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Diastereoselectivity, substituted anomeric

The conversion of anomerically linked enol ethers 29 into either the cis- or trans-substituted pyranyl ketones with high diastereoselectivity and yield involves a Lewis acid-promoted O —> C rearrangement (Scheme 19) <00JCS(P1)2385>. Under similar conditions, homoallylic ethers 30 ring open and the oxonium ions then recyclise to new pyran derivatives 31. Whilst the product is a mixture of alkene isomers, catalytic hydrogenation occurs with excellent diastereoselectivity (Scheme 20) <00JCS(P1)1829>. [Pg.322]

Beckwith AU, Duggan PJ (1998) The quasi-homo-anomeric interaction in substituted tetrahydropyranyl radicals diastereoselectivity. Tetrahedron 54 6919-6928... [Pg.282]

Furanones, maleic anhydride, maleimides, and cyclopentenones behave similarly when irradiated in the presence of alkenes. [2-1-2]-Photocycloaddition reactions of furanones, especially y-substituted furanones with alkenes, can be highly diastereoselective. A detailed analysis of the cycloaddition of ethylene with substituted furanones gave a deep insight into the origin of the diastereoselectivity. Based on product ratio dependence on temperature and the substituents, it was proposed that a pyramidalization of the P-carbon of furanones in their relaxed excited state and a homo-anomeric effect determined the... [Pg.1462]

See other pages where Diastereoselectivity, substituted anomeric is mentioned: [Pg.65]    [Pg.65]    [Pg.107]    [Pg.129]    [Pg.181]    [Pg.67]    [Pg.370]    [Pg.1040]    [Pg.181]    [Pg.282]    [Pg.38]    [Pg.246]    [Pg.68]    [Pg.7]    [Pg.19]    [Pg.290]    [Pg.38]    [Pg.133]    [Pg.624]    [Pg.22]   


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Anomeric substitution

Diastereoselectivity, substituted anomeric radicals

Substitution diastereoselection

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