Enantioselective 1,4-Addition of Ar3Bi, [ArBF3]K, and ArSiF3 to Enones Catalyzed by a Dicationic Palladium(II)−Chiraphos or −Dipamp Complex
journal contribution
posted on 2005-10-10, 00:00 authored by Takashi Nishikata, Yasunori Yamamoto, Ilya D. Gridnev, Norio MiyauraChiral complexes of [Pd(S,S-chiraphos)(PhCN)2](SbF6)2 (2b) and [Pd(S,S-dipamp)(PhCN)2](SbF6)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)2 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.
