Eglė Arbačiauskienė, G. Vilkauskaitė, A. Šačkus
Apr 1, 2011
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Influential Citations
20
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Journal
European Journal of Organic Chemistry
Abstract
The easily obtainable title compounds ethyl 5- and 3-triflyloxy-1H-pyrazole-4-carboxylates (2 and 5) have been used as precursors in Sonogashira-type cross-coupling reactions with various alkynes to obtain the corresponding 5- and 3-alkynyl-4-(ethoxycarbonyl)pyrazoles 3 and 6. Cyclization of the latter ortho-difunctional synthons afforded different condensed pyrazoles such as pyrano[4,3-c]pyrazol-4(1H)-ones and -4(2H)-ones 7 and 10 as well as 1,5-dihydro- and 2,5-dihydro-4H-pyrazolo[4,3-c]pyridin-4-ones 9 and 12, respectively. Suzuki coupling of triflate 2 with phenylboronic acids gave the corresponding 5-arylpyrazoles. Heating of 5-(3-chlorophenyl)-1-phenyl-1H-pyrazole-4-carboxylic acid (16) with trifluoromethanesulfonic acid led to the formation of the unexpected tetracyclic system 18. Detailed NMR spectroscopic investigations were undertaken on all obtained products.