Eglington coupling

The cyclization of thienyl-substituted diacetylenes with hydrogen sulfide or sodium sulfide is also a very successful method for the synthesis of oligothiophenes. The key point here is the synthesis of the precursor diynes. Symmetrical diacetylenes can be obtained by the oxidative coupling of acetylenes with copper(I) or copper(II) salts ( Glaser, Hay, or Eglington coupling ). The synthesis of unsymmetric diynes proceeds best via the Cadiot-Chodkiewicz procedure in which an acetylene is reacted with an acetylic halide in the presence of copper(I) salts [117]. Therefore, thienyl-substituted acetylenes and bromoacetylenes are important starting materials. 

Some of the most useful synthetic transformations of terminal alkynes involve intermolecular and intramolecular homo- and cross-coupling reactions between their. sp-carbon centers, leading to butadiyne or polyyne derivatives. The two most widely used and practical systems are (i) oxidative homocoupling reactions, i.e. Glaser and Eglington reactions and (ii) heterocoupling reactions, i.e. Chodkiewicz-Cadiot coupling of a terminal alkyne with a haloalkyne. 

Toda and coworkers have found drastic differences in the reaction behavior of racemic and optically active 3,6-di-r-butylocta-l,4,7-triyne-3,6-diol (17) upon oxidative coupling by the Eglington method.- - Thus, the noncentrosymmetric cyclic dimers, (18a) and (18b), can be obtained from the racemic monomer, but the corresponding optically active monomer does not lead to any of the cyclic dimer. In the latter case the optically active polymer (19) is obtained as the sole isolable product (Scheme 7). 

Recently oxidative coupling reactions of a,a>-diethynyl compounds have been applied in the synthesis of cyclophanes, which are interesting functional host molecules. Whitlock and coworkers, - for example, have reported the synthesis of the water-soluble cyclophane (21), designed as an esterase mimic by the Eglington reaction of (20 Scheme 8). 

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