Photo-induced sp C-H bond arylation, cyanation and nitroalkylation of tetrahydroisoquinolines (THIQs) under visible light irradiation using a combination of NHPI and Rose Bengal.

This work reports a sustainable protocol for α-arylation of tetrahydroisoquinolines (THIQs) with aryl diazonium salts using a combination of a cheap and stable oxidant, N-hydroxyphthalimide (NHPI), and an inexpensive dye photosensitizer, Rose Bengal (RB), for the first time. The reaction was performed at ambient temperature using green LED light irradiation under an oxygen atmosphere. The developed α-arylation protocol shows a diverse substrate scope for various THIQs and aryl diazonium salts. The work also explores nitroalkylation and cyanation under the developed reaction conditions. A possible SET mechanism is involved which was confirmed by ESI-MS analysis of the reaction mixture.