Optimization of pinacol coupling in aqueous media

The optimization of magnesium as well as Al-KOH mediated pinacol coupling of benzaldehyde is described. Exchange of the magnesium turnings for magnesium powder permitted the use of a significantly lower excess of magnesium and shortened the reaction time, while the conversion of starting material as well as the yields of products were preserved. Ultrasound had a beneficial effect on the reaction using magnesium. Using water instead of methanol as the reaction medium for Al-KOH mediated reactions resulted in raising the yields. The lowering of the Al:KOH ratio was also possible.