Synthesis
At room temperature, 1H-indazol-5-ol (1.60 g, 11.9 mmol) was dissolved in tetrahydrofuran (50 mL) and N-chlorosuccinimide (1.59 g, 11.9 mmol) was added. After 1 hour of reaction, the mixture was warmed up to 40 °C to continue the reaction for 2 hours, followed by warming up to 50 °C for 5 hours. Upon completion of the reaction, the reaction solution was poured into water (100 mL) and extracted with ethyl acetate (3 × 100 mL). The organic layers were combined, dried with anhydrous magnesium sulfate and concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (eluent: hexane/ethyl acetate) to afford 4-chloro-5-hydroxy-1H-indazole (1.7365 g, 86% yield).1H-NMR (DMSO-d6) δ: 7.09 (1H, d, J = 8.8 Hz), 7.33 (1H, d, J = 8.8 Hz), 7.90 (1H, s) 9.71 (1H, s), 13.10 (1H, s).
