To a mixture of 5-({2-[4-(2-tert-butylphenyl)piperazin-1-yl]-2-oxoethyl}sulfanyl)-1,3-dimethyl-1H-pyrazole-4-carbaldehyde (900 mg), sodium dihydrogen phosphate (1.19 g), 2-methyl-2-butene (1.17 mL), tetrahydrofuran (10 mL), tert-butanol (3 mL), and water (1.5 mL) was added sodium chlorite (393 mg) at 0° C. and stirred at room temperature for 1 h. Aqueous sodium hydrogen sulfite was added to the reaction solution, and the mixture was extracted with ethyl acetate. The ethyl acetate layer was washed with saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure to provide the title compound (550 mg, 59%) as a colorless solid.
