,4-diene (101 and 102). Both adducts 101 and 102 were synthesized by sealed tube thermolysis of a mixture of duroquinone (154)^ 9trans,trans-2,4-hexadiene, and -. 80 -hydroquinone, a few crystals of which were added to i n h i b i t polymerization of the diene. I t was found that on heating t h i s mixture at 140°, adduct 102 was the major compound obtained. Raising the reaction temperature to 180° resulted, i n addition to considerable tar formation, the formation of 101, with only a trace of 102 being observed. The synthetic r e s u l t s are summarized i n Scheme 27. In both cases, yields SCHEME 27. 101 were very low (5 - 10%). The stereochemistry of the C^/Cg methyl groups i n 101 and 1C2 was assigned on the basis of two arguments: a) the endo stereochemistry 102 was assigned to the product formed at low temperature ( k i n e t i c product) since k i n e t i c control of 7 0 the Diels-Alder reaction normally leads to endo addition.. The exo - 81 -stereochemistry 101 on the other hand was assigned to the high temperature (thermodynamic) product since thermodynamic control favors exo stereochemistry 7 0 That 1Q1 i s the thermodynamically more stable adduct was supported by the observation that 102, on heating to 180° i n a sealed tube, was transformed to 101, although extensive decomposition occurred and the y i e l d was therefore low. b) the difference i n the chemical s h i f t s of the C C/C Q protons J o i n 101 (T7.17) and i n 102 (T7.85), may be attributed to the anisotropic deshielding 5"effect of the adjacent c i s carbonyl groups i n the case of 101. A si m i l a r but less pronounced effect was observed for the C c/C 0 methyls (T9.02) i n 102 r e l a t i v e to those i n 101 (T9.12). The J o nmr spectra of 101 and 102 are compared i n figure 17. a. Photolysis of 2,3,4a$,53,83,8a3-Hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (101). I r r a d i a t i o n of a benzene solution of 101 resulted i n a rapid, smooth conversion to two photoproducts 155 and 156 i n the time independent r a t i o of 1:2, as shown i n equation 28. Column chromatography (eq. 28) 155 156 1 : 2 - 82 -Figure 17. NMR Spectra of Adducts 101 and 102. - 8 3 -afforded 155 and 156 i n 25% and 56% y i e l d s , respectively. The structures of the photoproducts were assigned on the basis of t h e i r spectral s i m i l a r i t i e s to the analogous compounds _53_ and 54 2 5 Enone alcohol 155, a colorless c r y s t a l l i n e s o l i d , features hydroxyl (2.88y) and a,$-unsaturated carbonyl (6.05y) bands i n i t s i r spectrum. The nmr spectrum, shown i n figure 18 displays a single Figure 18. NMR Spectrum of Enone Alcohol 155. v i n y l resonance at T4.15 (Cg proton) and a si n g l e t at T7.67 which disappears on adding deuterium oxide, in d i c a t i n g i t i s due to the -84 -hydroxyl proton. Vi n y l methyl signals appear at T8.16 and T8.25 (2 methyls), while two t e r t i a r y methyls show singlets at T9.20 and 9.34. The C^Q methine appears as a broad m u l t i p l e t , centered at T7.79. The C^Q methyl group, coupled to the C^Q methine (J=7.5Hz) gives r i s e to a doublet at T9.29. The structure of ene-dione 156 was indicated by i t s i r spectrum, featuring two carbonyl bands at 5.66 (four-membered c y c l i c ketone) and 5.85u (six-membered c y c l i c ketone). The nmr spectrum of 154 i s shown i n figure 1_9_. A double doublet at T4.03 i s assigned to Figure 19. NMR Spectrum of Ene-dione 156. - 85 -the C „ v i n y l proton, coupled to the C n v i n y l (J=10Hz) and to the C 7 methine (J=5.5Hz). The C v i n y l signal at T4.495zshows a s p l i t t i n g / 9 of 1.5Hz, superimposed on the 10Hz coupling, which i s due to a l l y l i c coupling with the methine. The quartet (J=7.5Hz) at T7.30 i s assigned to the methine, while the methine gives r i s e to a multiplet at T7.82. Two doublets, each with a s p l i t t i n g of 7.5Hz, are found at T8.98 and T9.02 due to the two methyls on C ^ a n d respectively. In addition, four other methyl singlets are observed at T8.98, 9.01, 9.03 and 9.09. Spin-spin decoupling experiments v e r i f i e d the above assignments. Thus i r r a d i a t i n g the quartet at T7.30 causes the doublet at T8.98 to collapse to a si n g l e t . I r r a d i a t i o n at T7.S5 resu l t s i n the s i m p l i f i c a t i o n of the v i n y l resonances to an AB type system, and to collapse of the doublet at T9.02 to a s i n g l e t . The stereochemistry at C ^ Q i n 155, and at and Cj i n 156, i s assumed, based on the proposed mechanism for t h e i r formation. Support for the stereochemistry at i n 156 was found i n the thermal conversion of 156 to 157 (eq. 29). This reaction p a r a l l e l s the 0 156 sealed tube 195° 157 (eq. 29) - 86 -54 _56 conversion 2 5 (see Introduction) and may be considered as an example of a retro-ene r e a c t i o n 2 8 ( a r r o w s ) , although an a l t e r n a t e , non-concerted mechanism cannot be ruled out at present. The structure of 157 follows d i r e c t l y from i t s s p e c t r a l data, which are reported i n the experimental s e c t i o n , and which are found to be s i m i l a r to those f o r compound 5 6 2 3 The competitive processes of 3-hydrogen ab s t r a c t i o n by oxygen and y-hydrogen a b s t r a c t i o n by enone carbon which form b i r a d i c a l intermediates 158 and 159 (Scheme 28) r e s p e c t i v e l y , appear to account f o r the formation of products 155 and 156. Thus the photochemistry SCHEME 28. 156 - 87 -of 101 i s analogous to that observed f o r adduct 54. b. Photolysis of 2,3,4aB,5a,8a,8a3-Hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (102) . I r r a d i a t i o n of 102, the course of the r e a c t i o n being followed by glpc, l e d to the formation of two products subsequently i d e n t i f i e d as the intramolecular oxetane 160 and the cage compound 161 (Scheme 29). Glpc showed that 160 was formed r a p i d l y u n t i l i t reached a r e l a t i v e r a t i o to 102 of 1:1.9; ther e a f t e r , t h i s r a t i o was found to be time independent. Cage diketone 161 was formed more slowly, at the SCHEME 29. 0 .0 161 expense of both 160 and 102, u n t i l i t remained the sole product. Workup of the r e a c t i o n thus, allowed f o r the i s o l a t i o n of a q u a n t i t a t i v e - 88 -y i e l d of 161. Small quantities of oxetane 160 could be obtained by preparative glpc i f the photoreaction was interrupted before ->• complete conversion to 161 had occurred. The 102 160 equilibrium was v e r i f i e d by photolyzing a sample of 160 i n benzene. This photolysis was monitored by glpc, which showed a rapid formation of 102 u n t i l the 160:102 r a t i o reached a value of 1:1.9. On prolonged photolysis (12 hours) cage isomer 161 was again formed at the expense of both 102 and 160. Both products were shown to be isomeric with 102 by t h e i r mass spectra and elemental analyses. Cage dione 161 was isolated as a colorless s o l i d whose structure was indicated by i t s spectral data. The infrared spectrum features two carbonyl bands at 5.68 and 5.75y. Similar s p l i t carbonyl peaks have been observed1°for the bridged cage compounds 10 (n = 1,2). The nmr spectrum of 161 i s displayed i n figure 20, and supports the symmetrical structure 161 i n that several sets of magnetically equivalent protons are indicated. Thus, the two proton quartet at T7.40 (J=7Hz) i s assigned to the C 7/C i n methines, coupled to the C 7 /C O 10 n = 1,2 - 89 -methyl groups; these give r i s e to a doublet (J=7Hz) at T9.33. Two other sharp s i n g l e t s , each integrating for 6 protons, are present at T8.97 and x9.06, which account for the remaining methyl groups. The C Q and C n methines show a sharp singl e t at T7.60. The lack of any coupling between the C g/C g and C 7/C 1 Q protons suggests that t h e i r dihedral angle i s approximately 90°?° Examination.of a molecular model of 161 reveals t h i s to be the case. Figure 20. NMR Spectrum of Cage-dione 161. The stereochemistry at C^/C^ i s assumed on the basis of 1) the proposed mechanism and 2) the altern a t i v e symmetrical stereochemical arrangement of methyl groups at C7/C^Q would be s t e r i c a l l y highly unfavorable. - 90 -The structure of 160 also rests on i t s spectral data. The i r spectrum (KBr) shows an a,B-unsaturated carbonyl stretch at 6.04y, but no hydroxyl band. The nmr of _1_60 shown i n figure 21, proved to Figure 21. NMR Spectrum of Oxetane 160. be most informative. The proton situated at Cg shows a doublet at T5.64, coupled to the C^  methine (J=4Hz) which appears at T7.40. Two quartets at T7.78 (J=7Hz) and T8.35 (J=7.5Hz) may be attributed to the C, and C Q methines, interacting with the C, and C Q methyls, b y b y which are assigned to doublets occurring at T9.01 (J=7Hz) and T9.46 (J=7.5Hz). A molecular model of 160 reveals that the C, methyl o hydrogens may possibly experience an anisotropic shielding effect - 91 -caused by the nearby carbonyl group 5"and thus may give r i s e to the doublet at higher ( T 9 . 4 6 ) f i e l d , although such an assignment can only be regarded as tentative. Broad singlets at T8.03 and 8.33 are attributed to the and v i n y l methyls, respectively; th e i r r e l a t i v e s h i f t s again r e f l e c t the p o l a r i z a t i o n i n the unsaturated carbonyl chromophore and the r e s u l t i n g deshielding effect at the atom. Sharp singlets at T8.97 and 9 .30 are assigned to the methyls situated at C , . and C ^ Q , respectively. Again, the stereochemistry at C , / C „ i s assumed to be that shown, on the basis of the proposed 6 9 mechanism. The photochemistry of 102 thus departs from that of k2 (see Introduction) i n that no product was observed, the formation of which could be accounted for by a hydrogen abstraction process (cf., the 42 ->• 4_4 conversion). A process such as that encountered i n the case of adduct 42 would have given r i s e to compound 163, v i a b i r a d i c a l 162 (eq. 31 ) . H»C OH hv Y~H abstraction by oxygen 102 (eq. 31) 163 (not formed) Instead, photoproducts 160 and 161 are observed, both formally the r e s u l t of intramolecular Jjr2 g + 7T2 1 cycloadditions involving - 92 -the remote double bond and either a carbonyl group (oxetane 160 formation) or the ene-dione double bond (cage product 161 formation). Both processes are i n theory o r b i t a l symmetry allowed\ 8although they are r a r e l y , i f ever, actually o b s e r v e d ? 1 - 7 3 The divergent photochemistry of 102 again suggests that a conformational effect has been introduced into the system by the presence of the bridgehead methyl groups i n 102. On t h i s basis, the presence of structure 164 ( i e . twist conformer C, Scheme 10) i s suggested, which may i n turn suggest two s i m i l a r mechanisms leading to the formation of oxetane 160. These are shown i n Scheme 30. 164 Path A involves i n i t i a l overlap of proximate p_-orbitals on carbons C. and C, (164) , r e s u l t i n g i n b i r a d i c a l intermediate 165 1 o which can collapse d i r e c t l y to 160. Path 3, on the other hand, t involves i n i t i a l overlap of the p - o r b i t a l s on oxygen and carbon C 7 to give b i r a d i c a l 167, which subsequently collapses to oxetane 160. SCHEME* 30. 167 I t should be pointed out that path A represents an unusual mechanistic route to oxetane formation. Path B, on the other hand, i s modelled after the f a m i l i a r Paterno-Buchi reaction 7 1*in which an excited carbonyl compound undergoes reaction with an o l e f i n , r e s u l t i n g i n the formation of oxetanes v i a a b i r a d i c a l intermediate' 1 (figure 22). « - 94 -A + Figure 22. Paterno-Buchi Reaction. However, i t i s u n l i k e l y that path B i s the mechanism which accounts for the formation of 160, because b i r a d i c a l 167 v i o l a t e s Bredt's ru l e . The twist conformer 164 i s also the l i k e l y s t r u c t u r a l precrusor to 161, since the only vi a b l e a l t e r n a t i v e , structure 168, would be disfavored by bridgehead methyl e c l i p s i n g . The slower rate of 168 formation of 161 r e l a t i v e to faster 102 160 equilibrium may i n fact be due to either a) the much smaller amount of prerequisite conformer 168 present at equilibrium compared to twist conformer 164; or b) the remoteness of the double bonds i n twist conformer 164. - 95 -I t i s conceivable that cage product 161 could a r i s e v i a Path A (Scheme 30) through a jl,3].suprafacial sigmatropic s h i f t of the C^ - C bond, which would give b i r a d i c a l 166. Closure then between carbons 2 and 8 would result i n the formation of 161. Such a rearrangement i s unusual, however, and to the best of the author's knowledge, unprecedented. In addition to these considerations, the p o s s i b i l i t y of i n i t i a l excited molecular complex, or exciplex formation should be considered. In the past decade, a great deal of evidence has been presented supporting the contention that the i n i t i a l i n t e r a c t i o n between an excited state molecule and a ground state molecule i s often the formation of an exciplex (excited molecular complex)? 5 In the case of 102, the exciplex formation would be intramolecular, with an excited ene-dione chromophore interacting with the isolated double bond; t h i s then would collapse, possibly to products 160 and 161 d i r e c t l y or, more l i k e l y , to b i r a d i c a l intermediate 165. No evidence for such exciplex formation was observed i n the u l t r a v i o l e t spectrum of 102. However, as many studies have shown 7 6lack of ground state i n t e r a c t i o n does not necessarily mean that interaction does not occur i n the excited state. The photochemistry of 102 thus proved unique for the series of ] - 96 -Diels-Alder adducts studied i n our laboratory. Indeed, the formation of cage dione 161 represented the f i r s t known example of cage isomer formation for a Diels-Alder adduct lacking a C r - C„ bridge or bond (cf. Introduction). Thus the potential a v a i l a b i l i t y of other s t r u c t u r a l l y s i m i l a r compounds led to an investigation of the dicyano adduct 103. v B. 4aB,8a3-Dicyano-5a,8a-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (103). Adduct 103 was synthesized i n a manner analogous to 9J3, as shown i n Scheme 31. SCHEME 31. 135 103 Photolysis of 103 i n either benzene or tert-butanol resulted i n the formation of a single photoproduct, i d e n t i f i e d to be oxetane 169 by i t s spectral data and isolated i n 50 - 60% y i e l d a f ter column chromatography. - 97 -Product 169 exhibits a 5.93y band i n the i r spectrum, c h a r a c t e r i s t i c of the unsaturated carbonyl group. The nmr spectrum of 169, l i k e that of the analogous oxetane 160, was p a r t i c u l a r l y informative, and i s reproduced i n figure 23. The C 9 and v i n y l protons show ^ ' ! 1 • i 1 \ 1 i 1 ' 1 i 1 1 ' ' 1 I ' ' '' i ' •' i 1 •'• i ' r-r'-'—r L Figure 23. NMR Spectrum of Oxetane 169. an AB system, located at T 2 . 4 6 and T3.73, respectively, with a coupling constant of 10Hz. A doublet at T5.23 (J=4Hz) i s due to the Cg methine; coupled to the C^ methine, i t s e l f also a doublet, located at T6.83. As was the case with oxetane 160, approximate 90° dihedral angles for the C n - C D hydrogens, as w e l l as for the C, - C, hydrogens, account for the lack of coupling i n either case. The Cfi and C Q methines - 98 -show sharp quartets at T7.11 and T7.35, with coupling constants of 7 and 7.5Hz, respectively. The C, and C_ methyl resonances (each 6 9 a doublet) are located at T8.60 (J=7Hz) and at T9.05 (J=7.5Hz). Once again, the u p f i e l d doublet i s te n t a t i v e l y assigned to the C, b methyl by v i r t u e of anisotropic shielding by the nearby carbonyl. Double resonance experiments also v e r i f i e d the above assignments. Thus i r r a d i a t i o n at T9.05 led to collapse of the T7.35 quartet to a s i n g l e t ; i r r a d i a t i o n at T5.23 resulted i n the collapse of the T6.83 doublet to a s i n g l e t ; i r r a d i a t i o n at T3.73 caused the doublet at T2.46 to collapse to a s i n g l e t . Ultimate support for structure 169 was obtained by an x-rav c r y s t a l structure determination, which v e r i f i e d that structure 169 i s indeed correct and the Cg/Cy stereochemistry i s as shown. The s i m i l a r i t i e s i n the nmr spectra of 169 (figure 23) and 160 (figure 21), coupled with the x-ray r e s u l t s , also lends credence to the structure proposed for 160. The author would l i k e to thank Dr. J. Trotter and Dr. S. P h i l l i p s for the x-ray determination. Unlike oxetane 160, compound 169 was found to be inert to prolonged photolysis i n either benzene or tert-butanol, even when irr a d i a t e d with l i g h t f i l t e r e d through Pyrex (transmitting X > 290 nm). - 99 -None of the cage isomer 170, analogous to 161, was ever observed. 