A Bench-Stable Homodinuclear Ni₂−Schiff Base Complex for Catalytic Asymmetric Synthesis of α-Tetrasubstituted <i>anti</i>-α,β-Diamino Acid Surrogates

Abstract

Catalytic asymmetric direct Mannich-type reactions of α-substituted nitroacetates using a new bench-stable homodinuclear Ni2−Schiff base 1b complex are described. The Ni2−1b complex gave Mannich products, precursors for anti-α,β-diamino acids with an α-tetrasubstituted carbon stereocenter, in >99−91% ee. The Ni2−1b complex was also applicable to direct Mannich-type reactions of malonates and β-keto ester, giving products in high stereoselectivity (up to 99% ee, dr >97:3). Preliminary mechanistic studies suggested that the dinuclear Ni metal centers had key roles to achieve good reactivity and high stereoselectivity.