B) To a 25 mL round bottom flask were sequentially added 6-hydroxy-2-(pyridin-2-yl)pyrimidin-4(5H)-one (1 g, 5.29 mmol), phosphorus trichloride (4.82 mL, 52.9 mmol) and phosphorus pentachloride (1.10 g, 5.29 mmol). The reaction mixture was heated to 106 °C and refluxed overnight. After the reaction was completed, the solvent was removed by evaporation. The pH of the reaction mixture was adjusted to 7-8 with saturated sodium bicarbonate solution. the aqueous phase was extracted with ethyl acetate (40 mL × 2) and the organic layers were combined. The organic layer was washed sequentially with 80 mL of water and 80 mL of saturated saline, and then dried over anhydrous sodium sulfate. The dried organic phase was concentrated and the resulting residue was quickly purified by silica gel column chromatography with the eluent of petroleum ether/ethyl acetate (V/V = 8:1). 4,6-Dichloro-2-[2-pyridyl]pyrimidine (0.96 g, white solid) was finally obtained in 80% yield.
