[Br:1][C:2]1[C:3]2[N:4]([N:9]=[N:10][N:11]=2)[C:5](Cl)=[N:6][CH:7]=1.[N:12]1([C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[CH2:17][CH2:16][NH:15][CH2:14][CH2:13]1.C(N(CC)CC)C>C(O)C>[Br:1][C:2]1[C:3]2[N:4]([N:9]=[N:10][N:11]=2)[C:5]([N:15]2[CH2:14][CH2:13][N:12]([C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[CH2:17][CH2:16]2)=[N:6][CH:7]=1A 250 mL round bottom flask was charged with 8-bromo-5-chlorotetrazolo[1,5-c]pyrimidine (10 g, 42.7 mmol), tert-butyl piperazine-1-carboxylate (11.9 g, 64 mmol), triethylamine (13 g, 0.13 mol) and ethanol (200 mL). The resulting mixture was heated at 30° C. for 2 h under N2 and then cooled to room temperature. The mixture was concentrated under reduced pressure to dryness. The residue was diluted with water (20 mL) and extracted with dichloromethane (20 mL×3). The combined organic layers were washed with brine (20 mL), dried over anhydrous Na2SO4 and concentrated in vacuo, to afford 15.4 g (94%) of the product as an off-white solid.
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