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General procedure for the synthesis of 2,4-dichloro-6,7-dihydrothieno[3,2-d]pyrimidine (VII) from 6,7-dihydrothieno[3,2-d]pyrimidine-2,4-diol (VI): 2.4 g (14.1 mmol) of 6,7-dihydrothieno[3,2-d]pyrimidine-2,4-diol (VI) was suspended in 14 mL of phosphorus oxychloride and added with 4.5 mL (28.2 mmol) of diethylaniline and the mixture was stirred at 80 °C for 22 hours. Upon completion of the reaction, it was cooled to room temperature and the reaction mixture was slowly poured into ice water, the precipitate formed was collected by filtration and washed with cold water. The resulting precipitate was dissolved in dichloromethane and the water was removed by a phase separator. The organic phase was concentrated to dryness under reduced pressure to give 2.5 g of the target product VII in 85% yield.

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