Catalytic Asymmetric Direct α-Amination Reactions of 2-Keto Esters: A Simple Synthetic Approach to Optically Active syn-β-Amino-α-hydroxy Esters

The catalytic enantioselective direct α-amination reaction of 2-keto esters with easily available azo dicarboxylates as the nitrogen source and chiral bisoxazoline−copper(II) complexes as the catalyst is presented. The reations proceed with excellent enantioselectivities and high yields. The scope of the reation is demonstrated by the direct amination of a series of 2-keto esters having different substituent patterns. The reaction provides an easy catalytic route to optically active syn-β-amino-α-hydroxy esters, as demonstrated for the synthesis of masked syn-β-amino-α-hydroxy esters (as oxazolidinones) and N-Boc-syn-β-amino-α-hydroxy esters. On the basis of the absolute configuration of the products a tentative model for the transition state is suggested.