Photochemistry of cyclic α-hydroxy ketones. II. The nature of the photoproducts from 8a-hydroxy-4a-methyl-trans- and -cis-octahydronaphthalen-1(2H)-one and an interpretation of the contrast between the photochemistry of these and of analogous steroidal α-hydroxy ketones

Abstract

Photolysis of either 8a-hydroxy-4a-methyl-trans- or -cis-octahydro-naphthalen-1(2H)-one (3 or 4) in benzene gives a 96:4 mixture of the lactones, 5a-methyl-trans- and -cis-octahydro-1-benzoxepin-2(3H)-ones (7 and 8). Photolysis of 3 or 4 in ethanol gives identical mixtures of the lactones 7 and 8 and ethyl (2S*,1R*)- and (2R*,1R*)-2-hydroxy-1-methylcyclo-hexanebutyrates (11 and 12). Photolysis of the 2α-deutero derivatives of 3 or 4 in benzene gives mixtures of the 9a-, 3α-, and 3β-deutero derivatives of lactone 7. The striking difference between these results and those for photolyses of analogous 5α- and 5β-hydroxy 6-keto steroids, which are stereospecific, is interpreted in terms of the greater flexibility in the cases of 3 and 4 of the acyl side chain in the acyl alkyl diradicals formed by α-cleavage. A further difference—the sole formation of lactones on photolysis of the steroidal α-ketols in ethanol—is interpreted in terms of an analogous increased flexibility in the cases of 3 and 4 of the ketene side chain in the hydroxy ketene intermediates formed from the acyl alkyl diradicals.