Sunlight induced C-H arylation of aromatic heterocycles: First example of A3 and A2B type corroles as photoredox catalysts

The visible light mediated metal-free approach has been developed for C–H arylation and borylation employing anilines as starting material. A series of meso-aryl corroles (A<inf>3</inf> and A<inf>2</inf>B type) were synthesized and their catalytic potential was tested in blue light and sunlight. The method includes substituted anilines as source of expensive aryl diazonium salts and utilizes only 0.5 to 1 mol% of corrole catalyst at room temperature. Corrole catalyst worked efficiently under the blue light/sunlight to produce heterobiaryls and aryl boronic esters in decent to good yields (15–80 %). Mechanistic insight was obtained from TD-DFT studies, which suggested single electron transfer (SET) from the singlet state of corrole catalyst to the aryl diazonium salt. The paper demonstrates corrole based photo-redox catalysis as a mild, green and eco-sustainable alternative for the C–H arylation reactions.