Stereoselective C-C Bond Formation in Carbohydrates by Radical Cyclization Reactions; V. Application for the Synthesis of α-C (2) -Branched Sugars

Alain De Mesmaeker; Pascale Hoffmann; Tammo Winkler; Adrian Waldner

doi:10.1055/s-1990-21033

Synlett 1990; 1990(4): 201-204
DOI: 10.1055/s-1990-21033

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Stereoselective C-C Bond Formation in Carbohydrates by Radical Cyclization Reactions; V. Application for the Synthesis of α-C (2) -Branched Sugars

Alain De Mesmaeker^* , Pascale Hoffmann, Tammo Winkler, Adrian Waldner

^*Central Research Laboratories, Ciba-Geigy Ltd., CH-4002 Basel, Switzerland

Abstract

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The stereoselectivity of the 5-exo radical cyclization reaction of allylic 2-deoxy-2-iodoglucopyranosides leading to α-C(2)-branched sugars is influenced by the substitution of the allylic double bond. The observed stereoselectivity for the formation of the chiral center on the newly formed tetrahydrofuran ring results from a less sterically hindered transition state of cyclization, except in the case of a cis phenyl substituted C=C double bond.

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