Catalysis of Radical Cyclizations from Alkyl Iodides under H: Evidence for Electron Transfer from [CpV(CO)H].

Radical cyclizations are most often achieved with BuSnH in the presence of a radical initiator, but environmental considerations demand that alternative reagents be developed-ones that can serve as a synthetic equivalent to the hydrogen atom. We have revisited [CpV(CO)H], a known replacement for BuSnH, and found that it can be used catalytically under H in the presence of a base. We have carried out tin-free catalytic radical cyclizations of alkyl iodide substrates. The reactions are atom-efficient, and the conditions are mild, with broad tolerance for functional groups. We have, for example, achieved the first 5-exo radical cyclization involving attack onto a vinyl chloride. We suggest that the radicals are generated by an initial electron transfer.