3- Ethynyl-l-methylpyrazole

The composition of the mixture of products of different structures depends on the diacetylene diazomethane ratio (68LA124). With a 1 1 ratio of butadiyne and diazomethane, 3(5)-ethynylpyrazole dominates (55%). The yields of isomeric 3- and 5-ethynyl-l-methylpyrazoles are 8 and 11%, respectively. The double excess of diazomethane leads mainly to a mixture of N-methylated isomers (81%), 10% of 3(5)-ethynylpyrazole, and a small amount (3%) of bipyrazole (68LA124) (Scheme 3). 

By the chlorination of 3-ethynyl-, 4-ethynyl-, and 5-ethynyl-l-methylpyrazole with KOCl the corresponding compounds were synthesized in 98%, 100%, and 94% yields. The typical procedure is as follows To an aqueous solution of KOX (0.64 N) in 12.5% KOH, prepared from the corresponding halogen and potassium hydroxide in water at 5-10°C, was added the terminal acetylene, followed by stirring at room temperature until the complete disappearance of the starting material. 

For example, 3-ethynylpyrazole shows bands at 2120 cm and 3275 cm . 5-Ethynyl-l-methylpyrazole shows bands at 3290 cm and 2120 cm (68LA113). 

Thus, the hydrogenation of isomeric l-ethynyl-3-methyl- and l-ethynyl-5-methylpyrazoles by hydrogen with 10% Pd/C in l-ethyl-3-methyl- and 1-ethyl-5-methylpyrazoles was used to prove the structure of iV-ethynylpyrazoles formed from pyrolysis of the corresponding iV-propynoylazoles (94AJC991) (Scheme 79). 

For 1-ethynylpyrazole, l-ethynyl-3,5-dimethylpyrazole, l-ethynyl-3-methylpy-razole, and l-ethynyl-5-methylpyrazole, the ehemieal shifts of the methyne protons appear in CDCI3 at 3.14, 3.22, 3.05, and 3.21 ppm, respeetively (94AJC991). 

The NMR spectra for several alkynylpyrazoles have been measured, and selected data are presented in this section. The signals of the C=C atoms in the NMR spectraresonate in the range 70-95 ppm. For l-ethynyl-3-methylpyrazole the chemical shift of C=CH atom appears at 58.3 ppm the chemical shift of the C=CH atom is 61.7. For l-ethynyl-5-methylpyrazole the chemical shift of the C=CH atom is 58.3 ppm, and the chemical shift of the C=CH atom is 61.7 ppm (94AJC991). The direct spin-spin coupling constant of ( 7c c) is 179.9... 

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