Ethyl-2,4-dioxohexanoate → ethyl 5-ethyl-1-butyl-1H-pyrazole-3-carboxylate

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Reaction Steps

A solution of ethyl 2,4-dioxohexanoate (approximately 60% pure, 45.0 g, 0.232 mol), prepared as described in Part A of Example 10, in glacial acetic acid (150 mL) was cooled to 0° C. Butylhydrazine oxalate (25.0 g, 0.139 mol) was added slowly. The reaction was allowed to warm to ambient temperature, stirred overnight, and concentrated under reduced pressure. The residue was adjusted to pH 10 with the addition of 2 M aqueous sodium carbonate. The mixture was extracted with chloroform and an emulsion that contained solid material formed. The solid was isolated by filtration, and the filtrate was transferred to the separatory funnel. The organic layer was separated. The aqueous layer was extracted with chloroform three times. The combined organic layers were dried over sodium sulfate, filtered, and concentrated under reduced pressure to provide an oil that was purified by chromatography on a HORIZON HPFC system (silica gel, gradient elution with CMA in chloroform) to yield 13.27 g of ethyl 5-ethyl-1-butyl-1H-pyrazole-3-carboxylate as a yellow oil.

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