Stereochemistry of β-lactam formation of β-branched a-amino acid derivatives via a MOC strategy was investigated. The 4-exo-trig cyclization of axially chiral enolates generated from L-threonine and L-allo-threonine derivatives proceeded predominately with inversion of the configuration at the newly formed tetrasubstituted carbon, irrespective of the chirality at the β-carbon of the β-lactam precursors. These results indicated that C-N axial chirality of the intermediary enolates generated from the α-amino acid derivatives has decisive effects on the stereochemical course of β-lactam formation even in the presence of an sp3-chiral center at the β-carbon.