To a suspension of 1-[2,4-bis(trifluoromethyl)benzyl]piperidine-4-carbaldehyde (15 g) and 4-(prop-2-yn-1-ylamino)-1,3-thiazol-2(5H)-one (8.18 g) in ethanol (150 mL) was added potassium tert-butoxide (5.95 g), and the reaction mixture was stirred at 80° C. for 30 min. The reaction mixture was concentrated, saturated aqueous ammonium chloride solution/ethyl acetate were added to the residue, and the organic layer was separated, washed with water and saturated brine, and dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/hexane), and the residue was washed with diisopropyl ether to give the title compound (9.96 g).
