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

Abstract

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, 1.56 g 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.magnified image

Alternating Current Electrolysis for the Electrocatalytic Synthesis of Mixed Disulfide via Sulfur–Sulfur Bond Metathesis towards Dynamic Disulfide Libraries

“…Accordingly, the effect of the electrode material upon the formation of the mixed disulfides could be investigated. The best results were observed when the reactions were performed at a platinum electrode or glassy carbon electrode whereas inferior results were obtained when copper, stainless steel and carbon fiber electrodes were used (see Supporting Information chapter 2.7, Table S11) . Based on these positive effects all other disulfide metathesis reactions were conducted with the alternating current electrolysis setup.…”

Rhodaelectrocatalysis for Annulative C−H Activation: Polycyclic Aromatic Hydrocarbons through Versatile Double Electrocatalysis

“…After having established the robust rhodaelectrocatalyzed [2+2+2] cycloaddition, we turned our attention towards extending the π‐conjugation of the thus‐formed products 3 through dehydrogenation of the aryl moieties. Here, we obtained the desired product 6 a in the presence of catalytic quantities of the redox mediator DDQ at room temperature (Scheme ). In this way, a wealth of decorated PAHs was accessed under metal‐free, mild conditions ( 6 b – 6 e ), and the reaction fully tolerated synthetically meaningful halo groups.…”

Unravelling the enigma of ligninOX: can the oxidation of lignin be controlled?

“… 34 Alternatively catalytic DDQ systems in conjunction with a range of co-oxidant systems have been used (for example, NaNO 2 or t BuONO and molecular O 2(g) ; 8 Mn(OAc) 3 ( ref. 34 ) and more recently the use of electrochemistry 37 ). DDQ has been reported to be an ideal oxidant for selective benzylic oxidation of β–O-4 units in model compounds 33 and in a birch lignin.…”