Synthesis
General procedure for the synthesis of 5-bromo-7-nitro-1H-indazole from 2-methyl-4-bromo-6-nitroaniline: the raw material 2-methyl-4-bromo-6-nitroaniline (1.00 g, 4.32 mmol) was dissolved in 15 mL of acetic acid. An aqueous solution (2 mL) of sodium nitrite (0.66 mg, 9.52 mmol) was added slowly at 0 °C. After addition, the reaction mixture was gradually warmed up to room temperature with continuous stirring. The progress of the reaction was monitored by thin layer chromatography (TLC) until complete conversion of the feedstock. Upon completion of the reaction, the solvent was removed by rotary evaporation followed by extraction operation. The crude product was purified by column chromatography to afford the final target compound 5-bromo-7-nitro-1H-indazole (0.5 mg, 2.07 mmol) in orange powder form in 47.7% yield.
References
[1] Indian Journal of Chemistry - Section B Organic and Medicinal Chemistry, 2000, vol. 39, # 5, p. 339 - 345
[2] Journal of Medicinal Chemistry, 2015, vol. 58, # 9, p. 3892 - 3909
[3] Patent: CN108689937, 2018, A. Location in patent: Paragraph 0179; 0181; 0182
[4] Patent: CN108689936, 2018, A. Location in patent: Paragraph 0118; 0119; 0120; 0121
