Pentamethylbenzene (4.85 g) and a n-heptane solution (16.3 mL) containing 1.0 M of boron trichloride were added to a solution of (1s)-1,5-anhydro-1-[3-(1-benzothien-2-ylmethyl)-4-fluorophenyl]-2,3,4,6-tetra-O-benzyl-D-glucitol (2.5 g) dissolved in dichloromethane (50 mL, cooled to −78° C.) in an argon stream. The mixture was stirred at the same temperature for 2 hours. After the completion of the reaction, methanol (100 mL) was added for decomposition of the excessive reagent, and the solvents were removed by vacuum distillation. The residue was purified by silica gel column chromatography (chloroform-methanol). The obtained residue was suspended in a mixed solvent of ethanol and water and was refluxed with heating to dissolve. The resulting solution was slowly cooled to room temperature for recrystallization. The obtained crystal was collected by filtration and then dried under vacuum and heating to obtain (1S)-1,5-anhydro-1-[3-(1-benzothien-2-ylmethyl)-4-fluorophenyl]-D-glucitol (known compound A) (1.1 g) as a white crystal. The differential scanning calorimetry analysis chart (DSC analysis chart) of the known compound A obtained is shown in FIG. 1, and its X-ray powder diffraction chart is shown in FIG. 2.
