Synthesis of unsymmetrical ketones by palladium-catalyzed cross-coupling reaction of carboxylic anhydrides with organoboron compounds

On the basis of fundamental studies on oxidative addition of carboxylic anhydrides to zerovalent palladium complexes to yield acyl(carboxylato)bis(tertiary phosphine)palladium(II) complexes and their reactions with organoboronic acids to yield ketones, a novel catalytic process has been developed. This converts carboxylic anhydrides and organoboron compounds into ketones catalyzed by palladium complexes under mild conditions. The process provides a general, versatile, synthetic method to produce various symmetrical and unsymmetrical ketones with aromatic, aliphatic, and heterocyclic groups. The catalytic cycle is proposed to comprise a) oxidative addition of a carboxylic anhydride to produce an acyl(carboxylato)palladium intermediate, (b) transmetallation with an organoboron compound to give an acyl(organo)palladium intermediate, and (c) its reductive elimination to yield a ketone. Not only homogeneous catalyst systems but also heterogeneous systems were found to give ketones under mild conditions.