Synthesis
The general procedure for the synthesis of 5-methyl-6-nitroindazole from 2,4-dimethyl-5-nitroaniline is as follows:
1. 2,4-dimethyl-5-nitroaniline (1.662 g, 10.00 mmol) was dissolved in glacial acetic acid (100 ml) and the mixture was cooled to 0°C.
2. Sodium nitrite solution (1 equiv, 690 mg dissolved in 2 ml of water) was slowly added while keeping the reaction temperature below 25 °C.
3. Stirring of the reaction mixture was continued for 3 hours, followed by filtration.
4. The filtrate was allowed to stand at room temperature for 3 days and then concentrated under reduced pressure.
5. The concentrated residue was diluted with water and the resulting mixture was vigorously stirred.
6. The solid product was collected by filtration, washed thoroughly with cold water and dried. 7.
7. Finally, the product was purified by fast chromatography (dichloromethane/methanol with an eluent ratio of 99:1) to give 1.030 g (58.1% yield) of 5-methyl-6-nitro-1H-indazole in solid form.
References
[1] Bioorganic and Medicinal Chemistry, 2016, vol. 24, # 3, p. 403 - 427
[2] Patent: US2010/160373, 2010, A1. Location in patent: Page/Page column 28-29
[3] Patent: US2011/71143, 2011, A1. Location in patent: Page/Page column 37
[4] Journal of Medicinal Chemistry, 2015, vol. 58, # 21, p. 8413 - 8426
[5] Patent: WO2007/95124, 2007, A2. Location in patent: Page/Page column 89-90
