Rhodium(I)- or Palladium(II)-Catalyzed 1,4-Additions of Organoboron, -silicon and -bismuth Compounds to Electron-deficient Alkenes

Abstract

An enantioselective synthesis of cyclic and acyclic β-aryl ketones and esters via palladium (II) - or rhodium (I) -catalyzed 1, 4-addition of Ar- [m] (m=B(OH)2, BF3K, Si(OMe)3, SiF3, BiAr2) to α, β-unsaturated ketones or esters is described. The catalytic cycle involves transmetalation between Ar- [M] and palladium (II) or rhodium (I) complexes as the key process, the mechanism of which is discussed on the basis of characterization of the transmetalation 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 DFT computational studies on the modes of coordination of the substrates to the phenylrhodium (I) / (S, S) -chiraphos intermediate.