9.3.2 The Coupling of Alkynes

Copper(II) complex catalyzes the coupling of acetylene and monosubstituted acetylenes to yield diynes in the presence of base such as pyridine. The reaction probably takes place via one-electron oxidation of the acetylide anion by copper(II) ion followed by dimerization of the resulting acetylide radicals:

Alternative method has also been developed using an aqueous mixture of copper(I) chloride and ammonium chloride under air. Under these conditions, removal of the proton may be facilitated by complexing between the carbon-carbon triple bond and copper(I) ion.

Since the reaction functions under air, some of the Cu(I) could be oxidized to Cu(II) which in turn could oxidize the acetylide ion to the acetylide radical that could dimerize to yield diynes. The following are examples of many synthetic applications. The synthesis of phellogenic acid has been accomplished from undecylenic acid: