Photochemical Reactions. 148th Communication. Photochemistry of Acylsilanes: Preparation, Photolyses, and Thermolyses of α,β-Unsaturated Silyl Ketones

Article abstract of DOI:10.1002/hlca.19860690612

The syntheses, photolyses, and thermolyses of the α,β-unsaturated silyl ketones (E/Z)-7, (E)-8, and (E)-9 are described.On n,?*-excitation (λ > 347 mm), the aforementioned compounds undergo (E/Z)-isomerization followed by γ-H abstraction.The intermediate enols are trapped intermolecularly by siloxycarbenes leading to the dimeric acetals 27A + B, 30A + B, and 31A + B.In addition, the acylsilanes (E/Z)-7 undergo photoisomerization by δ-H abstraction furnishing the acylsilanes 29A + B.Flash vacuum thermolyses (FVT) of (E/Z)-7, (E/Z)-8, and (E)-9 give rise to intramolecular reactions of the siloxycarbene intermediates.Thus, FVT (520 deg) of (E)- and (Z)-7 selectively leads to the enol silyl ethers 32 and (E)-33, respectively, arising from carbene insertion into an allylic C-H bond.FVT of (E/Z)-8 (560 deg) and (E)-9 (600 deg) affords the trienol silyl ethers 34A + B and the cyclic silyl ethers 37A + B, respectively, which are formed by CH insertion of the siloxycarbenes.As further products of (E)-8 and (E)-9, the bicyclic enol ethers 35 and 36 are formed, presumably via siloxycarbene addition to the cyclohexene C=C bond.