Spontaneous oxidation of organic donors to their cation radicals using Brønsted acids. Identification of the elusive oxidant†

Various electron-rich aromatic and olefinic donors (D) are readily converted to their cation radicals (D!!) in the presence of strong protic acids, even in nonpolar solvents such as dichloromethane. By using the three prototypical organic donors octamethylbiphenylene (OMB), adamantylideneadamantane (AA) and the isomeric fused homoadamantene (FHA), we identify the protonated donor (D-H) as the effective oxidant for electron transfer from the organic donor (i.e., D-H ! D → D-H! ! D!!). The subsequent reduction of (D-H!) to the dihydro product D-H2 is demonstrated by the isolation of 2,2"-biadamantane, the structure of which is established by X-ray crystallography.