Ketones with arylpalladium complexes

Early findings by Suzuki and co-workers [109] showed that the palladium-catalyzed iminocarbonylative cross-coupling reaction between 9-alkyl-9-BBN derivatives, t-butylisocyanide, and arylhalides gives access to alkyl aryl ketones 132 after hydrolysis of the corresponding ketimine intermediates 131. Presumably, the concentration of free isocyanide is kept to a minimum by its coordination with the borane. Formation of an iminoacylpalladium(II) halide 130 by insertion of isocyanide to the newly formed arylpalladium complex followed by a transmetallation step afford the ketimine intermediates 131 (Scheme 8.52). 

Vinyl substitution of primary or secondary allylic alcohols with aryl halides usually produces 3-aryl aldehydes or ketones, respectively. The reaction is believed to involve an addition of the intermediate arylpalladium halide to die double bond, placing the aryl group mainly on the more distant carbon from the hydroxy group, followed by palladium hydride elimination, a reverse readdition and another elimination with a hydrogen atom on the carbon bearing the hydroxy group. The product is probably a ir-com-plex of the enol which ultimately either dissociates or collapses to a a-complex with palladium on the... 

The arylation is explained by the following mechanism. Arylpalladium halides 28 are formed by oxidative addition of aryl halides. Then the arylpalladium eno-lates 30 are generated by transmetallation of 28 with alkali enolates of ketones 29. Finally reductive elimination of the arylpalladium enolates 30 affords a-aryl ketones. Hartwig isolated the arylpalladium enolate complexes 31 of ketones, esters and amides, and confirmed formation of or-arylated products on heating [23]. 

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