Rhodium(III)-Catalyzed Annulation of 2-Arylimidazo[1,2-a]pyridines with Maleimides: Synthesis of 1H-Benzo[e]pyrido[1′,2′:1,2]imidazo[4,5-g]isoindole-1,3(2H)-Diones and their Photophysical Studies

Abstract

Rhodium(III)-catalyzed dehydrogenative annulation of 2-aryl-imidazo[1,2-a]pyridines with maleimides is described. The reaction afforded 1H-benzo[e]pyrido[1′,2′:1,2]imidazo[4,5-g]isoindole-1,3(2H)-diones in high yields with wide range of functional group tolerance. The reaction proceeds through Rh(III)-catalyzed C−H bond activation, followed by maleimide insertion and intramolecular cyclization. Photophysical properties of 1H-benzo[e]pyrido[1′,2′:1,2]imidazo[4,5-g]isoindole-1,3(2H)-diones were studied with UV-visible and fluorescence spectroscopy and validated by quantum chemical calculations. All the annulated products showed large Stokes shift values with emission in the range of 530–618 nm, and moderate to high quantum yields.