Practical Synthesis of (S)-1-(3-Trifluoromethylphenyl)ethanol via Ruthenium(II)-catalyzed Asymmetric Transfer Hydrogenation

( S )-1-(3-Trifluoromethylphenyl)ethanol which is useful as an agrochemical intermediate was prepared from the corresponding acetophenone by asymmetric transfer hydrogenation. Removal of acetone raised the yield and maintained the optical purity when i -PrOH was used as the hydrogen source; however, this operation was not practical at industrial scale. Then formic acid was examined as the hydrogen source, and dramatic acceleration of the reaction rate was achieved by optimization of the reaction conditions to establish asymmetric transfer hydrogenation at industrial scale.