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.

An efficient organo-photocatalytic method for the synthesis of tetrasubstituted pyrroles bearing a ketone, ester, alcohol, or nitro group at the 3-position has been developed. The reaction involves visible-light-mediated formal [3+2] dipolar cycloaddition between 2H-azirines and α-substituted nitroalkenes followed by a denitration or debromination sequence. The notable features of the protocol are excellent regioselectivity, wide substrate scope, and high yields of the products.

An efficient organo-photocatalytic method for the synthesis of 6-β-disubstituted phenanthridines has been developed. The reaction documents unprecedented generation of enolate vinyl radicals from corresponding diazo compounds in the presence of photocatalyst Rh-6G. Subse-quent trapping of these radical intermediates by o-aryl vinyl azides followed by intramolecular cyclization affords the final products in excellent yields and regioselectivity. The reaction is notable for its mild conditions, high yields and wide substrate scope.