intramolecular opening of the 1-Boc-β-lactam, initiated by 7-exotrig ring closure from the NH2 of the Orn side chain. The synthetic route is applied to the stereoselective preparation of enantiomerically pure 4-amino-3-methyl-2-oxoazepane-4-carboxylate derivatives, for which the structure and configuration is confirmed by X-ray diffraction. Molecular modeling and NMR experiments indicate that these quaternary