Catalyst-free photoarylation of 2-aryl-2-indazoles by carbon-iodine bond activation.

A photocatalyst-free visible-light induced arylation of 2-aryl-2-indazoles with aryl iodides has been developed for the first time to produce 3,2-diaryl-2-indazoles in good to moderate yields. In this transformation, potassium -butoxide acts as an activator of the C-I bond and also as a scavenger of generated HI in the reaction. This method exhibits high functional group tolerance with a wide substrate scope and it has been successfully applied to the synthesis of liver X receptor agonists and also for fluorescent probes. This is the first report on the photoarylation of 2-arylindazoles at the C3-position with aryl iodides under catalyst-free conditions.