N‑Heterocyclic Carbene Catalyzed [4 + 2] Annulation Reactions with in Situ Generated Heterocyclic ortho-Quinodimethanes

An efficient strategy for the in situ generation of heterocyclic ortho-quinodimethanes (oQDMs) from 2-methyl-heteroarene-3-carboxylic esters by N-heterocyclic carbene (NHC) catalysis is disclosed. These heterocyclic oQDMs undergo highly enantioselective [4 + 2] annulation reactions with isatin-derived ketimines to afford optically pure heteroarene-fused δ-lactams bearing a quaternary stereogenic center. The main features of this reaction include challenging direct C­(sp3)–H bond functionalizations, excellent enantioselectivities, readily available starting materials, mild reaction conditions, high efficiency, and operational simplicity.