[Br:1][C:2]1[CH:7]=[N:6][C:5]([C:8]([O:10]CC)=[CH2:9])=[CH:4][N:3]=1.C1C(=O)N([Br:20])C(=O)C1>C1COCC1.O.CCOC(C)=O.[F-].[K+]>[Br:20][CH2:10][C:8]([C:5]1[CH:4]=[N:3][C:2]([Br:1])=[CH:7][N:6]=1)=[O:9]
To a solution of 2-bromo-5-(1-ethoxyvinyl)pyrazine (0.65 g, 2.84 mmol) in THF and water was added NBS (0.505 g, 2.84 mmol) at 0° C. The reaction mixture was stirred at 0° C. for 1 hr, then diluted with EtOAc and aq. KF. The two phase mixture was stirred for 20 min at rt before being filtered through diatomaceous earth (Celite®). The filtrate was washed with sat. NaHCO3, sat. NaCl, dried over anhydrous Na2SO4, concentrated. The crude product was purified by silica gel chromatography (0-100% EtOAc in hexane) to yield 2-bromo-1-(5-bromopyrazin-2-yl)ethanone (0.38 g) as a yellow oil. LC/MS (Cond. N-1): [M+H]+ 280.91, RT=2.945 min.
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