Deciphering the Access to Fused Oxepinone/Aza‐Oxepinone Scaffold Involving Paradoxical O‐Nucleophilicity Enabled by Amide–Imide Tautomerization

ABSTRACT An atom‐economical Rh(III)‐catalyzed regioselective one‐pot C(sp 2 )─H activation/[5 + 2] annulation–lactonization sequence has been materialized allowing 3‐arylquinoxalin‐2(1H)‐ones/ 3‐arylquinolones/ N‐phenylbenzamide (amide/ lactam skeleton) and maleimides to interact, which eventually led to the straightforward access to biologically relevant and structurally unique lactone‐fused heterocyclic scaffolds. The transformation proceeds through a cascade sequence involving C(sp 2 )─H functionalization followed by O‐annulation (5 + 2 cyclization) enabled by amide–imide or lactam–lactim tautomerization resulting O‐centered nucleophilicity which leads to paradoxical lactonization under redox‐neutral condition, averting the demand of any sacrificial oxidant. The methodology exhibits broad substrate scope, excellent functional‐group tolerance, and is applicable to both cyclic and acyclic amide substrates, providing easy access to diverse seven‐membered fused‐lactone frameworks in good to excellent yields. Mechanistic investigations, including control experiments, isotope‐labeling studies, and DFT calculations, support the proposed catalytic pathway and provide insight into the observed reactivity and selectivity.