Ethanol → ethyl 5-chloro-3-(trifluoromethyl)-1H-pyrazole-1-acetate

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To a mixture of ethyl hydrazinoacetate hydrochloride (2.8 g, 18.1 mmol) and triethylamine (9.2 g, 91 mmol) in a solution of ethanol (20 mL) and N,N-dimethylformamide (1 mL), a solution of crude 4,4-dichloro-1,1,1-trifluoro-3-buten-2-one in dichloromethane (20 mL) was added dropwise while keeping the temperature of the reaction mixture below 10° C. After stirring a further 2 h at below 10° C., the reaction mixture was concentrated under reduced pressure. The residue was diluted with diethyl ether, and the mixture was filtered. The resulting filtrate was concentrated to give 4.34 g of the title compound as a solid. This compound was of sufficient purity to use in subsequent reactions.

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