Glaser coupling

The Glaser coupling is a name reaction in organic chemistry that was named after its discoverer, Carl Glaser . It is used to couple two terminal alkynes to diynes and is the oldest known coupling reaction for alkynes.

Overview reaction

In the Glaser coupling, two terminal alkynes react with the addition of bases and through catalysis of copper salts to form symmetrical diynes .

mechanism

The Glaser coupling takes place in an aqueous or alcoholic ammonia solution . Copper (I) salts are used as the catalyst . Copper (I) chloride , copper (I) bromide or copper (I) acetate , for example, are suitable for this purpose . In the first step, a base (typically ammonia ) is used, which splits off the CH-acidic proton of the alkyne . Since the mechanism is complex and not yet completely clear, the next step will probably go like this: The acetylide anion forms a copper complex with copper (II) cations. The copper (II) cations are produced by oxidizing the copper (I) salts with the oxidizing agent oxygen . In the copper complex , the acetylide anions each transfer one electron to a copper (II) cation. Thus the acetylide anions are oxidized and the copper (II) cations are reduced to copper (I) cations . A symmetrical diin is created .

The Glaser coupling and the Eglinton coupling are suitable for the synthesis of cyclic polyynes.

Versions

Hay clutch

The Hay coupling is analogous to the Glaser coupling. It only uses TMEDA (TEMED) as a base, which increases the solubility in organic solvents and thus enables the use of a wider range of solvents.

Eglinton clutch

The Eglinton coupling is closely related to the Glaser coupling. The difference lies in the use of copper (II) instead of copper (I) salts as an oxidizing agent . In addition, the copper salts are not required in catalytic, but stoichiometric amounts. Since the stoichiometric use of the copper salt does not have to be reoxidized, no oxygen is required for the Eglinton coupling. Copper (II) acetate , for example, is used as the copper source, and pyridine or another organic nitrogen base is usually used as the base.

Cadiot-Chodkiewicz coupling

While the Glaser coupling only enables the coupling of two identical alkynes, the Cadiot-Chodkiewicz coupling allows the use of two different radicals on the alkyne and enables the selective synthesis of unsymmetrical diynes :

Cadiot-Chodkiewicz Coupling (Synthesis of Unsymmetrical Diynes)

literature

R. Brückner: reaction mechanisms . 3rd edition, Spektrum Akad. Verlag, Munich 2004, ISBN 3-8274-1579-9 , p. 693.
T. Laue, A. Plagens: Name and keyword reactions . 4th edition, Teubner, Wiesbaden 2004. ISBN 3-519-33526-3 .

Individual evidence

^ C. Glaser: Contributions to the knowledge of Acetenylbenzols . In: Reports of the German Chemical Society . Vol. 2, No. 2, 1869, pp. 422-424.
↑ T. Laue, A. Plagens: Name and catchword reactions of organic chemistry . Teubner Verlag, 2006, ISBN 3-8351-0091-2 , p. 153-155 .
^ László Kürti , Barbara Czakó: Strategic Applications of Named Reactions in Organic Synthesis . Elsevier Academic Press, Burlington / San Diego / London 2005, ISBN 0-12-369483-3 , p. 186.
^ Ferdinand Bohlmann , Hubert Schönowsky, Eberhard Inhoffen, Gerhard Grau: Polyacetylenverbindungen, LII. About the mechanism of the oxidative dimerization of acetylene compounds . In: Chemical Reports . tape 97 , no. 3 , March 1964, p. 794-800 , doi : 10.1002 / cber.19640970322 .
↑ T. Laue, A. Plagens: Name and catchword reactions of organic chemistry . Teubner Verlag, 2006, ISBN 3-8351-0091-2 , p. 153-155 .
↑ Allan S. Hay: Oxidative Coupling of Acetylenes. II . In: The Journal of Organic Chemistry . tape 27 , no. 9 , September 1962, p. 3320-3321 , doi : 10.1021 / jo01056a511 .
↑ G. Eglinton, AR Galbraith: Macrocyclic acetylenic compounds. Part I. Cyclotetradeca-1: 3-diyne and related compounds . In: Journal of the Chemical Society (Resumed) . 1959, p. 889-896 , doi : 10.1039 / JR9590000889 .

[1] C. Glaser: Contributions to the knowledge of Acetenylbenzols . In: Reports of the German Chemical Society . Vol. 2, No. 2, 1869, pp. 422-424.

[2] T. Laue, A. Plagens: Name and catchword reactions of organic chemistry . Teubner Verlag, 2006, ISBN 3-8351-0091-2 , p. 153-155 .

[Kürti-3] László Kürti , Barbara Czakó: Strategic Applications of Named Reactions in Organic Synthesis . Elsevier Academic Press, Burlington / San Diego / London 2005, ISBN 0-12-369483-3 , p. 186.

[4] Ferdinand Bohlmann , Hubert Schönowsky, Eberhard Inhoffen, Gerhard Grau: Polyacetylenverbindungen, LII. About the mechanism of the oxidative dimerization of acetylene compounds . In: Chemical Reports . tape 97 , no. 3 , March 1964, p. 794-800 , doi : 10.1002 / cber.19640970322 .

[5] T. Laue, A. Plagens: Name and catchword reactions of organic chemistry . Teubner Verlag, 2006, ISBN 3-8351-0091-2 , p. 153-155 .

[6] Allan S. Hay: Oxidative Coupling of Acetylenes. II . In: The Journal of Organic Chemistry . tape 27 , no. 9 , September 1962, p. 3320-3321 , doi : 10.1021 / jo01056a511 .

[7] G. Eglinton, AR Galbraith: Macrocyclic acetylenic compounds. Part I. Cyclotetradeca-1: 3-diyne and related compounds . In: Journal of the Chemical Society (Resumed) . 1959, p. 889-896 , doi : 10.1039 / JR9590000889 .