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General procedure for the synthesis of 3-amino-5-bromo-1H-pyrazolo[3,4-b]pyridine from 5-bromo-2-chloronicotinonitrile: Compound 3 (5-bromo-2-chloronicotinonitrile, 307 mg, 1.4 mmol) was dissolved in ethanol (10 mL) in a microwave reactor tube, followed by the addition of 5 equiv. of hydrazine hydrate (NH2NH2-H2O) to the solution. The reaction mixture was placed in a microwave reactor and radiated at 170 °C for 10 min. Upon completion of the reaction, the solvent was removed by rotary evaporator to afford the target product 3-amino-5-bromo-1H-pyrazolo[3,4-b]pyridine (4) in quantitative yield.

[1] Patent: WO2007/59219, 2007, A1. Location in patent: Page/Page column 54-55
[2] Patent: WO2016/26549, 2016, A1. Location in patent: Page/Page column 43
[3] Bioorganic and Medicinal Chemistry Letters, 2013, vol. 23, # 20, p. 5578 - 5585
[4] Bioorganic and Medicinal Chemistry Letters, 2003, vol. 13, # 9, p. 1577 - 1580
[5] Patent: WO2013/42035, 2013, A1. Location in patent: Page/Page column 17