Alkynylcopper Sonogashira reaction

It is speculated that an alkynylcopper species, which undergoes the transmetalation process more readily, is generated during the reaction with the aid of an amine. The aliphatic amine also serves as a reducing agent to generate Pd(0). For recent reviews on the Sonogashira reaction, see references [60] and [61]. 

A typical Sonogashira reaction involves heating an aryl halide, catalyst and a terminal alkyne with cuprous iodide and triethylamine. This reaction does not require the preparation of an organometallic reagent, because transmetaUation occurs via an alkynylcopper, formed in situ. The main use of the Sonogashira reaction in heterocyclic chemistry is probably for the synthesis of intermediates for ring synthesis. ... 

In the next chapter we will discuss the use of alkynes as nucleophiles. From the reaction mechanism for Sonogashira reactions, the in situ-formed alkynylcopper intermediate should do transmetalation with palladium center and followed by reductive elimination, which is similar to the carbonylative reactions described in this chapter. 

Oxidative addition of alkenyl halides, triflates, and other esters to zerovalent palladium compounds has been long known as a viable route to palladium(ii)-alkenyl complexes. Stereospecific coupling reactions involving mono- and (E)- or (Z)-dihalo-alkenes with palladium-copper catalysis under modified Sonogashira conditions are quite versatile and useful. These proceed through oxidative addition of the alkenyl halide via palladium(ii) alkenyl complexes, followed by coupling with a nucleophile (usually an alkynylcopper reagent obtained in situ with co-catalytic copper(i) from terminal alkynes in the presence of, in this case, a base like piperidine instead of diethylamine). ... 

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