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

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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Abstract

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 3.0).
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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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