[Br:1]Br.[C:3]1([N:9]2[C:13]3[NH:14][C:15](=[O:18])[CH:16]=[CH:17][C:12]=3[CH:11]=[N:10]2)[CH:8]=[CH:7][CH:6]=[CH:5][CH:4]=1>C(O)(=O)C.O>[Br:1][C:16]1[C:15](=[O:18])[NH:14][C:13]2[N:9]([C:3]3[CH:4]=[CH:5][CH:6]=[CH:7][CH:8]=3)[N:10]=[CH:11][C:12]=2[CH:17]=1Bromine (76 μl, 1.47 mmol) was added to a solution of 1-phenyl-1,7-dihydropyrazolo[3,4-b]pyridin-6-one (0.31 g, 1.47 mmol) in acetic acid (7 ml) and the mixture was stirred for 30 min. The suspension was diluted with water, stirred for 10 min and then the precipitate filtered off, washing with water. The product was dried in a desiccator at 40° C. under vacuum for 17 h to give 5-bromo-1,7-dihydro-1-phenylpyrazolo[3,4-b]pyridin-6-one (0.29 g, 68%) as a brown solid. δH (400 MHz; DMSO) 7.32-7.37 (1H, m), 7.52-7.58 (2H, m), 8.12-8.24 (3H, m), 8.50 (1H, s); m/z (ES+) 290 (M+H+), 292 (M+H+).
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