Acetylene derivatives of heterocycles - 5. Some peculiarities in the synthesis of 4-ethynyl-3,5-dimethylpyrazole

1. A method was developed for the synthesis of 4-ethynyl-3,5-dimethylpyrazole from 4-acetyl-3,5-dimethylpyrazole. 2. The reaction of 4-acetyl-3,5-dimethylpyrazole with excess phosphorus pentachloride at elevated temperatures is anomalous and leads, in addition to replacement of the carbonyl oxygen by chlorine, to the replacement of hydrogen in the methyl group attached to the carbonyl group by chlorine. 3. On removal of hydrogen chloride with sodamide in liquid ammonia (3,5-dimethyl-4-pyrazolyl)-α,β-diehloroethylene gives a high yield of (3,5-dimethyl-4-pyrazolyl)-chloroacetylene.