Asymmetric Aza-Mannich Addition of Oxazolones to <i>N</i>-Tosyl Aldimines: Synthesis of Chiral α-Disubstituted α,β-Diamino Acids

An organocatalytic enantioselective addition of oxazolones to N-tosyl aldimines has been developed. The process is promoted by a readily prepared cinchona alkaloid ligand and affords a series of valuable α-disubstituted α,β-diamino acid derivatives with excellent enantioselectivities (up to 97% ee) and diastereoselectivities (up to >30:1 dr). The adducts can be transformed into the corresponding protected chiral α-disubstituted α,β-diamino acids by a one-pot hydrolyzed reaction smoothly.