Spiro-fused beta-lactam oxadiazoline 2a was prepared from acetone semicarbazone in five steps. Thermolysis of 2a at 100 degrees C in benzene led to carbene 3a, which cyclized to the benzo-fused oxapenem derivative 4 via intramolecular OH insertion. Compound 10, with a beta-lactam ring linked to an azetidinedione ring, was a minor product.
Spiro-fused beta-lactam oxadiazoline 2a was prepared from acetone semicarbazone in five steps. Thermolysis of 2a at 100 degrees C in benzene led to carbene 3a, which cyclized to the benzo-fused oxapenem derivative 4 via intramolecular OH insertion. Compound 10, with a beta-lactam ring linked to an azetidinedione ring, was a minor product.