Phosphine-Promoted Photoredox [3+2] Cycloaddition of Alkynes and Isocyanides

While the [3+2] cycloaddition of alkynes and isocyanides has been established on the basis of transition metal catalysis, a photochemical protocol is alternatively disclosed in the present work. This novel phosphine-promoted photoredox catalysis enables the regioselective formation of 2,4-disubstituted pyrroles with broad functional group tolerance under mild conditions. Mechanistically, the ready addition of the phosphine radical cation formed via photoredox catalysis to alkynes is the key to initiating the cycloaddition with isocyanides.