Cadiot-Chodkiewicz coupling

The Cadiot-Chodkiewicz coupling in organic chemistry is a coupling reaction between a terminal alkyne and a haloalkyne catalyzed by a copper(I) salt such as copper(I) bromide and an amine  base. The reaction product is a di-acetylene or di-alkyne.



The reaction mechanism involves deprotonation by base of the acetylenic proton followed by formation of a copper(I) acetylide. A cycle of oxidative addition and reductive elimination on the copper center then creates a new carbon carbon bond.

Related couplings are the Glaser coupling and the Eglinton coupling.

Cadiot-Chodkiewicz coupling
In one study the Cadiot-Chodkiewicz coupling has been applied in the synthesis of acetylene macrocycles starting from cis-1,4-diethynyl-1,4-dimethoxycyclohexa-2,5-diene. This compound is also the starting material for the dibromide through NBS and silver nitrate:



The coupling reaction itself takes place in methanol with piperidine, the hydrochloric acid salt of hydroxylamine and copper(I) bromide.

Eglinton reaction
In the related Eglinton reaction two terminal alkynes are coupled directly a copper(II) salt such as cupric acetate. This procedure was used in the synthesis of cyclooctadecanonaene. Another example is the synthesis of diphenyldiacetylene from phenylacetylene

Glaser coupling
The Glaser coupling (1870) is by far the oldest acetylenic coupling and is based on cuprous salts like copper(I) bromide and an additional oxidant like oxygen. The base in its original scope is ammonia.

Hay coupling
The Hay coupling (1962) is another version of the Glaser coupling with the TMEDA complex if copper(I) chloride .An example is the the coupling of trimethylsilylacetylene