Ethyl 2,4-dioxovalerate → Ethyl 1-ethyl-5-methyl-1H-pyrazole-3-carboxylate

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Reaction Steps

Ethylhydrazine oxalate (23.7 g, 158 mmol) was added slowly to an 11° C. solution of ethyl acetopyruvate (50.0 g, 316 mmol) in ethanol so that the internal temperature did not exceed 14° C. The reaction was allowed to warm to ambient temperature and was stirred overnight. The reaction was concentrated under reduced pressure and 2 M sodium carbonate was added to adjust the mixture to pH 9. The mixture was transferred to a separatory funnel. The aqueous phase was extracted with methyl tert-butyl ether (3×600 mL). The organic layers were combined, dried over magnesium sulfate, filtered, and concentrated under reduced pressure to yield 28.94 g of ethyl 1-ethyl-5-methyl-1H-pyrazole-3-carboxylate as an orange oil that was used without purification in the next reaction.

Provenance & Evidence