Elsevier

Tetrahedron Letters

Volume 55, Issue 40, 1 October 2014, Pages 5495-5498
Tetrahedron Letters

[CpIrCl2]2-catalysed cyclization of 2-alkynylanilines into indoles

https://doi.org/10.1016/j.tetlet.2014.08.053Get rights and content

Abstract

[CpIrCl2]2 catalyses the cyclization of 2-alkynylanilines into indoles. A wide variety of substrates is tolerated. A reaction pathway involving intramolecular hydroamination is proposed.

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Acknowledgments

This work was supported by Nanyang Technological University and the Ministry of Education (Research Grant No. M4011017). One of us (E.K.) thanks the Nanyang Technological University for a Research Scholarship.

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    This is reported to be the first example of a combined catalytic indole generation and subsequent enantioselective addition of carbonyl compounds (14CS1585). Other indole syntheses of this type include a [Cp∗IrCl2]2-catalyzed cyclization of 2-alkynylanilines (14TL5495), a dearomatization/metal-catalyzed domino reaction of 2-alkynylanilines to give azepino[5,4,3-cd]indoles (14OL816) or 4-acetonylindoles (14OL3600), triazoloindoles as α-imino rhodium carbene precursors (14OL1244), and the silver-catalyzed one-pot cyclization/fluorination of 2-alkynylanilines (14CC3024). As an orthogonal approach to the direct trifluoromethylation of indole derivatives, 2-trifluoromethylated indole 93 was prepared by subjecting isonitrile 92 to the hypervalent iodide (Togni) reagent and catalytic amounts of tetrabutylammonium iodide.

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