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 Ar3Bi, [ArBF3]K, and ArSiF3 to cyclic and acyclic enones in aqueous methanol. The complexes catalyzed the reactions of Ar3Bi and ArSiF3 at 0-5°C in the presence of Cu(BF4) or ZnF2, whereas they smoothly prompted the addition of [ArBF3]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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry