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

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-haloarenecarbonyl 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-6(9H)-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. © 2007 by MDPI.