Dissociative electron transfer to dihaloalkanes. electrochemical reduction of 1,3-dihaloadamantanes, 1,4-dihalobicyclo[2.2.2]octanes, and 1,3-dihalobicyclo[1.1.1]pentanes

Article abstract of DOI:10.1021/ja00090a013

The electrochemical reductive cleavage of the title compounds was investigated by means of cyclic voltammetry and electrolysis. The reaction is a two-electron process that yields competitively ring closure (or fragmentation) products and the monohalide resulting from the expulsion of the best leaving halide ion. Product selection occurs at the level of the carbanion resulting from the reduction of the one-electron reductive cleavage radical. In the formation of the latter, electron transfer and bond breaking are concerted; thus, the anion radical is not involved as an intermediate. The variations in the reduction potential observed in the three series of compounds can be rationalized, by application of the dissociative electron-transfer theory, as related variations of the bond dissociation energy of the first carbon-halogen bond to be cleaved. In the adamantane and bicyclopentane series, these are mainly the result of through-space-bonded interactions in the one-electron reductive cleavage radical and, to a lesser extent, in the starting dihalide itself, while through-bond interactions appear to prevail in the bicyclooctane series.