3.5- Diethynyl-l-methylpyrazole

Moreover, it has been established that dehydrocondensation can also be applied to 3,5-diethynyl-l-methylpyrazole, which makes it possible to produce polymer (88%) with an extended system of conjugate bonds possessing semiconductor properties (2001UP2). 

The same regularities are observed for polyethynylpyrazoles. Thus, for 3,5-diethynyl-l-methylpyrazole, the ehemieal shifts (in CCI4) are 3-C=CH 2.95,... 

The above method can also be used to simultaneously transform two acetyl groups into acetylenic ones in positions 3 and 5 of the pyrazole ring. This is demonstrated by the synthesis of 3,5-diethynyl-1 -methylpyrazole (yield 62%) from 3,5-diacetyl-l-methylpyrazole (Scheme 30). 

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). 

For aeetylenes elose in strueture, the values of the eharaeteristie frequeneies of the tiiple bond ehange negligibly. Thus, 3,4-diethynyl-, 4,5-diethynyl-, and 3,4,5-tiiethynyl-l-methylpyrazoles have the following values for the C=C bond frequeneies 2132, 2135, and 2138 em , respeetively and the band typieal of the =C—H bond has the same value for all three polyethynylpyrazoles (3320 em ) (71IZV1764). 

---