β-Silylcarbonyl compounds as masked enones

Abstract

β-Trimethylsilylketones and lactones can be brominated (3)→(4) and desilylbrominated (4)→(5) specifically to place a double bond between the carbonyl group and the β-carbon atom to which the silicon had originally been bound. The silyl group therefore is a base- and acid-stable group masking the α,β-unsaturation of enones. Several α-methylene-ketones and -lactones have been prepared in this way. With ketones, the bromination step seems always to introduce bromine mainly or exclusively at the α-position on that side of the ketone on which the β-silyl group is placed, regardless of whether it is the more or the less substituted α-position.