Organocatalytic Asymmetric Synthesis of Protected α,β-Diamino Acids

In the presence of the readily available quinine-derived catalyst 4d, highly diastereo- and enantioselective Mannich reactions of tosyl-protected imines and alpha-isothiocyanato imides proceeded to afford the protected alpha,beta-diamino acids, useful building blocks for natural products and biologically active compounds, in good to excellent yields.