Sonogashira Coupling - History

History

The Sonogashira cross-coupling reaction was first reported by Kenkichi Sonogashira, Yasuo Tohda, and Nobue Hagihara in their 1975 publication. It is an extension to the Cassar and Dieck and Heck reactions, which afford the same reaction products, but use harsh reaction conditions, such as high temperature, to do so. Both of these reactions make use of a palladium catalyst to carry out the coupling, while Sonogashira uses both palladium and copper cataylysts simultaneously. This results in the increased reactivity of the reagents and the ability of the reaction to be carried out at room temperature, making the Sonogashira cross-coupling reaction a highly useful reaction, particularly in the alkynylation of aryl and alkenyl halides. The reaction's remarkable utility can be evidenced by the amount of research still being done on understanding and optimizing its synthetic capabilities. A search for the term "Sonogashira" in Scifinder provides over 1500 references for journal publications between 2007 and 2010. It has become so well known that often, all reactions that use a palladium(0) catalyst to couple a sp2 and even sp3 halide or triflate with a terminal alkyne, regardless of whether or not a copper co-catalyst is used, are termed "Sonogashira reactions," despite the fact that these reactions are not carried out under true Sonogashira reaction conditions.