Glycine and Alanine Imines as Templates for Asymmetric Synthesis of α-Amino Acids

The present paper is an overview of new methods for the asymmetric synthesis of different types of α-amino acids. These methods are based on alkylation and condensation reactions of glycine and alanine imine derivatives, which can be carried out under very mild and simple reaction conditions. The enolates generated from these types of reagents are very soft and can be alkylated in a highly diastereoselective manner, even at room temperature, by using chiral templates or asymmetric PTC conditions. These methodologies afford monoalkylated and dialkylated α-amino acids as well as heterocyclic derivatives. In the case of cyclic imine derivatives with oxazinone or pyrazinone structures, the condensation reaction under PTC conditions or with Eschenmoser’s salt allows the preparation of chiral α,β-didehydro-α-amino acid derivatives which can be hydrogenated, cyclopropanated or submitted to Diels−Alder cycloadditions to afford N-methylated and cyclic α-amino acids.