Asymmetric Synthesis of Chiral α‑Methyl-α,β-diamino Acid Derivatives via Group-Assisted Purification Chemistry Using N‑Phosphonyl Imines and a Ni(II)-Complexed Alanine Schiff Base

The Mannich reaction between chiral N-phosphonyl imines and a Ni­(II)-complexed alanine Schiff base (Ala-Ni) is reported. With a chiral phosphonyl auxiliary, a single isomer of α-methyl-α,β-diamino acid derivative containing vicinal chiral centers, including a chiral quaternary carbon center, can be obtained simply by washing the crude mixture with cosolvents. The absolute stereochemistry of the enantiomerically pure product has been unambiguously determined by X-ray crystallographic analysis.