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.