Consistent with our continued studies on the Ti-Claisen condensation and relevant reactions, we have developed a TiCl₄ – N-methylimidazole-promoted Morita-Baylis-Hillman-type acylation reaction of a,b-unsaturated esters with acyl chlorides through a reactive acyl ammonium intermediate to give a-methylene-b-ketoesters. The present reaction proceeded in a significantly short reaction period, compared with conventional base-mediated methods.
Michael addition of the obtained a-methylene-b-ketoesters, a kind of powerful Michael acceptor, with ketene silyl acetals gave the desired adducts in high yields without any use of catalyst. a-Methylene-b-keto esters and their derivatives were expected to serve achiral and chiral synthons utilizing recent asymmetry reductions.