HETEROCYCLES

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■ Tri- and Tetracyclic Heteroaromatic Systems: Synthesis of Novel Benzo-, Benzothieno- and Thieno-Fused Pyrano[2,3-c]pyrazol-4(1H)-ones

Gernot A. Eller,* Andreas W. Haring, Barbara Datterl, Maryam Zwettler, and Wolfgang Holzer*

*Department of Drug Synthesis, Faculty of Life Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria

Abstract

A straightforward, two-step synthesis of chromeno[2,3-c]pyrazol-4(1H)-ones, thieno[2’,3’:5,6]pyrano[2,3-c]pyrazol-4(1H)-ones, and [1]benzothieno[2’,3’:5,6]pyrano[2,3-c]pyrazol-4(1H)-ones, respectively, is presented. Hence, treatment of 1-substituted or 1,3-disubstituted 2-pyrazolin-5-ones with 2-fluorobenzoyl chloride, 2-chlorobenzoyl chloride, 3-chlorothiophene-2-carbonyl chloride, or 3-chloro-1-benzothiophene-2-carbonyl chloride using calcium hydroxide in refluxing 1,4-dioxane gave the corresponding 4-aroylpyrazol-5-ols, which were successfully cyclized into the fused ring systems (NaH/DMF). The N-unsubstituted title compounds were obtained upon treatment of 1-(4-methoxybenzyl) protected congeners with trifluoroacetic acid. Detailed NMR spectroscopic investigations (¹H, ¹³C, ¹⁵N) with the obtained compounds were undertaken.