90914-41-3

4-Chloro-1H-pyrazolo[3,4-d]pyrimidine (1.1 g, 7.1 mmol) was used as starting material and suspended in CHCl3 (50 mL). N-bromosuccinimide (NBS, 1.49 g, 8.4 mmol) was added to the suspension under stirring. The reaction mixture was stirred at room temperature for 5 h and subsequently cooled to 0°C. The resulting solid product was separated by vacuum filtration and washed with cold CHCl3. The solid product was dried over air and further purified by silica gel column chromatography (eluent: 50% EtOAc/hexanes) to afford finally 3-bromo-4-chloro-1H-pyrazolo[3,4-d]pyrimidine (1.3 g, 77% yield).

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