Isopropyl iodide → Ethyl 1-(1-methylethyl)-1H-pyrazole-5-carboxylate

To a solution of ethyl 1H-pyrazole-5-carboxylate (1 g) (for example, available form Bio-Farma) in acetonitrile (80 ml) was added cesium carbonate (2.32 g). 20 min later 2-iodopropane (0.714 ml) was added and the mixture stirred under nitrogen at 20° C. for 18 h. 2-Iodopropane (0.714 ml) was added and the mixture stirred under nitrogen at 20° C. for 5 h. Then further 2-iodopropane (0.714 ml) was added and the mixture was stirred at 20° C. for 18 h. The solvent was removed in vacuo and the residue was partitioned between water (30 ml) and DCM (30 ml). The aqueous phase was extracted with DCM (2×20 ml) and separated by hydrophobic frit. The combined organic layers were concentrated in vacuo. Purification of the residue by chromatography on silica gel (70 g silica), eluting with a gradient of 0-100% ethyl acetate in cyclohexane over 30 min gave the title compound (513 mg) as a yellow oil.