Racemization of secondary alcohols catalyzed by ruthenium: application to chemoenzymatic dynamic resolution

In this paper, we have shown that the [RuCl₂(p-cymene)]₂ complex associated with simple hemisalen ligands is able to racemize (S)-1-phenylethanol. The influence on the racemization process of the ligand’s structure as well as the nature of a co-catalyst have been evaluated and optimized. This [RuCl₂(p-cymene)]₂/Ligand/TEMPO racemization system was then associated with the Candida Antarctica B lipase in order to carry out dynamic kinetic resolution experiments on rac-phenylethanol. This led us to identify the best conditions for effective DKR, which was then applied to various secondary benzylic and aliphatic alcohols. It was thus possible to obtain (R)-1-cyclohexylethyl acetate from rac-1-cyclohexylethanol in quantitative conversion and with high enantioselectivity (98%).