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 α,β-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 (>30:1 dr) and high yields (91-97 %). The absolute stereochemistry was unambiguously determined by X-ray structure analysis.