Eglinton—Glaser coupling

Although copper acetylides seem to be able to perform a nucleophilic substitution reaction at the sp-carbon atom of a bromo- or iodoacetylene (Cadiot-Chodkievicz reaction), this reaction has only rarely been used for the preparation of cyclic 1,3-diacetylenes. Copper-mediated oxidative coupling reactions (Glaser, Hay and Eglinton coupling) are more popular in this area and have attracted much attention in the construction of carbon-rich cyclic and polycyclic systems (see Chapter 13). One of the earliest carbon-rich systems of this type was the CzoHg system 19 [11,16] [Eq. (5)]. 

Glaser Coupling Eglinton Reaction Cadiot-Chodkiewicz Coupling... 

The Glaser reaction is an oxidative coupling of terminal alkynes 1 to yield a symmetrical Z -acetylene 2 the coupling step is catalyzed by a copper salt. Closely related is the Eglinton reaction, which differs from the Glaser reaction mainly by the use of stoichiometric amounts of copper salt as oxidizing agent. 

The Glaser coupling reaction is carried out in aqueous ammonia or an alcohol/ammonia solution in the presence of catalytic amounts of a copper-I salt. The required copper-II species for reaction with the acetylide anion R-C=C are generated by reaction with an oxidant—usually molecular oxygen. For the Eglinton procedure, equimolar amounts of a copper-II salt are used in the presence of pyridine as base. 

All three coupling procedures are suitable to give high yields under mild reaction conditions. Many functional groups do not interfere. For the application in organic synthesis the Eglinton variant may be more convenient than the Glaser method a drawback however is the need for stoichiometric amounts of copper salt. 

The dimerization of terminal alkynes, known as the Glaser coupling, the Eglinton coupling, and the Cadiot-Chodkiewicz coupling, is one... 

The most useful approaches to the synthesis of di- and poly-ynes from terminal alkynes are undoubtedly the copper-catalyzed couplings discovered by Glaser (CuCl, NH4OH, EtOH, 02)," Eglinton [Cu(OAc)2, hot pyridine or quinoline, 02], and Hay [Cu(I), tmed, 02]. Some of the many applications of these reactions are discussed in the following. 

The Glaser Coupling (or Hay Coupling) is a synthesis of symmetric or cyclic bisacetylenes via a coupling reaction of terminal alkynes. Mechanistically, the reaction is similar to the Eglinton Reaction the difference being the use of catalytic copper(I), which is reoxidized in the catalytic cycle by oxygen in the reaction medium. 

The oxidative coupling of two terminal alkynes via their copper acetylide complexes to form a 1,3-butadiyne function is known variously as Glaser, Eglinton, or Hay... 

For Glaser oxidative coupling of phenylacetylene to Campbell and Eglinton used cupric acetate in pyridine-methanol. The deep blue suspension became green when refluxed (1 hr.). The cooled mixture was acidified with stirring and cooling and the product was collected by ether extraction. 

Standard oxidative coupling methods for acetylenes use the Glaser method (CuCl, NH4CI, aqueous alcohol, O2) or Eglinton and Galbraith s method [Cu(OAc)a, pyridine, alcohol]. The former reaction can be accelerated by addition of JYiV A -tetramethylethylenediamine and the yield improved by using dimethoxyethane as solvent. ... 

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