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

Catalytic asymmetric direct Mannich-type reactions of alpha-substituted nitroacetates using a new benchstable homodinuclear Ni-2-Schiff base 1b complex are described. The Ni-2-1b complex gave Mannich products, precursors for anti-alpha,beta-diamino acids with an alpha-tetrasubstituted carbon stereocenter, in >99-91 % ee. The Ni-2-1b complex was also applicable to direct Mannich-type reactions of malonates and beta- keto ester, giving products in high stereoseleclivity (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.