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Asymmetric epoxidation carbon-oxygen bond formation

Promising examples of the catalytic asymmetric Darzens condensation, which yields an epoxide product via carbon-carbon and carbon-oxygen bond formation, have been reported recently by two groups (Scheme 10.11). Toke and co-workers used crown ether 24 in the reaction to form the a,P-unsaturated ketone 78 [38b] with 64% ee, whereas the Shioiri group used the cinchona-derived salt 3a [52], which resulted in 78 with 69% ee. The latter authors propose a catalytic cycle involving generation of a chiral enolate in situ from an achiral inorganic base... [Pg.742]

The oxidation of the simplest symmetrically substituted alkene, ethylene, is noteworthy in that an asymmetric spiro transition state is observed. When constrained to Cs symmetry with eqnal forming carbon-oxygen bond lengths, the energy increases by only 0.1 kcalmol. The spiro TS has the plane of the HO—ONO (or peracid) at right angles to the axis of the C=C bond. In an idealized spiro TS this angle is exactly 90°. While the formation of snlfoxides from snlhdes by peroxynitrons acid is well-established , epoxidations have not yet been observed in solution. [Pg.18]

R. A. Johnson, K. B. Sharpless, Addition Reactions with Formation of Carbon-Oxygen Bonds (ii) Asymmetric Methods of Epoxidation, in Comprehensive Organic Synthesis (B. M. Trost, I. Fleming, Eds.), Vol. 7, 389, Peigamon Press, Oxford, 1991. [Pg.155]

Addition Reactions with Formation of Carbon-Oxygen Bonds (ii) Asymmetric Mediods of Epoxidation... [Pg.997]


See other pages where Asymmetric epoxidation carbon-oxygen bond formation is mentioned: [Pg.11]    [Pg.742]    [Pg.18]    [Pg.798]    [Pg.377]    [Pg.23]   
See also in sourсe #XX -- [ Pg.433 ]




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Asymmetric carbon

Asymmetric epoxidation

Asymmetric formation

Carbon oxygenated

Carbon oxygenation

Carbon-oxygen bond

Epoxidations, asymmetric

Epoxides 2,3-epoxide formation

Epoxides asymmetric epoxidation

Epoxides bonding

Epoxides formation

Epoxidizing oxygen

Formation, epoxidation

Oxygen, formation

Oxygenates formation

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