Iron-Catalyzed Reductive Radical Cyclization of Organic Halides in the Presence of NaBH4: Evidence of an Active Hydrido Iron(I) Catalyst

Iron made‘em: Iron(II) complexes such as FeCl2 and [FeCl2(dppe)2] (dppe=1,2‐bisdiphenylphosphinoethane) are efficient precatalysts for the radical cyclization of unsaturated iodides and bromides in the presence of NaBH4 (see scheme). Cyclic voltammetry studies suggests that the reaction occurs through a radical mechanism via an anionic hydrido iron(I) species as the key intermediate for the activation of the substrates by electron transfer.