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 i ntermediate 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, th is operation was not practical at industrial scale. Then formic acid was ex amined as the hydrogen source, and dramatic acceleration of the reaction ra te was achieved by optimization of the reaction conditions to establish asy mmetric transfer hydrogenation at industrial scale.