170 Furthermore, no products a r i s i n g from a. hydrogen abstraction process could be detected. The formation of 169 from 103 very l i k e l y p a r a l l e l s the formation of 160 from 102, discussed previously (Scheme 30) i n terms of i n i t i a l overlap of proximate p_-orbitals on carbon atoms 1 and 6. Again, the p o s s i b i l i t y of intramolecular exciplex formation should not be ignored. 5. Discussion The formation of photoproduct 5_4 from adduct 5_2 marked a turning point i n the photochemistry of Diels-Alder adducts of substituted jv-benzoquinones with acyclic-1,3-dienes. P r i o r to t h i s novel r e s u l t , the products derived from Diels-Alder adducts were nicely explained on the basis of the mechanism involving 6-hydrogen abstraction by carbonyl oxygen. To explain the divergent nature of the photochemistry of _5_2, two alternatives seemed l i k e l y : - 100 -1) The presence of methyl substituents on the ene-dione chromophore a l t e r s the energies of the electronic (presumably t r i p l e t ) * excited states, making the TT - TT state lower i n energy than the * n — TT (cf. , the Barltrop suggestion, Introduction). The formation * * of _54_ thus originates from a TT - TT state, rather than an n — TT state, the l a t t e r accounting for the formation of JJ$ - ^0 o n photolysis of _17_, and analogous products from analogous adducts lacking ene-dione double bond substituents. 2) The presence of bridgehead methyl substituents favors a twisted conformer i n the ground state (conformer C, Scheme 10), which i n turn f a c i l i t a t e s the process of y-hydrogen abstraction by enone carbon which i s the l i k e l y mechanism of formation of 54. The results presented i n t h i s thesis disfavor the f i r s t of the two proposals presented above. Adducts 9_5 and 9_6, each with one substituent on the ene-dione double bond, display a regioselective product d i s t r i b u t i o n , i n much the same manner as adduct 36_, on i r r a d i a t i o n , i n l i n e with the expected r e l a t ive s t a b i l i t i e s of the proposed b i r a d i c a l intermediates. However, neither the mono adducts 95 and nor adduct 9_7, with two methyl substituents on the ene-dione double bond, give r i s e to products which can reasonably be attributed to a process other than 3-hydrogen abstraction by carbonyl oxygen. In the case of 9_7, the chromophore i s i d e n t i c a l to that present i n adduct 52. - 101 -Thus the second factor came to be.considered; namely, that the photochemical reaction was under the influence of ground state conformational control. An ever-increasing number of l i t e r a t u r e reports have been appearing recently i n which the photochemical reactions observed r e f l e c t the influence of ground state conformation on excited state behaviour. Baldwin and Krueger 7 7provided an early example when they studied the photochemistry of a-phellandrene (171). I r r a d i a t i o n of 171 led to two primary photoproducts 172 and 174, which suffered secondary photolysis to give 173 and 175 (eq. 33). The appearance of 172 and (eq. 33) ;-CH, 174 i.C3HT 175 174 corresponds to the two possible conrotatory e l e c t r o c y c l i c reactions possible for 171, and the authors became interested i n the p o s s i b i l i t y that these two conrotatory modes were related to the two p r i n c i p l e conformational isomers of 171 ( i e . 171e, where the isopropy group - 102 -i s pseudoequatorial, and 171a, where i t i s a x i a l ) . They reasoned that i f the photoisomerization of conformers 171a and 17le was highly s t e r e o s e l e c t i v e , giving r i s e to the product anticipated from examining a model emphasizing ground state geometry as a stereochemical determinant, then the r a t i o of products 174/172 should be a quant i t a t i v e measure of the equilibrium constant K = (Scheme 32). SCHEME 32. 171e/171a hv hv 172 174 The equilibrium constant K could be determined through a study of the ord and cd spectra of 171 as a function of temperature. The temperature dependence of product r a t i o 174/172 was then determined and was found to be consistent with the postulated s t e r e o s e l e c t i v i t y i n the conversions 171a 172 and 171e + 174. Thus, they concluded that the stereochemistry of a common type of valence isomerization was con t r o l l e d by conformer population i n the reactant. - 103 -Lewis and co-workers ; 8have provided another example of conformational control of photoproduct formation. They noted the results reported by Baldwin, but observed that the chromophore i n 171 i s part of the conformationally mobile system, and thus the energy barriers to conformational isomerization i n the ground state and excited state need not be the same. The simplest s i t u a t i o n for studying conformational effects i n photochemistry occurs when two conformers A and B of a substrate give r i s e to d i f f e r e n t photoproducts (X and Y, respectively). This i s summarized i n Scheme 33. Two l i m i t i n g cases are possible. In case I , SCHEME 33. hv * A -> A *" X hv * kB • B > Y the a c t i v a t i o n energy for conformational isomerization i s lower than that for formation of X or Y ( k ^ * » k^.kg). In t h i s case the r a t i o of products w i l l depend upon the difference i n energy of the t r a n s i t i o n states leading to X and Y (Curtis - Hammett p r i n c i p l e 7 9 3 ) , and the l i f e t i m e s of both excited state conformers w i l l be the same. In case I I , the act i v a t i o n energy for conformational isomerization - 104 -i s greater than that for formation of X or Y (k^g* < < k^,kg). -*-n t h i s case, the r a t i o of products w i l l depend on the population of A and B and t h e i r e f f i c i e n c i e s of product formation. And since e l e c t r o n i c e x c i t a t i o n i s much f a s t e r than nuclear motion (Franck -Condon P r i n c i p l e 0 0 ) , the i n i t i a l populations of A and B w i l l be determined by ground state populations of conformers A and B and. th e i r respective e x t i n c t i o n c o e f f i c i e n t s . Here t h e i r l i f e t i m e s need not be the same. The systems chosen for study consisted of some cyclohexyl-phenyl ketones 176 - 178 and cyclopentylphenyl ketone 179. The well known a-cleavage and y-hydrogen abstra c t i o n reactions of phenyl a l k y l ketones (eq. 34 and 35) were used as probes for conformational e f f e c t s . As the chromophore i n each case i s not a part of the c y c l o a l k y l r i n g , conformational analysis was a n t i c i p a t e d to be f a i r l y straightforward since e l e c t r o n i c e x c i t a t i o n should have very l i t t l e i f any perturbing e f f e c t on the conformational isomerization process. 0 0 R ^ C = CH 2 - 105 -The re s u l t s of t h i s study are presented i n Scheme 34, which shows the observed photoproducts a r i s i n g from ketones 176 - 179. v ——— Table V l i s t s corresponding quantum y i e l d data for the formation of benzaldehyde ($^) and bicyclobutanol , and corresponding rate constants (k ,k ) for these processes as determined by Stern-Volmer a y quenching techniques. SCHEME 34. 183 - 106 -TABLE V. Quantum Y i e l d s and K i n e t i c Data for C y c l o a l k y l Phenyl Ketones. Ketone Solvent <J> $ k (sec J') k (sec • _a _y_ a y 176 Ph + RSH 0.20 0.045 2.5 x 10 7 1.7 x 10 8 177 Ph 0.09 6.9 x 10 8 178 Ph + RSH 0.31 2.1 x 10 ? 179 Ph + RSH 0.03 0.19 1.3 x 10 7 1.3 x 10 ? The t e r t - b u t y l d e r i v a t i v e s 177 and 178 serve as fixed models for the two possible conformational isomers of 176. The products formed by photolysis of 177 and 178 were those of y-hydrogen abstraction (182) and a-cleavage (181) r e s p e c t i v e l y . The absence of an a-cleavage product from 177 was considered to r e f l e c t the considerably f a s t e r rate constant f o r y-hydrogen abst r a c t i o n , whereas the l a c k of y-hydrogen ab s t r a c t i o n products from 178 was a t t r i b u t e d to the large 0 - H distance. Y The photochemistry of 176 was then described, on the basis of the r e s u l t s f o r 177 and 178, i n terms of the r e l a t i v e populations of conformers 176a (benzoyl group a x i a l ) and 176e (benzoyl group e q u a t o r i a l ) , as.shown i n Scheme 35. A x i a l conformer 176a led to 180 while 176e resulted i n a-cleavage to give benzaldehyde 181. 7 fl _ I t was known that the a c t i v a t i o n energy f o r cyclohexyl chair inversion + -1 (AG = 9.9 kcal mole ) was much larger than that f o r y-hydrogen - 107 -SCHEME 35. 176a 180 abstraction from valerophenone (184 - E approx. 3.5 kcal mole ); The ac t i v a t i o n energv for a-cleavage had not been measured, but was 184 reasoned to be less than 10 kcal mole . On t h i s basis then, i t was reasoned that conformers 176a and 176e should react more rapidly than invert (k * << k ,k ). This prediction was born out by the ae a y markedly d i f f e r e n t slopes of the Stern - Volmer plots for quenching of bicyclobutanol and benzaldehyde formation and the subsequently derived rate constants for these processes (Table V). From th i s i t followed that product $'s should depend upon conformational populations, - 108 -and e f f i c i e n c y of product formation from the excited state conformers. After correcting for the observed78somewhat greater absorption of the a x i a l vs equatorial model compounds 177 and 178, an excited state population of 176a was determined to be 35% and of 176e, 65%. The quantum y i e l d for benzaldehyde formation ($ a) from 176e was found to be exactly 65% of the value for the model compound 178. Thus the res u l t s for compound 176 were i n accord with the hypothesis that conformational populations influence product quantum y i e l d s , and compound 176 belongs to case I I . In contrast to the above, the energy b a r r i e r for cyclopentane pseudorotation i s considerably smaller than that for cyclohexane rin g inversion 7 9^thus the authors f e l t that the pseudorotation i n 179 might compete e f f i c i e n t l y with a-cleavage and y-hydrogen abstraction. This was born out by the i d e n t i c a l Stern - Volmer slopes 7 for quenching of benzaldehyde and bicyclobutanol formation from 179 (and thus the i d e n t i c a l rate constants for these processes - Table V). This r e s u l t exactly p a r a l l e l s the s i t u a t i o n observed 8*for both a c y c l i c ketones 185 and 186, where the Stern - Volmer plots for quenching of benzaldehyde and cyclobutanol formation have i d e n t i c a l 185 186 - 109 -slopes i n each instance. Here, the energy b a r r i e r for r o t a t i o n about a single bond (3.5 - 4.5 kcal mole * ) 8 l s known to be comparable to that for y-hydrogen abstraction? 3 Thus the r e s u l t s observed for photoreaction of 179 are consistent with case I , where the rate of conformational isomerization competes, e f f e c t i v e l y with the rates of chemical reaction. Here product composition depends upon the r e l a t i v e rates of formation of products and not upon conformational populations. One example of apparent ground state conformational control has been observed previously i n our laboratory, i n the photochemistry of adduct 187, shown i n Scheme 36. The formation of 188 as the sole SCHEME 36. 187 188 189 190 - 110 -product on i r r a d i a t i o n of 187 was s u r p r i s i n g , as molecular models of 187 suggested that 189 should be formed p r e f e r e n t i a l l y . However, structure 188 for the photoproduct was determined unambiguously by x-ray crystallography. The formation of 188 was r a t i o n a l i z e d on the basis of conformational an a l y s i s . Of the f i v e conformers p o s s i b l e i n Scheme 10, only two could account for the J2 + 2J c y c l o a d d i t i o n observed i n the case of 187. These are 190 and 191 (Scheme 36), i n which the ex o c y c l i c v i n y l group i s c l o s e to the ene-dione double bond. As the formation of product was l i k e l y s t e p w i s e 7 3 > 8 i t was reasoned that the formation of b i r a d i c a l intermediate 192 which gives 188 on closure, was favored over that of 193, which would give 189, due to the l e s s e r non-bonded i n t e r a c t i o n s experienced during i t s formation, such as the carbonyl-vinyl i n t e r a c t i o n i n conformer 190 and the C c a x i a l hydrogen-vinyl i n t e r a c t i o n o i n conformer 191. Thus, i t was reasoned that the v i n y l group preferred to rotate so as to occupy the "outer" or exo p o s i t i o n 8 4 which leads to 192 as opposed to the more congested "inner" or endo p o s i t i o n which would a f f o r d 193. 192 193 The photoisomerization of cyclobutylphenyl ketone 194 to the - I l l -SCHEME 37. Y-H abstraction Ph arrows 194e O + OH Ph' CH2CH2CH=CH2 195 Ph 196 i n i t i a l l y discussed i n terms of ground state conformational control!* The reaction i s characterized by a very low quantum e f f i c i e n c y ($) and a very slow rate of Y~hydrogen abstraction (Ky) r e l a t i v e to other a l k y l phenyl ketones. These data are summarized i n Table VI. The slow rate was attributed to the low concentration of the reactive quasi-axial isomer 194a; t h i s was confirmed by the higher observed k for compound 199, a r i g i d model for conformer 194a. The low quantum y i e l d i n the case of 199 was attributed to a rapid t r i p l e t ft fi deactivation mechanism, that of hydrogen back transfer. However, the r e a c t i v i t y ( i e . k ) of 199 was now si m i l a r to that of valerophenone (184), which implied then that the low r e a c t i v i t y observed for 194 - 112 -TABLE VI. $ arid of some Phenyl A l k y l Ketones. Ketone k (sec _ L _ 1 PK 194 0.03 5.5 x 10" 0 P K 0.40 6.7 x 10 197 184 0.49 0.44 8.3 x 10 1.3 x 10 8 199 0.06 3.9 x 10 8 0 200 Ph 0.20 4.1 x 10' - 113 -( i e . k ) was due to the low concentration of reactive conformer 194a. Y ' Alexander then studied 8 7a series of j J-substituted aryl-cyclobutyl ketones 201, and found that the quantum y i e l d for reaction of ketones 201 changed dramatically i n much the same way as observed of other phenyl a l k y l ketones 8 8as the electron withdrawing power of the substituent increased (as shown i n Table VII). TABLE VII. Quantum Y i e l d Dependence of Reaction of Aryl-cyclobutyl Ketones on p-Substituent (x). p-CH3. 0.001 p-F 0.050 p-CF 3 0.089 ^ 1 X = CH3,F,CF3 Three possible mechanisms were considered 8 7to account for the low concentration of the reactive a x i a l conformer (cf. 194a), and therefore low quantum y i e l d of reaction of ketone 194; namely 1) control by ground state conformational equilibrium, 2) control by r i n g inversion i n the excited state, 3) control by excited state conformational equilibrium. Alexander determined that these three 8 7 mechanisms were distinguishable by k i n e t i c analysis. From the quantum y i e l d data (Table VII) for the reaction of ketone 201, the t h i r d mechanism, namely control by excited state conformational equilibrium, was indicated. - 114 -Conformational effects on the behavior of b i r a d i c a l intermediates have also been demonstrated i n the l i t e r a t u r e . Agosta and Schreiber 8 9 reinvestigated the photochemistry of cyclohexanone 202 which had previously been shown 9 0' 3 8to y i e l d unsaturated aldehyde 203 and ketene 204 (trapped as the methyl ester). They focused t h e i r attention on the stereochemistry of the hydrogen transfer from C^ or C^ to C^  i n the -reaction leading to 203 (Scheme 38) and considered two p o s s i b i l i t i e s : SCHEME 38. 