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36. Thermal cyclization of 2-hydrazonoacyl-3-oxo-heterocycles to pyrazolo[4,3-c]fused heterocycles.
Stadlbauer W., Hojas G., Fiala W.
Second International Electronic Conference on Synthetic Organic Chemistry (ECSOC-2), http://www.mdpi.org/ecsoc/, September 1-30, 1998

Abstract: 1-Azido-2-hydrazonoacyl-3-oxo-heterocycles 2 such as 4-azido-3-hydrazonoacyl- 2-quinolones, 4-azido-3-hydrazonoacyl-coumarins or 4-azido-3-hydrazonoacyl- 2-pyridones, which were obtained from the corresponding acyl derivatives 1, cyclize upon thermolysis to give 2-arylamino-pyrazolo[4,3-c]fused compounds 3. The cyclization conditione were studied by differential scanning calorimetry (DSC) . Structure elucidation of 3 by 13C nmr excluded the formation of triazino isomers.
Attempts to use a reversed reaction path by azidation of the tosylate 4 to 2 resulted always in the cyclization to the 1-aryl-pyrazolo[4,3-c]fused compounds 5. The pyrazols 5 could be obtained also from the precursors of 1 or 4, the corresponding hydroxy-hydrazonoacyl compounds by thermal decomposition. 1-Aryl-pyrazolo[4,3-c]quinolin-2-ones 5 are of interest because of their potential biological activity .

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