[NH2:1][C:2]1[N:3]=[C:4](Cl)[C:5]2[S:11][CH2:10][CH2:9][CH2:8][C:6]=2[N:7]=1.[O:13]=C1CCCSC1C(OCC)=O.[Na].O>C(O)C.C(O)(=O)C>[NH2:1][C:2]1[N:3]=[C:4]([OH:13])[C:5]2[S:11][CH2:10][CH2:9][CH2:8][C:6]=2[N:7]=1The starting material, 2-amino-4-chloro-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine, was prepared in the following manner. 56.4 g of ethyl 3-oxotetrahydrothiopyran-2-carboxylate was added to a solution of 6.9 g of sodium metal in 300 ml of ethanol at room temperature while stirring. After stirring overnight, water was added to the mixture, and the mixture was rendered acidic with acetic acid. The precipitated crystals were filtered, washed with water and then with a small amount of isopropyl alcohol and air-dried to obtain 45 g of 2-amino-4-hydroxy-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine as colorless needles having a melting point above 300° C.
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