Palladium, organo-, intermediates

The most important palladium-catalyzed processes include Heck vinylation of halides and sulfonates and various cross-coupling reactions in which a nucleophilic intermediate (stannane, organo-zinc halide or boronic acid) is coupled with an electrophile (halide or sulfonate). These coupling reactions are usually restricted to arylation and vinylation because of the tendency of alkylpalladium species to undergo elimination. The pyrrole and indole rings can participate in cross-coupling as either the nucleophilic or electrophilic component. 

Reviews have appeared on the use of the Wittig reaction in industrial practice, the Claisen rearrangement, synthetic applications of the retro-Diels-Alder reaction, organo-palladium intermediates for the alkylation and arylation of olefins, the Prins reaction to give 1,3-dienes, and intramolecular [4 + 2] (Diels-Alder) and [3 + 2] cycloadditions.An interesting discussion of the regiospecificity of the Diels-Alder reaction in terms of frontier orbital overlap favours the Woodward-Katz concept. Useful alkyne and polyene coupling reactions are described in reviews on the chemistry of vitamin the synthesis of insect sex... 

The combination of a Mizoroki-Heck reaction with a C—H activation is a domino process that has been encountered with increasing frequency in the past few years. This type of transformation takes place if the organo-palladium intermediate does not react in the usual way but activates an aryl- or vinyl-H bond in close vicinity, forming a new palladium(II) species that can react further with electrophiles or nucleophiles and giving rise to the formation of another C—C or C-Tieteroatom bond. 

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