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Synthesis 2006(24): 4219-4229  
DOI: 10.1055/s-2006-950324
PAPER
© Georg Thieme Verlag Stuttgart · New York

An Efficient Approach to Heterocyclic Analogues of Xanthone: A Short Synthesis­ of All Possible Pyrido[5,6]pyrano[2,3-c]pyrazol-4(1H)-ones

Gernot A. Eller*, Veronika Wimmer, Andreas W. Haring, Wolfgang Holzer*
Department of Drug Synthesis, University of Vienna, Faculty of Life Sciences, 1090 Vienna, Austria
Fax: +43(1)42779556; e-Mail: gernot.eller@univie.ac.at; e-Mail: wolfgang.holzer@univie.ac.at;
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Publication History

Received 24 July 2006
Publication Date:
13 November 2006 (online)

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Abstract

An efficient and generally applicable synthesis of various [5,6]pyrano[2,3-c]pyrazol-4(1H)-ones by the reaction of either 1-substituted or 1,3-disubstituted 2-pyrazolin-5-ones with different o-halopyridinecarbonyl chlorides or with 3-chloroquinoline-2-carbonyl chloride, using calcium hydroxide in 1,4-dioxane, is described. In the course of the preparation of pyrazolo[4′,3′:5,6]pyrano[2,3-c]pyridin-4(1H)-ones, the intermediate 4-(3-chloroisonicotinoyl)-1H-pyrazol-5-ols did not cyclize spontaneously and thus were transformed into the corresponding tricycles by treatment with NaH in DMF. The N1-unsubstituted title compounds were obtained upon treatment of the corresponding 1-(4-methoxybenzyl) protected congeners with trifluoroacetic acid.

Key words

pyrazolones - acylations - nucleophilic aromatic substitutions - fused-ring systems - cyclizations