205 a) the transformation could be st e r e o s p e c i f i c , with either the a x i a l or equatorial hydrogen s e l e c t i v e l y migrating to the carbonyl carbon (structure 205); or b) the o r i g i n a l d i s t i n c t i o n between a x i a l and equatorial hydrogen at C^ or C,. i s l o s t before the hydrogen transfer occurs. The compounds chosen to c l a r i f y the nature of the rearrangement were the deuterated methyl cyclohexanones 206-208. Photolysis of 206 and 207 - 115 -led to corresponding aldehyde 209 (eq. 36), and i r r a d i a t i o n of 208 gave 210 predominantly, plus a l i t t l e 211 (eq. 37). In the instances of 209 and 210 the deuterium l a b e l l i n g at and C,. was determined O 206 207 208 210 211 by nmr spectroscopy. The data obtained for the l a b e l l i n g i s recorded i n Table VIII. TASLE VIII. Labelling paterns of deuterated 209 and 210. Compound and Position % Protium C x of 209 from 206 85 C 5 of 209 from 206 72 C x of 209 from 207 ' ' 18 C 5 of 209 from 207 29 C x of 210 65 C c of 210 37 - 116 -From these data, the percentages of a x i a l hydrogen transfer were calculated, as reproduced i n Table IX. TABLE IX. Percentage A x i a l H-transfer, ketone -*• aldehyde. 206 + 209 207 209 208 -> 210 Based on C 1 64 63 68 Based on C 5 74 64 68 From these r e s u l t s , the authors concluded that there i s very l i t t l e s p e c i f i c i t y i n the reaction of 202 (approximately 2/3 of the aldehyde protons came from the a x i a l position while 1/3 originated from the equatorial) and postulated the intermediacy of a b i r a d i c a l such as 212 with a l i f e t i m e s u f f i c i e n t to permit free r o t a t i o n about the - C,. bond leading to the c h a i r l i k e intermediates 213 and 214. The observed preference for a x i a l migration could then be interpreted i n terms of 213, i n which the methylene group i s equatorial, being energetically favored over 214, where i t i s a x i a l . - 117 -A second study by Agosta and Wolff ^ o f the more r i g i d b i cyclo [3.2.1] octan-6-one (215) system also demonstrated conformational effects on the behavior of b i r a d i c a l intermediates. Photolysis of 215 results i n a-cleavage to give the a x i a l b i r a d i c a l 216a (Scheme 39). I t had been shown 9 2that cyclohexyl r a d i c a l s behave conformationally l i k e cyclohexane or cyclohexanone. Radical 216a can then suffer a second hydrogen transfer from the side chain to the rin g to give ketene 217, or.from the rin g to the side chain to give aldehyde 218. I f 216a inverts to the equatorial conformer 216e, then only aldehyde 218 i s possible. A f i n a l p o s s i b i l i t y i s the presence of boat SCHEME 39. CHjCHO 216b - 118 -conformer 216b, which would give r i s e to aldehyde 219 by hydrogen transfer from ring to side chain. As i n s u f f i c i e n t quantitative information was available to r e l i a b l y predict the conformational behavior of 216, several substituted bicyclo-octanones of known stereochemistry were i n v e s t i g a t e d 9 1 t o determine the role of conformational control on the behavior of the b i r a d i c a l . Agosta's results are reproduced i n Table X. , The data presented i n Table X give an excellent c o r r e l a t i o n between the' fate of the b i r a d i c a l 216 and expected conformational effects i n the six-membered rin g . Ketones 220 and 221, for which the a x i a l conformer 216a i s the stable one, y i e l d ketene and v i r t u a l l y no aldehyde. For ketones 222 - 224, where conformer 216e i s c l e a r l y more stable, e s s e n t i a l l y the sole product observed i s the corresponding aldehyde. For ketone 225, i n which both conformers 216a and 216e should be r e l a t i v e l y equal i n energy and hence concentration, a product mixture of aldehyde and ketene i s observed. In no instance was the boat conformer 216b detected (via aldehydes 219). From these r e s u l t s , Agosta 9 1 concluded that conformational equilibrium shown i n Scheme 39 must be considered i n the reaction of 215, and that disproportionation of the b i r a d i c a l intermediate 216 - 119 -TABLE X. Products of Photolysis of Bicyclo [3.2. l] oetan-6-ones. Substrate Aldehyde < 0.5% 220 Methyl Ester (from ketene) 96% 221 < 4% CH1COlMe 75% 222 CHtCHO 93% < 0.5% 223 CHTCHO 85% < 2% H.CO O 224 CH TCHO OCKs 85% < 0.5% CH,CO,M« 225 44% 54% - 120 -occurs from the stable cyclohexane chair conformer i n each instance. Returning now to the photochemistry of Diels-Alder adducts of £-benzoquinones with a c y c l i c dienes, the influence of conformational control on product formation appears to be implicated by the resu l t s presented here and previously. The i n i t i a l case to be considered i s conformational control in the ground state; i e . the presence of bridgehead substituents in adducts 52 and j)8_ - 103 favoring a twisted conformation, such as conformer C (Scheme 10, Introduction), which leads to the unusual products observed, such as 54_ (from 52) , 156 (from 101), 160 and 161 (from 102) and 169 (from 103). For convenience, these transformations are reproduced i n Scheme 40. SCHEME 40. - 121 -The absence of bridgehead substituents (other than hydrogen) then permits the molecule to assume one or more of the other possible conformers (Scheme 1 0 ) , and thus gives r i s e to products with structures t y p i f i e d by those found i n products 1_8 - ^0 (eq. 38). To gain information on t h i s point, x-ray structure determinations were carried out on a number of the adducts studied both p r i o r to and i n t h i s work. Figure 24 shows computer drawn stereodiagrams of adducts JJO, _52, _97, 9_8 and 101. At t h i s point the author wishes to acknowledge and thank Drs. J.R. Trotter and S. P h i l l i p s for the i r x-ray structure determinations and h e l p f u l discussions. The detailed results of t h e i r work i s being published, separately. On examination of figure 24, one fact i s immediately obvious: a l l adducts assume the twisted conformation, depicted i n figure 25, i n the s o l i d state, regardless of bridgehead substitution. Therefore, 9 3 very l i k e l y , the twisted conformer i s predominant i n solution as w e l l , although others are also possible depending on the b a r r i e r to conformational isomerism. - 122 -Figure 25. Table XI l i s t s pertinent 0-Ho and C_-H contact distances for P J Y .the adducts shown i n figure 25, along with the dihedral angles a and 3, as defined i n figure 25. These data were determined i n the course of the x-ray structure determinations, and serve to show the very si m i l a r nature of the s o l i d state conformation of each adduct. I t TABLE XI Compound 0-H g(X)* c 3-H y (£)+ a ( ) 3(°) 10 2.49(3) 2.96(3) 63(2) 68.9(2) 52 2.47(6) 2.89(6) 60^0(6) 61.4(5) 97 2.42(6) 3.09(6) 56(3) . 71.4(4) 98 2.58(3) 2.92(3) 60.9(2) 64.0(2) 101 2.26(3) 2.70(3) 62.6(3) 60.7(3) * i n Figure 24 these are the C^ -H -+ 0^ distances, except for 52, where i t i s the C,-H*0„ distance. o I t i n Figure 24 these are the C,-H->C„ distances, except for 5_2, where 6 .i. i t i s C„-H-»-C0 distance. - 123 -Figure 24. Stereodiagrams of Diels-Alder Adducts. Adduct 10. 0(1) 0(1) 0(2) 0(2) Adduct 52. CU2) C112) Adduct 97. can can 0(21 Adduct 101. C18)£ IC(14) - 125 -seems then that while small conformational differences are observed i n adducts with bridgehead substituents (52, 98, 101) r e l a t i v e to those with hydrogen (10, 97), the ground state conformational argument cannot completely explain the di f f e r e n t photochemistry observed for adducts with bridgehead substituents. An examination of molecular models of these Diels-Alder adducts, b i r a d i c a l intermediates and f i n a l products reveals an important fact. In order f o r the b i r a d i c a l formed by the process of 6-hydrogen abstraction to collapse to an ene-dione photoproduct (cf. Scheme 5, 21 18 + 19), a conformational rotation about the C, - C_ bond — — — 4a 8a i s required to situate the p_-orbitals of the b i s - a l l y l i c system such that bonding may occur. This i s i l l u s t r a t e d i n Figure 26. Abstraction of the B-nydrogen by excited carbonyl oxygen gives structure 226 ( i e . b i r a d i c a l 21). The formation of 18 then requires a rotat i o n about the C, - C„ — M 4a 8a bond (represented by the 226 •+ 227 transformation) to bring the £-orbitals on and Cg o f the b i s - a l l y l i c system into proximity. For the formation of J_9, the b i r a d i c a l must assume structure 228, where the bridgehead substituents ( i e . hydrogens) are nearly eclipsed, to favorably situate the p - o r b i t a l s on C^ and Cfi for bonding. -126 -Figure 26. However, the formation of an enone alcohol photoproduct from the b i r a d i c a l (cf. 21 •*• 2Q, Scheme V) requires no, or very l i t t l e , conformation change p r i o r to bond formation. The jp_-orbitals on - 127 -carbon atoms C, and C of the b i s - a l l y l i c system (structure 226) are already favorably situated for bonding to occur. Figure 27 shows by means of computer drawn stereodiagrams t h i s conformational s i m i l a r i t y of enone alcohol photoproduct to substrate (the Diels-Alder adduct) for the s p e c i f i c case of adduct 98_ and product 136. Figure 27. - 128 -Models reveal a s i m i l a r s i t u a t i o n to be true for formation of 54 from 52 (and 156 from 101) namely bonding between C„ and C„ requires very l i t t l e conformational change i n the b i r a d i c a l intermediate. The s i t u a t i o n for adducts 54 and K)_l can thus be summarized i n Figure 28. 230 Figure 28. Thus, the formation of enone alcohol photoproducts ( l i k e 53 and 155 and of the ene-dione products 54 and 156 requires very l i t t l e ne£ conformational change to undergo 1,6 or 2,8 bonding, respectively, - 129 -from t h e i r respective b i r a d i c a l intermediates. These considerations thus suggest that the photochemistry of Di e l s - A l d e r adducts of p_-benzoquinones and a c y c l i c 1,3-dienes thus f a r studied i s c o n t r o l l e d i n part by conformational e f f e c t s on the b i r a d i c a l intermediates involved. In molecules where a 3-hydrogen a b s t r a c t i o n process i s po s s i b l e , the presence of bridge-head substituents p r o h i b i t s a conformational r o t a t i o n about the C. - C Q bond by r a i s i n g the energy b a r r i e r f o r such a r o t a t i o n , 4a oa and thus photoproducts with the structures found i n 18. a n < * 12. are not observed. Only enone alcohol ( c f . structure 20) and, i n some cases, ene-dione of structure 54_ are observed, both of which possess the same r e l a t i v e conformations as t h e i r respective b i r a d i c a l intermediates (and s t a r t i n g D i e l s - A l d e r adducts). The e f f e c t of bridgehead substituents on the energy b a r r i e r to conformational r o t a t i o n i n the c l o s e l y r e l a t e d c i s - d e c a l i n system (231 232) has been measured using nmr techniques by Altman, et a l 9 1 * f o r a s e r i e s of substituents. Their data are reproduced i n Table XII, along with data f o r c i s - d e c a l i n (231, R=H), and 4a-methyl-cis-decalin (231, R=H, R'=Me), as determined by Gerig and Roberts? 5 231 132 - 130 -TABLE XII. Energy t e r r i e r s to Inversion for Some C ^ - Cg^ Disubstituted c i s - d e c a l i n s . Compound R, R' = H R = H, R' = Me R, R' = CH 2C0 2CH 3 R, R' = CH 2Br R = Br, R' = CN E (kcal mole S —a approximately 14 approximately 10 20.6 ± 0.6 18.7 ± 1.2 18.3 ± 0.9 A s i g n i f i c a n t increase i n the energy b a r r i e r to conformational i n v e r s i o n i n c i s - d e c a l i n i s thus introduced by bridgehead s u b s t i t u t i o n . For the r e l a t i v e l y s i m i l a r tetrahydronaphthoquinone r i n g system, i t i s reasonable to suspect that the energy b a r r i e r s to inversion of conformation,although l i k e l y somewhat smaller than those for the c i s -d e c a l i n system9, 6may be s i m i l a r l y a f f e c t e d . An apparent exception to the above conformational arguments i s found i n the formation of ene-dione 148 on i r r a d i a t i o n of adduct 100. hV 100 E = C02Me - 131 -Compound 148 i s the only photoproduct of t h i s type observed thus f a r where the bridgehead positions which are nearly eclipsed are occupied by a substituent other than hydrogen. A l l that can be said here i s that the energy b a r r i e r to conformational isomerization of the b i r a d i c a l i s s u f f i c i e n t l y less for carbomethoxy substituents, r e l a t i v e to methyl substituents, to permit the formation of 148 to occur. C l e a r l y , a complete conformational rotat i o n about the C^&- C g a bond i n the b i r a d i c a l i s an unfavorable process, as ene-dione 149, the formation of which requires such a conformational change, i s not observed. Additional insight into the photochemistry of tetrahydro-naphthoquinones has been obtained from the work of Scheffer and Louwerens, who recently studied 9 8the Stern-Volmer quenching k i n e t i c s for adducts 52 and 1_7. For the case of 52, i t was found that the formation of ene-dione 54_ can be quenched be adding cyclohexa-1,3-diene to the photoreaction mixture, while the formation of enone alcohol _53 i s unaffected, suggesting that products _53 and 54 originate from singlet and t r i p l e t excited states respectively. There i s l i t e r a t u r e precedent for these observations. Recently, Agosta 9 9published some data relevant to the reactions l i s t e d i n Scheme 13 (introduction). - 132 -He found that the processes of 3-hydrogen a b s t r a c t i o n by oxygen, leading to cyclopropane products, and y-hydrogen a b s t r a c t i o n by oxygen, g i v i n g cyclobutane products (Scheme 1 3 ) , were both o r i g i n a t i n g from the s i n g l e t excited s t a t e , as neither process was af f e c t e d by the presence of quencher. S i m i l a r l y , the process of hydrogen abstraction by enone carbon has been shown by several workers ' to involve a t r i p l e t excited s t a t e . The case of adduct _ 1 7 , i n which 3-hydrogen a b s t r a c t i o n by oxygen i s the only process g i v i n g r i s e to products i s also i n l i n e with the above. A l l the products J J ? - 2MD (Scheme 4 ) were found to o r i g i n a t e from the s i n g l e t excited s t a t e , although f o r the two products formed i n benzene (namely _19 and 2 0 ) , a t r i p l e t excited state r e a c t i o n i s also indicated. The f a c t that only two of the adducts studied thus far (namely 5 2 and 1 0 1 ) react v i a a y-hydrogen a b s t r a c t i o n by carbon mechanism merits some discu s s i o n at t h i s point. The r e s u l t s obtained f o r those adducts i n which a 3-hydrogen ab s t r a c t i o n by oxygen process i s p o s s i b l e can be summarized by Scheme -41. I t appears that intersystem crossing (a) from the s i n g l e t to t r i p l e t excited state i s not an e f f i c i e n t process i n the photochemistry of tetrahydronaphthoquinones; rather, 3-hydrogen a b s t r a c t i o n (k„) - 133 -SCHEME 4 1 . ( 5 3 , 1 5 5 , 2 0 ) ene-diones (^ 8 and 19) occurs to generate a b i r a d i c a l intermediate. In those cases where the b i r a d i c a l contains bridgehead hydrogens, conformational isomerization (k ) competes with formation of enone alcohol (k,,), and with c lp reversion to ground state a d d u c t 1 0 0 ( k D ) and results i n the formation " P of ene-dione photoproducts such as 28 and 19. On the other hand, the presence of bridgehead substituents, as i n adducts _52 and 1 0 1 , makes conformational changes i n the b i r a d i c a l less l i k e l y (k « k 1 A and k„). Thus, formation of enone alcohol and - 1 3 4 -reversion to ground state adduct are the only reaction pathways available to the b i r a d i c a l derived from the excited s i n g l e t state. This should i n turn allow for an ever increasing f r a c t i o n of singlet excited states to undergo intersystem crossing and subsequently suffer y-hydrogen abstraction to give product 54_ or 156. This -explanation finds some support i n the solvent dependence observed for the product d i s t r i b u t i o n i n the case of adduct 52. 