Intramolecular 1,8-hydrogen atom transfer. Stereoselectivity of the hexopyranos-5'-yl radical reactions in Hex p-(1→4)-Hex p disaccharide systems

Abstract

The stereoselective reduction of hexopyranos-5′-yl radicals in α-d-Hexp-(1→4)-d-Hexp disaccharide models is described. These radicals are generated from a 6-O-yl radical located in the other monosaccharic unit through a 1,8-hydrogen atom transfer. The reaction, which is strongly influenced by steric and stereoelectronic effects, permits in some cases the transformation of α-d-Hexp-(1→4)-d-Hexp into β-l-Hexp-(1→4)-d-Hexp disaccharides in a single step with high diastereoselectivity.