9,10-Dihydronaphthalene photocyclization

The corresponding photocyclization of S-arylvinyl sulfides to dihydro-thiophens has been shown to proceed via short-lived thiocarbonyl ylide intermediates, formed in turn by cyclization of triplet excited states. 1-Phenylthio-3,4-dihydronaphthalene (49), for example, affords the colored thiocarbonyl ylide (50)44 the isolated products are derived by processes involving hydrogen abstraction and migration. The greater efficiency of the photocyclization of 2-thioaryloxyenones (51) to dihydrothiophens (52) has been attributed to the additional stabilization afforded to the ylide (53) by the carbonyl group.45 Other similar photocyclizations have been reported.46... 

Photochromism of fulgides is a molecular phenomenon based on the photocyclization of substituted bis-methylenesuccinic anhydrides or fulgides (328) to l,8 -dihydronaphthalene (l,8a-DHN, 329)2 (Scheme 33). 

Further studies and numerous synthetic applications of the photocyclization of enamides have been reported. Irradiation of JV-methyl- and JV-benzyl-cyclohex-l-enecarboxanilide (20) affords a mixture of cis- (21) and trans-phen-anthridones (22).17 JV-Methyl-3,4-dihydronaphthalene-l-carboxanilide is analogously converted into the corresponding benzophenanthridones. Formation of... 

An analogous mechanism must govern also the reverse photoreaction. According to the calculations [58], the photocyclization of l-(3-phenyl) butadiene-1,3 to l,8a-dihydronaphthalene proceeds by the same route. 

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