Enhanced nucleophilic character of the 1-adamantyl radical in chlorine atom abstraction and in addition to electron-poor alkenes and to protonated heteroaromatic bases. Absolute rate constants and relationship with the Gif reaction

The absolute rate constants for reactions of the 1-adamantyl radical with electron-deficient substrates have been measured by competition kinetics. Addition to electron-poor alkenes or to protonated heteroaromatic bases, as well as chlorine abstraction from CCl4 and CHCl3, are two to three orders of magnitude faster than the corresponding reactions of the tert-butyl radical. This behaviour is ascribed to the enhanced nucleophilic character of the 1-adamantyl radical compared to generic tertiary alkyl radicals; it is related to the particular stability of the 1-adamantyl cation and to the low oxidation potential of adamantane. These results contribute to the understanding of the Gif reaction mechanism; in this debate, adamantane oxidation was one of the most controversial aspects because the 1-adamantyl radical is trapped by pyridinium ions, while the 2-adamantyl radical is not. This behaviour is explained by the large difference in the reactivity of the two isomeric adamantyl radicals towards protonated pyridine.