86 ' I t i s known that the hydrogen atom back transfer mechanism for the Norrish I I reaction can be made less important by conducting the reaction i n solvents of increasing p o l a r i t y . This also seems to be the case for adduct _52_ (see Scheme 11) - increasing r e l a t i v e amounts of enone alcohol 53_ are formed at the expense of 54_ as the solvent p o l a r i t y i s increased. In the cases of adducts 9_8_ - 100, where i t i s also indicated that k « k,, and k 0 (Scheme 41), reason for the fact that no c 1,6 -8 compound analogous to _54 i s observed i s not obvious. One possible explanation i s that the absence of methyl substituents on carbon atoms and i n j)8 - 100 make the process of hydrogen abstraction by carbon unfavorable, owing to the lesser s t a b i l i t y of the b i r a d i c a l intermediate which would be formed, namely 233, r e l a t i v e to that of ^0 (cf. Scheme X I I ) . ' . Another possible explanation analogous to the proposals of Barltrop 1* 7and Schaf f ner 3 8 (cf. Introduction) i s that i n the case of * 54 (and hence 101) , intersystem crossing gives r i s e to a TI — TT t r i p l e t state-(due to the presence of the and methyl groups) which leads to hydrogen abstraction by enone carbon. For those compounds lacking methyl substituents on and (10, 17, 98, 99, 100) intersystem crossing occurs to a t r i p l e t n - TT state * which, l i k e the (presumably) n - TT s i n g l e t state, reacts v i a the process of 3-hydrogen abstraction by oxygen. Some support for this l a t t e r explanation i s found i n the work of Louwerens 9 8where photolysis of adduct _17_ i n benzene was found to give r i s e to JL9_ and 20 from both the singlet and t r i p l e t excited states. A comparison of the photochemistry of adducts 102 and 103 suggests a contribution by ene-dione methyl substituents, i n l i n e with those proposed above, for these substrates as w e l l . While both 102 and 103 give r i s e to oxetane photoproducts, adduct 102 eventually reacts quantitatively to give cage compound 161, the formal resu l t of a cycloaddition reaction between the isolated double bond and the substituted ene-dione double bond. In the case of 103, where the ene-dione double bond i s unsubstituted, no corresponding cage - 136 -isomer 170 i s observed. A conformational control argument can also account for the observed difference i n the photochemistry of adducts 102 and 103, from that of 4_2_. Again models reveal that b i r a d i c a l 4_5 (Scheme 9) , formed by y-hydrogen abstraction by oxygen from the nearby methyl group i n 42_, (structure 234), must undergo a conformational r o t a t i o n (as shown by the 235 -*• 236 transformation i n figure 29) to bring the exocyclic methylene r a d i c a l into p o s i t i o n for bonding to carbon atom 3. Figure 29. - 137 -For compounds 102 and 103, such conformational r o t a t i o n i s again prevented by the presence of bridgehead substituents. Thus while hydrogen abstra c t i o n from the methyl by oxygen may be a ready process, the b i r a d i c a l so derived i s conformationally immobile during the b i r a d i c a l l i f e t i m e and subsequently d e a c t i v a t e s 8 6 b a c k to s t a r t i n g material. Thus the only photochemical pathway a v a i l a b l e to 102 and 103 leading to products appears to be oxetane formation (160 and 169, r e s p e c t i v e l y ) . Again the conformation of the oxetane i s very s i m i l a r to that of i t s precursor, as shown i n f i g u r e 30, where the conformations of adduct 103 and oxetane 169 are compared. While the net change i n • conformation i n the 103 169 transformation appears to be greater than that f or the s i m i l a r 9J3 ->• 136 transformation, (f i g u r e 28) no r o t a t i o n about the substituted C. - C„ bond i s ° 4a 8a required to form 169 from 103. Another possible process a v a i l a b l e to 102 and 103 would appear to be a b s t r a c t i o n of a methyl hydrogen by an enone carbon atom. Structure 234 (figure 29) shows that such a process i s c e r t a i n l y p o s s i b l e i n that the methyl H - carbon contact can be as l i t t l e as 2.91 X (as determined by x-ray a n a l y s i s ) . However, the derived b i r a d i c a l i n t h i s case (eq. 39, 237) would lac k resonance s t a b i l i z a t i o n which seems to be a requirement for success of these reactions (cf. compound _70, Introduction). - 138 -Figure 30. Adduct 103. Oxetane 169. - 139 -(eq. 39) 102 R=R'=Me 237 103 R=H, R'=CN A f i n a l point to be noted i s the emergence of new product structures from the photolysis of adducts 102 and 103. I t has been previously noted 2 5that photolysis of Diels-Alder adducts _17 and j42 offers ready entry into the ring systems found i n certain natural products. I t may thus be suggested that photolysis of tetrahydro-naphthoquinone ring systems which are substituted appropriately can give r i s e to yet other novel, and po t e n t i a l l y useful compounds and r i n g systems through the influence of conformational effects introduced into the system by those substituents. The formation of oxetanes 160 and 169, and cage dione 161 readily attest to th i s proposal. I t may also be stated that for many, i f not a l l , of the D i e l s -Alder adducts synthesized i n our laboratory, the stereochemistry was completely unknown i n i t i a l l y . However, the photoreactions of these adducts c e r t a i n l y establish t h e i r stereochemistry, and i t i s anticipated that these reactions may be s i m i l a r l y used for other adducts. - 140 -EXPERIMENTAL General Procedures Infrared ( i r ) spectra were recorded on a Perkin-Elmer 137 spectrophotometer i n one of three ways: a) from neat l i q u i d samples between sodium chloride plates, b) using KBr p e l l e t s containing 0.5% by weight of sample, and c) as 5% chloroform or carbon tetrachloride solutions. Nuclear magnetic resonance (nmr) spectra were recorded by the departmental nmr service on the following instruments: Varian Model A-60, T-60, HA-100 and XL-100 spectrophotometers; i n a l l cases, tetramethylsilane was used as the i n t e r n a l standard. Mass spectra were obtained on Atlas CH-4-B and AEI-MS-902 spectrometers, and 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 indicated. Microanalyses were performed by Mr. P. Borda of t h i s department. Melting points were determined on a Fisher-Johns melting point apparatus and are uncorrected, unless otherwise spe c i f i e d . Gas l i q u i d p a r t i t i o n chromatography was carried out on Varian Aerograph Model 90-P and Varian Aerograph Autoprep Model A 700 chromatographs; both were connected to Honeywell Electronik 15 s t r i p chart recorders. The - 141 -c a r r i e r gas was helium i n a l l cases.. The following columns were employed: 20% DEGS, 5' x h" (column A); 10% FFAP, 5' x V (column. B); 10% 0V-1, 7' x V (column C). In the text, the column w i l l be given, followed by the column oven temperature and c a r r i e r gas flow rate i n parentheses. For column chromatography, S i l i c a Gel ( p a r t i c l e s i z e less than 0.08 mm) from E. Merck AG was employed, and was packed as a s l u r r y i n the eluting solvent; packing and elution were carried out under 5-10 p s i nitrogen pressure. Alumina used was Woelm, neutral, a c t i v i t y grade I. Thin-layer chromatography ( t i c ) was performed on pre-coated aluminum f o i l t i c sheets obtained from E. Merck AG, either Aluminum Oxide F-254 neutral (type T) or S i l i c a Gel 60 F-254. In both cases, the layer thickness was 0.2 mm. Unless otherwise indicated, 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 . Interposed between the lamp and reaction vessel was a 15 x 15 cm plate of Corning #7380 glass (transmitting l i g h t of X >_ 340 nm), which was cooled by a stream of a i r . The reaction vessel was 6 - 1 0 inches from the lamp. Solutions to be ir r a d i a t e d were f i r s t degassed for at least h hour with Canadian Liquid A i r argon. A l l solvents used were reagent grade and were d i s t i l l e d p r i o r to use. - 142 -4a8,5,8,8a3-tetrahydro-2,6,7-trimethyl-l,4-naphthoquinone (95). This material was prepared by the method of Bergmann and Bergmann!*9 A s l u r r y of 2 g (0.016 mole) of methyl-_p_-benzoquinone (Eastman, p r a c t i c a l ) , 3.5 g (0.043 mole) of 2,3-dimethyl-l,3-butadiene and 0.01 g of hydroquinone was placed i n a sealed Pyrex tube and heated for 1 hour at 110°. The now pale yellow reaction mixture, which s o l i d i f i e d upon cooling to a pale yellow s o l i d , was r e c r y s t a l l i z e d from methanol to give 2.52 g (77%) of 95, mp 89-91° ( l i t ! * 9 9 3 - 94°). Distinguishing spectral ch a r a c t e r i s t i c s were as follows: i r (KBr) 5.98 (C=0) , 6.15 (C=C)u; nmr (CCl^T 3.53 (m, 1, v i n y l ) , 6.7 - 7.0 (m, 2, C^^ and C g a methines), 7.5 - 8.0 (m, 4, C c and C Q methylenes), 8.03 (d, 3, J=1.5Hz, C_ 5 o 2. methyl), 8.37 (br s, 6, C, and C, methyls); uv max (methanol) 6 / long shoulder (e at 340 = 130). Photolysis of Adduct 95_ i n Benzene. A sol u t i o n of 804 mg (3.94 mmoles) of 95_ i n 250 ml of benzene was i r r a d i a t e d with l i g h t of wavelength _> 340 nm. The reaction was monitored by glpc (column A, 175°, 160 ml/min) which showed a rapid buildup of 4 new products; after 6.5 hours, a l l _95_ had reacted, and the r a t i o of products was 106:107:108:109 = 3.8:1:2.6:3.4 as determined by cutting out and weighing peaks from the glpc chart paper. I s o l a t i o n of the products was achieved by preparative glpc (same column and conditions as above). A l l were collected as colorless o i l s which - 143 -c r y s t a l l i z e d on standing, and were characterized by the following properties: for 106_, 5-hydroxy-3,8,9-trimethyltricyclo [4.4.0.05'9] deca-3,7-diene-2-one: colorless s o l i d , r e c r y s t a l l i z e d from petroleum ether (68 ), mp 90 - 91.5°; i r (CC14) 2.78 (OH), 5.93 (C=0)y; nmr (CC1 4)T 3.61 (m, 1, v i n y l ) , 4.43 (m, 1, C ? v i n y l ) , 7.05 (m, l , methine), 7.6 - 7.9 (m, 1, C, methine), 7.70 (s, 1, OH) 8.22 (br s, 6, C, and C Q methyls), 8.6 (m, 2, G.. methylenes), 8.91 (s, 3, C. methyl); o lu y uv max (methanol) 244 (e 6200), 325 nm (e 58); mass spectrum (70 eV) m/e parent 204. Anal. Calcd.. for C-.H-.O.: C, 76.44; H, 7.90. Found: C, 76.25; i j l o 2 H, 7.79. for 107, 3,8,9-trimethyltricyclo 3 7 4.4.0.0 ' dec-8-ene-2,5-dione: colorless s o l i d , r e c r y s t a l l i z e d from petroleum ether (68°), mp 69 - 70°; i r (CCI.) 5.70 (C=0)y; nmr (CC1.)T 7.40 (m, 1, Cr methine), 7.5 -4 4 6 7.65 (m, 2), 7.65 - 7.8 (m, 2), 7.79 (dd, 1, J=18Hz, 1Hz, C^ exo-methylene), 8.01 (d, 1, J=18Hz, C^ endo-methylene), 8.28 (br s, 3, C g or methyl), 8.38 (br s, 3, C g or C g methyl), 8.84 (s, 3, C 3 methyl); uv max (methanol) 286 nm (e 78); mass spectrum (70 eV) m/e parent 204. Anal. Calcd. for C._H..0o: C, 76.44; H, 7.90. Found: C, I J l o 2 76.15; H, 7.92. - 144 -for 108, 3,8,9-trimethyltricyclo J4.4.0.03'^J dec-7-ene-2,5-dione: colorless s o l i d , r e c r y s t a l l i z e d from petroleum ether (68°), mp 108.5 -109.5°; i r (CC14) 5.68 and 5.80 (C=0)y; nmr (CC1 4)T 4.42 (br d, 1, J=7Hz, C, v i n y l ) , 6.77 (dd, 1, J , ,=7Hz, =8Hz, C, methine), 7.14 / o, / 6,1 b (d, 1, J=17.5Hz, C, exo-methine), 7.35 (dt, 1, J. ,=8Hz, J. . =2Hz, 4 1 , o 1 , 1 U C. methine), 8.12 (d, 3, J=1.5Hz, C„ methyl), 8.15 (d, 1, J=17.5Hz, 1 o endo-methylene), 8.3 - 8.7 (m, 2, C^Q methylenes), 8.73 (s, 3, Cg methyl), 9.02 (s, 3, C 3 methyl); uv max (methanol) 294 (e 481), sh 307 nm (e 426); mass spectrum (70 eV) m/e parent 204. Anal. Calcd. for CloH.,0„: C, 76.44; H, 7.90. Found: C, 76.53; H, 7.85. for 109, 5-hydroxy-4,8,9-trimethyltricyclo [4.4.0.05'9] deca-3,7-diene-2-one: colorless s o l i d , r e c r y s t a l l i z e d from petroleum ether (68 ), mp 92.5 - 93°; i r (CCl^) 2.80 (OH), 5.93 (C=0)y; nmr (CCl^T 4.29 (m, 1, C„ v i n y l ) , 4.36 (m, 1, C-, v i n y l ) , 7.00 (d, 1, J=3Hz, C, methine), 3 / o 7.51 (s, 1, OH), 7.83 (m, 1, methine), 8.06 (d, 3, J=1.5Hz, methyl), 8.20 (d, 3, J=1.5Hz, C Q methyl), 8.47 and 8.52 (each a o singlet,' 2, C^Q methylenes), 8.86 (s, 3, methyl); uv max (methanol) 244 (e 6100), a long t a i l i n g shoulder from 310 - 355 nm (e at 325 nm -51); mass spectrum (70 eV) m/e parent 204. Anal. Calcd. for C1oH.,0„: C, 76.44; H, 7.90. Found: C, 13 16 i. 76.23; H, 7.77. - 145 -Photolysis of Adduct 95 i n tert-Butanol. A solution of 500 mg (2.45 mmoles) of 95 i n 200 ml of 10% (v/v) benzene/tert-butanol was irr a d i a t e d with l i g h t of wavelength >^  340 nm. The reaction was monitored by glpc (column A, 175°, 160 ml/min) which showed the rapid buildup of 4 products at the expense of _95. Three of these products proved to be i d e n t i c a l to products 106, 107, and 109, obtained from the photolysis of 9_5 i n benzene. Compound 108 wasn't formed; rather a new product 110 was observed. After 17 hours of i r r a d i a t i o n , the r a t i o of products was 106:107:109:110 = 1:9.6:3:1, as determined by weighing the glpc peaks. The four products were successfully isolated by preparative glpc (same conditions as above). Products 106, 107 and 109 were i d e n t i f i e d by comparison of thei r spectral properties with those of the benzene photolysis products. Product 110 was also a colorless s o l i d , r e c r y s t a l l i z e d from petroleum ether (68°), mp 78 - 79°, and T 3 71 was i d e n t i f i e d as 4,8,9-trimethyltricyclo[4.4.0.0 ' Jdec-8-ene-2,5-dione on the basis of these spectral properties: i r (KBr) 5.72 (C=0)y; nmr (CDCl^x 6.9 - 7.1 (m, 1, C 3 methylene), 7.2 - 7.3 (m, 1, C £ methylene), 7.4 - 7.6 (m, 2), 7.6 - 7.8 (m, 3), 8.27 (br s, o 3, Cg or C 9 methyl), 8.39 (br s, 3, C g or C g methyl), 8.95 (d, 3, J=7.5Hz, C^ methyl); uv max (methanol) 283 nm (e 78); mass spectrum (7Q eV) m/e parent 204. Anal. Calcd. for C^H^O-: C, 76.44; H, 7.90. Found: C, lo lo 76.23; H, 7.82. - 146 -Base Catalyzed Deuterium Exchange of Ene-Dione 107. To a solution of 15 mg (0.073 mmol) ene-dione 107 i n 0.5 ml deuterochloroform i n an nmr tube was added 5 drops of a 2N solution of KOH i n D^O. The tube was p e r i o d i c a l l y shaken for one day, after which time the nmr spectrum showed the complete disappearance of the signal due to the C^ exo-proton at T 7.79. The doublet due to the endo-proton collapsed to a broad t r i p l e t at x 8.01, J=2.5Hz, and the C, methine signal at 7.40 collapsed to a doublet. The 6 remainder of the spectrum was unchanged. Thermolysis of Enone Alcohol 106. Enone alcohol 106 (10 mg, 0.049 mmol) was placed i n a sealed ampoule and heated to 200° for 5 hours. The dark product was taken up i n chloroform and eluted through a short column of alumina to give 5 mg of product, i d e n t i f i e d as ene-dione 107 by glpc retention time and i r spectrum. Photolysis of Enone Alcohol 106 i n tert-Butanol. A solution of 15 mg (0.073 mmol) of 106 i n 8 ml of 10% benzene/ tert-butanol. (v/v) was ir r a d i a t e d as usual, the reaction being monitored by glpc (column A, 175°, 160 ml/min). After 5 hours, complete reaction had occurred, and the product is o l a t e d by chromatography (alumina, chloroform) - 10 mg (67%) - was i d e n t i f i e d as ene-dione 107 on the basis of glpc retention time, i r and nmr spectra. - 147 -Photolysis of Enone Alcohol 106 i n Benzene. A solu t i o n of 64 mg (0.31 mmol) of 106 i n 30 ml of benzene was i r r a d i a t e d as usual. After 26 hours, glpc showed the reaction was about 85% complete, with two products being formed, subsequently i d e n t i f i e d as ene-dione 107 and ene-dione 108. The r e l a t i v e r a t i o was 106:107:108 = 1:3.2:3.6. After evaporation and column chromatography ( S i l i c a Gel, 25% ethyl acetate/benzene), 20 mg of 107 and 23 mg of 108 were i s o l a t e d . Each was i d e n t i f i e d by comparison of glpc retention times, i r and nmr spectra to those of authentic samples. I t was shown that 108 does not rearrange under the conditions of glpc, and therefore 107 i s a true photoproduct from 106. Thermolysis of Enone Alcohol 109. Compound 109 (14 nig, 0.07 mmol) was placed i n a sealed ampoule and heated for 3 hours at 200°. Glpc showed two products, corresponding i n retention times to ene-diones 107 and 110, i n a r a t i o of 1:3.2. Owing to the small quantity of material available, only 110 was isolate d successfully which showed i r and nmr spectra i d e n t i c a l to those of an authentic sample obtained from the photolysis of adduct jj>5_ i n tert-butanol. Photolysis of 109 i n tert-Butanol. A s o l u t i o n of 25 mg (0.12 mmol) of 109 i n 10 ml of 10% benzene/ tert-butanol was irr a d i a t e d for 19 hours, at which time glpc showed - 1A8 -complete conversion to photoproduct 110. Column chromatography afforded 16 mg (64%) of 110, i d e n t i f i e d by i t s glpc retention time, i r and nmr spectra. Photolysis of Enone Alcohol 109 i n Benzene. A solution of 6 mg (0.03 mmol) of 109 i n 3 ml of benzene was i r r a d i a t e d as usual. Glpc showed only a gradual disappearance of 109 with no v o l a t i l e products being formed. After 45 hours, the reaction was stopped; a l l 109 was gone, and no product appeared. Thermolysis of Ene-Dione 108. Compound 108 (5 mg, 0.024 mmol) was placed i n a sealed ampoule and heated at 182° for 5 hours. The golden product was checked by glpc, which showed the presence of a single product, i d e n t i f i e d as ene-dione 107 by i t s retention time and i r spectrum. 