1,4-Additions of arylboron, -silicon, and -bismuth compounds to α,β-unsaturated carbonyl compounds catalyzed by dicationic palladium(II) complexes

An enantioselective synthesis of cyclic and acyclic β-aryl ketone and aldehydes via Pd(II)-catalyzed 1,4-addition of Ar-m[m= B(OH)2, BF3K, Si(OMe)3, SiF3, BiAr2] to α,β-unsaturated ketones or aldehydes is described. The catalytic cycle involves transmetallation between Ar-mand Pd complexes as a key process, the mechanism of which is discussed on the basis of characterization of the transmetallation intermediate and electronic effect of the substituents. The enantioselection mechanism and efficiency of a chiraphos ligand for structurally planar α,β-unsaturated ketones are discussed on the basis of the X-ray structure of the catalyst and results of density functional theory (DFT) computational studies on the model of coordination of the substrates to the phenylpalladium(II)/(S,S)-chiraphos intermediate.