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In organic chemistry, a Sonogashira coupling is a coupling reaction of terminal alkynes with aryl or vinyl halides. This reaction was first reported by Kenkichi Sonogashira and Nobue Hagihara in 1975.
Additional recommended knowledge
Typically, two catalysts are needed for this reaction: a zerovalent palladium complex and a halide salt of copper(I). The palladium complex activates the organic halides by oxidative addition into the carbon-halogen bond. Phosphine-palladium complexes such as tetrakis(triphenylphosphine)palladium(0) are used for this reaction, but palladium(II) complexes are also available because they are reduced to the palladium(0) species by the consumption of terminal alkynes in the reaction medium. In contrast, copper(I) halides react with the terminal alkyne and produce copper(I) acetylide, which acts as an activated species for the coupling reactions.
The reaction medium must be basic to neutralize the hydrogen halide produced as the byproduct of this coupling reaction, so alkylamine compounds such as triethylamine and diethylamine are sometimes used as solvents, but also DMF or ether can be used as solvent. In addition, deaerated conditions are formally needed for Sonogashira coupling reactions because the palladium(0) complexes are unstable in the air, and oxygen promotes the formation of homocoupled acetylenes. Recently, development of air-stable organopalladium catalysts enable this reaction to be conducted in the ambient atmosphere.
The Sonogashira coupling is a modification of the Castro-Stephens coupling with added palladium and in situ preparation of the copper acetylide. The reaction mechanism is not clearly understood but in the textbook mechanism revolves around a palladium cycle and a copper cycle.
The palladium cycle:
The copper cycle:
Typical reagents and reaction conditions are copper(I) iodide, N,N-diisopropylethylamine, tetrakis(triphenylphosphine)palladium(0) and dimethylformamide, copper(I) iodide, diethylamine, dichlorobis(triphenylphosphine)palladium(II) or n-butylamine, copper(I) iodide, tetrakis(triphenylphosphine)palladium(0) and toluene as solvent
The Sonogashira coupling is applied in synthesis of cross-conjugated oligo(phenylene enynylene)s and phenanthroline derivatives.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sonogashira_coupling". A list of authors is available in Wikipedia.|