Remote control of α- or β-stereoselectivity in (1→3)-glucosylations in the presence of a C-2 ester capable of neighboring-group participation Original Research Article

In (1→3)-glucosylation the glycosyl bond originally present in either donor or acceptor is shown to control the stereoselectivity of the forthcoming bond, i.e., the newly formed glycosidic linkage has the opposite anomeric configuration of that of either the donor or acceptor. Therefore, with α-(1→3)-linked disaccharides with nonreducing ends that have the 3-OH free as the acceptor and an acetylated glucosyl trichloroacetimidate as the donor, or with an α-(1→3)-linked acetylated disaccharide trichloroacetimidate as the donor and a glucoside with 3-OH free as the acceptor, β-linked trisaccharides were obtained. Meanwhile, with β-(1→3)-linked disaccharides that have nonreducing ends with the 3-OH free as the acceptor and an acetylated glucosyl trichloroacetimidate as the donor, or with a β-(1→3)-linked acetylated disaccharide trichloroacetimidate as the donor and a glucoside with the 3-OH free as the acceptor, α-linked trisaccharides were obtained in spite of the C-2 neighboring group participation.