Cascade carbopalladation carbon nucleophiles

A cascade Heck reaction with termination by nucleophiles is considered to start with an oxidative addition of a heteroatom-carbon bond (starter) onto a palladium(O) species (startup reaction), followed by carbopalladation of a nonaromatic carbon-carbon double or triple bond without subsequent dehydropalladation (relay), a second and possibly further carbopalladation of a carbon-carbon double or triple bond (second etc. relay). The terminating step is a displacement of the palladium residue by an appropriate nucleophile. It is crucial for a successful cascade carbopalladation that no premature dehydropalladation takes place, and that can be prevented by using alkynes and 1,1-disubstituted alkenes (or certain cycloalkenes) as relay stations since they give kinetically stable alkenyl- or neopentylpalladium intermediates, respectively. In addition, reaction of haloalkenes with alkenes in certain cases may form rr-allyl complexes, which are then trapped by various nucleophiles. 

IV.3.2 CASCADE CARBOPALLADATION TERMINATED BY NUCLEOPHILES 1407 B.ii. Termination by Carbon Nucleophiles... 

The carbonylative palladium-catalyzed reactions discussed in this section proceed by oxidative addition of palladium (0) to the carbon-X bond of aryl/vinyl/acyl halides and pseudohalides followed by carbon monoxide insertion, giving rise to an acylpalla-dium intermediate. The acylpalladium intermediate can in turn react with various tethered nucleophiles (a), be involved in activation/hetero or carbopalladation steps with unsaturated carbon-carbon bonds (b), or participate in cascade reactions (c) (Scheme 13.1). 

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