Carbon-Hydrogen vs. Carbon-Carbon Bond Cleavage of 1,2-Diarylethane Radical Cations in Acetonitrile-Water

Article abstract of DOI:10.1021/jo00183a023

Radical cations of 1,2-diarylethanes and 1-phenyl-2-arylethanes (Ar = phenyl, p-tolyl, p-anisyl) were generated in acidic 70percent acetonitrile-water by Cu²⁺-catalyzed peroxydisulfate oxidation.The radical cations fragment mainly by loss of benzylic protons (C-H cleavage) rather than by alkyl C-C bond cleavage.The radical cation of 2,3-dimethyl-2,3-diphenylbutane fragments efficiently by C-C cleavage, forming cumyl radical and cumyl cation.Oxidations of bibenzyl-bicumyl mixtures show selective oxidation of bicumyl dependent on total substrate concentration, providing evidence of equilibrating radical cations and showing that bicumyl fragments faster than bibenzyl loses protons.The effects of reaction conditions and substrate structure on reactivity are discussed.