Synthesis of Pyrrolone- and Isoindolinone-Fused Benzimidazole-4,7-diones by Stepwise Palladium-Catalyzed Carbonylative Cyclization and Oxidation

2-(2-Bromovinyl)- and 2-(2-bromoaryl)-4,7-dimethoxybenzimidazoles react with carbon monoxide (10 atm) in toluene in the presence of a catalytic amount of PdCl₂ and PPh₃ along with NaOAc to produce the corresponding pyrrolone- and isoindolinone-fused 4,7-dimethoxybenzimidazoles, respectively, in good yields. Oxidation of such binuclear N-fused hybrid scaffolds with ceric ammonium nitrate in acetonitrile-H₂O gives unprecedented pyrrolone- and isoindolinone-fused benzimidazole-4,7-diones in high yields.