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Polysubstituted 3-trifluoromethylpyrazoles: regioselective (3 + 2)-cycloaddition of trifluoroacetonitrile imines with enol ethers and functional group transformations

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Abstract

Non-catalysed addition of trifluoroacetonitrile imines to enol ethers provided fully regioselectively (3 + 2)-cycloadducts, which either spontaneously or via Brønsted acid-induced elimination of ROH molecules led to the formation of 3-trifluoromethylated pyrazoles. In the case of 2,3-dihydrofuran, the respective bicyclic intermediate was isolated and its structure was confirmed by X-ray analysis. Using the developed protocol the synthesis of a known antitumor compound SC-560 was performed in 45% yield. Subsequent functionalisations of selected 4-(ω-hydroxyalkyl)pyrazoles at C(5) through lithiation/addition, cross-coupling reactions or via intramolecular Pd-catalysed C–H arylations opened up an access to polysubstituted pyrazoles including unusual tricyclic systems comprising 7-membered rings (oxepane, thiepane and azepane) as the central unit.

Graphical abstract: Polysubstituted 3-trifluoromethylpyrazoles: regioselective (3 + 2)-cycloaddition of trifluoroacetonitrile imines with enol ethers and functional group transformations

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Publication details

The article was received on 18 Dec 2017, accepted on 22 Jan 2018 and first published on 22 Jan 2018


Article type: Communication
DOI: 10.1039/C7OB03126B
Citation: Org. Biomol. Chem., 2018, Advance Article
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    Polysubstituted 3-trifluoromethylpyrazoles: regioselective (3 + 2)-cycloaddition of trifluoroacetonitrile imines with enol ethers and functional group transformations

    G. Utecht, A. Fruziński and M. Jasiński, Org. Biomol. Chem., 2018, Advance Article , DOI: 10.1039/C7OB03126B

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