Stereoselective C-C Bond Formation in Carbohydrates by Radical Cyclization Reactions; VI. Influence of the Conformation of Anomeric Radicals on the Stereoselectivity of Their Cyclization

All articles of this category The stereoselectivity of the 5- exo cyclization of anomeric radicals prepared from phenyl 2- O -allyl-1-seleno-glycopyranosides leading to C(1)-branched sugars is influenced by the conformation of these radicals. It is proposed that high stereoselectivity in the formation of the new chiral center C(8) is obtained, especially at low temperature, when the anomeric radical can adopt a chair or a half-chair conformation. In contrast, no stereoselectivity is observed for boat-like anomeric radicals.