BrBr.[Cl:3][C:4]1[C:5]([NH:10][NH:11][C:12]([NH:14][C:15](=[O:19])[O:16][CH2:17][CH3:18])=S)=[N:6][CH:7]=[CH:8][N:9]=1.[OH-].[NH4+]>C(O)(=O)C.O.C(Cl)(Cl)Cl>[Cl:3][C:4]1[C:5]2[N:6]([C:12]([NH:14][C:15](=[O:19])[O:16][CH2:17][CH3:18])=[N:11][N:10]=2)[CH:7]=[CH:8][N:9]=1A solution of bromine (653 μl, 12.74 mmol) in acetic acid (9 mL) was added to a solution of ethyl 2-(3-chloropyrazin-2-yl)hydrazinecarbonothioylcarbamate (3.523 g, 14.40 mmol) in acetic acid (30 mL) at room temperature and stirred for a further 80 minutes. The mixture was cooled in an ice-bath while 15% ammonium hydroxide solution (180 mL) was added to the reaction mixture, ensuring the reaction temperature remained below 30° C. The mixture was diluted with water (50 mL) and chloroform (120 mL) and filtered. The cake was washed with chloroform (50 mL) and dried under high vacuum at 50° C. to yield ethyl 8-chloro-[1,2,4]triazolo[4,3-a]pyrazin-3-ylcarbamate (1.69 g) as a brown solid.
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