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{{Reactionbox|Name = Glaser coupling|Type = Coupling reaction|NamedAfter = Carl Andreas Glaser|Section3 = {{Reactionbox Identifiers|OrganicChemistryNamed = glaser-coupling|RSC_ontology_id = 0000098}}}}The Glaser coupling is a type of coupling reaction. It is by far the oldest acetylenic coupling and is based on cuprous salts like copper(I) chloride or copper(I) bromide and an additional oxidant like oxygen. The base in its original scope is ammonia. The solvent is water or an alcohol.The reaction was first reported by {{ill|Carl Andreas Glaser|de|Carl Glaser}} in 1869.JOURNAL, Glaser, Carl, Untersuchungen über einige Derivate der Zimmtsäure, Annalen der Chemie und Pharmacie, 154, 2, 137–171, de, Studies on some derivatives of cinnamic acid, 10.1002/jlac.18701540202, 1870,weblink JOURNAL, Glaser, C., Beiträge zur Kenntniss des Acetenylbenzols, Berichte der Deutschen Chemischen Gesellschaft, 2, 1, 422–424, 10.1002/cber.186900201183, 1869,weblink He suggested the following process for his way to diphenylbutadiyne:

Modifications

Eglinton reaction

{{Reactionbox|Name = Eglinton reaction|Type = Coupling reaction|NamedAfter = Geoffrey Eglinton|Section3 = {{Reactionbox Identifiers|OrganicChemistryNamed = eglinton-reaction|RSC_ontology_id = 0000099}}}}In the related Eglinton reaction two terminal alkynes are coupled by a copper(II) salt such as cupric acetate.JOURNAL, Eglinton, G., Galbraith, A. R., J. Chem. Soc., 1959, 889, 10.1039/JR9590000889, Macrocyclic Acetglenic Compounds. Part I. cyclo-Tetradeca-1:3-diyne and Related Compounds., The oxidative coupling of alkynes has been used to synthesize a number of fungal antibiotics. The stoichiometry is represented by this highly simplified scheme:Eglinton, G.; McRae, W. Adv. Org. Chem. 1963, 4, 225. Such reactions proceed via copper(I)-alkyne complexes.This methodology was used in the synthesis of cyclooctadecanonaene.{{OrgSynth | title = [18]Annulene | author = K. Stöckel and F. Sondheimer | prep = cv6p0068| volume= 54 | page = 1| year = 1974 | doi= 10.15227/orgsyn.054.0001}} Another example is the synthesis of diphenylbutadiyne from phenylacetylene.{{OrgSynth | author = I. D. Campbell and G. Eglinton | title = Diphenyldiacetylene | volume = 45| page = 39 | year = 1965 | doi = 10.15227/orgsyn.045.0039}}

Hay coupling

The Hay coupling is variant of the Glaser coupling. It relies on the TMEDA complex of copper(I) chloride to activate the terminal alkyne. Oxygen (air) is used in the Hay variant to oxidize catalytic amounts of Cu(I) to Cu(II) throughout the reaction, as opposed to a stoichiometric amount of Cu(II) used in the Eglington variant.JOURNAL, Hay, Allan S., Oxidative Coupling of Acetylenes. II, The Journal of Organic Chemistry, 27, 9, 3320–3321, 10.1021/jo01056a511, 1962, The Hay coupling of trimethylsilylacetylene gives the butadiyne derivative.JOURNAL, 10.15227/orgsyn.065.0052, 1,4-Bis(trimethylsilyl)buta-1,3-diyne, Organic Syntheses, 1987, 65, 52, Graham E. Jones, David A. Kendrick, Andrew B. Holmes,

Scope

In 1882 Adolf von Baeyer used the method to prepare 1,4-bis(2-nitrophenyl)butadiyne, en route to indigo dye.JOURNAL, Baeyer, Adolf, Ueber die Verbindungen der Indigogruppe, Berichte der Deutschen Chemischen Gesellschaft, 15, 1, 50–56, 10.1002/cber.18820150116, 1882,weblink JOURNAL, Johansson Seechurn, Carin C. C., Kitching, Matthew O., Colacot, Thomas J., Snieckus, Victor, Palladium-Catalyzed Cross-Coupling: A Historical Contextual Perspective to the 2010 Nobel Prize, Angewandte Chemie International Edition, 21 May 2012, 51, 21, 5062–5085, 10.1002/anie.201107017, 22573393, (File:Baeyer indigo synthesis.svg|Baeyer indigo synthesis)Shortly afterwards, Baeyer reported a different route to indigo, now known as the Baeyer–Drewson indigo synthesis.

See also

• Cadiot–Chodkiewicz coupling - Another alkyne coupling reaction catalysed by copper(I).
• Sonogashira coupling - Pd/Cu catalysed coupling of an alkyne and an aryl or vinyl halide
• Castro–Stephens coupling - A cross-coupling reaction between a copper(I) acetylide and an aryl halide
• Fritsch–Buttenberg–Wiechell rearrangement - can also form diynes

References

{{Reflist}}{{Alkynes}}