Abstract
Phenylhydrazine reacted regioselectively with 6-substituted 4-pyrone-2-carboxylic acids (or esters) in protic and aprotic solvents, leading to phenylhydrazones of 3-(3-R-1-phenylpyrazol-5-yl)- or 3-(5-R-1‑phenylpyrazol-3-yl)pyruvic acids (or esters), respectively. 6-Di(tri)fluoromethylcomanic acids (or esters) reacted analogously, forming the corresponding phenylhydrazones with R F group in the side chain. The obtained phenylhydrazones underwent Fischer reaction under acidic conditions, forming the respective 3-( N -phenylpyrazolyl)indoles. In contrast to comanic acid and its ester, the reactions of 2‑substituted 4-pyrones occurred non-selectively and gave mixtures of regioisomeric pyrazoles with phenylhydrazone group in the side chain or 3-( N -phenylpyrazolyl)indoles. A mechanism was proposed to explain the effect of solvent on the course of reaction. Obydennov, D. L.; Usachev, B. I.; Sosnovskikh, V. Ya. Chem. Heterocycl. Compd. 201 5 , 50 , 1388. [ Khim. Geterotsikl. Soedin. 2014 , 1510.] For this article in the English edition see DOI 10.1007/s10593-014-1603-3
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