Am etal-free, regioselective synthesis of trisubstituted pyrroles has been developed throughaformal [3+ +2] cycloaddition reactionb etween 2H-azirines and nitroalkenes under visible light/photoredox-catalyzedc onditions. The re-action proceeds through 2H-azaallenyl radical addition on bnitrostyrenes in aM ichael fashion followed by ab ase-mediated denitration reaction. The directive group influence of the nitro group controlst he regiochemistry of the reaction.

A novel visible light mediated redox-neutral 1,3-dipolar cycloaddition of 2H-azirines with 2,4,6-triarylpyrylium tetrafluoroborate salts providing tetrasubstituted pyrroles has been developed. The 2,4,6-triarylpyrylium salt acts as dipolarophile as well as photosensitizer in the reaction, under blue light irradiation. The control experiments indicated single electron oxidation of 2H-azirines by photoexcited pyrylium salts, followed by coupling between an azaallenyl radical cation and triarylpyranyl radical as the key mechanistic feature. The mild conditions, wide substrate scope, and complete regioselectivity are the noticeable attributes of the reaction.

The α-keto vinyl radicals generated from α-bromochalcones under visible light photoredox catalyzed conditions were trapped by chalcones.