[Cl:1][C:2]1[N:7]=[N:6][C:5]([NH2:8])=[C:4]([CH3:9])[CH:3]=1.[C:10](Cl)(Cl)=[S:11].O.C([O-])(=O)C>C(=O)(O)[O-].[Na+].O1CCCC1>[Cl:1][C:2]1[N:7]=[N:6][C:5]([N:8]=[C:10]=[S:11])=[C:4]([CH3:9])[CH:3]=1To a solution of 6-chloro-4-methylpyridazin-3-amine (2.86 g, 20.0 mmol) in aqueous sodium bicarbonate (10 mL) and tetrahydrofuran (40 mL) was added thiophosgene (1.69 mL, 22.0 mmol) dropwise at 0° C. After stirring for 1 hr, water and ethyl, acetate were added to the mixture and the insoluble materials were filtered off. The filtrate was washed with brine, dried over anhydrous sodium sulfate and concentrated in vacuo. The residue was purified by flash chromatography on silica gel eluting with a 10-50% ethyl acetate/n-hexane gradient mixture. The filtrate was concentrated in vacuo to give the title compound (304 mg, 1.64 mmol, 8%) as a pale yellow solid.
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