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

The electrochemical reductive cleavage of the title compounds was inve stigated 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 expulsio n of the best leaving halide ion. Product selection occurs at the leve l of the carbanion resulting from the reduction of the one-electron re ductive cleavage radical. In the formation of the latter, electron tra nsfer 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 app lication of the dissociative electron-transfer theory, as related vari ations of the bond dissociation energy of the first carbon-halogen bon d to be cleaved. In the adamantane and bicyclopentane series, these ar e mainly the result of through-space-bonded interactions in the one-el ectron reductive cleavage radical and, to a lesser extent, in the star ting dihalide itself, while through-bond interactions appear to prevai l in the bicyclooctane series.