- Arabinose-derived ketones as catalysts for asymmetric epoxidation of alkenes
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Readily available arabinose-derived ketones, containing a tunable butane-2,3-diacetal as the steric blocker, displayed increasing enantioselectivity (up to 90% ee) with the size of the acetal alkyl group in catalytic asymmetric epoxidation of trans-disubstituted and trisubstituted alkenes. The stereochemical communication between our ketone catalysts and the alkene substrates is mainly due to steric effect, and electronic effect involving π-π interaction between phenyl groups of substrate and of catalyst did not appear to be operative in our system.
- Shing, Tony K. M.,Leung, Gulice Y. C.,Luk, To
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p. 7279 - 7289
(2007/10/03)
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- A catalytic asymmetric synthesis of chiral glycidic acid derivatives through chiral dioxirane-mediated catalytic asymmetric epoxidation of cinnamic acid derivatives
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A novel and practical asymmetric synthesis of chiral glycidic acid derivatives involving methyl (2R,3S)-3-(4-methoxyphenyl)glycidate ((2R,3S)-2a), a key intermediate for diltiazem hydrochloride (1), was developed. Treatment of methyl (E)-4-methoxycinnamate ((E)-3a) with chiral dioxirane, generated in situ from a catalytic amount (5 mol %) of an 11-membered C2-symmetric binaphthyl ketone (R)-7a, provided (2R,3S)-2a in 92% yield and 80% ee. Other cinnamic acid esters and amides were epoxidized by the use of the same procedure to give the corresponding chiral glycidic acid derivatives with up to 95% yield and 92% ee. Higher enantioselectivities in the asymmetric epoxidation of (E)-cinnamates than that of (E)-stilbene derivatives were observed and were proposed to be attributed to a dipole-dipole repulsion between oxygen atoms of an ester group in the cinnamates and those of the lactone moieties in the binaphthyl dioxirane.
- Imashiro, Ritsuo,Seki, Masahiko
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p. 4216 - 4226
(2007/10/03)
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- Improved procedure for Julia-Colonna asymmetric epoxidation of α,β-unsaturated ketones: Total synthesis of diltiazem and Taxol side-chain
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Poly-L-leucine catalyses the asymmetric epoxidation of enones 1-6 efficiently in a non-aqueous medium to provide the epoxy ketones 7-12 (70-91% yield; 80 to ≥95% ee). The strategy was used to make diltiazem 16 and the Taxol side chain 23 in single enantiomer form.
- Adger, Brian M.,Barkley, James V.,Bergeron, Sophie,Cappi, Michael W.,Flowerdew, Benjamin E.,Jackson, Mark P.,McCague, Ray,Nugent, Thomas C.,Roberts, Stanley M.
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p. 3501 - 3507
(2007/10/03)
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