New findings in the richter reaction in series of vicinal alkynylpyrazolyldiazonium salts

Eugene V. Tretyakov, Sergei F. Vasilevsky

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When treated with sodium nitrite in hydrochloric or hydrobromic acid, positional isomers of vic-alkynylaminopyrazoles were transformed to the pyrazolopyridazines via cyclization of the corresponding alkynylpyrazolyldiazonium salt. The reaction was found to depend on the position of alkynyl and diazonium group in pyrazole nuclei: the heterocyclization of 5-alkynylpyrazolyl-4-diazonium salts underwent at 100-105 °C and gave 7-chloro-1H-pyrazolo[4,3-c]p;yridazines; the heterocyclization of 4-alkynylpyrazolyl-3-diazonium salts at 50-60 °C gave 6-hydroxy-2H-pyrazolo[3,4-c]pyridazines as major component and 6-halogeno-2H-pyrazolo[3,4-c]pyridazines as minor component; the cyclization of 3-alkynylpyrazolyl-4-diazonium salts accompanying with methyl group migration towards the neighbouring nitrogen atom afforded 7-chloro-1H-pyrazolo[4,3-c]pyridazines.

Original languageEnglish
Pages (from-to)519-524
Number of pages6
JournalHeterocyclic Communications
Issue number6
Publication statusPublished - 1 Jan 1998
Externally publishedYes


ASJC Scopus subject areas

  • Organic Chemistry

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