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Synthesis 2003(10): 1615-1619
DOI: 10.1055/s-2003-40527
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© Georg Thieme Verlag Stuttgart ˙ New York

Aza-enamines X: [1] Formylation of Pyrazole-4-carbaldehyde Hydrazones at the Hydrazonoazomethine C-Atom

R. Brehme*a, E. Gründemannb, M. Schneiderb, R. Radegliac, G. Reckc, B. Schulzc
a Max-Planck-Institut für Kolloid- und Grenzflächenforschung, Abt. Grenzflächen, 14424 Potsdam, Germany
b Berlin, Institut für Angewandte Chemie Adlershof, Richard-Willstätter-Straße 12, 12489 Berlin, Germany
c Bundesanstalt für Materialforschung und -prüfung, Richard-Willstätter-Straße 11, 12489 Berlin, Germany
Fax: +49(30)81045927; e-Mail: guenter.reck@bam.de;
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Publication History

Received 19 December 2002
Publication Date:
08 July 2003 (online)

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Abstract

1,3-Disubstituted 1H-pyrazole-4-carbaldehyde-N,N-di­methylhydrazones 1 reacted with the Vilsmeier-Haack reagent, corresponding to the aza-enamine concept, in an electrophilic substitution reaction at the azomethine C-atom yielding the 1,4,5-triaza-pentadienium salts 2. These were hydrolysed to give 2-hydrazono-2-(1H-pyrazole-4-yl)ethanals 3. The electrophilic attack did not take place at the vinylogous position 5′ of the pyrazoles.

Key words

aza-enamines - hydrazones - heterocycles - formylation - α-oxoethanals