Science of Synthesis

Zhang, M.; Su, W., Science of Synthesis: Cross Coupling and Heck-Type Reactions, (2013) 3, 112.

Although a copper-catalyzed decarboxylative biaryl coupling was reported as early as 1966, the catalytic decarboxylative Heck reaction was not realized until much later, with the achievement of a palladium-catalyzed coupling of arenecarboxylic acids.[‌11‌] Many methods for transition-metal-catalyzed decarboxylative coupling have since been reported, and provide a more straightforward synthetic route than decarbonylative coupling due to the elimination of the need for preactivation by derivative formation. Furthermore, the ready availability of carboxylic acids renders this transformation extremely attractive. Based on detailed studies on the decarboxylative Heck reaction, the mechanism is proposed to be as outlined in ‌Scheme 9‌.[‌12‌] Unlike the typical decarbonylative coupling, the catalytic cycle begins with a palladium(II) species ‌17‌, which takes up the carboxylic acid by salt exchange. An arylpalladium(II) species ‌18‌ is subsequently formed after decarboxylation and loss of carbon dioxide, followed by insertion of the alkene and β-hydride elimination to release 1,2-disubstituted alkene ‌19‌. Oxidation then converts the released palladium(0) species back into palladium(II) complex ‌17‌ to close the catalytic cycle.

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References