(2RS,3RS)-2-(2,4-difluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-2,3-butanediol (11 g) was dissolved in a mixture of ethyl acetate (200 ml) and methylene chloride (50 ml), to which triethylamine (6.21 ml) was added under ice-cooling. Then, methanesulfonyl chloride (3.46 ml) was added dropwise to the mixture over the period of 3 minutes under ice-cooling and stirring. After the addition, the resultant solution was stirred for 45 minutes at room temperature. Thereafter, water (100 ml) was added to the solution to separate the organic layer. The organic layer was washed with water, dried over anhydrous magnesium sulfate and distilled off to remove the solvent under reduced pressure, obtaining (2RS,3RS)-2-(2,4-difluorophenyl)-3-methanesulfonyloxy-1-(1H-1,2,4-triazol-1-yl)-2-butanol as an oil. Thus obtained compound was dissolved in methanol (200 ml), to which a sodium methylate methanolic solution (8.84 g, 28%) was added under ice-cooling. The resultant solution was stirred for 30 minutes at room temperature. The solvent was removed under reduced pressure, and the residue was extracted with ethyl acetate (200 ml) and water (100 ml). The ethyl acetate layer was washed with water, dried over anhydrous magnesium sulfate and distilled off the solvent under reduced pressure. The residue was purified by a silica gel column chromatography (ethyl acetate-methylene chloride=4:1) and crystallized from hexane to give (2RS,3SR)-2-(2,4-difluorophenyl)-3-methyl-2-(1H-1,2,4-triazol-1-yl)methyloxirane (8.3 g) as colorless crystals which was a single diastereomer.
