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.
Facile access to 4,3-fused 1,2,4-triazolyl-isoquinolines, pyridines and phenanthridines is achieved through electrophilic diazomethylation of the azaarenes with hypervalent iodine diazo reagents followed by 1,5-cyclization of the resulting ammonium diazonium ylides.
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.
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