Cascade carbopalladation alkyne termination

Negishi E, Coperet C (2002) Palladium-Catalyzed Tandem and Cascade Carbopalladation of Alkynes and 1,1-Disubstituted Alkenes Terminated by Carbonylative Reactions. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 1431... 

On the other hand, an alkenylpalladium intermediate formed by intramolecular carbopalladation from a 2-bromo-l-en-6-yne carbopalladates an external mono-or disubstituted alkyne, and the cascade process is terminated by cyclization of the 1,3,5-hexatrienylpalladium intermediate through intramolecular carbopalladation or 67T-electrocyclization and ensuing dehydropalladation (Scheme... 

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.3.3 Palladium-Catalyzed Tandem and Cascade Carbopalladation of Alkynes and 1,1-Disubstituted Alkenes Terminated by Carbonylative Reactions... 

B. Pd-CATALYZED TANDEM AND CASCADE CARBOPALLADATION OF ALKYNES TERMINATED BY CARBONYLATION... 

In more complex reaction cascades an additional alkyne-insertion step can occur. Thus starting with intramolecular carbopalladation of a vinyl iodide to a carbon-carbon triple bond, followed by two intramolecular alkene-insertion steps and termination with dehydropalladation, a palladium-catalyzed synthesis of l-(5 -methylbicyclo[3.1.0]hex-T-yl)-5,5-bis(carboethoxy)cyclo-hexadiene (52) starting from l-iodo-4,4-bis(carboethoxy)-ll-methyldodeca-l,ll-dien-6-yne (51) is achieved. ... 

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