Efficient Synthesis of Fused and Bridged Cyclic Pyrrolo[3,4‐a]carbazoles via NH4I Promoted Three‐component Reaction

Abstract

AbstractNH4I promoted three‐component reaction of indoles, cyclic ketones and maleimides in toluene at 140 °C afforded polysubstituted cyclic fused pyrrolo[3,4‐a]carbazoles in good yields. The reaction mechanism included sequential Lewis acid catalyzed 3‐alkenylation of indole, Diels‐Alder reaction and aromatization process. More importantly, the similar NH4I promoted reaction of indoles and acetophenones with two molecules of maleimides in refluxing toluene resulted in the complex tetrahydro‐4,10a‐[3,4]epipyrrolopyrrolo[3,4‐a]carbazoles in satisfactory yields via double Diels‐Alder reaction. On the other hand, tetrahydropyrrolo[3,4‐a]carbazoles can be easily prepared in high yields by conc. HCl catalyzed three‐component reaction of indole and acetophenone and one molecules of maleimide in refluxing ethanol.