Synthesis
General procedure for the synthesis of indazole-5-carboxylic acid hydrochloride from methyl 1H-indazole-5-carboxylate: 1H-indazole-5-carboxylic acid methyl ester (6.5 g, 1.0 eq.) and 200 mL of methanol (MeOH) were added to a stirred 1 L reaction flask, followed by a solution of sodium hydroxide (NaOH, 4.4 g, 3.0 eq.) dissolved in 150 mL of water (H2O). The reaction mixture was heated to reflux for 1 hour. Upon completion of the reaction, the organic solvent was evaporated under reduced pressure. The remaining aqueous phase was washed with ethyl acetate (EtOAc) and then acidified with 3N hydrochloric acid (HCl) to pH=5~6. The precipitate was collected by filtration and washed with deionized water to afford the target product, indazole-5-carboxylic acid hydrochloride, as a yellow solid (6.2 g, 98% yield).
References
[1] Patent: WO2013/97773, 2013, A1. Location in patent: Paragraph 0261
[2] Patent: US2012/277224, 2012, A1. Location in patent: Page/Page column 40
[3] Patent: WO2014/66743, 2014, A1. Location in patent: Paragraph 0146
[4] Bioorganic and Medicinal Chemistry, 2006, vol. 14, # 24, p. 8219 - 8248
