A NEW AND SELECTIVE ALPHA'-BROMINATION OF ALPHA,BETA-UNSATURATED KETONES

Alpha'-Bromination of alpha,beta-unsaturated ketones was carried out via trialkylsilyl dienol ethers with phenyltrimethylammonium tribromide. This reagent, which has not been previously used to brominate such derivatives, allows a high degree of selectivity under mild reaction conditions with the further advantage of not requiring the isolation of the silyl intermediates. The bromination selectivity is dependent on the trialkylsilyl group present on the dienol ether.