A convenient pinacol coupling of diaryl ketones with Bpin pyridine catalysis

A convenient, pyridine-boryl radical-mediated pinacol coupling of diaryl ketones is developed. In contrast to the conventional pinacol coupling that requires sensitive reducing metal, the current method employs a stable diboron reagent and pyridine Lewis base catalyst for the generation of a ketyl radical. The newly developed process is operationally simple, and the desired diols are produced with excellent efficiency in up to 99% yield within 1 hour. The superior reactivity of diaryl ketone was observed over monoaryl carbonyl compounds and analyzed by DFT calculations, which suggests the necessity of both aromatic rings for the maximum stabilization of the transition states. A practical pinacol coupling of diaryl ketones is developed by employing a stable diboron reagent and pyridine Lewis base catalyst. The operationally simple process affords the desired diols with excellent efficiency in up to 99% yield within 1 hour.