Enantioselective 1,4-Addition of Ar3Bi, [ArBF3]K, and ArSiF3 to Enones Catalyzed by a Dicationic Palladium(II)−Chiraphos or −Dipamp Complex

Chiral complexes of [Pd( S,S -chiraphos)(PhCN) 2 ](SbF 6 ) 2 ( 2b ) and [Pd( S, S -dipamp)(PhCN) 2 ](SbF 6 ) 2 ( 2c ) catalyzed the highly enantioselective 1,4-additions of Ar 3 Bi, [ArBF 3 ]K, and ArSiF 3 to cyclic and acyclic enones in aqueous methanol. The complexes catalyzed the reactions of Ar 3 Bi and ArSiF 3 at 0−5 °C in the presence of Cu(BF 4 ) 2 or ZnF 2, whereas they smoothly prompted the addition of [ArBF 3 ]K at −15 °C without further activation of the catalysts. The highest enantioselectivities giving β-aryl ketones up to 99% ee were attained when using 2b for 2-cyclopentenone and acyclic ( E )-enones, whereas 2c resulted in the best selectivities for 2-cyclohexenone and 2-cycloheptenone (89−96% ee). The effects on enantioselection of chiral ligands and substituents on α,β-unsaturated ketones are discussed on the basis of X-ray structures of 2b and 2c as well as DFT computational studies on mechanistic aspects of the catalytic cycle.