Phosphorus oxychloride → 2-benzylthio-7-chloro-6-methyl-5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one
Reaction equation
[CH2:1]([S:8][C:9]1[S:20][C:12]2=[N:13][C:14](O)=[C:15]([CH3:18])[C:16](=[O:17])[N:11]2[N:10]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.P(Cl)(Cl)(Cl)(Cl)[Cl:22].P(Cl)(Cl)(Cl)=O>>[CH2:1]([S:8][C:9]1[S:20][C:12]2=[N:13][C:14]([Cl:22])=[C:15]([CH3:18])[C:16](=[O:17])[N:11]2[N:10]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1Participants
4
Procedure
A mixture of 18.3 g of the thus obtained 2-benzylthio-7-hydroxy-6-methyl-5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one, 13.1 g of phosphorus pentachloride and 36.8 g phosphorus oxychloride was stirred at 85°-95° C. for 1.5 hours. Thereafter, the reaction mixture was concentrated under reduced pressure, and the residue was dissolved in toluene. The organic layer was washed with an aqueous potassium carbonate solution and water respectively, and dried over anhydrous sodium sulfate. The solvent was distilled off and the residue was purified by silica gel column chromatography using an ethyl acetate/toluene (3:7) mixture as an eluent. Then the solvent was distilled off, and thus 14.0 g of 2-benzylthio-7chloro-6-methyl-5H-1,3,4-thiadiazolo[3,2-a]pyrimidin-5-one was obtained m.p. 102°-104° C. Yield 72%.