Diazacyclobutene Ring Cleavage Provides 1,2-Diazetidin-3-ones via Intramolecular Nucleophilic Cyclization

We report an efficient two-step strategy for the synthesis of 1,2-diazetidin-3-ones (or aza-β-lactams) from thiolated diazacyclobutene intermediates. The transformation involves acid-promoted ring scission, followed by base-induced intramolecular nucleophilic cyclization, affording the desired diazetidinones in good yields. This method offers straightforward access to a structurally unique and underexplored four-membered heterocycle, expanding the synthetic toolbox for strained nitrogen-containing ring systems.