6, 7-Dimethyl-2-phenyl-4a3,5,8,8aB-tetrahydro-l, 4-naphthoquinone (96) i * 9 A s l u r r y of 3.5 g (0.019 moles) of phenyl-p_-benzoquinone (Eastman, r e c r y s t a l l i z e d from petroleum ether prior to use), 7.3 g (0.089 moles) of 2,3-dimethyl-l,3-butadiene, and a few crystals of hydroquinone was heated i n a sealed Pyrex tube for 1 hour at 100°. O n cooling, the deep amber mixture s o l i d i f i e d to a yellow mass, which was washed with acetone. R e c r y s t a l l i z a t i o n twice from petroleum ether (68°) resulted i n 3.68 g (73%) of 96 as a l i g h t yellow s o l i d , - 149 -mp 108 - 109.5° (lit!* 9113 - 114°). Distinguishing spectral features were: i r (CCl^) 5.94 (C=0)y; nmr ( C C l ^ x 2.60 (s, 5, phenyl), 3.33 (s, 1, C 3 v i n y l ) , 6.5 - 7.0 (m, 2, and C g a methines), 7.5 -8.0 (m, 4, C„ and C D methylenes), 8.33 (s, 6, Q, and C-. methyls); D O fa / uv max (methanol) 225 (log e 4.57), 301 nm (log e 3.98). Photolysis of 96^ i n Benzene. A solution of 211 mg (0.8 mmol) of 96_ i n 50 ml of benzene was i r r a d i a t e d with l i g h t of wavelength 340 run. The reaction was monitored by i r spectroscopy which showed a f a i r l y rapid change i n the f i n g e r p r i n t region. This was accompanied by a more gradual buildup of a 5.70y peak u n t i l a fter 18.5 hours, i t was v i r t u a l l y the only carbonyl signal present. Evaporation of solvent followed by column chromatography ( S i l i c a Gel, 15% ethyl acetate/benzene) resulted i n 95 mg of pale yellow o i l . A second chromatography ( S i l i c a Gel, chloroform) yielded 83 mg of o i l which c r y s t a l l i z e d on standing to colorless 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 ether/ petroleum ether (38°) gave 70 mg (33%) of 8,9-dimethyl-3-phenyltricyclo-r 3 7l [4.4.0.0 ' dec-8-ene-2,5-dione (117) as colorless c r y s t a l s , mp 109 - 110°C, i d e n t i f i e d on the basis of the following spectral data: i r (CC14) 5.70 (C=0)y; nmr (CDCl 3)l 2.64 (s, 5, phenyl), 7.06 (dd, 1, J=18Hz, 1.5 Hz, C 4 exo-methylene), 7.23 (br s, 1), 7.2 - 7.4 (m, 2), 7.50 (br s, 2), 7.62 (d, 1, J=18Hz, endo-methylene), 8.32 (s, 3, Cg or C g methyl), 8.69 (s, 3, C g or C g methyl); uv max (methanol) a long featureless absorption (e at 252 nm 800, e at 290 nm 140); mass spectrum (70 eV) m/e parent 266. Anal. Calcd. for C. oH. o0 o: C, 81.17; H, 6.81. Found: C, l o l o Z 81.09; H, 6.73. Base Catalyzed Deuterium Exchange of Ene-Dione 117. To a deuterochloroform solution of 117 i n an nmr tube was added 8 drops of a 1.2 N solution of potassium hydroxide i n D2O. After periodic shaking for one day, the nmr spectrum was measured, and the following changes noted: the double doublet at T7.06 due to the C^ exo-proton had disappeared completely; the doublet at T7.62 due to C^ endo-proton collapsed to a broad s i n g l e t ; the remainder of the spectrum remained unchanged. Short Period Photolysis of 9_6 i n Benzene. A solution of 500 mg (1.9 mmol) of 96_ i n 125 ml of benzene was i r r a d i a t e d with l i g h t of wavelength > 340 nm, and the reaction was interrupted after 3.5 hours at which time the i r spectrum of an aliquot showed the presence of 2 carbonyls at 5.70 and 5.93y. Chromatography of the intensely yellow solution ( S i l i c a Gel, 25% ethyl acetate/benzene) yielded 42 mg of ene-dione 117 and 102 mg of a yellow o i l , the i r of which showed 1 carbonyl at 5.93M> plus the presence of OH. The nmr spectrum of t h i s l a t t e r material indicated a mixture of 2 isomeric enone alcohols 120 and 121 i n a - 151 -r a t i o of about 6:1 (from integration). Chromatography of t h i s mixture ( S i l i c a Gel, 8% ethyl acetate/benzene) was accompanied by a good deal of decomposition, but allowed for p a r t i a l separation of the isomers. After passing each through a short column of alumina (chloroform eluent), 25 mg of 120 and 14 mg of 121 were obtained, each of which s o l i d i f i e d i n a small amount of petroleum ether. I d e n t i f i c a t i o n was based on the following spectral data: r 5 a for 120, 8,9-dimethyl-5-hydroxy-3-phenyltricyclo14.4.0.0 'J deca-3,7-diene-2-one: mp 68 - 70°; i r (CC14) 2.80 (OH), 5.92 (C=0)y; nmr ( C C ± 4 ) T 2.6 (m, 5, phenyl), 3.20 (s, 1, C 4 v i n y l ) , 4.37 (m, 1, C-, v i n y l ) , 6.87 (d, 1, J=3Hz, C, methine), 7.50 (s, 1, OH), 7.4 -/ o 7.8 (m. 1. C. methine), 8.21 (d. 3. J=1.5Hz, C Q methyl), 8.3 -i ' o 8.5 (m, 2, C^Q methylenes), 8.83 (s, 3, C^  methyl); uv max (methanol) 220 (e 6200), 270 (e 3800), sh 340 nm (e 61); mass spectrum (70 eV) m/e parent 266. r 591 for 121, 8,9-dimethyl-5-hydroxy-4-phenyltricyclo 4.4.0.0 ' Jdeca-3,7-diene-2-one: mp 103 - 106°; i r (KBr) 2.9 (OH), 6.03 (C=0)y; nmr ( C C l ^ T 2.7 (m, 5, phenyl), 4.03 (d, 1, J=1.5Hz, C 3 v i n y l ) , 4.32*(m, 1, C_ v i n y l ) , 6.86 (br d, 1, C, methine), 7.60 (s, 1, OH), / o 7.4 - 7.8 (m, 1, C 1 methine), 8.20 (br s, 3, C g methyl), 8.3 -8.5 (m, 2, C 1 Q methylenes), 8.75 (s, 3, C^ methyl); uv max (methanol) 281 (c 5400), a t a i l i n g absorption (e at 345 nm = 105); mass spectrum (70 eV) m/e parent 266. - 152 -Samples of both 120 and 121 were quite impure, and owing to lack of material, the usual p u r i f i c a t i o n procedures (sublimation, r e c r y s t a l l i z a t i o were not successful. Thus high resolution mass spectra were obtained: Calcd. for C 1 QH. o0 o = 266.1306 lo lo 2 for 120: observed 266.1285 (A = 0.0021) for 121: observed 266.1349 (A = 0.0043) Photolysis of Adduct 96^  i n tert-Butanol. A solution of 150 mg (0.56 mmol) of j)6_ i n 50 ml of 10% benzene-tert-butanol was ir r a d i a t e d for 24 hours. Evaporation of solvent followed by chromatography through a short column of alumina (chloroform) gave 113 mg of yellow o i l . The i r showed one main carbonyl band at 5.70u and a small, shoulder at 5.9y. Chromatography on S i l i c a Gel (10% ethyl acetate/benzene), which was accompanied by a great deal of decomposition, yielded 43 mg (29%) of ene-dione 117, i d e n t i c a l with that obtained from the benzene photolysis, and a trace of material, the i r and nmr spectra of which showed the sample to be a mixture of isomers 120 and 121 i n a r a t i o of approximately 6:1. Photolysis of j)6_ i n tert-Butanol-0-d. A solution of 90 mg (0.34 mmol) of 96_ i n 10 ml of tert-butanol-0-d was ir r a d i a t e d for 6 hours. The ene-dione subsequently isolated by column chromatography ( S i l i c a Gel - 8% ethyl acetate/benzene) showed an nmr spectrum i d e n t i c a l with that obtained from the base-catalyzed deuterium exchange of ene-dione 117, ind i c a t i n g deuterium - 153 -incorporation had occurred at the exo-position. From the mass spectrum, i t was calculated that 90% deuterium incorporation had occurred (see Appendix for c a l c u l a t i o n ) . Manganese Dioxide. This material was prepared i n the same way as that described by Attenburrow et a l 6 0 f o r "active" manganese dioxide. A solution of 38.4 g (0.24 mole) of potassium permanganate i n 250 ml water was heated on a hot plate/magnetic s t i r r e r . Meanwhile solutions of 44 g (0.2 mole) of manganese sulphate tetrahydrate i n 100 ml of water and 18.8 g (0.48 mole) of sodium hydroxide i n 70 ml of water were prepared. Then, with s t i r r i n g , these two solutions were added simultaneously to the hot permanganate solution. A fine brown pre c i p i t a t e formed almost immediately. S t i r r i n g was continued for an additional hour, after which the mixture was f i l t e r e d with suction. The s o l i d was washed with several portions of water u n t i l the f i l t r a t e was colorless; then i t was washed with acetone, dried i n an oven at 110°, and ground to a powder. Y i e l d was 45 gm. 2,3-Dimethyl-l,4-benzoquinone (129). This preparation 5 9was carried out i n the following apparatus: a 2 l i t r e , 3 neck round bottom receiving f l a s k , equipped with an e f f i c i e n t condenser, was submerged i n an i c e water bath. To one neck was f i t t e d , by means of a bent adaptor, a second condenser which - 154 -was connected to the side arm of a 500 ml d i s t i l l a t i o n f l a s k set up for steam d i s t i l l a t i o n . The t h i r d neck of the receiver was stoppered. To the 500 ml f l a s k were added 8 g (0.07 mole) of 2,3-dimethylaniline, 16 ml of concentrated sulphuric acid, and 100 ml of water. After thorough mixing of reagents, and with the cooling water running, 24 g (0.28 mole) of manganese dioxide were introduced to the f l a s k , the f l a s k b r i e f l y swirled, and steam d i s t i l l a t i o n started immediately. When the water d i s t i l l i n g over became c o l o r l e s s , the apparatus was disconnected, and both condensers were rinsed with ether. The contents of the receiving f l a s k were dilut e d with 100 ml of water, and the mixture was extracted with 3 x 150 ml portions of ether. The combined ether extracts were washed with 100 ml of water, dried over sodium sulphate, f i l t e r e d , and evaporated i n vacuo at room temperature to give 3.6 g (38%) of 129 as a yellow c r y s t a l l i n e s o l i d . This was used without further p u r i f i c a t i o n . 4a3,5,8,8a3-Tetrahydro-2,3,6,7-Tetramethyl-i,4-naphthoquinone (97). Following the procedure reported by Fieser and Chang 5 8a mixture of 1.65 g (0.012 mole) of 2,3-dimethyl-l,4-benzoquinone (129) and 2.92 g (0.036 mole) of 2,3-dimethyl-l,3-butadiene i n 5 ml of ethanol was refluxed for 10 hours. On cooling, the reaction, mixture s o l i d i f i e d to a mass. R e c r y s t a l l i z a t i o n from ethanol yielded 2.11 g (81%) of 97_ as small, colorless c r y s t a l s , mp 104.5 - 105° ( l i t 5 8 1 0 5 - 106.5°). Distinguishing spectral features were as follows: uv max (methanol) - 155 -253 (e 9420), 330 nm (e 115); I r (CCl^) 5.95 (C=0)y; nmr (CCl 4)x 6.95 (m, 2, and C g a methines), 7.85 (m, 4, C,. and C g methylenes), 8.07 (s, 6, C„ and C_ methyls), 8.35 (s, 6, C, and C., methyls); Z J D / mass spectrum (70 eV) m/e parent 218. Photolysis of Adduct 97_ i n Benzene. A solution of 600 mg (2.8 mmol) of 97_ i n 200 ml of benzene was placed i n a Pyrex vessel and i r r a d i a t e d with l i g h t of wavelength A. >^  340 nm. The reaction was monitored by a n a l y t i c a l glpc (column A, 160°, 150 ml/min.), which showed complete reaction of 9_7_ had occurred after 6.5 hours with the formation of one photoproduct. After evaporation of solvent, the residue was subjected to column chromatography on 40 g of S i l i c a Gel using 20% ethyl acetate/benzene as the eluting solvent. This resulted i n the i s o l a t i o n of 137 mg (23%) of c r y s t a l l i n e material, mp 55 - 56°, i d e n t i f i e d as 5-hydroxy-3,4,8,9-tetramethyltricyclo [4.4.0.0 ' Jdeca-3,7-diene-2-one (130) on the basis of the following spectral data: uv max (methanol) 252 (e 8600), 325 nm (e 80); i r (KBr) 2.94 (OH), 6.05 (C=0)y; nmr (CDCl^T 4.42 (m, 1, v i n y l H), 7.13 (d, 1, J=3Hz, C, methine), 7.70 (s, 1, disappears on adding D o0, o Z OH), 7.84 (m, 1, methine), 8.16 (s, 3, C^ methyl), 8.25 (d, 3, J=1.5Hz, C g methyl), 8.30 (s, 3, C 3 methyl), 8.59 (d, 1, J=3Hz, o n e o f the C^Q methylenes), 8.65 (s, 1, the other methylene), 8.93 (s, 3, C Q methyl)5 mass spectrum (70 eV) m/e parent 2 1 8 . - 156 -Anal. Calcd. for c 1 4 H 1 8 0 2 i c» 7 7 - 0 3 5 H» 8- 3 1> Found: C, 77.10; H, 8.44. Photolysis of Adduct 97_ i n t e r t - B u t y l Alcohol. Compound 9_7 (110 mg, 0.5 mmol) i n 20 ml of tert-butanol was placed i n a quartz tube and i r r a d i a t e d with l i g h t of wavelength _> 340 nm. A n a l y t i c a l glpc (column A, 170°, 150 ml/min) showed complete reaction of 91_ after 4.5 hours and the formation of two photoproducts i n a r a t i o of about 2:1; the products were isolated by preparative glpc (same conditions as above). The minor product, 17 mg (15%), was i d e n t i f i e d as enone-alcohol 130, i d e n t i c a l i n a l l properties (glpc retention time, mp, spectral data) to that isolated from the photolysis of 97_ i n benzene. Of the major product, 36 mg (33%) were obtained which, on r e c r y s t a l l i z a t i o n from petroleum ether (68°), formed colorless c r y s t a l s , mp 88.5 - 89°. On the basis of the following spectral data, t h i s product was assigned the structure 3,4,8,9-tetramethyltricyclo ^ 4.4.0.03'7] dec-8-ene-2,5-dione (131): uv max (methanol) 290 nm (e 57); i r (KBr).5.74 (C=0)y; nmr (CDC13)T 7.24 (dd, 1, J. =1.5Hz, 3C ,=2Kz, C, methine), 7.5 - 7.8 (complex 6,4 6,1 o m u l t i p l e t , 4), 7.73 (dd, 1, J. =1.5Hz, J=7Hz, C. methine), 8.25 4,0 4 (s, 3, C g or C g methyl), 8.40 (s, 3, C g or CQ methyl), 8.85 (s, 3, C 3 methyl), 9.09 (d, 3, J=7Hz, C^ methyl); mass spectrum (70 eV) m/e parent 218. Anal. Calcd. for C..H l o0 o: C, 77.03; H, 8.31. Found: C, 76.80; 14 lo 2 H, 8.36. - 157 -Base-Catalyzed Deuterium Exchange of Ene-Dione J_31. A so l u t i o n of 15 mg (0.07 mmol) of ene-dione 131 i n 0.5 ml of CDCl^ i n an nmr tube was treated with 10 drops of a 1.2 N s o l u t i o n of potassium hydroxide dissolved i n deuterium oxide. The tube was shaken repeatedly and the exchange was followed by nmr spectroscopy, which showed a slow exchange of the C^ methine proton. A f t e r 14 days, the exchange was complete, and nmr showed 1 proton had exchanged. The differences between the nmr of deuterio-ene-dione 131 and protio-ene-dione 131 were as follows: the doublet of doublets at T7.24 (C^ methine) i n the l a t t e r collapsed to a doublet (J=2Hz); the s i g n a l at Tl.13 (due to C^ methine) disappeared; the doublet at 9.09 (C^ methyl) collapsed to a broad s i n g l e t . Other features remained unchanged. Attempted Thermolysis of Enone Alcohol 130 under Photolysis Conditions. Enone alcohol 130 (15 mg, 0.07 mmol) i n 3 ml of tert-butanol was heated to 65° (representing extreme conditions) i n a sealed ampoule. The mixture was tested a f t e r 23 hours and 45 hours by a n a l y t i c a l glpc (column A, 160°, 150 ml/min). No detectable reaction had occurred, and enone alcohol 130 was recovered unchanged. Attempted Photolysis of Enone Alcohol 130 i n Benzene. A s o l u t i o n of 50 mg (0.23 mmol) of 130 i n 10 ml of benzene i n the quartz tube was i r r a d i a t e d as usual (X >_ 340 nm). The reaction - 158 -was monitored by glpc (same conditions as above) which showed no detectable reaction after 28 hours. Starting material was recovered unchanged. Photolysis of Enone Alcohol 130 i n tert-Butanol. A solution of 52 mg (0.24 mmol) of 130 i n 10 ml of tert-butanol was i r r a d i a t e d i n the usual manner. The reaction was monitored by glpc (same conditions) which showed complete conversion to ene-dione 131 after 6 hours ( i d e n t i f i c a t i o n based on retention time from glpc co-injection of authentic sample). No intermediate could be detected during the course of the transformation. 