[Cl:1][C:2]1[C:3]([NH:8][NH:9][C:10](=[O:15])[C:11]([F:14])([F:13])[F:12])=[N:4][CH:5]=[CH:6][N:7]=1.C1C(=O)N([Br:23])C(=O)C1>C(Cl)Cl.O>[Br:23][C:6]1[N:7]=[C:2]([Cl:1])[C:3]([NH:8][NH:9][C:10](=[O:15])[C:11]([F:12])([F:13])[F:14])=[N:4][CH:5]=1N′-(3-chloropyrazin-2-yl)-2,2,2-trifluoroacetohydrazide E-1 (19.5 g; 81.1 mmol) is dissolved in 300 ml anhydrous DCM and cooled down to −40° C. Afterwards NBS (18.8 g; 105 mmol) is added and stirred for 1 hour. The solution is diluted with water and extracted with DCM. The organic phase is then purified with flash chromatography: cHex/(EtOAc/CH3COOH=9/1)=80%/20% to 70%/30% within 10 column volumes.
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