General procedure for the synthesis of 4-chloro-7-methylthieno[3,2-d]pyrimidin-4(1H)-one from 7-methylthieno[3,2-d]pyrimidin-4-one: 7-methyl-3H-thieno[3,2-d]pyrimidin-4-one (167, 10.6 g, 64.0 mmol) was dissolved in phosphorus nitrogen oxide (42 mL), and the reaction was carried out for 2 h under nitrogen protection at reflux. Upon completion of the reaction, the reaction solution was cooled to room temperature and slowly poured into saturated aqueous sodium carbonate solution (300 mL) for neutralization. Subsequently, the aqueous phase was extracted with ethyl acetate, and the organic layers were combined, washed with water and saturated brine sequentially, and then dried with anhydrous magnesium sulfate. The organic solvent was removed by concentration under reduced pressure and the resulting residue was dried under vacuum overnight in the presence of phosphorus pentoxide to afford the white solid product 4-chloro-7-methylthieno[3,2-d]pyrimidine (168, 11.2 g, 95% yield).
![7-METHYL-3,4-DIHYDROTHIENO[3,2-D]PYRIMIDIN-4-ONE](/CAS/GIF/175137-13-0.gif)
![4-CHLORO-7-METHYLTHIENO[3,2-D]PYRIMIDINE](/CAS/GIF/175137-21-0.gif)