Reactions of saturated and unsaturated tertiary alkyl halides and saturated secondary alkyl iodides with lithium aluminum deuteride. Convincing evidence for a single-electron-transfer pathway

Reactions of saturated secondary and tertiary alkyl halides with LiAlH4 (LAH) and LiAlD4 (LAD) have been carried out, and convincing evidence for a single-electron-transfer (SET) pathway has been obtained. Reactions involving saturated alkyl halides with LAD provide a model system in which a halogen-atom radical chain process is not possible, and therefore, the observation of large quantities tin some cases >90%) of protium in the reduction product provides strong evidence for a radical intermediate and a SET pathway. Specifically, the reaction of 2-iodooctane (10) with LAD produced octane with a deuterium content as low as 21%. Also, the reaction of the tertiary halide 2-iodo-2-methylheptane (15) with LAD produced 2-methylheptane (16) with a deuterium content as low as 8%. The effect of stoichiometry, halogen type, and reaction vessel surface on these reactions was studied. Reaction of the unsaturated tertiary halide 6-iodo-6-methyl-1-heptene (25) with LAD was also studied and was found to proceed predominantly by a SET process involving a halogen-atom radical chain process. The possibility of a carbocation intermediate in all of these reactions is discussed.