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A 500 ml Erlenmeyer flask was charged with 25.0 g of 3-butyne-2-one and ethyl ether (200 ml). To the resulting solution, 41.9 g of ethyl diazoacetate were added slowly with stirring. After 30 minutes of stirring, the ether solution began refluxing by itself. After stirring for 1 hour, the mixture was chilled at 0° C. for 1 hour and filtered to yield 28.5 g of 5-acetylpyrazole-3-carboxylic acid ethyl ester as white solids, mp 114°-115° C. NMR: 1.42 (t, 3H), 2.62 (s, 3H), 4.44 (q, 2H), 7.36 (s, 1H).

1. stirringAfter 30 minutes of stirring
2. stirringAfter stirring for 1 hour
3. filtrationfiltered