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 LiAlH 4 (LAH) and LiAlD4 (LAD) have been carried out, and convincing evidenc e for a single-electron-transfer (SET) pathway has been obtained. Reac tions involving saturated alkyl halides with LAD provide a model syste m in which a halogen-atom radical chain process is not possible, and t herefore, the observation of large quantities tin some cases >90%) of protium in the reduction product provides strong evidence for a radica l intermediate and a SET pathway. Specifically, the reaction of 2-iodo octane (10) with LAD produced octane with a deuterium content as low a s 21%. Also, the reaction of the tertiary halide 2-iodo-2-methylheptan e (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 unsatu rated tertiary halide 6-iodo-6-methyl-1-heptene (25) with LAD was also studied and was found to proceed predominantly by a SET process invol ving a halogen-atom radical chain process. The possibility of a carboc ation intermediate in all of these reactions is discussed.