The Glaser coupling is a type of
coupling reaction A coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R ...
. 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
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogeno ...
. The solvent is water or an alcohol.
The reaction was first reported by in 1869. He suggested the following process for his way to diphenylbutadiyne:
:CuCl + PhC
2H + NH
3 → PhC
2Cu + NH
4Cl
:2PhC
2Cu + O → PhC
2C
2Ph + Cu
2O
Modifications
Eglinton reaction
In the related Eglinton reaction two terminal alkynes are coupled by a copper(II) salt such as
cupric acetate
Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO− is acetate (). The hydrated derivative, Cu2(OAc)4(H2O)2, which contains one molecule of water for each copper atom, is avail ...
.
:
2R-\!\!-H -> ce\ce] R-\!\!-\!\!-R
The oxidative coupling of alkynes has been used to synthesize a number of fungal antibiotics. The stoichiometry is represented by this highly simplified scheme:
:
Such reactions proceed via
metal-alkyne complex, copper(I)-alkyne complexes.
This methodology was used in the synthesis of
cyclooctadecanonaene. Another example is the synthesis of
diphenylbutadiyne from
phenylacetylene.
Hay coupling
The Hay coupling is variant of the Glaser coupling. It relies on the
TMEDA
Tetramethylethylenediamine (TMEDA or TEMED) is a chemical compound with the formula (CH3)2NCH2CH2N(CH3)2. This species is derived from ethylenediamine by replacement of the four amine hydrogens with four methyl groups. It is a colorless liquid, ...
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. The Hay coupling of
trimethylsilylacetylene gives the butadiyne derivative.
Scope
In 1882
Adolf von Baeyer
Johann Friedrich Wilhelm Adolf von Baeyer (; 31 October 1835 – 20 August 1917) was a German chemist who synthesised indigo and developed a nomenclature for cyclic compounds (that was subsequently extended and adopted as part of the IUPAC or ...
used the method to prepare 1,4-bis(2-nitrophenyl)butadiyne, en route to
indigo dye
Indigo dye is an organic compound with a distinctive blue color. Historically, indigo was a natural dye extracted from the leaves of some plants of the ''Indigofera'' genus, in particular '' Indigofera tinctoria''; dye-bearing ''Indigofera'' p ...
.
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
{{Alkynes
Carbon-carbon bond forming reactions