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The general procedure for the synthesis of 4-methoxy-1H-pyrazolo[3,4-d]pyrimidin-6-amine from sodium methanol and 4-chloro-1H-pyrazolo[3,4-d]pyrimidin-6-amine was as follows: 4-chloro-1H-pyrazolo[3,4-d]pyrimidin-6-amine (800 mg, 4.73 mmol) was dissolved in 12.5 mL anhydrous methanol and purged with nitrogen to remove the oxygen. Subsequently, the solution was transferred to a methanol solution containing 2.3 M sodium methanol. After the reaction was refluxed at 65 °C for 2 h, 7.5 mL of acetic acid was slowly added and stirring was continued for 5 min. Upon completion of the reaction, the solvent was removed by rotary evaporation and dried under vacuum to give 745 mg of tan solid product in 95.4% yield.

[1] Patent: CN103804447, 2016, B. Location in patent: Paragraph 0076; 0086; 0087; 0088
[2] Helvetica Chimica Acta, 1986, vol. 69, # 7, p. 1602 - 1613
[3] Heterocycles, 1985, vol. 23, # 10, p. 2521 - 2524