4- methylpyrazol-3-ones synthesis

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-1-methylpyrazole (Scheme 30). 

The reaction of 4-diethylaminobut-3-en-2-one with monosubstituted hydrazines (95°C, H+, MeOH, HjO, 10 h) leads to pyrazoles 261 and 263 (yield 54%) at a ratio depending on the acidity of the medium. In an acidic medium the isomers 263 are predominantly obtained (76ZOR2063). Aminobutenones with hydrazine give only 5-methylpyrazoles (263) (69ZOR223). Enhydrazones 260 and 262 appear to be the synthesis intermediates. 

Based on the assumptions about the reaction mechanism, one can predict that this technique will be applicable to other binucleophiles for the synthesis of perfluoroalkylated heterocyclic compounds. For example, the reaction of arylhydrazine with perfluoro-2-methylpent-2-ene in the presence of triethylamine led to N-arylperfluoro-3-ethyl-4-methylpyrazole 58 and N-arylperfluoro-4-methyl-5-ethylpyrazole 59 in different ratios depending on the reaction conditions (89RP1456419, 87RP1456418, 90IZY2583 89JAP(K)01 22855 99JFC(98)29). Syn- and /-aminoimines are intermediates in syntheses of pyrazoles they were isolated individually. On heating in the presence of triethylamine they are transformed into mixtures of 58 and 59. 

---