Photochemical Arylation of Brønsted Acids with 2‐Azidobenzimidazole

Irradiation of N-benzylated 2-azidobenzimidazoles at 300 nm in the presence of an excess amount of carboxylic acids results in a novel regioselective synthesis of 2-amino-6-oxybenzimidazoles in isolated yields of 60–70 %. It is also possible to regioselectively introduce 6-bromo, 6-chloro, and 6-triflyloxy groups. Irradiation in dichloromethane in the absence of external nucleophiles revealed that after loss of nitrogen, the benzimidazolylnitrene probably undergoes coarctate ring opening to an N-cyano diaza-o-xylylene intermediate.