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

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\u27,5\u27:5,6]pyrano[2,3-c]pyrazol-4(1H)-one, thieno[3\u27,2\u27:5,6]pyrano[2,3c]pyrazol- 4-(1H)-one, thieno[3\u27,4\u27:5,6]pyrano[2,3-c]pyrazol-4(1H)-one, thieno[3\u27\u27,2\u27\u27:4\u27,5\u27]thieno[2\u27,3\u27:5,6]-pyrano[2,3-c]pyrazol-4(1H)-one, [1,3]dioxolo[5\u27,6\u27][1]benzothieno[2\u27,3\u27:5,6]pyrano-[2,3-c]- pyrazol-4(1H)-one, pyridazino[4\u27,3\u27:5,6]pyrano[2,3-c]pyrazol-4(1H)-one and pyrazolo-[4\u27\u27,3\u27\u27:5\u27,6\u27]pyrido[3\u27,4\u27:5,6]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