As stable metalloradicals with open-shell d7 electronic structure, cobalt(II) complexes of porphyrins, [Co(Por)], have emerged as a new class of carbene transfer catalysts for selective cyclization reactions of alkynes. With a D2-symmetric chiral porphyrin ligand, a highly enantioselective Co(II)-based process for cyclopropenation of alkynes with a-cyanodiazoacetamides and a-cyanodiazoacetates has been developed, providing the corresponding trisubstituted cyclopropenes in high yields with excellent enantiocontrol of the all-carbon quaternary stereogenic centers. By controlling reaction conditions, Co(II)-catalyzed radical cyclization of alkynes can be effectively switched from cyclopropenation to furan formation. This new cyclization process has been successfully applied for regioselective syntheses of multisubstituted furans and a-oligofurans. Among several salient features, Co(II)-based metalloradical cyclization enjoys a wide substrate scope with an unusual degree of functional group tolerance.

Enantioselective cyclopropenation and regioselective furan formation viaCo(II)-based metalloradical cyclization

245th National Meeting (2013)

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