text: The Heck reaction is the palladium-catalyzed coupling of an aryl or alkenyl halide with an alkene to form a substituted alkene. Intramolecular variants of the reaction may be used to generate cyclic products containing endo or exo double bonds. Ring sizes produced by the intramolecular Heck reaction range from four to twenty-seven atoms. Additionally, in the presence of a chiral palladium catalyst, the intramolecular Heck reaction may be used to establish tertiary or quaternary stereocenters with high enantioselectivity. A number of tandem reactions, in which the intermediate alkylpalladium complex is intercepted either intra- or intermolecularly before β-hydride elimination, have also been developed.