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- 2003 (2)
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- Heterocycles (2) (entfernen)
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.
Synthesis and Reactions of (1E,2Z)-2-N,N-Dialkylhydrazono-2-phenylethanal N,N-Dimethylhydrazones
(2003)
(1E,2Z)-2-N,N-Dialkylhydrazono-2-phenylethanal N,N-dimethylhydrazones 3a-e weresynthesised by the reaction of 1,4,5-triazapentadienium salts 2 with N,N-dimethylhydrazine. The compounds 3a and 3d didnot react with tosyl isocyanate in an electrophilic substitutionreaction at the azomethine C-1 as aza-enamines, but they reactedat room temperature in benzene in a 1,4-dipolar cycloaddition toyield 1,3,5-triazinan-2,4-diones 5a and 5d, whereas at 70 °Coctahydroimidazoimidazol-2,5-dione 6a wasformed via criss-cross addition reaction. With dimethyl sulfatein DMF, 3a was transformed into the trimethylhydrazoniumsalts 7a and 8a,isolated as co-crystallised perchlorates (molar ratio 1:1).