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Synlett 2005(18): 2823-2825  
DOI: 10.1055/s-2005-918948
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Novel Indium-Catalyzed Sonogashira Coupling Reaction, Effected in the Absence of a Copper Salt, Phosphine Ligand and Palladium

Harsha N. Borah, Dipak Prajapati*, Ramesh C. Boruah
Department of Medicinal Chemistry, Regional Research Laboratory, Jorhat - 785 006, Assam, India
Fax: +91(376)2370011; e-Mail: dr_dprajapati@rediffmail.com;
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Publication History

Received 21 July 2005
Publication Date:
12 October 2005 (online)

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Abstract

An efficient copper-, phosphine ligand- and palladium-free indium-catalyzed Sonogashira coupling reaction has been developed in the presence of 1 mol% indium trichloride. Coupling of various aryl halides with terminal alkynes afforded the corresponding aryl alkynes in moderate to excellent yields.

Key words

Sonogashira coupling reaction - indium trichloride - aryl halides - terminal alkynes

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Representative Experimental Procedure for the Synthesis of Aryl Alkynes 3.
In a typical procedure, a mixture of anhyd InCl3 (0.03 g, 0.1 mmol), iodobenzene (0.2 g, 1 mmol) and phenyl acetylene (0.12 g, 1.2 mmol) was taken up in dry benzene (10 mL) in a 50-mL round-bottom flask and was refluxed at 80 °C until the completion of the reaction (monitored by TLC). After completion of the reaction (3.5 h), the reaction mixture was filtered, and the residue obtained, after evaporation of the solvent, was chromatographed (silica gel column) using CHCl3-PE (60-80, 1:3) to afford pure diphenyl acetylene in 80% yield; mp 60-61 °C. Similarly, other aryl halides were reacted with terminal alkynes in the presence of InCl3 and the corresponding aryl alkynes were obtained in high yields. The reactions are generally clean and side products could be detected in the NMR spectra of the crude products. All the products were characterized by high resolution spectral analyses and comparison with literature data. The results of this study are summarized in Table [1] .