Efficient Oxidative Coupling of Arenes via Electrochemical Regeneration of 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) under Mild Reaction Conditions

The intramolecular dehydrogenative carbon-carbon bond formation of aromatic rings in the presence of catalytic amounts of an oxidising agent is herein described. The oxidative coupling is realised under indirect anodic conditions, utilising 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an efficient redox mediator under acidic conditions. In comparison, for the stoichiometric oxidative coupling reaction of hexakis(4-tert-butylphenyl) benzene on a 1.0 gram scale, 1.56g of DDQ were applied, whereas in the present indirect electrochemical version, only 15 mg of DDQ were needed, resulting in significantly easier purifications of the products. The reaction proceeds smoothly using a variety of polyaromatics including terphenyl, quaterphenyl and heptaphenyl derivatives to give polyphenylenes in excellent yields and current efficiencies. A detailed optimisation study, investigations on the electrochemical behaviour of the redox mediator and synthetic applications of the method are discussed.