A Water/Toluene Biphasic Medium Improves Yields and Deuterium Incorporation into Alcohols in the Transfer Hydrogenation of Aldehydes.

Deuterium labeling is an interesting process that leads to compounds of use in different fields. We describe the transfer hydrogenation of aldehydes and the selective C1 deuteration of the obtained alcohols in D₂O, as the only deuterium source. Different aromatic, alkylic and α,β-unsaturated aldehydes were reduced in the presence of [RuCl(p-cymene)(dmbpy)]BF4, (dmbpy=4,4'-dimethyl-2,2'-bipyridine) as the pre-catalyst and HCO₂Na/HCO₂H as the hydrogen source. Moreover, furfural and glucose, were selectively reduced to the valuable alcohols, furfuryl alcohol and sorbitol. The processes were carried out in neat water or in a biphasic water/toluene system. The biphasic system allowed easy recycling, higher yields, and higher selective D incorporation (using D₂O/toluene). The deuteration took place due to an efficient effective M-H/D⁺ exchange from D₂O that allows the inversion of polarity of D⁺ (umpolung). DFT calculations that explain the catalytic behavior in water are also included. [ABSTRACT FROM AUTHOR]