An Improved Procedure for Asymmetric Aldol Additions withN-Acyl Oxazolidinones, Oxazolidinethiones and Thiazolidinethiones

Abstract

Asymmetric aldol additions using chlorotitanium enolates of N-acyl oxazolidinones, oxazolidinethiones and thiazoli­dinethiones proceed with high diastereoselectivity for the ‘Evans syn’ product using one equivalent of titanium tetrachloride, one equivalent of diisopropylethylamine and one equivalent of N-methyl-2-pyrrolidinone. Typical selectivities of 94:6 to >98:2 were obtained using N-propionyl oxazolidinones, oxazolidinethiones and thiazolidinethiones at 0 °C with stoichiometric amounts of aldehyde. Glycolate imides also gave high selectivities and high yields using this procedure.