Photochemical Reactions. 153th communication . Photochemistry of acylsilanes: Photolyses and thermolyses of α,β‐epoxy silyl ketones

The photolyses and thermolyses of the α,β‐epoxy silyl ketones 5 and 6 are described. On n,π*‐excitation, the silyl ketones 5 and 6 were transformed to the ketone 7 and the ketene 8 in quantitative yield. The formation of 8 may be explained by initial cleavage of the C(α)O bond and subsequent C(1)→C(2) migration of the ( t ‐Bu)Me 2 Si group. In contrast to the acylsilanes 5 and 6 , the photolyses of the analogous methyl ketones 11 and 12 gave a very complex mixture of products. On thermolysis, 5 and 6 yielded the ketone 7 and the acetylenic compound 9 , which were probably formed via a siloxycarbene intermediate. In addition, the 1,3‐dioxle 10 was formed via an initial C(α)C(β) bond cleavage leading to the ylide g and subsequent intramolecular addition of the carbonyl group. The analogous 1,3‐dioxole 13 was obtained on pyrolysis of the methyl ketones 11 and 12 .