Evaluation of boron doped diamond electrodes for organic electrosynthesis on a preparative scale

We have investigated some anodic and cathodic transformations using boron doped diamond (BDD) electrodes. The oxidn. of a propargylic alc. as well as the arom. side chain oxidn. in water as electrolyte did not yield the desired products in high yield and selectivity and led mainly to the formation of CO2 due to electrochem. incineration of the starting material. With methanol as electrolyte, however, the reactivity of BDD electrodes is similar to graphite in most anodic methoxylation reactions, but the inactive behavior of BDD electrodes leads to a different reaction pathway possibly involving methoxyl radicals with charge transfer from the electrolyte. It has been found that at BDD anodes benzylic single and double bonds can be split yielding arom. acetals and esters. With phenanthrenes as starting material, o,o'-disubstituted biaryls were obtained. So the use of BDD electrodes provides an efficient and environmentally friendly access to this interesting class of compds. The high H2 overpotential of BDD cathodes enables smooth and selective redn. of functional groups like oximes. Due to the high chem. and mech. stability of the diamond layer of today's electrodes, electrode lifetime as well as reproducibility of the electrosyntheses has improved markedly. Aq. basic conditions, however, must be avoided for BDD anodes. These conditions result in degrdn. of the diamond surface. [on SciFinder (R)]