2,3-Dicyano-l,4-benzoquinone (135). Using a s l i g h t l y modified procedure of Brook 6 2excess nitrogen dioxide was condensed i n a small fl a s k cooled to l i q u i d nitrogen temperature. The flask was then allowed to warm up slowly, and as the N^O^ melted, i t was added dropwise, with s t i r r i n g , to a magnetically s t i r r e d suspension of 10 g (0.063 moles) of 2,3-dicyanohydroquinone (Aldrich) i n 50 ml of carbon tetrachloride contained i n a 125 ml Erlenmeyer f l a s k . The greenish suspension rapidly became yellow; s t i r r i n g was continued an additional % hour. After the excess ^ 0 ^ was removed as N0^ with a stream of nitrogen, the product was collected by suction f i l t r a t i o n . Y i e l d was 9.6 g (97%) of quinone 135 as a yellow s o l i d , mp 176 - 178° ( l i t 6 2 1 7 8 - 180°). This material - 159 -was found to be s u f f i c i e n t l y pure for subsequent Diels-Alder reactions and was used without further p u r i f i c a t i o n . 4a8,8aB-Dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-l,4-naphthoquinone (98). Following the reported procedure of A n s e l l , et a l 8 3 t o a solution of 2.5 g (0.016 mole) of 2,3-dicyano-l,4-benzoquinone (135) i n 100 ml of benzene-ethanol (9:1 v/v) was added 2.5 g (0.030 mole) of 2,3-dimethyl-1,3-butadiene. The reaction mixture was allowed to stand at room temperature for 18 hours, after which i t was evaporated to dryness. The r e s u l t i n g s o l i d was r e c r y s t a l l i z e d twice from acetone/ petroleum ether (68°) to give pale yellow cr y s t a l s of 98_, mp 158 -159° ( l i t 6 3 1 5 7 - 158°). The y i e l d was 2.85 g (75%), and distinguishing spectral features were as follows: i r (KBr) 4.43 (weak, C=N), 5.79 and 5.86 (C=0)y; nmr (CDCl 3)x 3.06 (s, 2, C 2 and C 3 v i n y l s ) , 7.28 (br s, 4, C c and C 0 methylenes), 8.30 (s, 6, C, and C, methyls); D O O / uv max (methanol) 225 nm (£ 8900), a long featureless t a i l i n g absorption (e at 340 nm = 93); mass spectrum (70 eV) m/e parent 240. Photolysis of Compound 98 i n tert-Butanol. A solution of 485 mg of j)8_ (2 mmol) i n 250 ml of 10% benzene-tert-butanol was irr a d i a t e d and the reaction followed by glpc (column C, 180°, 160 ml/min) which showed no s t a r t i n g material remaining a f t e r 3 hours. Evaporation of solvents l e f t a pale brown residue which, on t r i t u r a t i o n with benzene followed by f i l t r a t i o n , l e f t 265 mg of - 160 -colorless s o l i d . R e c r y s t a l l i z a t i o n of the s o l i d from acetone-petroleum ether (68°) gave 240 mg (50%) of 1,6-dicyano-8,9-dimethyl-5-T 5 9l hydroxytricyclo 4.4.0.0 ' Jdeca-3,7-diene-2-one (136) as colorless c r y s t a l s , mp 188 - 190°. The structure was deduced from the following spectral c h a r a c t e r i s t i c s : i r (KBr) 2.90 (OH), 4.41 (weak, CSN), 5.87 (C=0)y; nmr (acetone-dg)! 2.99 (d, 1, J=10Hz, C 4 v i n y l ) , 3.69 (d, 1, J=10Hz, C 3 v i n y l ) , 4.07 (m, 1, C ? v i n y l ) , 7.19 (s, 1, disappears on adding D2O, OH), 7.67 (d, 1, J=13Hz, one of C^Q methylenes), 7.7 - 8.2 (m, other C^Q methylene and acetone resonances), 8.03 (d, 3, J=1.5Hz, Cg methyl), 8.73 (s, 3, C g methyl); uv max (methanol) 239 (e 3800), t a i l i n g absorption (e at 315 = 141); mass spectrum (70 eV) m/e parent 240. Anal. Calcd. for C 1 4 H 1 2 N 2 ° 2 : C, 69.99; H, 5.03; N, 11.66. Found: C, 69.87; H, 4.96; N, 11.63. Meanwhile, the benzene extract was evaporated to give 287 mg of pale yellow o i l . Following column chromatography ( S i l i c a Gel, 33% ethyl acetate-benzene), 175 mg of 137 were obtained as a colorless o i l , the mass spectrum of which showed a parent ion at 314, indicating the addition of one molecule of tert-butanol had occurred. See discussion for spectral data and conclusions. , Photolysis of Enone Alcohol 136 i n tert-Butanol. , A solution of 28 mg (0.12 mmol) of 136 i n 10 ml of tert-butanol was i r r a d i a t e d for 18 hours. After evaporation of the solvent, i r and nmr spectra showed no 136 remained; these spectra were - 161 -i d e n t i c a l to those of 137 obtained from the photolysis of 9J8 i n tert-butanol. Photolysis of i n A c e t o n i t r i l e . A solution of 80 mg (0.33 mmol) of 9j8 i n 25 ml of a c e t o n i t r i l e was photolyzed for 2 hours. After evaporation i n vacuo, followed by chromatography (alumina, ether) 47 mg (59%) of enone alcohol 136 were obtained, i d e n t i f i e d by melting point, i r and nmr spectra. No other product was detected or isol a t e d . Photolysis of 9_8 i n Methanol. A solution of 97 mg (0.4 mmol) of 9_8 i n 50 ml of anhydrous methanol was irr a d i a t e d for 1 hour. Evaporation of solvent followed by column chromatography gave 35 mg of unreacted 9_8 and 20 mg (32%, based on recovered s t a r t i n g material) of enone alcohol 136. Again, no other product was detected. Attempted Thermolysis of Enone Alcohol 136. Compound 136 (25 mg, 0.1 mmol) was heated at 185° i n a sealed tube for 14 hours. The dark brown product was extracted with chloroform which gave 21 mg of a brown gum. I r showed the presence of carbonyl stretches at 5.68, 5.80 sh and 5.85. However, t i c ( S i l i c a Gel, 25% ethyl acetate/benzene) showed the presence of several products, so the material was not investigated further. - 162 -2,3-Dichloro-5,6-dicyano-l,4-benzoquinone ( 1 4 1 ) 6 6 A mixture of 5 g (0.031 moles) of 2,3-dicyanohydroquinone (Aldrich) i n 70 ml of 50% aqueous hydrochloric acid was placed i n a 250 ml Erlenmeyer f l a s k equipped with a magnetic s t i r r i n g bar and warmed to 35°. Then, over a 45 minute period, 9.4 g of concentrated n i t r i c a c i d was added with s t i r r i n g ; the mixture foamed a b i t and became yellow. Af t e r the add i t i o n was complete, s t i r r i n g was continued for an a d d i t i o n a l hour. The mixture was then f i l t e r e d and washed with carbon t e t r a c h l o r i d e , r e s u l t i n g i n a d i r t y yellow s o l i d . D i s s o l v i n g t h i s i n hot benzene, t r e a t i n g with Norit, f i l t e r i n g and f i n a l l y evaporating jthe solvent l e f t 6.8 g (96%) of yellow s o l i d 141, mp 202 - 204° ( l i t ! 6 2 1 2 - 213°); i r (KBr) no C-H s t r e t c h , 4.42 (C=N), 5.94 (C=0), 12.5 (C-Cl)y. The product was used i n the next step without further p u r i f i c a t i o n . 2,3-Dichloro-4ap,8a8-dicyano-6,7-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (99). To a s o l u t i o n of 4.16 g (0.018 mole) of 141 i n 100 ml of methanol was added 1.5 g (0.019 mole) of 2,3-dimethyl-l,3-butadiene. The re a c t i o n mixture r a p i d l y became green i n color and s l i g h t l y warm. A f t e r allowing the s o l u t i o n to stand at room temperature for 1 hour, solvent was evaporated to give a greenish-brown residue. R e c r y s t a l l i z a t i o n from methanol resulted i n 4.5 g (81%) of green colored c r y s t a l s of 99, mp 178 - 179°, i d e n t i f i e d by the following properties; - 163 -i r (KBr) 5.82 (C=0), 12.62 (C-Cl)y; nmr (CDC1 3)T 7.23 (s, 4, C 5 and Cg methylenes), 8.28 (s, 6, v i n y l methyls); uv max (methanol) 270 nm (e 6000) and a long featureless absorption from 300 to 360 (e at 340 nm = 400); mass spectrum (70 eV) m/e parent 308, 310, 312. Anal. Calcd. for C 1 4 H 1 0 C 1 2 N 2 ° 2 : C' 5 4 ' 3 9 ; H> 3 - 2 6 5 c l» 22.94; N, 9.06. Found: C, 54.58; H, 3.26; C l , 22.70; N, 9.18. Photolysis of 97 i n tert-Butanol. A solution of 600 mg (2 mmol) of S>9_ i n 300 ml tert-butanol was i r r a d i a t e d , and the course of the reaction was monitored by glpc (column C, 180°, 180 ml/min) which showed complete reaction of s t a r t i n g material after 24 hours. Evaporation of the now yellow solution resulted i n a reddish residue which was dissolved i n 100 ml of ether, washed with 4 x 15 ml water, 4 x 15 ml sodium bicarbonate, and 4 x 15 ml water. After drying (Na^SO^), the ether was evaporated to give 400 mg of pale yellow s o l i d . R e c r y s t a l l i z a t i o n from methanol-water twice gave 250 mg (42%) of colorless needles, mp 226 - 228°, i d e n t i f i e d as 3,4-dichloro-l,6-dicyano-8,9-diraethyl-5-hydroxytricyclo ,o.o5>9 4.4.0.0 ' deca-3,7-diene-2-one (142) on the basis of the following spectral data: i r (KBr) 2.92 (OH), 5.90 (C=0), 12.45 (C-Cl)y; nmr (acetone-d,)T 4.07 (m, 1, C-, v i n y l ) , 7.07 o / (br s, 1, disappears on adding D2O, OH), 7.47 and 7.81 (each d, 2, J=14Hz, C 1 Q methylenes), 8.02 (d, 3, J=1.5Hz, C g methyl), 8.67 (s, 3, C g methyl), the T values for the methylenes were calculated 5 - 164 -uv max (MeOH) 265 nm (e 9100); mass spectrum (70 eV) m/e parent 308, 310, 312. A sample was sublimed at 190° and 0.01 tor r to give an a n a l y t i c a l sample. Anal. Calcd. for c 1 4 H 1 0 c l 2 N 2 O 2 : °' 5 4 * 3 9 ; H» 3-26'> c l» 22.94; N, 9.06. Found: C, 54.13; H, 3.15; C l , 22.92; N, 8.76. 2,3-Dicarbomethoxy-l,4-benzoquinone (145). Following the procedure of A n s e l l , et a l 6 7 5 g (0.031 mole) of 2,3-dicyanohydroquinone (Aldrich) was added to a solution of 40 g of potassium hydroxide i n 40 ml of d i s t i l l e d water and the mixture refluxed for 75 minutes under a nitrogen atmosphere. The now dark mixture was then a c i d i f i e d with excess, ice cold 7N s u l f u r i c acid and extracted with s i x 50 ml portions of ethyl acetate. After drying (Na2S0^), f i l t r a t i o n , and evaporation of solvent, 5.3 g of l i g h t brown s o l i d was obtained. R e c r y s t a l l i z a t i o n from water gave 2.4 g (39%) of 3,6-dihydroxyphthalic acid (143), mp 214.5 - 216° ( l i t 6 7 213° dec) as a l i g h t brown s o l i d . This was e s t e r i f i e d as follows: a mixture of 2.4 g of di a c i d i n 50 ml of methanol plus 3 ml cone s u l f u r i c acid was refluxed .overnight. The methanol was then removed i n vacuo leaving a damp white s o l i d residue which was washed with water and collected by suction f i l t r a t i o n . The f i l t e r cake was repeatedly washed with small portions of cold d i s t i l l e d water u n t i l the washings were neutral. R e c r y s t a l l i z a t i o n from water gave 1.19 g (43%) of 3,6-dihydroxydimethylphthalate (144) as colorless c r y s t a l s , - 165 -mp 131 - 133° ( l i t ? 7 1 4 1 - 142°). The above diester was suspended i n 40 ml of carbon tetrachloride. Then, with s t i r r i n g , excess dinitrogen tetroxide (nitrogen dioxide condensed into a f l a s k at -196°) was added dropwise, whereupon the suspended s o l i d rapidly became yellow. After 5 minutes of additional s t i r r i n g , the product was collected by suction f i l t r a t i o n . The y i e l d of 2,3-dicarbomethoxy-l,4-benzoquinone (145) was 1.15 g (97%, o v e r a l l y i e l d was 16.5% from dicyanohydroquinone), obtained as a yellow s o l i d , mp 153 - 155° after r e c r y s t a l l i z a t i o n from benzene - petroleum ether ( l i t ? 7 1 5 5 - 157°). 4aB,8a8-Dicarbomethoxy-6,7-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (100)? 3 A solution of 1.15 g (5.1 mmol) of quinone 145, 1 g (12 mmol) of 2,3-dimethyl-l,3-butadiene and 50 ml of anhydrous methanol was refluxed for 2.5 hours and then s t i r r e d at room temperature for 4 more hours. Evaporation of solvent yielded a yellow o i l which was chromatographed on 75 g of .nuetral Alumina using ethyl acetate as the eluting solvent. Two components were obtained; the f i r s t to be eluted consisted of 530 mg of crude adduct 100. R e c r y s t a l l i z a t i o n from benzene-petroleum ether (68°) yielded 400 mg (26%) of 100 as colorless c r y s t a l s , mp 132 - 133.5° ( l i t ? 3 1 3 2 - 135°). Spectral c h a r a c t e r i s t i c s were: i r (KBr) 5.79, 5.91 (C=0), 6.21 (C=C)y; - i66 -nmr (CDCl ^ T 3.27 (s, 2,, and v i n y l s ) , 6.23 (s, 6, methoxy methyls), 7.28 (br s, 4, C c and C Q methylenes), 8.38 (br s, 6, C. and C, methyls); uv max (methanol) 229 (e 7900), a featureless sloping absorption from 300 - 350 nm (e at 340 = 147). The second component (490 mg) was i d e n t i f i e d as crude 2,3-dicarbomethoxy-5,8-dihydro-6,7-dimethyl-1,4-naphthoquinol (146) : nmr (CDCl ^ T 0.73 (s, 2, disappears on adding D2O, OH), 6.1 (s, 6, ester methyls), 6.77 (s, 4, C,- and Cg methylenes), 8.22 (s, 6, v i n y l methyls). R e c r y s t a l l i z a t i o n from ethanol - petroleum ether (68°) gave pure 146 as colorless needles, mp 187 - 188° ( l i t 6 3 1 8 9 - 190°). Photolysis of Adduct 100. A solution of 190 mg (0.62 mmol) of 100 i n 50 ml of benzene was i r r a d i a t e d for 5 hours, after which the uv spectrum of the reaction mixture remained unchanged. Evaporation of solvent i n vacuo resulted i n a residue which showed two main components on t i c ( S i l i c a Gel; 40% ethyl acetate-benzene). Column chromatography on S i l i c a Gel (40% ethyl acetate-benzene) gave 110 mg (58%) of ene-dione 148 and 15 mg (8%) of enone alcohol 147, both as colorless s o l i d s . In a second experiment, 80 mg (0.26 mmol) of 100 i n 40 ml of benzene were i r r a d i a t e d for a shorter length of time (2.5 hrs.). Workup as above gave 28 mg (35%) of 148 and 24 mg (30%) of 147. These structures were assigned on the basis of the following spectral data: r 3 gi -for 148, 1,6-dicarbomethoxy-8,9-dimethyltricyclo.14.4.0.0 ' J dec-7-ene-2,5-dione: i r (KBr) 5.58, 5.72, 5.78, 5.86 (C=0)y; nmr (CDC1 3 )T 3.51 (m, 1, C 7 v i n y l ) , 6.22 and 6.26 (each s, 6, Cj and Cg carbomethoxy methyls), 6.2 - 6.4 (m, I, C^ methine), 7.32 (dd, 1, J=5Hz, 16Hz, C 4 exo-methylene), 7.53 (dd, 1, J=4Hz, 16Hz, C^ endo-methylene), 7.76 (d, 1, J=14Hz, C 1 Q methylene) 8.12 (d, 3, J=lHz, C. v i n y l methyl), 8.14 (d, 1, J=14Hz, C,„ methylene), 8.75 o • lU (s, 3, Cg methyl); the chemical s h i f t s of the C^ exo and endo-protons and the C^Q methylenes were calculated? 2 Uv max (methanol) 300 (e 165), sh 313 nm (e 134); mass spectrum (70 eV) m/e parent 306. R e c r y s t a l l i z a t i o n from benzene-petroleum ether (68°) gave an a n a l y t i c a l l y pure sample, mp 96.5 - 97°. Anal. Calcd. for C.,H100,: C, 62.74; H, 5.92. Found: C, lo lo o 63.03; H, 5.89. [ 5 o"| for 147, 1,6-dicarbomethoxy-8,9-dimethyl-5-hydroxytricyclo [4.4.0.0 ' J deca-3,7-diene-2-one: i r (KBr) 2.92 (OH), 5.80, 5.90 .