In the presence
of palladium–phosphine catalysts such as tetrakis(triphenylphosphine)
palladium(0), the unsymmetrically substituted
disilane PhCl2SiSiMe3 reacts with α,β-unsaturated ketones in refluxing
benzene to give γ-(phenyldichlorosilyl) silyl enol ethers,
which can be converted into β-(phenyldiethoxysilyl) ketones
by treatment with ethanol and triethylamine (eq 1).Oxidation
of the phenyldiethoxysilyl group with hydrogen peroxide
in the presence of fluoride gives β-hydroxy ketones in high
yields. γ-(Phenyldimethylsilyl) lithium enolates, generated by
treatment of the γ-(phenyldichlorosilyl) silyl enol ethers with
methyllithium, undergo alkylation with alkyl halides to give β-
(phenyldimethylsilyl)-α-alkyl ketones with high anti selectivity
(eq 2). These β-(phenyldimethylsilyl) ketones are subjected to fluorodephenylation
followed by oxidation to give anti-β-hydroxy-
α-alkyl ketones. The 1,4-addition of the disilane is enantioselective
when catalyzed by PdCl2[(R)-BINAP], thereby providing
optically active anti-β-hydroxy-α-alkyl ketones with 66–92% ee
(Table 1).
