Synthesis of (3,4) β-Methylenecepham and (3,4) β-Methylene-carbacepham via intramolecular carbene addition to double bond

A series of new (3,4) β-methylenecepham and carbacepham analogues were synthesised as potential antibacterial agents. The key step of the synthesis included presumed generation of the carbene species from the oxalimide substrate effected by triethylphosphite and its intramolecular addition to the double bond. The stereochemistry of the tricyclic system has been elucidated by NMR and X-ray crystallography. In preliminary screening, two of the synthesised compounds exhibited modest antibacterial activity at 1.5–2.0 mg/mL against a number of bacterial strains.