Evidence for Single Electron Transfer in the Reactions of Lithium Dimethylcuprate with Alkyl Halides

Article abstract of DOI:10.1021/jo00229a023

A variety of methods have been utilized to explore the occurence of radical intermediates and free-radical chain processes initiated by electron transfer in the reactions of lithium dimethylcuprate with alkyl halides.The effect of leaving group, nature of the cuprate species, and ratio of cuprate to substrate, solvent, hydrogen atom donor, and other additives on the rate of and product distribution were investigated by using a cyclooctenyl radical probe.The presence of significant amounts of radicals strongly supports single electron transfer (SET) as a major pathway for the reaction of secondary iodides with LiCuMe2.There is some evidence of single electron transfer also accurring with secondary bromides, but tosylates appear to be reacting entirely by a S_N2-like pathway.The role of dicyclohexylphosphine (DCPH) as an additive in the reaction was investigated with the result that it was shown to be capable of behaving in a unique manner depending on wheter the substrate is an alkyl iodide or bromide.The product distribution, rate, and effect of p-dinitrobenzene on the reaction of 5-iodo-1-cyclooctene were compared with three other probes and the results demonstrate that at least three reaction pathways are involved to varying degrees.These pathways could involve the initiation of free radicals or radical anion (S_RN1) chain processes. these studies also demonstrate how changes in the substrate can alter the predominant reaction pathways that are followed.