Synthesis
General procedure for the synthesis of 4-nitroindazole from 2-methyl-3-nitroaniline:
A. Preparation of 4-nitroindazole
An aqueous sodium nitrite solution was prepared by dissolving sodium nitrite (20 g, 0.29 mol) in 50 mL of water. This aqueous sodium nitrite solution was added at once to a glacial acetic acid solution containing 2-methyl-3-nitroaniline (20 g, 0.13 mol) at 0 °C. The reaction system was vigorously stirred using an overhead stirrer. Immediately after the addition of sodium nitrite solution, precipitation generation was observed. Subsequently, the reaction mixture was gradually warmed up to room temperature and stirring was continued overnight. Upon completion of the reaction, the precipitate was separated by filtration and the filtrate was concentrated under vacuum. The resulting dark orange solid was suspended in water, filtered again and dried to give 14-21 g of dark orange solid product in 99% yield.
References
[1] Patent: US6534504, 2003, B1
[2] Bioorganic and Medicinal Chemistry Letters, 2005, vol. 15, # 11, p. 2752 - 2757
[3] Journal of Medicinal Chemistry, 2006, vol. 49, # 7, p. 2339 - 2352
[4] Organic Process Research and Development, 2007, vol. 11, # 3, p. 578 - 584
[5] Journal of Medicinal Chemistry, 2010, vol. 53, # 2, p. 649 - 659
