Aromatization of cyclohexadienes by TEMPO electro-mediated oxidation: Kinetic and structural aspects

Cyclohexadienes are easily converted into the corresponding aromatics in excellent yield (>90%) in the presence of 2,2,6,6-tetramethyl-1-oxopiperidinium ion (TEMPO⁺). The TEMPO radical was used in catalytic amount and was electrochemically regenerated in the presence of 2,6-lutidine as a base in hydro-organic medium (AcCN/H₂O 95/5). This work has been focused on the kinetic aspects. We have demonstrated that the reactivity of different cyclohexadienes is strongly dependent on the configuration of the double bonds and on the nature of the substituents. Competition between allylic functionalization and aromatization has been observed during the oxidation of 1,2-dihydro-4-phenylnaphthalene.