During our research on novel, non-traditional, bicyclic β-lactams as potential inhibitors of Penicillin Binding Proteins (PBPs), we focused on the synthesis of 1, 3-bridged 2- azetidinones by RCM reaction from 1, 3-bis-ω-alkenoyl-3 (S)-amino-2-azetidinone precursors. Submitting the precursors to RCM, we faced an unexpected problem: cyclodimerization was the preferred outcome. This peculiar reactivity, explained by a ...