Visible Light Initiated Hantzsch Synthesis of 2,5-Diaryl-Substituted Pyrroles at Ambient Conditions

Irradiation of a mixture of enamines and α-bromo ketones, with a catalytic amount of Ir(ppy)3 by visible light (λ = 450 nm), enables the production of various 2,5-diaryl-substituted pyrroles in good to excellent yields. The key intermediates in this reaction have been identified as alkyl radicals, generated from single-electron transfer from the photoexcited Ir(ppy)3* to α-bromo ketones, which subsequently react with a broad range of enamines to undergo the Hantzsch reaction rapidly at ambient conditions.