Asymmetric C-C Bond Formation between Chiral N-Phosphonyl Imines and a Nickel(II)-Complexed Glycine Schiff Base Provides Efficient Synthesis of α,β-syn-Diamino Acid Derivatives

The group-assisted purification asymmetric synthesis of alpha,beta-diamino acid derivatives was achieved by treating chiral N-phosphonyl imines with a Ni-II-complexed glycine-derived enolate; traditional purification techniques such as chromatography and recrystallization are not required. Successful control of the syn stereochemistry of the vicinal diamino products complements our previous methods that afforded anti stereoisomers; thus, all four individual isomers can be synthesized simply by changing the geometry of the enolate. In contrast to our previous synthesis in which at least 5 equiv. of the glycine Schiff base enolate was required for complete conversion, the new synthesis only needs 1.1 equiv. of the glycine Schiff base enolate to give complete diastereoselectivity (>30:1dr) and high yields (91-97%). The absolute stereochemistry was unambiguously determined by X-ray structure analysis.