A practical procedure composed of an asymmetric Mannich-type reaction between N-tosyl imine and a Ni(II) complex of glycine with (R)-o-[N-(N-benzylprolyl)amino]bezaophenone (BPB) as a chiral auxiliary catalyzed by Et3N in DMF to (R,2R,3S)-complexes, and decomposition of products with HCl to offer syn-(2R,3S)-α,β-diamino acids, was developed. Stereochemical mechanism of the Mannich reaction was proposed and supported by determining the absolute configuration of the product of the Mannich reaction relying on X-ray analysis. This two-step approach to amino acids was a general method and adapted to large-scale preparation.
