Ketone-catalyzed epoxidation of alkenes with oxone and palladium-catalyzed biaryl synthesis via silacyclobutanes.

摘要

The mechanism of ketone-promoted epoxidation of olefins with Oxone has been investigated by O-18 labeling studies. Dioxiranes were unambiguously demonstrated to be the active oxidizing agents.; A series of mono-, di- and trifluorinated ketones has been surveyed as catalysts for epoxidation of alkenes with Oxone. Five conformationally defined alpha-mono-, alpha,alpha- and alpha,alpha'-difluorinated cyclohexanones were all found to function as catalysts under monophasic conditions. The orientation of the alpha-fluorine substituents had a profound effect on reactivity. Ketones flanked by equatorially oriented fluorine substituents were substantially more effective epoxidation catalysts than those with axial fluorine substituents. This stereoelectronic effect was also manifest in the Baeyer-Villiger reaction of these ketones.; A new ketone-containing framework bearing two flanking ammonium groups has been developed for catalytic epoxidation of alkenes with Oxone. Under neutral and even slightly acidic (pH 6.0) conditions, a variety of olefins was successfully oxidized to the corresponding epoxides with 5--10 mol% of the parent diazepinium salt in 74--94% yield. On the basis of this bis(ammonium) template, several structurally diverse chiral non-racemic bis(ammonium) ketones have been designed and prepared. Even though excellent catalytic activities were observed, the enantioselectivities were low.; Aryl(fluoro)silacyclobutanes and aryl(chloro)silacyclobutanes have been found to undergo cross-coupling reactions with aryl iodides. The rate of reaction and extent of homocoupling were dramatically affected by the addition of ligands for the palladium catalyst. A wide range of electronically different and structurally diverse unsymmetrical biaryls have been prepared in good to excellent yields.