A green approach for the synthesis of π conjugated phosphonium salts under visible-light irradiation using air as oxidant

We have developed a strategy for synthesizing π-conjugated phosphonium salts through visible-light-induced cyclization of aryl phosphines in the presence of air and protonic acid. The mechanism study revealed that this C−H bond activation/cyclization of aryl phosphine reaction was initiated from the homolysis of P-H bond of phosphonium salts, which is induced by visible light. This reaction is transition metal free, exhibits good chemo-selectivity and has a high atomic economy.