81560-03-4

63810-78-6

Step 3, Preparation of 5-bromo-4-chloro-2-methylthiopyrimidine: 5-bromo-2-(methylthio)pyrimidin-4(3H)-one (110 g) was dissolved in pyridine (400 g) and heated to 80°C. Phosphorus trichloride (100 g) was added dropwise with stirring. After the dropwise addition, the reaction temperature was maintained and stirring was continued for 5 hours. After completion of the reaction, the reaction mixture was cooled to room temperature and subsequently placed in an ice bath. The pH was adjusted to 8-9 with saturated sodium bicarbonate solution and then extracted with ethyl acetate (500 mL). The organic phase was dried with anhydrous magnesium sulfate, filtered and the filtrate was concentrated under reduced pressure to remove the solvent. The residue was recrystallized by a solvent mixture of petroleum ether and ethyl acetate (1:3, v/v) to give a pale yellow solid powder (98 g) in 83% yield.