4- Ethynylpyrazole, formation

Using chloro- or bromoenines, one can immediately obtain 4-ethynylpyrazoles (omitting the stage of pyrazolenine isolation) which is accompanied by methylation and the formation of the mixture of 3- and 5-sulfonyl-l-methyl-4-acetylenylpyra-zoles in about 1 2 ratio (total yield 37%) (Scheme 14). 

The same type of reaction occurs in the work of Hauptman (76T1293), who, studying the chemistry of diethynylcarbenes, found that the pyrolysis of the lithium salts of diethynylketone tosylhydrazones 5 (140-150°C) in the presence of olefins leads to cyclopropanes. This process results in the formation of the corresponding 3-ethynylpyrazoles. The formation of l-p-tolylsulfonyl-3-alkynylpyrazoles from hydrazone runs in milder conditions (50°C, 14 h) (Scheme 24). 

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