Green Cross-Couplings Via Electrosynthesis

By using organic electrosynthesis, a research team in Germany has developed a one-step protocol for cross-coupling phenols to make nonsymmetrical biaryl diols, which are useful in natural product synthesis, in materials science, and as catalyst ligands (Angew. Chem. Int. Ed. 2014, DOI: 10.1002/anie.201400627). In the green method, the team led by Siegfried R. Waldvogel of Johannes Gutenberg University, and including researchers at specialty chemical company Evonik Industries, takes advantage of electric current as a highly selective oxidizing agent. Leaving groups, protecting groups, and a catalyst often needed in cross-coupling reactions aren’t required, they note, thereby streamlining the process while avoiding hazardous reagents, generating less waste, and reducing cost. “The process uses a very simple setup, readily available electrodes, mild reaction conditions, and a recyclable solvent system,” notes R. Daniel Little, an electrosynthesis expert at the University of California, Santa Barbara. The researchers use a traditional power supply, Little adds, but a simple sunlight-driven photovoltaic power supply should suffice and help minimize scale-up cost for commercialization. Waldvogel and his colleagues suggest the chemistry could also be accomplished using a microflow reactor, which would further increase efficiency and reduce waste.