A mixture of 7-methoxy-2-(propylsulfanyl)-3-[4-(2,2,2-trifluoroethoxy)phenyl]pyrido[2,3-d]pyrimidin-4(3H)-one (213 mg), pyridine hydrochloride (1156 mg) and N,N-dimethylformamide (10 ml) was stirred at 120° C. for 3 hr. The mixture was allowed to be cooled to room temperature, and to the reaction mixture was added water thereto, and the mixture was extracted with ethyl acetate. The extract was washed with aqueous sodium hydrogen carbonate solution and saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/hexane) to give the title compound (183 mg).
