Regioselective Synthesis of Multisubstituted Furans via Metalloradical Cyclization of Alkynes with α‑Diazocarbonyls: Construction of Functionalized α‑Oligofurans

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-DitBu-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.