Two-carbon homologation of ketones via silylketene acetals:: Synthesis of α,β-unsaturated acids and α-trimethylsilyl δ-ketoacids

The reaction of C,O,O-tris(trimethylsilyl)ketene acetal I with saturated, cyclic and aromatic ketones 2 proceeds smoothly in the presence of titanium chloride to give (E)-alpha,beta-unsaturated carboxylic acids 3 with fairly good stereoselectivity. With alpha, beta-unsaturated ketones 4, alpha-trimethylsilyl delta-ketoacids 5 (syn + anti) are obtained according to Michael-type 1,4 addition. These diastereoisomers are separated and the configurations of 5a are achieved by X-ray molecular analysis. (c) 2005 Elsevier B.V. All rights reserved.