The ambident reactivity of triphenylmethyl radicals in hydrogen-abstraction reactions and the mechanism of the base-catalysed rearrangement of (diphenylmethylene)cyclohexadienes (a type of semibenzene) into triphenylmethane

Abstract

Thermolysis of tri([²H₅]phenyl)(phenylazo)methane (2) in non-deuteriated 2,2-dimethoxypropane in the presence of non-deuteriated sodium methoxide furnishes, among other products, mixtures of the deuteriated analogues of triphenylmethane (1c) and of deuteriated analogues of (p-biphenylyl) diphenyl-methane (3a). The former was shown to be a mixture of the hexadecadeuterio derivative (6c) and the isomeric monoprotiopentadecadeuterio derivatives (6a and b), while the latter proved to be a mixture of the pentaprotio derivative (3d) and the isomeric hexaprotio derivatives (3b and c). The formation of compound (6b) proves the ambident reactivity of triphenylmethyl radicals in hydrogen-abstraction reactions, while the observed ratio of compounds (6a and b) indicates the rearrangements of the intermediate semibenzenes (7) and (8) to be multistep conducted-tour rearrangements (Scheme 1).