(C=0)y; nmr (CDC1 3 ) T 3.41 (d, 1, J=10Hz, C 4 v i n y l ) , 3.78 (d, 1, J=10Hz, C 3 v i n y l ) , 4.17 (m, 1, C^ v i n y l ) , 6.27 (s, 6, carbomethoxy methyls), 7.22 (s, 1, disappears on adding D2O, OH), 8.03 (br s, 2, methylenes), 8.19 (d, 3, J=1.5Hz, C g methyl), 8.86 (s, 3, C g methyl), the C3 and C 4 v i n y l resonance s h i f t s were calculated ; uv max (methanol) 241 (e 3630), long sloping t a i l (e at 325 =* 50); mass spectrum (70 eV) m/e parent 306. R e c r y s t a l l i z a t i o n from benzene-petroleum ether - 168 -(68°) gave an a n a l y t i c a l l y pure sample, mp 158.5 - 159? Anal. Calcd. for C..H1Q0.: C, 62.74; H, 5.92. Foung: C, lo lo o 62.85; H, 5.89. Thermolysis of Ene-Dione 148. Product 148 (20 mg, 0.065 mmol) was placed i n a sealed ampoule and heated for 3.5 hours at 190°. The golden product was dissolved i n chloroform and chromatographed through a short column of alumina (chloroform), giving 19 mg of a pale yellow o i l . Chromatography on S i l i c a Gel (40% ethyl acetate-benzene) gave 10 mg (50%) of enone alcohol 147, whose i r and nmr spectra were i d e n t i c a l to those of material obtained from photolysis of 100 i n benzene. Photolysis of Adduct 100 i n tert-Butanol. A solution of 106 mg (0.35 mmol) of 100 i n 25 ml of 5% benzene-tert-butanol was irr a d i a t e d for 5 hours. Evaporation of solvent followed by column chromatography (40% ethyl acetate-benzene, S i l i c a Gel) gave two components. The f i r s t f r a c t i o n , 48 mg, proved to be a complex mixture of many products ( t i c , i r and nmr), a r i s i n g possibly from abstraction of a carbomethoxy methyl hydrogen atom and was not investigated further. The second component, 41 mg, was i d e n t i f i e d as enone alcohol 147 on the basis of i t s melting point and spectral data. This represented a y i e l d of 39%. * - 169 - 1 . Synthesis of Duroquinone (154). Duroquinone was prepared i n three steps following the procedure reported by Smith 6 9 A. Dinitrodurene. A solution of 13.4 g (0.1 mole) of durene (freshly r e c r y s t a l l i z e d from methanol) i n 100 ml of chloroform was added to 75 ml of concentrated sulphuric acid contained i n a 1 l i t r e Erlenmeyer f l a s k . After cooling the mixture below 10° C using an ice-salt-water slush, 16 g (11 ml) of fuming n i t r i c acid were added dropwise with s t i r r i n g over a 20 minute period. As soon as the addition was complete, the reaction mixture was transferred to a separatory funnel and the lower acid layer was drawn off. The chloroform layer was added to 500 ml of saturated sodium bicarbonate solution, after which the layers were separated. The organic phase was washed with water, dried over calcium chloride, f i l t e r e d and concentrated i n vacuo. When crystals began to form, 150 ml of hot ethanol were added to the mixture, which was then c h i l l e d i n the r e f r i g e r a t o r . The s o l i d was f i l t e r e d and washed twice with cold ethanol. The mother liquor was concentrated, and a second crop of c r y s t a l s was collected. Total y i e l d was 18.65 g (83%). B. Reduction of dinitrodurene. The dinitrodurene obtained above (18.65 g, 0.083 mole) was dissolved i n 250 ml of g l a c i a l acetic acid i n a 2 l i t r e f l a s k , and - 170 -the solution was heated to b o i l i n g . Meanwhile a solution of 175 g of stannous chloride i n 200 ml cone hydrochloric acid was also heated to b o i l i n g . The heat was removed, and the stannous chloride solution was poured very c a r e f u l l y into the dinitrodurene solution over 10 minutes. A vigorous reaction took place. After s t i r r i n g for 15 minutes the mixture was cooled and the s o l i d which precipitated was f i l t e r e d and washed with ethanol, ether, and then was dried. Y i e l d was quantitative (33 g) and consisted of ^ ( C H ^ (NH2*HC1) •SnCl.. 4 C. Duroquinone. A solution of 193 g of f e r r i c chloride hexahydrate i n 125 ml water and 8 ml cone hydrochloric acid was prepared i n a 500 ml Erlenmeyer f l a s k , and to i t was added, with s t i r r i n g , the t i n compound prepared above, which resulted i n a thick yellow suspension. After s t i r r i n g overnight, the mixture was f i l t e r e d , and the s o l i d was a i r dried for an hour. After t h i s , the s t i l l s l i g h t l y damp s o l i d was dissolved i n 400 ml of petroleum ether (68°) and the residual water was removed with calcium chloride. After f i l t r a t i o n , the bright yellow solution was evaporated to dryness. The crude yellow s o l i d was r e c r y s t a l l i z e d from petroleum ether (68°) to give b r i l l i a n t yellow needles of duroquinone (154); mp 111 - 112°. Y i e l d was 10.2 g (62% from durene). « I - 171 -2,3, 4aS,56,88,8a3-Hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (101). A mixture of 1.6 g (9.8 mmol) of duroquinone (154), 2 g (24.4 mmol) of freshly d i s t i l l e d trans,trans-2,4-hexadiene, and a few crystals of hydroquinone was heated i n a sealed Pyrex tube at 190° for 20 hours. The dark reaction mixture was dissolved i n acetone and evaporated i n vacuo, r e s u l t i n g i n a dark brown gum. Extraction with refluxing methanol, followed by evaporation of solvent and preparative glpc (column A, 160°, 160 ml/min) yielded 120 mg (5%) of adduct 101, which upon r e c r y s t a l l i z a t i o n from petroleum ether (30 - 60°) formed pale yellow needles, mp 103 - 104°, and exhibited the following properties: uv max (methanol) 251 (e 8700), 340 nm (e 70); i r (KBr) 5.99 (C=0), 6.13 (C=C)y; nmr ( C C l ^ T 4.58 (s, 2, v i n y l s ) , 7.17 (q, 2,. J=7Hz, C c and C Q methines), 8.07 (s, 6, C. and C„ methyls), 8.93 (s, 6, C, - > o . 2 5 ita and C Q methyls), 9.12 (d, 6, J=7Hz, C c and C 0 methyls); mass spectrum oa ^ J O (70 eV) m/e parent 246. Anal. Calcd.' for C.,Ho.0_:- C, 78.01; H, 9.00. Found: C, 77.75; l o 22 2 H, 9.11. Photolysis of Adduct 101. A solution of 110 mg (0.49 mmol) of 101 i n 50 ml of benzene was placed i n a quartz tube and irr a d i a t e d with l i g h t of wavelength >_ 340 nm. The reaction was monitored by glpc (column A, 160°, 160 ml/min), which showed the formation of two new products at the expense of 101. - 172 -After 3 hours, 101 had completely reacted, and the two products 155 and 156 remained i n a r a t i o of 1:2 (determined by weighing glpc traces). Evaporation of solvent followed by column chromatography (10 g S i l i c a Gel, 10% ethyl acetate/benzene) afforded 62 mg (56%) of 156 and 27 mg (24.5%) of 155 whose structures were assigned on the basis of the following properties: for compound 156, 1,3,4,6,7,10-hexamethyltricyclo [4.4.0.0 3' 1 0] dec-8-ene -2,5-dione: colorless o i l ; uv max (methanol) 290 nm (e 68); i r (neat) 5.66, 5.85 (C=0)y; nmr (CDCl-)x 4.03 (dd, 1, J D =10Hz, J Q = 3 o , y o , / 5.5Hz, C Q v i n y l ) , 4.49 (dd, 1, Jn Q=10Hz, Jn =1.5Hz, C„ v i n y l ) , o 9,o 9,/ 9 7.30 (q, 1, J=7.5Hz, C 4 methine), 7.82 (m, 1, C ? methine), 8.98 (s, 3, methyl), 8.98 (d, 3, J=7.5Hz, C 4 methyl), 9.01 (s, 3, methyl), 9.02 (d, 3, J=7.5Hz, C ? methyl), 9.03 (s, 3, methyl), 9.09 (s, 3, methyl). I r r a d i a t i o n at T7.30 leads to the collapse of the doublet at T8.98 to a s i n g l e t . I r r a d i a t i o n at T7.82 leads to the collapse of the doublet at X9.02 to a s i n g l e t , and to s i m p l i f i c a t i o n of the v i n y l signals to an AB system with a mutual coupling constant of 10Hz. Mass spectrum (70 eV) m/e parent 246. D i s t i l l a t i o n (Kugelrohr) at 0.005 to r r and 65°C yielded an a n a l y t i c a l l y pure sample. Anal. Calcd. for C.,Ho„0o: C, 78.01; H, 9.00. Found: C, lo // / 78.30; H, 9.20. T 5 9l for compound 155, 1,3,4,6,7,10-hexamethyl-5-hydroxytricyclo 4.4.0.0 ' deca-3,7-diene-2-one: colorless c r y s t a l l i n e s o l i d ; mp 156.5 - 157° - 173 -(petroleum ether 68 ); uv max (methanol) 247 (e 5700), broad featureless absorption (e 175 at 340 nm); i r (KBr) 2.88 (OH), 6.05 (C=0)y; nmr (CC14)T 4.15 (m, 1, v i n y l ) , 7.45 (dd, 1, J g g=3Hz, Jg ^=3Hz, methine), 7.67 (s, 1, disappears on adding V^O, OH), 7.79 (m, 1, C 1 Q methine), 8.16 (s, 3, C 3 methyl), 8.25 (br s, 6, and C 7 methyls), 9.20 (s, 3, ^  methyl), 9.29 (d, 3, J=7Hz, C 1 Q methyl), 9.34 (s, 3, C, methyl); mass spectrum (70 eV) m/e parent o 246. Anal. Calcd. for C^H.^O.: C, 78.01; H, 9.00. Found: C, io zz z 78.01; H, 9.01. Thermolysis of Ene-Dione 156. Ene-dione 156 (21 mg, 0.09 mmol) was placed i n a sealed ampoule and thermolyzed for 21 hours at 195°. The crude product was taken up i n chloroform and chromatographed on 5 g of S i l i c a Gel using chloroform as the eluting solvent. In th i s way, a s l i g h t l y yellow o i l was obtained, which was d i s t i l l e d at 70° and 0.005 to r r to give 13 mg (63%) of 2,3,4aB,5,83,8a3-hexamethyl-4a,7,8,8a-tetrahydro-1,4-naphthoquinone (157) as a colorless o i l . Distinguishing spectral features of 157 were as follows: uv max (methanol) 254 (e 11,000), 352 nm (e 70); i r (neat) 5.98 (C=0)u; nmr (CC1 4)T 4.50 (m, 1, v i n y l ) ; 8.07 (s, 6, v i n y l methyls), 8.12 (br s, 3, v i n y l methyl), 8.40 (centre of broad m u l t i p l e t , 1, Cg methine), 8.75 - 9.25 (broad m u l t i p l e t , 2, C 7 methylenes), 8.84 (s, 3, methyl), 9.05 (s, 3, C g a methyl), - 174 -9.37 (d, 3, J=6Hz, C„ methyl); mass spectrum (70 eV) m/e parent 246. o Anal. Calcd. for C1,H„„0o: C, 78.01; H, 9.00. Found: C, lo 22 2 78.16; H, 9.20. 2,3,4aB,5a,8a,8a8-Hexamethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (102). A mixture of 1.6 g (9.8 mmol) of duroquinone (154), 2 g (0.024 mole) of trans,trans-2,4-hexadiene and a few cr y s t a l s of hydroquinone was placed i n a sealed Pyrex tube and heated at 140° for 40 hours. The mixture was cooled and then extracted with hot petroleum ether (68 ). After f i l t r a t i o n and concentration, the solution was c h i l l e d i n the freezer whereupon a crop of unreacted 154 precipitated. After a second f i l t r a t i o n and further concentration, the solution was again c h i l l e d whereupon 400 mg of yellow s o l i d , mp 40 - 42°, were deposited. This s o l i d was collected by suction f i l t r a t i o n and r e c r y s t a l l i z e d twice more from a small amount of petroleum ether (68°). In t h i s way, 246 mg (10%) of 102 could be isolated. This material had a mp o f 47 - 50 and was found to be suitable for photolysis. An a n a l y t i c a l sample could be obtained by preparative glpc (column A, 170°, 150 ml/min) followed by r e c r y s t a l l i z a t i o n from petroleum ether (68°). Adduct 102 thus obtained was pale yellow needles, mp 57 - 58°. The following spectral data support the structure of 102: uv max (benzene) 350 nm (e 83); i r (KBr) 5.94, 6.00 (C=0)y; nmr (CCl^)T 4.57 (s, 2, v i n y l H), 7.85 (q, 2, J=7Hz, C 5 and C g methines), 8.10 (s, 6, C 2 and C 3 methyls), 8.81 (s, 6, C^a and C g a methyls). - 175 -9.02 (d, 6, J=7Hz, C c and C 0 methyls); mass spectrum (70 eV) J O m/e parent 246. Anal. Calcd. for C,,H o o0 o: C, 78.01; H, 9.00. Found: C, lo 2.1 2 77.96; H, 8.86. Photolysis of Adduct 102 i n Benzene. Adduct 102 (130 mg, 0.53 mmol) i n 25 ml of benzene was placed i n a quartz tube and ir r a d i a t e d with 340 nm l i g h t . The reaction was monitored by a n a l y t i c a l glpc (column A, 170°, 150 ml/min) which showed the formation of two new products; one product, subsequently i d e n t i f i e d to be oxetane 160, was observed to buildup rapidly u n t i l i t reached a constant r a t i o with 102 of about 1:1.9 (weight of glpc traces). The other product formed more slowly, at the expense of both 102 and 160, u n t i l after 18 hours of i r r a d i a t i o n , i t was the only detectable product. Evaporation of the solvent yielded 110 mg of pale yellow semi-solid, which was r e c r y s t a l l i z e d from petroleum ether (68°) to give 93 mg of colorless c r y s t a l s . This represented a y i e l d of approximately 95%, after consideration of the material withdrawn during the course of the reaction to monitor i t s progress. An additional r e c r y s t a l l i z a t i o n from petroleum ether (68°) yielded 80 mg of a n a l y t i c a l l y pure material which was i d e n t i f i e d as l,3,4,6,7,10-hexamethyltetracyclo[4.4.0.0 .0 ' J deca-2,5-dione (161) on the basis of the following properties: mp 144 - 146°; i r (CCI.) 5.68, 5.75 (C=0)y; nmr (CCl.)t 7.40 (q, 2, J=7Hz, C 7 and - 176 -C,_ methines), 7.60 (s, 2, C 0 and C. methines), 8.97 (s, 6, C. and C, 10 o 9 1 6 methyls), 9.07 (s, 6, C 3 and methyls), 9.33 (d, 6, J=7Hz, C 7 and C 1 Q methyls); uv max (methanol) 227 (e 333), 299 (e 40), 315 nm (e 33); mass spectrum (70 eV) m/e parent 246. Anal. Calcd. for C.-H.-O.: C, 78.01; H, 9.00. Found: C, lo 22 2 77.82; H, 9.12. Iso l a t i o n of Oxetane 160. A solution of 24  mg (1.0 mmol) of 102 i n 40 ml of benzene was irrad i a t e d as usual, the reaction being followed by glpc (column A, 170° 150 ml/min). The photolysis was interrupted after 4 hours, at which time the r a t i o of products was 160:102:161 = 1:1.9:1.2. After evaporation of solvent, the residue was subjected to preparative glpc (column A, 170° 150 ml/min) from which was isolated 14 mg 160, 46 mg of unreacted 102 and 16 mg of cage compound 161. R e c r y s t a l l i z a t i o n of 160 from petroleum ether (30 -60°) yielded colorless c r y s t a l s , mp 59.5 - 60° deduced to be 2,3,5,6,9,10-hexamethyl-ll-oxatetracyclo |j6.2.1.0^,^.0^'''"^] undeca-2-ene-4-one (160) from the following spectral evidence: i r (KBr) 6.04 (C=0)y; nmr ( C C l ^ T 5.64 (d, 1, J=4Hz, C D methine), 7.40 (d, 1, J=4Hz, C_. methine), 7.78 (q, o / 1, J=7Hz, C & or C g methine), 8.03 (br s, 3, C 2 methyl), 8.33 (br s, 3, C 3 methyl), 8.35 (q, 1, J=7.5Hz, C, or C„ methine), 8.97 (s, 3, C c or C l f t methyl) o 9 _> |0 9.01 (d, 3, J=7Hz, Cg or C g methyl), 9.30 (s, 3, C 5 or C 1 Q methyl), 9.46 (d, 3, J=7.5Hz, C. or C n methyl); uv max (methanol) 266 (e 6100), 325 nm o 9 (e 240); mass spectrum (70 eV) m/e parent 246. Anal. Calcd. for C.,H..0o: C, 78.01; H, 9.00. Found: C, 78.18 l b 22 2 H, 9.05. - 177 -Photolysis of Oxetane _160. A solution of 11.5 mg (0.047 mmol) of 160 i n 4 ml of benzene was irr a d i a t e d as usual, the reaction being monitored by glpc (column A, 170° 150 ml/min) which showed rapid buildup of 102 (after h hour, r a t i o of 160; 102 = 1:1.9). Then at longer i r r a d i a t i o n times, cage compound 161 formed at the expense of both 160 and 102 u n t i l after 12 hours i t remained as the only product. The material isolated was i d e n t i c a l to that obtained from photolysis of 102 i n benzene. Photolysis of 102 i n tert-Butanol. A solution of 10 mg (0.04 mmol) of 102 i n 3 ml of tert-butanol was irr a d i a t e d . Glpc (column A, 170° 150 ml/min) showed gradual formation of cage compound 161; however, no oxetane 160 was observed, and no other product could be detected. Thermolysis of Adduct 102. Compound 102 (10 mg, 0.04 mmol) was placed i n a sealed ampoule and heated at 190° for 9 hours after which time, the dark reaction mixture was dissolved i n chloroform and analyzed .by glpc (column A, 170° 150 ml/min). This showed extensive decomposition to duroquinone and other products had occurred. However, the formation of compound 101 was confirmed by comparison of retention times, and by coinjection. The r a t i o of 102:101 was determined to be 1:3 (weight of glpc traces). 4aB,8aB-Dicyano-5a,8a-dimethyl-4a,5,8,8a-tetrahydro-1,4-naphthoquinone (103). To a solution of 1 g (6.5 mmol) of 2,3-dicyano-l,4-benzoquinone (135) i n 20 ml of benzene-ethanol (9:1 by volume) was added 1 g (12 mmol) of trans,trans-2,4-hexadiene. The mixture was allowed to stand at room temperature for 3 hours. Evaporation of solvent and excess diene yielded - 178 -1.2 g of s o l i d , which on r e c r y s t a l l i z a t i o n from methanol, gave 800 mg (52%) of 103 as pale yellow c r y s t a l s , mp 152 - 153°. Spectral c h a r a c t e r i s t i c s were as follows: i r (KBr) 4.43 (C=N), 5.79 and 5.90 (C=0), 6.23 (C=C)y; nmr (CDCl 3)x 3.01 (s, 2, C £ and C 3 v i n y l s ) , 4.32 (s, 2, Cg and C 7 v i n y l s ) , 6.85 (q, 2, J=7Hz, C,. and Cg methines), 8.69 (d, 6, J=7Hz, C c and C Q methyls); uv max (methanol) 240 (e 6200), j o 352 nm (e 64); mass spectrum (70 eV) m/e parent 240. Another r e c r y s t a l l i z a t i o n (methanol) yielded an a n a l y t i c a l sample of 103, mp 155 - 156°. Anal. Calcd. for C 1 4 H 1 2 N 2 ° 2 : C' 6 9 * 9 9 ; H» 5-03'> N» H.66. Found: C, 70.29; H, 5.25; N, 11.39. Photolysis of 103 i n Benzene. A solution of 412 mg (1.7 mmol) of 103 i n 200 ml of benzene was ir r a d i a t e d as usual, the reaction being monitored by uv spectroscopy which showed complete disappearance of the 352 nm peak and a buildup of a new absorption at 330 nm after 5 hours. Evaporation of solvent followed by column chromatography ( S i l i c a Gel; 30% ethyl acetate-benzene) yielded 253 mg of colorless o i l which c r y s t a l l i z e d on standing. R e c r y s t a l l i z a t i o n from ether-petroleum ether (68°) gave 215 mg (52%) of colorless c r y s t a l s , mp 137.5 - 139 . On the basis of the following spectral data, the compound was i d e n t i f i e d as 5,10-dicyano-6,9-dimethyl-11-oxatetracyclo {6.2.1.01,7.05,1°Jundec-2-ehe-4-one (169) : i r (KBr) 4.43 (CSN) 5.93 (C=0)u; nmr (CDC± 3)T 2.46 (d, 1, J=10Hz, C £ v i n y l ) , 3.73 (d, 1, J=10Hz, C_ v i n y l ) , 5.23 (d, 1, J=4Hz, Cfi methine), 6.83 - 179 -(d, 1, J=4Hz, C, methine), 7.11 (q, 1, J=7Hz, C- or C_ methine), / b y 7.35 (q, I , J=7.5Hz, C, or C 0 methine), 8.60 (d, 3, J=7Hz, C, or C N b y b y methyl), 9.05 (d, 3, J=7.5Hz, or Cg methyl). I r r a d i a t i o n of the doublet at T 9 . 