General procedure for the synthesis of 5-iodo-1-methyl-1H-indazole from 1-methyl-1H-indazol-5-amine:
1. add 1-methyl-1H-indazol-5-amine (500 mg, 3.40 mmol) to a mixture of concentrated sulfuric acid (1.3 mL) and water (5.5 mL) at 0 °C.
2. a solution of sodium nitrite (258 mg, 3.74 mmol) in water (0.5 mL) was added dropwise to the above mixture.
3. The reaction mixture was stirred at 0 °C for 10 min.
4. The stirred mixture was added dropwise to a solution of sodium iodide (1.5 g) in water (4.5 mL) cooled to 0 °C.
5. After addition, the reaction mixture was heated to 90°C and held for 20 minutes.
6. After completion of the reaction, the resulting mixture was alkalized with dilute sodium hydroxide solution and extracted with ethyl acetate.
7. The organic phase was washed with brine, dried over magnesium sulfate and then concentrated in vacuum.
8. The residue was purified by fast column chromatography on silica gel using a petroleum ether solution of 20% EtOAc as eluent to afford the title compound 5-iodo-1-methyl-1H-indazole (475 mg, 54% yield).
1H NMR (DMSO D6, 400 MHz) δ 4.03 (3H, s), 7.52 (1H, d), 7.63 (1H, dd), 7.99 (1H, s), 8.17 (1H, s).
