Rhodium(III)-Catalyzed Dehydrogenative Annulation of 2-Arylindazoles with Cyclic Enones

An oxidative annulation of 2-arylindazoles with cyclic enoneshas was developed using Rh(III)/Cu(OAc)(2) catalytic system for the first time to produce 3,4-dihydroindazolo[2,3-f]phenanthridin-1(2H)-one derivatives in good yields with high selectivity. When AgSbF6 was used instead of Cu(OAc)(2), the corresponding uncyclized products, 3-(2-(2H-indazol-2-yl)phenyl)cyclohexan-1-one scaffolds were formed exclusively. The reaction proceeds through a sequential conjugate addition of ortho-C-H bond of aryl group followed by an oxidative annulation of indazole ring to generate fused polycyclic scaffolds.