General procedure for the synthesis of ethyl 1-methyl-1H-pyrazole-4-carboxylate from ethyl 4-pyrazolecarboxylate and iodomethane: Ethyl 1H-pyrazole-4-carboxylate (2.5 g, 17.9 mmol) and iodomethane (3.1 g, 21.5 mmol) were dissolved in N,N-dimethylformamide (DMF, 10 mL), followed by addition of potassium carbonate (K2CO3, 5.0 g, 35.8 mmol). The reaction mixture was stirred at room temperature for 16 hours. Upon completion of the reaction, water (50 mL) was added to the mixture and then extracted with ethyl acetate (EA, 50 mL × 2). The organic layers were combined, washed with saturated saline (40 mL), dried over anhydrous sodium sulfate (Na2SO4), and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate = 8:1) to afford ethyl 1-methyl-1H-pyrazole-4-carboxylate (214 mg, yield: 85%) as a colorless oil.1H NMR (300 MHz, DMSO-d6): δ = 8.28 (s, 1H), 7.82 (s, 1H), 4.26 (q, J = 6.9 Hz, 2H), 3.87 (s, 3H), 1.25 (t, J = 6.9 Hz, 3H). Mass spectrum (MS): m/z 155.3 ([M + H]+).
