Strain‐Driven Formal [4+3] Cycloaddition of Cyclobutanones with Azomethine Imines: Access to 1,2‐Diazepinones

Abstract: A strain‐promoted annulation strategy for constructing seven‐membered N‐heterocycles via formal [4+3] cycloaddition of cyclobutanone carboxamides with azomethine imines has been reported. This method features operational simplicity, broad substrate scope, and high diastereocontrol, delivering structurally complex 1,2‐diazepinone derivatives in up to 87% yield. The synthetic utility was validated through gram‐scale preparation and unambiguous structural confirmation by X‐ray analysis. Notably, initial asymmetric catalysis studies provided encouraging enantioselectivity, highlighting the potential for developing stereoselective versions of this ring‐expansion process.