Synthesis
General procedure for the synthesis of 5-bromo-3-methyl-1H-indazole from 1-(5-bromo-2-fluorophenyl)ethanone: 1-(5-bromo-2-fluorophenyl)ethanone (66.0 g, 304 mmol) and 350 mL of anhydrous hydrazine were added to a 1-liter round bottom flask. The reaction mixture was refluxed at 117 °C for 5 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the excess hydrazine was removed by evaporation under reduced pressure to give a white solid. 400 mL of water was added to the solid and the aqueous phase was separated by filtration. The solid was washed twice with 400 mL of water. To remove trace hydrazine, the white solid was dissolved in 600 mL of ethyl acetate and washed sequentially with 300 mL of water twice and saturated brine. The organic phase was dried with anhydrous sodium sulfate and the solvent was concentrated under reduced pressure to give the white amorphous solid product 5-bromo-3-methyl-1H-indazole (60.0 g, 94% yield). The product did not require further purification and could be used directly in the subsequent reaction.
References
[1] Patent: WO2009/11880, 2009, A2. Location in patent: Page/Page column 95-96
[2] Patent: WO2006/44860, 2006, A2. Location in patent: Page/Page column 23-24
[3] Patent: WO2009/144554, 2009, A1. Location in patent: Page/Page column 43
[4] Journal of Medicinal Chemistry, 2012, vol. 55, # 2, p. 935 - 942
[5] Patent: US2006/142307, 2006, A1. Location in patent: Page/Page column 24
[6]
Dong, R., Zhang, C., Wang, C., Zhou, X., Li, W., Zhang, J.-Y., Wang, M., Xu, Y., Sun, L.-P. (2022). Design, synthesis and anticancer evaluation of 3-methyl-1H-indazole derivatives as novel selective bromodomain-containing protein 4 inhibitors. Bioorganic & Medicinal Chemistry, 55, 116592.
https://doi.org/10.1016/j.bmc.2021.116592
