A NEW METHOD FOR COUPLING AROMATIC-ALDEHYDES AND KETONES TO PRODUCE ALPHA-GLYCOLS USING ZN-ZNCL2 IN AQUEOUS-SOLUTION AND IN THE SOLID-STATE

The coupling of aromatic aldehydes and ketones to afford a-glycols has been carried out by heating with Zn-AcOH,1 Mg-MgX2,2 or Al(Hg).3 These methods were improved by using more active metals such as Al,4 TiCl4,5 or TiCl4-Zn.6 However, these reactions should be carried out at low temperature and in the presence of an inert gas, since the active reagents are sensitive to oxygen and the reaction with the reagents at high temperature gives an olefin. Previously, we have reported that Zn-ZnCl2 is an effective reagent for the reduction of activated olefins7 and ketones.8 Recently, we found further that the reagent is effective for the coupling of aromatic aldehydes and ketones to produce a-glycols, both in solution and in the solid state. Since the Zn-ZnCl2 reagent is effective at room temperature and not sensitive to oxygen, its handling is easy. For example, when a solution of benzaldehyde (la), commercially available Zn powder, and ZnCl2 in 50‥. © 1990, American Chemical Society. All rights reserved.