Synthesis
The general procedure for the synthesis of 3-iodo-1-methylpyrazole from N-methyl-3-aminopyrazole was as follows: N-methyl-3-aminopyrazole (2000 g, 20.6 mol, 1.0 eq.) was dissolved in a mixture of 6,000 mL of concentrated hydrochloric acid and 2,000 mL of water, which was cooled down to 0-5 °C in an ice-salt bath. Subsequently, 3.5 L of saturated aqueous sodium nitrite (NaNO2, 2842.8 g, 41.2 mol, 2.0 eq.) was slowly added dropwise, with mechanical stirring maintained during the dropwise addition. After 20 minutes of reaction, the reaction solution was slowly added dropwise to 8000 mL of aqueous potassium iodide solution (8549.0 g, 51.5 mol, 2.5 equiv.) that was pre-cooled to 0 °C. After the dropwise addition, the reaction mixture was allowed to warm naturally to room temperature and the reaction was continued for 4 hours. The progress of the reaction was monitored by thin layer chromatography (TLC) and after confirming the completion of the reaction, it was extracted twice with ethyl acetate. The organic phases were combined, washed with saturated brine and dried, followed by concentration of the organic phase. The crude product was purified by fast column chromatography to afford the target compound 3-iodo-1-methyl-1H-pyrazole (3473.8 g, 16.7 mol) in 81.0% yield.
References
[1] Patent: CN105669733, 2016, A. Location in patent: Paragraph 0031; 0032; 0033; 0034
[2] Patent: WO2015/175579, 2015, A1. Location in patent: Paragraph 351
