Chiral <i>N</i>‐Phosphonyl Imine Chemistry: Asymmetric Additions of Ester Enolates for the Synthesis of <i>β</i>‐Amino Acids

Abstract

Chiral phosphonyl imines attached by 1-naphthyl protection group were found to react with lithium ester enolates smoothly and give chiral beta-amino esters in good yields (70-88%) and up to excellent diastereoselectivity (>99:1 dr). Triisopropoxytitanium (IV) chloride was found to enhance diastereoseletivity when used as the Lewis acid promoter. The chiral auxiliary can be readily removed by treating with HBr to give free amino esters. The absolute structure has been unambiguously determined by converting one of the products into an authentic sample. This reaction provides an easy access to beta-amino acid derivatives.