Photochemical Reactions; Photochemistry of Acylsilanes: 1. Siloxycarbene Formation versus γ-H-Abstraction

Article abstract of DOI:10.1002/hlca.19840670711

The syntheses and the photolyses of the acylsilane 1 and the corresponding methyl ketone 2 are described.On n,?^*-excitation, the silyl ketone 1 as well as the methyl ketone 2 undergo a Norrish type II reaction involving γ-H-abstraction and fragmentation to the diene 12, and acetone (20) or the acylsilane 26, respectively.The methyl ketone 2, but not the acylsilane 1, isomerizes to cyclobutanols (21A-D).Additionally, compound 1 shows photochemical behavior typical of acylsilanes undergoing rearrangement to the siloxycarbene intermediate c.Insertion of c into the O-H-bond of the enol 28 leads to compound 13.Initial trapping of the siloxycarbene c by H2O, however, gives rise to the formation of compounds 16-18.As minor photolysis products of 1, the isomers 14 and (Z)-15 were formed; however, on vapor phase thermolysis (520^o) of 1, compounds 14 and (E/Z)-15 were obtained in 92percent combined yield.To a small extent the acylsilane 1 also undergoes Norrish type I cleavage leading to the acid 19.