Catalytic asymmetric synthesis of β-hydroxy-α-amino acid esters by direct aldol reaction of glycinate Schiff bases

A catalytic asymmetric synthesis of β-hydroxy-α-amino acid esters was developed using the direct aldol reaction of glycinate Schiff bases with aldehydes. The reaction was catalyzed by heterobimetallic asymmetric complexes without preformation of enol silyl ethers from glycinate Schiff bases. anti-β-Hydroxy-α-amino acid esters were obtained as the major diastereomer in most cases, and moderate enantiomeric excess (up to 76% ee) was achieved for the first time for this type of reaction. Various substrates were also examined to investigate the effects of the protective groups for the amine or for the carboxylic acid moiety in glycine.