[NH2:1][C:2]1[C:3]([N:9]2[CH2:14][CH2:13][N:12](C(OC(C)(C)C)=O)[CH2:11][CH2:10]2)=[N:4][CH:5]=[C:6]([Br:8])[N:7]=1.Br[CH2:23][C:24](=O)[C:25]([O:27][CH2:28][CH3:29])=[O:26]>CCO>[BrH:8].[Br:8][C:6]1[N:7]2[CH:23]=[C:24]([C:25]([O:27][CH2:28][CH3:29])=[O:26])[N:1]=[C:2]2[C:3]([N:9]2[CH2:10][CH2:11][NH:12][CH2:13][CH2:14]2)=[N:4][CH:5]=1A 100 mL round bottom flask was charged with tert-butyl 4-(3-amino-5-bromopyrazin-2-yl)piperazine-1-carboxylate (8.37 g, 0.0234 mol), ethyl 3-bromo-2-oxopropanoate (13.6 g, 0.070 mol) and EtOH (50 mL). The mixture was stirred at 90° C. for 6 h. Reaction progress was monitored by LC-MS. Work-up: the reaction mixture was filtered. The collected solid was washed with ethyl ether, to afford 5.7 g (56%) of ethyl 5-bromo-8-(piperazin-1-yl)imidazo[1,2-a]pyrazine-2-carboxylate hydrobromide. 1H NMR (300 MHz, DMSO-d6) δ: 8.43 (s, 1H), 7.73 (s, 1H), 4.37-4.32 (m, 6H), 3.16 (br, 4H), 1.34 (t, J=6.9 Hz, 3H).
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