An Asymmetric Nitro-Mannich Reaction Applicable to Alkyl, Aryl, and Heterocyclic Imines

A protocol for the enantioselective nitro-Mannich coupling between alkyl, aryl, and heterocyclic p-methoxybenzylimines and trimethylsilylnitropropanate catalyzed by a chiral ^tBu-BOX Cu(II) catalyst is described. It uses the lowest reported loading of commercially available metal catalyst and chiral ligand, and gives the highest yields and selectivities for a broad substrate range including nonaromatic aldimines. The resultant β-nitroamines are obtained in 70−94% enantiomeric excess in good yield and can be readily reduced to synthetically useful 1,2-diamines.