Catalytic asymmetric synthesis of β-hydroxy ketones by palladium-catalyzed asymmetric 1,4-disilylation of α,β-unsaturated ketones
作者:Yonetatsu Matsumoto、Tamio Hayashi、Yoshihiko Ito
DOI:10.1016/s0040-4020(01)80758-4
日期:1994.1
1,4-Disilylation of β,β-unsaturatedketones with 1,1-dichloro-l-phenyl-2,2,2-trimethyldisilane proceeded in the presence of phosphine-palladium catalysts in benzene. High enantio-selectivity (up to 92%) was observed in the disilylation with dichloro[(R)-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl]palladium(II) as a catalyst (0.5 mol %). The disilylation products, 1-(trimethyisilyloxy)-3-(dichlorophenylsilyl)propenes
Alkenylation of aldehydes with β-silyl ketones proceeded to afford β,γ-unsaturated ketones with skeletal rearrangement. The reaction mechanism involved tandem aldol/[1,4]-Brook/1,2-addition/ring cleavage of cyclopropane. [1,4] Brook rearrangement took place with complete inversion of configuration at the carbon center.
Acicular purplish crystals were obtained from Cu(acac)(2) and a chiral bipyridine ligand. Although the crystals were not soluble, they nevertheless catalyzed asymmetric silyl conjugate addition of lip ophilic substrates in water. Indeed, the reactions proceeded efficiently only in water; they did not proceed well either in organic solvents or in mixed water/organic solvents in which the catalyst/substrates were soluble. This is in pronounced contrast to conventional organic reactions wherein the catalyst/substrates tend to be in solution. Several advantages of the chiral Cu(II) catalysis in water over previously reported catalyst systems have been demonstrated. Water is expected to play a prominent role in constructing and stabilizing sterically confined transition states and accelerating subsequent protonation to achieve high yields and enantioselectivities.