A mixture of 1-[(1R,2R)-2-(2,4-difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2,4-triazol-1-yl)propyl]-3-[4-(1H-tetrazol-1-yl)phenyl]-2-imidazolidinone(0.5 g), chloromethyl pivalate (15.7 g) and acetonitrile (2.4 g) was stirred for 6.5 hours at 100° C. After having been cooled, the mixture was diluted with diisopropyl ether (10 ml), and the resulting powder was collected by filtration. The powder was subjected to silica gel column chromatography (eluent: ethyl acetate→acetone→acetone/ethanol=10/1→acetone/ethanol=5/1) to give 1-[(2R,3R)-2-(2,4-difluorophenyl)-2-hydroxy-3-[2-oxo-3-[4-(1H-tetrazol-1-yl)phenyl]-1-imidazolidinyl]butyl]-4-[(2,2-dimethylpropanoyloxy)methyl]-1H-1,2,4-triazolium chloride(Compound 2, 0.32 g) as a white powder. The above Compound 2 (0.4 g) was crystallized from ethyl acetate (20 ml) to give white crystals (0.3 g) of Compound -2.
