Water-based reactions palladium catalysis

The combination of water and an organic nitrile as the solvent system (aqueous bipha-sic system, ABS) permits one to separate the catalyst in the water solution, coordinated to a water-soluble phosphine, TPPTS, the trisodium salt of trisulfonated triphenylphos-phine.f" The groups of Sinou and Genet have studied this strategyy. " ° " ° Allylic carbonates are quite stable to the potentially hydrolytic conditions since the reactions occur in neutral medium and only traces of base are generated in the catalytic cycle. Organic-aqueous phase palladium catalysis has been reviewed extensively. 

The dependence of the rate upon the inverse of the hydrogen ion concentration (base-catalysis) is reasonably attributed to the necessity for the coordinated water molecule to lose a proton. The resulting ethyl-ene-hydroxypalladium species (the cis isomer), I, is then believed to undergo an internal addition reaction of the hydroxyl group to the coordinated ethylene to form the dichloro-2-hydroxyethylpalladium anion, II. The final step is a decomposition of the last compound into acetaldehyde, palladium metal, hydrogen ion and chloride anions. 

The Wacker oxidation [146], amongst other nucleophilic additions to alkenes, is the most important reaction based on a palladium(II) catalysis. It is also used industrially for the synthesis of acetaldehyde from ethene and water. This oxidative process has been combined with a Mizoroki-Heck reaction by Tietze and coworkers [13] for an enantioselective total synthesis of vitamin E (293) [147] using BOXAX ligand 291 [148]. In this way the chromane ring and parts of the side chain of vitamin E (293) can be introduced in one... 

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