Enantiopure (alpha)-Silyl-Substituted (alpha)-Hydroxyacetic Acids Using O-H Insertion Methodology and Boron-Based Asymmetric Reductions

Two routes to optically active (alpha)-silyl-substituted (alpha)-hydroxyacetic acids are described. As a key step, the first utilizes O-H insertion reactions of (R)-and (S)-phenylethanol into benzyl 2-silyl-2-diazoacetates in the presence of [Rh2(OAc)4]. Alternatively, asymmetric reductions of benzyl 2-silyl-2oxoacetates using (R)-Alpine-Borane(registered) afford the corresponding (alpha)-hydroxy esters with up to 91% ee.