0 5 leads to collapse of the quartet at T 7.35 to a s i n g l e t . I r r a d i a t i o n of the doublet at T 5 . 2 3 causes the doublet at T 6 . 8 3 to collapse to a si n g l e t . I r r a d i a t i o n at T 3 . 7 3 causes the doublet at T 2 . 4 6 to collapse to a si n g l e t . Uv max (methanol) 258 (e 3200), 330 nm (e 66); mass spectrum (70 eV) m/e parent 240. Anal. Calcd. for C 1 4 H 1 2 N 2 ° 2 : C ' 6 9 , 9 9 » H» 5 - 0 3 5 N » H.66. Found: C, 69.93; H, 5.10; N, 11.60. Photolysis of 103 i n tert-Butanol. A solution of 97 mg (0.4 mmol) of 103 i n 50 ml of 10% benzene-tert-butanol was irradiated i n the usual way, the reaction being followed by t i c and uv. After 2 hours, the reaction was complete; evaporation of solvent followed by chromatography ( S i l i c a Gel, 30% ethyl acetate-benzene) yielded 60 mg (62%) of oxetane 169, i d e n t i c a l i n a l l regards with the compound obtained from the benzene photolysis. Attempted Photolysis of Oxetane 169 i n Benzene. A solution of 55 mg (0.23 mmol) of 169 i n 25 ml of benzene was i r r a d i a t e d with l i g h t f i l t e r e d through a Pyrex f i l t e r (transmitting A >^  290 nm). Tic and uv analysis of aliquots showed no reaction had occurred after 10 hours of i r r a d i a t i o n . Starting material was quantitatively recovered. - 180 -Attempted Photolysis of Oxetane 169 i n tert-Butanol. A solution of 47 mg (0.2 mmol) of 169 i n 30 ml of 10% benzene-tert-butanol was irradiated for 22 hours. After t h i s time no new products were detected; oxetane 169 was recovered. - 181 -BIBLIOGRAPHY 1. R.O. Kan, "Organic Photochemistry", McGraw-Hill Book Co., New York, N.Y. 1966. 2. S.J. C r i s t o l and R.L. S n e l l , J. Amer. Chem. S o c , 80, 1951 (1958). 3. G. Buchi and I.M. Goldman, i b i d . , 79, 4741 (1957). 4. P.E. Eaton and T.W. Cole, J r . , i b i d . , 86, 962, 3157 (1964). 5. W.L. D i l l i n g , Chem. Rev., 66, 373 (1966). 6. J. Ipaktschi, Tetrahedron Lett., 3179 (1970). 7. H.E. Zimmerman, Angew. Chem. Int. Ed. Engl., 8^  1 (1969). 8. A. Padwa, Tetrahedron L e t t . , 3465 (1964); C. Walling and V. Kurkov, J. Amer. Chem. S o c , 88, 4727 (1966). 9. P.J. Wagner, Acc. Chem. Res., 168 (1971). 10. R.C. Cookson, E. Crundwell, R.R. H i l l and J. Hudec, J. Chem. S o c , 3062 (1964). . 11. P.E. Eaton and S.A. Cerefice, Chem. Commun., 1494 (1970). 12. J.R. Scheffer, J. Trotter, R.A. Wostradowski, C.S. Gibbons and K.S. Bhandari, J. Amer. Chem. S o c , 93, 3813 (1971). 13. The n — TT nature of the absorption was v e r i f i e d by i t s progressive blue s h i f t i n solvents of increasing p o l a r i t y : hexane, 370 nm; ether, 367 nm; ethyl acetate, 365 nm; acetone, 364 nm; a c e t o n i t r i l e , 362 nm; methanol, 358 nm. 14. C.S. Gibbons and J. Trotter, J. Chem. S o c , Perkin Trans. I I , 737 (1972). - 182 -15. J.R. Scheffer, K.S. Bhandari, R.E. Gayler and R.H. Wiekenkainp, J. Amer. Chem. Soc. , 94., 285 (1972). 16. T.T. Tidwell , i b i d , 92!, 1448 (1970). 17a. N.H. Werstiuk and R. T a i l l e f e r , Can. J. Chem., 48, 3966 (1970); b) S. Banerjee and N.H. Werstiuk, i b i d , 53, 1099 (1975). 18. R.B. Woodward and R. Hoffmann, "The Conservation of O r b i t a l Symmetry", Academic Press, New York, N.Y. 1970. 19a. R.L. C a r g i l l , B.M. Gimarc, D.M. Pond, T.Y. King, A.B. Sears and M.R. W i l l c o t t , J . Amer. Chem. Soc., 92, 3809 (1970); b) For r e l a t e d work and examples, see P.S. Mariano and D. Watson, J. Org. Chem., 39, 2774 (1974) and references c i t e d therein. 20. While these reactions l i k e l y involve b i r a d i c a l intermediates, another p o s s i b i l i t y cannot be discounted at present; namely, a concerted mechanism under the influence of subjacent o r b i t a l c o n t r o l . See J.A. Berson, Acc. Chem. Res. , 5_, 406 (1972); J.A. Berson, i b i d , J_, 152 (1968). 21. U. Klinsmann, J. Gauthier, K. Schaffner, M. Pasternak and B. Fuchs, Helv. Chim. Acta., 55, 2643 (1972). 22. H. Zimmerman7 proposed the formation of a solvated zwitterion i n the photochemistry of cyclohexadienohes, as shown below. The major d i f f e r e n c e , however, between zw i t t e r i o n ji and 35_ i s that jL forms a conjugated system which i s not the case i n 35. - 183 -0 0' P h P h Ph Ph O oe Ph Ph x 23. 24. 25. .26. 27. 28. 29. 30. 31. R.E. Gayler, Ph. D. Thesis, U n i v e r s i t y of B.C. 1973. G. S. Hammond, J. Amer. Chem. Soc. , 77, 334 (1955). J.R. Scheffer, K.S. Bhandari, R.E. Gayler and R.A. Wostradowski, J. Amer. Chem. S o c , 97, 2178 (1975). F.P. Lossing, Can. J. Chem., 50, 3973 (1972). As measured on Dreiding models. E.L. E l i e l , "Stereochemistry of Carbon Compounds", McGraw-Hill Inc., New York, N.Y. 1962. p. 205. H. M.R. Hoffman, Angew. Chem. Int. Ed. Engl., iB, 556 (1969). J. T r o t t e r and C A . Bear, J. Chem. Soc. , Perkin Trans. I I , 330 (1974). Such a s h i f t finds analogy i n the work of S. F a r i d , Chem. Commun. 303 (1970). - 184 -32. For a possible example, see A. Padwa and W. Eisenhardt, J . Amer. Chem. Soc., 93, 1400 (1971). In th i s case, however, i t i s a * negatively charged oxygen atom and not an n - IT excited state which i s responsible for the B-hydrogen abstraction. For other possible examples see E.J. Baum, L.D. Hess, J.R. Wyatt and J.N. P i t t s , J r . , i b i d , 91, 2461 (1969); P.A. Leermakers and G.F. Vesley, i b i d , 85, 3776 (1963); N.J. Turro and T.J. Lee, i b i d , 9_2, 7467 (1970); P. G u l l , H. Wehrli and 0. Jeger, Helv. Chem.  Acta., 54, 2158 (1971). 33. R.A. Cormier, W.L. Schreiber and W.C. Agosta, Chem. Commun., 729 (1972); J. Amer. Chem. Soc. , 9_5, 4873 (1973). 34. P.S. S k e l l and R.G. Doerr, J. Amer. Chem. Soc. , 89, 4688 (1967). 35. J.R. Scheffer and K.S. Bhandari, unpublished r e s u l t s . 36. W. Herz and M.G. Nair, J . Amer. Chem. Soc., 89, 5474 (1967); J.A. Turner, V. Iyer, R.S. McEwen and W. Herz, J. Org. Chem., 39, 117 (1974). 37. P.J. Wagner and G.S. Hammond, Advan. Photochem., _5, 21 (1968). 38. D. Bellus, D.R. Kearns and K. Schaffner, Helv. Chim. Acta., 52, 971 (1969). 39. T. Kobayashi, M. Kurono, H. Sato and K. Nakanishi, J . Amer.  Chem. Soc. , 94, 2863 (1972). 40. S.Wolff, W.L. Schreiber, A.B. Smith, I I I and W.C. Agosta, i b i d , 94, 7797 (1972). - 185 -41. A.B. Smith, I II and W.C. Agosta, Ibi d , _95, 1961 (1973). 42. A.B. Smith, I I I and W.C. Agosta, i b i d , 96, 3289 (1974). 43. For another r e l a t e d example, see A. Marchesini, U.M. Pagnoni and A. P i n e t t i , Tetrahedron L e t t . , 4299 (1973). 44. H.E. Zimmerman and L. C r a f t , Tetrahedron L e t t . , 2131 (1964); D. Bryce-Smith and A. G i l b e r t , i b i d , 2137 (1964). 45. R.C. Cookson, D.A. Cox, and J. Hudec, J. Chem. Soc., 4499 (1961). 46. See r e f . 23 and references contained therein. 47. J.A. Barltrop and B. Hesp, J. Chem. S o c , (C), 1625 (1967). 48. S.P. Pappas and N.A. Portnoy, Chem. Commun., 1126 (1970). 49. E. Bergmann and F. Bergmann, J. Org. Chem., _3» 1 2 5 (1938). 50. I. Fleming and D.II. Williams, "Spectroscopic Methods i n Organic Chemistry", McGraw-Hill Co. London, 1966. 51. K. Nakanishi, "Infrared Absorption Spectroscopy - P r a c t i c a l " , Holden-Day, Inc. San Francisco. 1962. 52. Chemical s h i f t s of AB systems where IT. - T_ I < 6 J 1 T, were 1 A B' AB cal c u l a t e d by using the following formula: til where i s the s h i f t of the i l i n e , r e l a t i v e to TMS, i n Hz. See r e f . 50. 53. W.C. Agosta and S. Wolff, J. Org. Chem., 40, 1665 (1975). 54. See r e f . 23, p. 126. - 186 -55. H. Labhart and G. Wagniere, Helv. Chim. Acta., 42, 2219 (1959); A. Moscowitz, K. Mislow, M.A.W. Glass and C. Djerassi, J. Amer.  Chem. S o c , 84, 1945 (1962); D. Chadwick, D.C. Frost, and L. Weiler, i b i d , 93, 4321, 4962 (1971). 56. Varian A s s o c , "High Resolution NMR Spectra Catalogue", 1963. Spectrum #638. 57. D.M. Golden and S.W. Benson, Chem. Rev., 69, 125 (1969). 58. L.F. Fieser and F.C. Chang, J. Amer. Chem. S o c , 64, 2043 (1942). 59. L.F. Fieser, "Experiments i n Organic Chemistry", 2nd ed., D.C. Heath and Co. , Boston. 1941 p. 228. 60. J. Attenburrow, A.F. B. Cameron, J.H. Chapman, R.M. Evans, B. A. Hems, A.B.A. Jansen and T. Walker, J. Chem. S o c , 1094 (1952). 61. E.L. E l i e l , N.L. A l l i n g e r , S.J. Angyal and G.A. Morrison, "Conformational Analysis", Interscience, New York. 1967. a) p. 42-44 b) p. 186. 62. A.G. Brook, J. Chem. S o c , 5040 (1952). 63. M.F. A n s e l l , B.W. Nash and D.A. Wilson, i b i d , 3012 (1963). 64. D.G.I. Felton and S.F.D. Orr, i b i d , 2170 (1955). 65. The t-butyl protons i n t e r t - b u t y l acetate give r i s e to a sharp single t at T8.55. Varian Associates, "High Resolution NMR Catalogue", 1963. Spectrum #141. 66. D. Walker and T.D.Waugh, J. Org. Chem., 30, 3240 (1965). 67. M.F. A n s e l l , B.W. Nash and D.A. Wilson, J.Chem. S o c , 3028 (1963). - 187 -68. 69. 70. 71. See J.D. Roberts and M.C. Caserio, "Basic P r i n c i p l e s of Organic Chemistry," W.A. Benjamin, Inc., New York, 1965. p. 536 - 538, for discussion and the nmr of 148 •<- 149. Duroquinone (151) was synthesized from durene i n the manner of L.I. Smith, Org. Synth., C o l l . Vol. I I , 254 (1947), as follows: WO, J. Sauer, Angew. Chem. Int. Ed. Engl., J5, 16 (1967). The intermediacy of a b i r a d i c a l i n the Paterno-Buchi reaction has been demonstrated many times i n the l i t e r a t u r e . • For acetone i n the presence of c i s or trans-l-methoxy-l-butene ( i ) leads to the formation of oxetanes i i i - v i i n good y i e l d . The loss of configuration of the o l e f i n i c double bonds was explained by the formation of intermediate iJL, which can suffer bond r o t a t i o n p r i o r to oxetane formation. example, Turro and Wriede 7 2have shown that i r r a d i a t i o n of - 188 -A + CH^ O-CH = CH-C2H5 i , c i s or trans hv l i , R = C 2H 5 or CH30 R'= CH30 or C 2H 5 CXHR — H OCM. I l l --ri -OCHj i v OCH3 -ri --H v H v i 72. N.J. Turro and P.A. Wriede, J. Amer. Chem. Soc. , 92, 320 (1970). 73. For a discussion of the non-concertedness of photochemical cyclobutane formation, see P. de Mayo, Acc. Chem. Res., 4_, 41 (1971) and references cited therein. 74. For reviews see: D.R. Arnold, Advan. Photochem., j i , 301 (1968); also L.L. Muller and J. Hamer, "1,2-cycloaddition Reactions", Interscience, New York 1967, p. 111. - 189 -75. See N.E. Schore and N.J. Turro, J. Amer. Chem. S o c , 97, 2482 (1975) and references therein. 76. Th. Forster, Angew. Chem. Int. Ed. Engl., 8, 333 (1969). 77. J.E. Baldwin and S.M. Krueger, J. Amer. Chem. S o c , 91, 6444 (1969). 78. F.D. Lewis, R.W. Johnson, and D.E. Johnson, J. Amer. Chem. S o c , 96, 6090 (1974). 79. E.L. E l i e l , "Stereochemistry of Carbon Compounds", McGraw-Hill, New York 1962. a) pp. 151, 237 b) p. 248. 80. D.C. Neckers, "Mechanistic Organic Photochemistry", Reinhold Corp.,.New York, 1967. p. 19. 81. F.D. Lewis and T.A. H i l l i a r d , J. Amer. Chem. S o c , 94, 3852 (1972); P.S. Wagner and J.M. McGrath, i b i d , 94, 3849 (1972). 82. H.E. O'Neal and S.W. Benson, J. Phys. Chem., 71, 2903 (1967). 83. F.D. Lewis, R.W. Johnson, and D.R. Kory, J . Amer. Chem. S o c , 95, 6470 (1973). 84. Y.-M. Ngan, M.Sc Thesis, University of B.C. 1975. 85. A. Padwa and W. Eisenberg, J. Amer. Chem. S o c , 94, 5859 (1972) and references therein. 86. P.J. Wagner, i b i d , 89, 5898 (1967). 87. E.C. Alexander and J.A. Uliana, i b i d , 96, 5644 (1974). 88. P.J. Wagner, A.E. Kernppainen and H.N. Schott, i b i d , 9_5, 5604 (1973). - 190 -89. W.C. Agosta and W.E. Schreiber, i b i d , 93, 3947 (1971). 90. CC. Badcock, M.J. Perona, G.O. Pritchard and B. Pickborn, J. Amer. Chem. S o c , 91, 343 (1969); J.C. Dalton and N.J Turro, Ann. Rev. Phys. Chem., 21, 499 (1970); J.A. Barltrop and J.D. Coyle, Chem. Commun., 1081 (1969); P.J. Wagner and R.W. Spoerke, J. Amer. Chem. S o c , 91, 4437 (1969). 91. W.C. Agosta and S. Wolff, i b i d , 97, 466 (1975). 92. F.R. Jensen, L.H. Gale, and J.E. Rogers, i b i d , 90, 5793 (1968) and references ci t e d therein; A. Rassat, Pure Appl. Chem., 25, 623 (1971); L. Kaplan i n "Free Radicals", J.K. Kochi, ed., Wiley, New York, 1973. Ch. 18. 93. F.R. Jensen and CH. Bushweller, J. Amer. Chem. S o c , 91, 3223 (1969); F.R. Jensen and R.A. Neese, i b i d , 93, 6329 (1971) 94. J. Altman, H. Gilboa, D. Ginzburg and A. Loewenstein, Tetrahedron  Le t t . , 1329 (1967). 95. J.T. Gerig and J.D. Roberts, J. Amer. Chem. S o c , 88, 2791 (1966). 96. I t i s known 9 7that cyclohexene i s conformationally more mobile than cyclohexane (E for conformational isomerization for cyclohexene, cl 5.93 kcal mole *; for cyclohexane, 10.3 kcal mole * ) . S i m i l a r l y , the energy b a r r i e r to conformational isomerization i n cyclohex,anone (approx. 6 kcal mole *) i s somewhat l o w e r 6 l b than that for cyclohexane. By analogy then, the presence of 6 sp centres (two double bonds plus 2 carbonyl groups) i n the tetrahydronaphtho-quinone ri n g system may be expected to reduce the energy b a r r i e r to conformational isomerization to the extent that i n adducts - 191 -where hydrogens are located at the bridgehead p o s i t i o n s , conformational r o t a t i o n about the C, -C_ bond i s an e n e r g e t i c a l l y 4a 8a p o s s i b l e process. 97. F.R. Jensen and C H . Bushweller, J . Amer. Chem. S o c , 87, 3286 (1965). 98. J . P. Louwerens, M.Sc. Thesis, U.B.C, 1975. 99. R.A. Cormier and W.C Agosta, J . Amer. Chem. Soc., 96, 618 (1974). 100. The d e a c t i v a t i o n mechanism to ground state adduct i s l i k e l y a hydrogen atom back t r a n s f e r from oxygen to carbon atom Cg, as shown below. This mechanism has been shown to contribute to the i n e f f i c i e n c y observed i n the Norrish I I reacti o n . Such a process i n the case of the D i e l s - A l d e r adducts should be f a c i l i t a t e d when conformational m o b i l i t y i n the b i r a d i c a l intermediate i s r e s t r i c t e d by the presence of bridgehead substituents. 101. K. Biemann, "Mass Spectrometry", McGraw-Hill Book Co., New York. 1962. Ch. 5. - 192 -APPENDIX A C a l c u l a t i o n of Deuterium i n c o r p o r a t i o n 1 0 1 i n ene-dione 117. Required are good mass spectra of deuterated and non-deuterated compounds. > Peak heights i n non-deuterated compound (measured i n mm). mass // height 266 (P) 65 mm 267 (P + 1) 13 mm P + 1 = 20% P (c o r r e c t i o n factor) Peak heights i n deuterated compound. mass # height 266 (P') 28 mm 267 (P + 1)' 250 mm Subtract the c o r r e c t i o n f a c t o r from (P + 1 ) ' . 20% P' = 5.6 (P + 1)" = (P + 1)' - 20% P' = 244.4 % D incorporated = 244.4 x 100 = 89.7% 28 + 244.4 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            data-media="{[{embed.selectedMedia}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
https://iiif.library.ubc.ca/presentation/dsp.831.1-0061060/manifest

Comment

Related Items