Vinyl substitutions organopalladium compounds

The vinyl substitution reaction often may be achieved with catalytic amounts of palladium. Catalytic reactions are carried out in different ways depending on how the organopalladium compound is generated. Usually copper(II) chloride or p-benzoquinone is employed to reoxidize palladium(0) to palla-dium(II) in catalytic reactions when methods (i) or (ii) are used for making the organopalladium derivative. The procedures developed for making these reactions catalytic are not completely satisfactory, however. The best catalytic reactions are achieved when the organopalladium intermediates are obtained by the oxidative addition procedures (method iii), where the halide is both the reoxidant and a reactant. Reviews of some aspects of these reactions have been published.u-le... 

It was demonstrated by Heck in the late 1960s that arylpaUadium salts, prepared by trans-metallation of organomercury compounds, constitute useful reactants in various vinylic substitution reactions.f t Independently, Moritani, Fujiwara, and colleagues conducted similar vinylic substitutions, but generated the organopalladium intermediates by direct electrophilic palladation of arenes.t ° In these reactions the palladium(II) salt employed is reduced to paUadium(O) (Scheme ). ... 

The Heck reaction consists in the Pd(0)-catalysed coupling of alkenes with an aryl or alkenyl halide or triflate in the presence of a base to form a substituted alkene (Scheme 7.1). The reaction is performed in the presence of an organopalladium catalyst. The halide or triflate is an aryl or a vinyl compound and the alkene contains at least one proton. 

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