REACTIONS OF 2-MONO- AND 2,6-DISUBSTITUTED 4-PYRONES WITH PHENYLHYDRAZINE AS GENERAL METHOD FOR THE SYNTHESIS OF 3-(<i>N</i>-PHENYLPYRAZOLYL)INDOLES

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. 2015, 50, 1388. [Khim. Geterotsikl. Soedin. 2014, 1510.]

For this article in the English edition see DOI 10.1007/s10593-014-1603-3