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Co(III)-carbene radicals generated from activation of α-diazocarbonyls by Co(II)-porphyrin complexes have been shown to undergo a new type of tandem radical addition reaction with alkynes that affords five-membered furan structures. The Co(II) complex of 3,5-Di(t)Bu-IbuPhyrin, Co(P1), is effective in catalyzing the metalloradical cyclization reaction under neutral and mild conditions. The Co(P1)-catalyzed process tolerates a wide range of α-diazocarbonyls and terminal alkynes with varied steric and electronic properties, producing polyfunctionalized furans with complete regioselectivity. The catalytic synthesis features a high degree of functional group tolerance and can be applied iteratively to construct functionalized α-oligofurans.
Cui et al. (Mon,) studied this question.