Nitrones and oxaziridines. XXXIV. Synthesis of medium-sized oxo-lactams by ring-opening of fused tricyclic oxaziridines

The medium-sized oxo lactams (9)-(11), (22)-(25), containing eight-to eleven-membered rings, have been synthesized by a three-atom condensative ring expansion of the related cyclic ketones. The key step involves the cleavage of a common ring-fusing bond brought about by the ring-opening of a structurally suitable oxaziridine. These oxaziridines were derived either from the corresponding hydroxy nitrones (13), (14), (18)-(21) or hydroxy imines (3), (9, (7).