Reactions with Participation of the C— X Bond

Synthetieally, the most important reaetions of this type are the eleavage of the =C—X bond and the formation of a new =C—H bond. 

The high stability of terminal aeetylenes of the pyrazole series allows the preparation of polyethynyl derivatives like 3,4-diethynyl-, 4,5-diethynyl-, and even 3,4,5-tiiethynyl-l-methylpyrazole in 64%, 78%, and 41% yields, respeetively, in these strong eonditions (71IZV1764) (Sehemes 93 and 94). 

The series of l,3-dimethyl-5-ethynylpyrazoles, including the functionally substituted ones, was obtained at lower temperature (100-105° C, 10 wt % of powdered KOH, 1.5-2 mm Hg) (86TH1). 

However, milder conditions are necessary for obtaining the less stable 1-methyl-3-butadiynyl- and l-methyl-5-butadiynylpyrazole. The acetylenic alcohols were stirred with KOH at room temperature in acetylene atmosphere (to bind the isolated carbonyl compound). The product yields were 68% and 65% (69IZV2546), respectively. 

the method of cleavage of the tertiary acetylenic alcohols in boiling benzene or toluene in the presence of NaOH or KOH was reported (88M253 2001UP1). 

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