[NH2:1][C:2]1[C:7](Br)=[N:6][C:5]([Br:9])=[CH:4][N:3]=1.[Cl:10][C:11]1[C:18]([F:19])=[CH:17][CH:16]=[C:15]([F:20])[C:12]=1[CH2:13][NH2:14].C(N(C(C)C)CC)C>CCCCO>[Br:9][C:5]1[N:6]=[C:7]([NH:14][CH2:13][C:12]2[C:15]([F:20])=[CH:16][CH:17]=[C:18]([F:19])[C:11]=2[Cl:10])[C:2]([NH2:1])=[N:3][CH:4]=1A solution of 2-amino-3,5-dibromopyrazine (29 mmol, 7.35 g), 2-chloro-3,6-difluorobenzylamine (29 mmol, 5.16 g), and N, N-diethylisopropylamine (32 mmol, 5.6 mL) in n-BuOH (20 mL) was refluxed for 72 hrs. After volatile components were removed on rotavap, EtOAc and water were added to the residue to facilitate the extraction. The combined organic layers were combined, dried, concentrated, and then subjected to a silica gel column chromatography by using hexanes/EtOAc (4:1) as eluents, furnishing 5-bromo-N3-(2-chloro-3,6-difluorobenzyl)pyrazine-2,3-diamine in 70% yield (7.14 g).
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