Photoisomerization of Acylsilanes to Siloxycarbenes, and Their Reactions with Polar Reagents

The photolysis of acylsilanes in a variety of polar reagents (alcohols, acetic acid, HCN, pyrrole, etc.) is shown to involve formation of isomeric siloxycarbenes which act as nucleophiles and insert into the polar H—X bonds present in the reagents. With alcohols as solvents, mixed acetals of an aldehyde with 1 mol each of silanol and alcohol are formed, but these subsequently undergo dark, acid-catalyzed reactions, by one of two mechanisms which involve either carbon–oxygen or silicon–oxygen bond cleavage. The acid catalyst appears to be a by-product of the photolysis reaction. Kinetic and stereochemical evidence is presented in support of the proposed reaction pathways.