1H-Indazole-7-carboxylic acid

synthetischeSynthesis of 1H-indazole-7-carboxylic acid, H2L4: To 60 mL anhydrous toluene under a nitrogen atmosphere was added methyl-2-amino-3-methylbenzoate (1.8 g, 11 mmol) and KOAc (560 mg, 5.7 mmol), and the mixture heated to reflux, at which time acetic anhydride (3.2 mL, 34 mmol) was added and the mixture stirred at reflux for 10 min. Isoamyl nitrite (2.3 mL, 18 mmol) was added over 30 min and the mixture refluxed overnight. On cooling, the mixture was filtered and evaporated to dryness to give 1.6 g of a pale brown solid, which analysed for methyl 1H-indazole-7-carboxylate. This material was taken up in 40 mL THF, added to a solution of LiOH (5 g, 210 mmol) in 40 mL water, and heated at reflux for 48 h. On cooling, the mixture was concentrated on a rotary evaporator and the resulting aqueous phase filtered and adjusted to pH 4 with dilute HCl, to precipitate the product, which was filtered, washed with water and dried under vacuum. Yield 810 mg, 45%; mp 218–222 °C (decomp); δH (500 MHz, d6-DMSO): 7.23 (t, 1H, J = 7.5 Hz, H4 ), 7.97 (dd, 1H, J = 7.5, 1.0 Hz, H3 ), 8.06 (dd, 1H, J = 7.8, 0.8 Hz, H5 ), 8.21 (s, 1H, H2 ), 13.1 (br s, 2H, H1 & H6 ); δc (125 MHz, d6-DMSO): 113.7, 120.1, 124.6, 126.5, 129.0, 134.3, 138.0, 167.0; HRMS-ESI m/z: found: 163.0503; C8H7N2O2 requires: 163.0502 [M + H+ ]; ˉνmax/cm1 (KBr): 3316 s br, 1700 s, 1619 m, 1592 m, 1509 m, 1285 s, 1201 m, 1145 m, 1078 m, 1056 w, 943 m, 858 s, 745 s, 638 m, 601 m.