Eglinton-Glaser oxidative coupling

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. 

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 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... 

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)]. 

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. ... 

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. 

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