Methyl acetopyruvate → 1-Benzyl-5-methyl-1h-pyrazole-3-carboxylate

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A mixture of methyl acetopyruvate (1.0 g, 6.94 mmol) and benzylhydrazine dihydrochloride (1.49 g, 7.63 mmol) in acetic acid (7 mL) was stirred for 4 h at 90° C. After removal of the solvent (rotavapor), the residue was subjected to MPLC (silica, cyclohexane/ethyl acetate 10:1→2:1, followed by dichloromethane/methanol 10:1). The eluate obtained with dichloromethane/methanol contained the title compound as a crude product. After evaporation of the solvent, this fraction was further purified by preparative HPLC to afford the title compound (260 mg, 17%): 1H NMR (400 MHz, DMSO-d6) δ 12.57 (s, 1H), 7.37-7.27 (m, 3H), 7.12 (d, 2H), 6.53 (s, 1H), 5.36 (s, 2H), 2.22 (s, 3H).

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