Rhodium(III)-Catalyzed Dehydrogenative Annulation and Spirocyclization of 2-Arylindoles and 2-(1-Pyrazol-1-yl)-1-indoles with Maleimides: A Facile Access to Isogranulatimide Alkaloid Analogues.

A Rh(III)-catalyzed dehydrogenative annulation and spirocyclization of 2-arylindoles and 2-(1-pyrazol-1-yl)-1-indole with maleimides is described. The cascade protocol provided highly functionalized benzo[]pyrrolo[3,4-]carbazole-1,3(2,8)-diones and spiro[isoindolo[2,1-]indole-6,3'-pyrrolidine]-2',5'-diones in good to excellent. The developed reaction methodology exhibited broad substrate scope with good functional group tolerance and is operationally simple and scalable. Photophysical properties of the annulated products were investigated. The annulated product of 2-(1-pyrazol-1-yl)-1-indole showed high absorption and emission values with a large red-shift as compared to that of 2-phenylindole.