A visible-light-mediated hydrotrifluoromethylation of unactivated alkenes that uses the Umemoto reagent as the CF(3) source and MeOH as the reductant is disclosed. This effective transformation operates at room temperature in the presence of 5 mol % Ru(bpy)(3)Cl(2); the process is characterized by its operational simplicity and functional group tolerance.

As an example of the general problem posed in the title, the reduction of CF3Br, CF3I, C6FI3I, and C8F17I by outer-sphere heterogeneous (glassy-carbon electrodes) and homogeneous (aromatic anion radicals) reagents is investigated, in a protic solvents containing tetralkylammonium salts, by cyclic voltammetry and preparative-scale electrolysis. A RF* chemistry is thus triggered in all cases with the exception of CF3Br where a mixed RF"/RF~chemistry is obtained by direct electrochemical reduction or by electron transfer from aromatic anion radicals having a close reduction potential. Quantitative analysis of the reduction kinetics of RFX (X = Br, I) and of RF" led to the following conclusions. RFX most likely undergoes a concerted electrontransfer-bond-breaking reduction involving a substantial overpotential (ca. 1.5 V for C-Br and 1.0 V for C-I), mainly governed by the C-X bond dissociation energy. RF* radicals are strongly stabilized by interaction with the solvent but are nevertheless easier to reduce than alkyl radicals on thermodynamical grounds, exhibiting however a high intrinsic barrier of the same order as for alkyl radicals. Unlike alkyl radicals, but similar to aryl radicals, RF* radicals are good H-atom scavengers and do not couple with aromatic anion radicals.Electron transfer from heterogeneous and homogeneous outer-sphere reagents to frangible organic substrates provides a means of generating either radicals or carbanions according to the re-duction characteristics of both the substrate and the radical/ carbanion couple. Investigation and rationalization of these characteristics should thus allow one to predict what type of 0002-7863/90/1512-3509S02.50/0 ©