Carbene-Catalyzed [4 + 3] Annulation Strategy for the Construction of Benzo-Fused Nitrogen-Rich Seven-Membered Heterocycles.

In this Letter, we describe an N-heterocyclic carbene (NHC)-catalyzed [4 + 3] annulation approach that enables the streamlined assembly of azepine architectures through an acyl azolium-driven process. The transformation employs ortho-functionalized benzaldehydes and hydrazonyl chlorides as readily available coupling partners. This process proceeds through the formation of an NHC-derived acyl azolium intermediate from ortho-functionalized benzaldehyde, which then undergoes in situ generation of an ortho-quinone methide (o-QM) or aza-o-QM acting as a 1,4-dipolar species. Concurrently, base-mediated activation of hydrazonyl chloride produces a 1,3-dipole in situ. The synergistic interplay of these reactive intermediates culminates in a facile formal [4 + 3] annulation, delivering structurally diverse benzo-fused triazepine and oxadiazepine derivatives in moderate to high yields.