Sodium dispersion-mediated reductive dimerization of benzylic halides for symmetrical bibenzyls: Column-free applications to natural products

We report a method for the synthesis of symmetrical bibenzyls by the reductive dimerization of benzylic halides using sodium dispersion (SD). SD, a reagent consisting of sodium particles dispersed in mineral oil, has recently attracted attention as a safer but more reactive source of sodium than sodium lump. We have found that the reductive dimerization of benzylic halides proceeds within 1 h at room temperature in tetrahydrofuran (THF) solvent using SD as a reducing agent. This method is highly sustainable for the synthesis of symmetrical bibenzyls since it uses sodium, which is abundant on earth. As the SD-derived mineral oil in the crude product can be readily removed, three natural products were synthesized on a gram scale without the need for column chromatography. The utility of this reaction was also exemplified by a decagram-scale reaction using 2-methyltetrahydrofuran, known as a green alternative solvent to THF.