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Molecules 2007, 12(1), 60-73; doi:10.3390/12010060

A Convenient Approach to Heterocyclic Building Blocks: Synthesis of Novel Ring Systems Containing a [5,6]Pyrano[2,3-c]pyrazol-4(1H)-one Moiety

*  and
Department of Drug and Natural Product Synthesis, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
* Author to whom correspondence should be addressed.
Received: 15 January 2007 / Revised: 24 January 2007 / Accepted: 24 January 2007 / Published: 26 January 2007
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Starting from commercially available educts, a straightforward synthetic route to new heterocyclic building blocks is exemplified with the one- or two-step synthesis of tri-, tetra-, or pentacyclic ring systems. Representatives of the following novel ring systems are prepared from 3-methyl-1-phenyl-2-pyrazolin-5-one and the corresponding o-halo-arenecarbonyl chloride using calcium hydroxide in refluxing 1,4-dioxane: pyrimidino[4',5':5,6]pyrano[2,3-c]pyrazol-4(1H)-one, thieno[3',2':5,6]pyrano[2,3c]pyrazol- 4-(1H)-one, thieno[3',4':5,6]pyrano[2,3-c]pyrazol-4(1H)-one, thieno[3'',2'':4',5']thieno[2',3':5,6]-pyrano[2,3-c]pyrazol-4(1H)-one, [1,3]dioxolo[5',6'][1]benzothieno[2',3':5,6]pyrano-[2,3-c]- pyrazol-4(1H)-one, pyridazino[4',3':5,6]pyrano[2,3-c]pyrazol-4(1H)-one and pyrazolo-[4'',3'':5',6']pyrido[3',4':5,6]pyrano[2,3-c]pyrazol-4(1H)-one. While the latter two ring systems are directly obtained due to a spontaneous intramolecular substitution reaction, in the other reactions uncyclised 4-aroylpyrazol-5-ols are produced, which are cyclised into the target heterocycles in a subsequent synthetic step (i.e. treatment with NaH in DMF). Detailed NMR spectroscopic investigations (1H-, 13C-, 15N-) with the obtained compounds were undertaken to unambiguously prove the new structures.
Keywords: Fused-ring systems;NMR spectroscopy;heterocyclic building blocks;acylations;pyrazolones. Fused-ring systems; NMR spectroscopy; heterocyclic building blocks; acylations; pyrazolones.
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Eller, G.; Holzer, W. A Convenient Approach to Heterocyclic Building Blocks: Synthesis of Novel Ring Systems Containing a [5,6]Pyrano[2,3-c]pyrazol-4(1H)-one Moiety. Molecules 2007, 12, 60-73.

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