Synthesis
Step 1. Synthesis of 1-(4-methoxybenzyl)-1H-pyrazol-5-amine. Hydrazine hydrate (NH2NH2-H2O, 23.19 mL, 478 mmol) was slowly added dropwise to a solution of tetrahydrofuran (THF, 250 mL) containing acrylonitrile (30 mL, 455 mmol) at 0 °C. After the dropwise addition, the reaction mixture was stirred at room temperature for 2 hours. Subsequently, 4-methoxybenzaldehyde (55.4 mL, 455 mmol) was added slowly dropwise. The reaction mixture was stirred overnight at room temperature and then continued to stir under reflux conditions for 2 hours. After completion of the reaction, it was cooled to room temperature and the reaction was quenched by the addition of 300 mL of ice water. The mixture was extracted with ethyl acetate (3 times) and the combined organic layers were extracted with 1N hydrochloric acid (HCl). The aqueous layer was neutralized with 10N aqueous sodium hydroxide (NaOH) and then extracted with ethyl acetate. The organic layer was washed sequentially with water and brine and dried over anhydrous sodium sulfate (Na2SO4). After filtration, it was recrystallized with ethyl ether (Et2O) to afford the target compound 1-(4-methoxybenzyl)-1H-pyrazol-5-amine as a white solid (50 g, 60% yield).
References
[1] Patent: WO2009/62308, 2009, A1. Location in patent: Page/Page column 51; 52
[2] Patent: WO2013/127266, 2013, A1. Location in patent: Page/Page column 132
[3] Patent: WO2013/127267, 2013, A1. Location in patent: Page/Page column 83
[4] Patent: WO2013/127269, 2013, A1. Location in patent: Page/Page column 145
[5] Bioorganic and Medicinal Chemistry Letters, 2013, vol. 23, # 20, p. 5488 - 5497
