Synergistic Chiral Ion Pair Catalysts for Asymmetric Catalytic Synthesis of Quaternary α,β-Diamino Acids

The combination of a chiral phosphate anion with a silver ion has been demonstrated as a powerful and synergistic ion pair catalyst for the aza-Mannich reaction. A series of valuable quaternary alpha,beta-diamino acid derivatives was obtained in high yield, and with excellent diastereo- (up to 25:1 dr) and enantioselectivity (up to 99% ee). The adducts can be smoothly transformed into the corresponding protected chiral quaternary alpha,beta-diamino acids by a one-pot hydrolysis reaction.