Vinyl halides migratory insertion reactions

Vinylation or arylation of alkenes with the aid of a palladium catalysts is known as the Heck reaction. The reaction is thought to proceed through the oxidative addition of an organic halide, RX onto a zero-valent [PdL2] species followed by coordination of the olefin, migratory insertion of R, reductive elimination of the coupled product and dehydrohalogenation of the intermediate [HPdXL2] (Scheme 6.1). 

Whether the reaction is inter- or intramolecular, the Heck reaction generates vinyl(hetero)arenes or dienes from an alkene and a (hetero)aryl or alkenyl halide [130]. This reaction has great versatility and is applicable to a wide range of aryl and alkene species. Mechanistically, the Heck reaction varies from that depicted in Fig. 4.3. While the oxidative addition of the halogen species occurs, the transmetalation step is replaced by the coordination of the alkene. This is followed by a migratory insertion which essentially substitutes for the cross-coupling step. The product is released not by a reductive elimination, but by a 3-hydride elimination sequence (Fig. 4.5). 

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