Formal [2 + 2] Cycloaddition of Ph ₃ PCCO with N-Cbz-Protected Aldimines: Access to N-Cbz-Protected α-Methylene-, α-Alkylidene-, and α-Arylidene-β-Lactams

We report an operationally simple one-pot synthesis of β-lactams bearing an exocyclic alkene via [2 + 2] cycloaddition of Ph3PCCO with N-Cbz aldimines, followed by Wittig olefination with aldehydes. The reaction proceeds cleanly to afford α-methylene-, α-arylidene-, and α-alkylidene-β-lactams in high yields and with excellent E/Z selectivity, while exhibiting broad tolerance for various aryl-, heteroaryl-, alkyl-, and carbonyl-functionalized substrates. The exocyclic alkene moiety provides a handle for thiol–Michael additions and for intramolecular Suzuki–Miyaura coupling to access β-lactam-fused carbocycles.