Sonogashira coupling

The Sonogashira coupling was originally developed to couple a terminal alkyne with an aryl or vinyl iodide under anaerobic and anhydrous conditions using a palladium catalyst, a copper(I) cocatalyst, and an excess of a secondary or tertiary alkyl amine. This reaction has proven to be extremely valuable for many multi-component, one-pot syntheses, including the synthesis of ynones, halofurans, benzofurans, lactams, pyrimidines, and enaminones for pharmaceuticals, as well as liquid crystalline polymers and optical materials. Although there have been many attempts to improve the palladium catalyst, it still often has the drawbacks of the need to store it under nitrogen and being sensitive to air. The long reaction times and the limited choice of reaction medium are also sited often as weaknesses of the Sonogashira coupling. In addition, the copper co-catalyst has drawbacks, because it is difficult and expensive to recover, especially for large-scale reactions. Therefore, it is currently a topic of much research investigation.