G. Eller, V. Wimmer, Andreas W. Haring
Nov 13, 2006
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17
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Journal
Synthesis
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 N 1-unsubstituted title compounds were obtained upon treatment of the corresponding 1-(4-methoxybenzyl) protected congeners with trifluoroacetic acid.