[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.[NH:13]1[CH2:18][CH2:17][NH:16][CH2:15][CH2:14]1.Cl>C1C=CC=CC=1.CO>[NH2:1][C:2]1[N:3]=[C:4]([N:13]2[CH2:18][CH2:17][NH:16][CH2:15][CH2:14]2)[C:5]2[S:11][CH2:10][CH2:9][CH2:8][C:6]=2[N:7]=111 g of 2-amino-4-chloro-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine was dissolved in 150 ml of benzene and 30 g of anhydrous piperazine was added thereto while hot. After heating for 3 hours, the mixture was concentrated under reduced pressure and water was added thereto. The mixture was rendered alkaline with potassium carbonate and extracted with chloroform. The organic layer was dried over magnesium sulfate and the solvent was distilled off to obtain crystals. The resulting crystals were converted into the corresponding hydrochloride in methanol and, after treatment with activated carbon, the hydrochloride was again converted into a free base form. The free base was recrystallized from a mixture of chloroform and diethyl ether to obtain 11 g of 2-amino-4-piperazino-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine as colorless needles having a melting point of 176°-178° C.
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