Synthesis
The general procedure for the synthesis of methyl indazole-4-carboxylate from methyl 3-amino-2-methylbenzoate was as follows: methyl 3-amino-2-methylbenzoate (0.3 g, 1.96 mmol) was dissolved in aqueous NaNO2 (0.62 g, 2 mmol), followed by the slow addition of dilute aqueous glacial acetic acid (7 mL, 3 mmol, the volume ratio of glacial acetic acid to water was 0.2:10). The reaction mixture was stirred at room temperature for 4-6 hours. After completion of the reaction, the reaction mixture was extracted with ethyl acetate (EtOAc) and the organic layer was washed with deionized water (2 x 10 mL). The organic layer was dried over anhydrous sodium sulfate (Na2SO4), concentrated under reduced pressure and purified by column chromatography to give the yellow powdery product indazole-4-carboxylic acid methyl ester. The yield was 0.22 g in 69%; the melting point was 153-155 °C. The product was purified by column chromatography. The 1H NMR (400 MHz, CDCl3, TMS as internal standard, δ in ppm) data of the product were as follows: δ2.55 (s, 3H), 7.37 (t, 1H, J=14.32 Hz), 7.53 (s, 1H), 7.67 (d, 1H, J=8.12 Hz), 7.82 (d, 1H, J=8.16 Hz), 9.79 (s, 1H).
References
[1] Patent: US2012/130078, 2012, A1. Location in patent: Page/Page column 4-5
[2] Patent: EP2141150, 2010, A1. Location in patent: Page/Page column 48
[3] Journal of Medicinal Chemistry, 2000, vol. 43, # 1, p. 41 - 58
[4] Asian Journal of Chemistry, 2014, vol. 26, # 7, p. 1921 - 1930
[5] Patent: WO2009/108838, 2009, A1. Location in patent: Page/Page column 104
