Methyl triflate → ethyl 2,3-dihydro-1-methyl-3-oxo-2-phenyl-1H-pyrazole-4-carboxylate

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To a solution of ethyl 3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate (1000 mg, 5.0 mmol) in dichloromethane (10 mL) was added methyl trifluoromethanesulfonate (1200 mg, 7.3 mmol). The red solution was stirred at room temperature. After 14 h, the mixture was partitioned between dichloromethane and NaHCO3 (sat). The aqueous was extracted with dichloromethane (2×). The combined organic was dried over Na2SO4, concentrated and purified on silica. The product was triturated with EtOAc-hexane-CHCl3 to give the pure product as crystals (260 mg, 21%). Calc'd for C12H12N2O3, 232.08; MS (ESI pos. ion) m/z: 233 (MH+). 1H NMR (400 MHz, CHLOROFORM-d): 1.36 (t, J=7.04 Hz, 3 H), 3.39 (s, 3 H), 4.32 (q, J=7.17 Hz, 2 H), 7.32 (d, J=7.43 Hz, 2 H), 7.42 (t, J=7.34 Hz, 1 H), 7.50 (t, J=7.73 Hz, 2 H), 7.99 (s, 1 H).

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