Ethyl-2,4-dioxohexanoate → Ethyl 5-ethyl-1-(4-methylbenzyl)-1H-pyrazole-3-carboxylate

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Reaktionsschritte

A solution of ethyl 2,4-dioxohexanoate (Step 1, 2.0 g, 11.6 mmol) and 4-(methylbenzyl)-hydrazine dihydrochloride (Step 3 of Intermediate A, 2.67 g, 12.8 mmol) in acetic acid (15 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 5:1) to afford the title compound as a highly viscous oil (1.93 g, 61%): 1H NMR (400 MHz, CDCl3) δ 7.10 (d, 2H), 6.98 (d, 2H), 6.62 (s, 1H), 5.33 (s, 2H), 4.40 (quart, 2H), 2.48 (quart, 2H), 2.31 (s, 3H), 1.40 (t, 3H), 1.18 (t, 3H); DCI(NH3)-MS m/z 273 (MH)+; HPLC RT (Method I) 4.75 min.

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