Asymmetric synthesis of beta-amino acids through application of chiral sulfoxide

This paper describes asymmetric synthesis of beta -aminophenylpropionic aci d through application of a homochiral sulfoxide auxiliary. High kinetically controlled (3R.2S.R-S)-diastereoselectivity (-60 degreesC) is achieved dur ing addition of the lithium enolate of tert-butyl (+)-(R)-p-toluenesulfinyl acetate to substituted N-(benzylidene)toluene-4-sulfonamides. The reductive cleavage of adduct 3a with sodium amalgam yielded tert-butyl 3-(toluene-4- sulfonamido)-3-phenylpropionate 5a. which was subjected to ester hydrolysis and subsequent detosylation with sodium in liquid ammonia to yield (S)-bet a -aminophenylpropionic acid in good yield and high 91% e.e. (C) 2001 Elsev ier Science Ltd. All rights reserved.