Eglinton reaction

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Eglinton reaction or Eglinton coupling is a name reaction of organic chemistry and was discovered in 1956 by Geoffrey Eglinton (1927-2016). It is used to synthesize symmetrical diynes from terminal alkynes (with a terminal alkynyl group ) and is a modification of the Glaser coupling .

Overview reaction

In 1869 Glaser discovered the synthesis of symmetrical diynes, for which he used copper (I) salts as oxidizing agents. The resulting explosive copper (I) phenylacetylide had to be isolated before oxidation. Eglinton improved the reaction by using stoichiometric amounts of copper (II) salts such as copper (II) acetate , which is dissolved in pyridine , and was thus able to avoid the isolation of copper acetylides. The organyl radical R is, for example, an aryl , alkyl or alkylaryl group.

Overview reaction

Compared to the Glaser reaction, the Eglinton coupling has the disadvantage that larger amounts of copper salt are required. The Cadiot – Chodkiewicz coupling is suitable for the synthesis of asymmetrical diynes .

mechanism

The mechanism of the Eglinton reaction has not been explored enough and can only be partially explained. The first step is a deprotonation of the ethyne derivative 1 , since acetylenic protons are acidic and can easily be split off by the base pyridine. The result is a acetylide - anion 2 . This is followed by a reaction with the copper (II) acetate, so that a copper complex is presumably formed. The final step is based on the dimerization of two radicals 3 and thus the symmetrical bisacetylene 4 is obtained.

mechanism

It is very similar to the Glaser clutch mechanism .

use

With the help of the Eglinton coupling, a variety of new unsaturated macrocyclic compounds can be prepared, which serve as building blocks for the synthesis of annulenes.

See also

Individual evidence

  1. ^ A b c P. Siemsen, RC Livingston, F. Diederich: Acetylenic Coupling: A Powerful Tool in Molecular Construction . In: Angew. Chem. Int. Ed. tape 39 , 2000, pp. 2633-2657 , doi : 10.1002 / 1521-3773 (20000804) 39:15 <2632 :: AID-ANIE2632> 3.0.CO; 2-F .
  2. ↑ a b c T. Laue, A. Plagens: Name and keyword reactions in organic chemistry . 5th edition. Teubner, 2006, ISBN 978-3-8351-0091-6 , pp. 153-155 .
  3. ↑ MB Smith: March's Advanced Organic Chemistry - Reactions, Mechanisms, and Structure . 7th edition. John Wiley & Sons, 2013, ISBN 978-0-470-46259-1 , pp. 840-843 .
  4. ^ Jie Jack Li: Name Reactions - A Collection of Detailed Reaction Mechanisms . 3. Edition. Springer, 2006, ISBN 978-3-540-30030-4 , pp. 265-266 .
  5. ↑ G. Eglinton, AR Galbraith: Macrocyclic Acetylenic Compounds. Part I. Cyclotetradeca-1,3-diyne and Related Compounds . In: Journ. Chem. Soc. tape 39 , 1959, pp. 889-893 , doi : 10.1039 / JR9590000889 .