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The reaction was carried out with 4-nitro-1H-pyrazole-3-carboxylic acid methyl ester (2.0 g, 11.7 mmol) and iodomethane (2.0 g, 14.0 mmol) in the presence of potassium carbonate (1.62 g, 11.7 mmol) in acetone (60 mL) and stirred for 5 hours at 30°C. After completion of the reaction, the mixture was diluted with water and extracted with chloroform. The organic phases were combined, dried with anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. The resulting crude product was purified by silica gel column chromatography (eluent: hexane-ethyl acetate from 4:1 to 1:1) to isolate two major products: methyl 1-methyl-4-nitro-1H-pyrazole-3-carboxylate (Rf values 0.43, 0.95 g, 44% yield) and methyl 1-methyl-4-nitro-1H-pyrazole-5-carboxylate (Rf values 0.71, 0.61 g, 28% yield).

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