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The Castro–Stephens coupling is a 
The reaction was described in 1963 by chemists Castro and Stephens. The reaction is similar to the much older Rosenmund–von Braun synthesis (1914) between aryl halides and 
cross coupling reaction
In organic chemistry, a cross-coupling reaction is a reaction where two different fragments are joined. Cross-couplings are a subset of the more general coupling reactions. Often cross-coupling reactions require metal catalysts. One important reac ...
between a copper(I) acetylide
Copper(I) acetylide, copper carbide or cuprous acetylide, is a chemical compound with the formula . It is a copper(I) salt of acetylene. It consists of cations and acetylide anions , with the triple bond between the two carbon atoms. Although nev ...
and an aryl halide
In organic chemistry, an aryl halide (also known as a haloarene) is an aromatic compound in which one or more hydrogen atoms directly bonded to an aromatic ring are replaced by a halide ion (such as fluorine F''−'', chlorine Cl−1,−3,−5, br ...
in pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...
, forming a disubstituted alkyne
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Acetylene
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Propyne
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1-Butyne
In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...
and a copper(I) halide.
:
The reaction was described in 1963 by chemists Castro and Stephens. The reaction is similar to the much older Rosenmund–von Braun synthesis (1914) between aryl halides and copper(I) cyanide
Copper(I) cyanide (cuprous cyanide) is an inorganic compound with the formula CuCN. This off-white solid occurs in two polymorphs; impure samples can be green due to the presence of Cu(II) impurities. The compound is useful as a catalyst, in ele ...
and was itself modified in 1975 as the Sonogashira coupling
The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon–carbon bonds. It employs a palladium catalyst as well as copper co-catalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or vi ...
by adding a palladium catalyst and preparing the organocopper compound
Organocopper chemistry is the study of the physical properties, reactions, and synthesis of organocopper compounds, which are organometallic compounds containing a carbon to copper chemical bond. They are reagents in organic chemistry.
The f ...
''in situ
is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...
'', allowing copper to also be used catalytically.
A typical reaction diphenylacetylene
Diphenylacetylene is the chemical compound C6H5C≡CC6H5. The molecule consists of two phenyl groups attached to a C2 unit. A colorless solid, it is used as a building block in organic synthesis and as a Transition metal alkyne complex, ligand in ...
is obtained by the coupling of iodobenzene
Iodobenzene is an aryl iodide and the simplest of the iodobenzenes, consisting of a benzene ring substituted with one iodine atom. Its chemical formula is . It is useful as a synthetic intermediate in organic chemistry. It is a volatile colorles ...
with Cu C2C6H5 in hot pyridine
Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom . It is a highly flammable, weak ...
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Unlike the Sonogashira coupling, the Castro–Stephens coupling can produce heterocyclic compounds when a nucleophilic group is '' ortho'' to the aryl halide, although this typically requires use of dimethylformamide
Dimethylformamide, DMF is an organic compound with the chemical formula . Its structure is . Commonly abbreviated as DMF (although this initialism is sometimes used for 2,5-dimethylfuran, dimethylfuran, or dimethyl fumarate), this colourless liqui ...
(DMF) as solvent.
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References
{{DEFAULTSORT:Castro-Stephens coupling Carbon-carbon bond forming reactions Name reactions