title: Synthesis of annulated bis-indoles through Au(i)/Brønsted acid-catalyzed reactions of (1H-indol-3-yl)(aryl)methanols with 2-(arylethynyl)-1H-indoles.
abstract: A general method to access annulated bis-indoles from (1H-indol-3-yl)(aryl)methanols and 2-(arylethynyl)-1H-indoles under the catalysis of the Ph3PAuOTf/Brønsted acid binary catalyst system has been developed. The reaction was found to proceed in a highly efficient manner and benefit from easy-to-make starting materials, broad substrate scope and operational simplicity. The potential of this method has also been exemplified for the synthesis of pyrrole-annulated indoles using 2-(phenylethynyl)-1H-indoles and phenyl(1H-pyrrol-2-yl)methanols. Furthermore, the use of a ternary catalyst system, involving PdCl2/Brønsted acid/Ph3PAuOTf catalysts, has been realized for the synthesis of annulated bis-indoles starting directly from 2-(phenylbuta-1,3-diyn-1-yl)aniline and (1H-indol-3-yl)(aryl)methanol. Mechanistically, this reaction is very interesting since the overall process involves three different catalytic cycles catalyzed by three different catalysts in a relay fashion.
authors.affiliation: Division of Organic Chemistry, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune - 411 008, India. n.patil@ncl.res.in.
authors.forename: Suleman M
authors.initials: SM
authors.lastname: Inamdar
authors.affiliation: Center for Material Characterization, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune - 411 008, India.
authors.forename: Rajesh G
authors.initials: RG
authors.lastname: Gonnade
authors.affiliation: Division of Organic Chemistry, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune - 411 008, India. n.patil@ncl.res.in and Academy of Scientific and Innovative Research (AcSIR), New Delhi - 110 025, India.
authors.forename: Nitin T
authors.identifier: http://orcid.org/0000-0002-8372-2759
authors.initials: NT
authors.lastname: Patil