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- Alpha-oxoethanals (1)
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Aza-enamines X - Formylation of Pyrazole-4-carbaldehyde Hydrazones at the Hydrazonoazomethine C-Atom
(2003)
1,3-Disubstituted 1H-pyrazole-4-carbaldehyde-N,N-dimethylhydrazones 1 reacted with the Vilsmeier-Haackreagent, corresponding to the aza-enamine concept, in an electrophilicsubstitution reaction at the azomethine C-atom yielding the 1,4,5-triaza-pentadieniumsalts 2. These were hydrolysed to give2-hydrazono-2-(1H-pyrazole-4-yl)ethanals 3. The electrophilic attack did not takeplace at the vinylogous position 5' of the pyrazoles.