Visible-Light-Promoted Metal-Free 3-Arylation of 2-Aryl-2H-indazoles with Triarylsulfonium Salts

An efficient approach for the photosynthesis of various arylated 2-aryl-2H-indazoles (38 examples) in moderate to good yields (up to 87% yield) under mild conditions was developed by employing 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as an inexpensive photocatalyst. This protocol features wide substrate scope, good functional group tolerance, and operational simplicity. In addition, the strategy was successfully applied to the late-stage modification of drug molecules, and the meaningful introduction of complex drugs to the skeleton of 2H-Indazole was achieved for the first time.