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A practical asymmetric synthesis of a wide-spectrum agricultural fungicide, (S)-MA20565 (1), is described. The convergent synthesis was achieved starting from commercially available 3-(trifluoromethyl)aniline (7) in 44% overall yield through five steps and 2-bromobenzaldehyde (9) in 48% overall yield through four steps, respectively. (S)-O-[1-(3-Trifluoromethylphenyl)ethyl]hydroxylamine (2), a key intermediate of 1, was prepared via ruthenium(II)-catalyzed asymmetric transfer hydrogenation of 1-(3-trifluoromethylphenyl)ethanone (6) followed by chlorination using methanesulfonyl chloride and oxyamination using potassium acetohydroxamate with high level of stereocontrol.

(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.

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