A bench-stable homodinuclear Ni₂-Schiff base complex for catalytic asymmetric synthesis of α-tetrasubstituted anti-α,β- diamino acid surrogates

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.