Glycosyl iodides are highly efficient donors under neutral conditions

Glycosyl iodides have been prepared and subjected to glycosylation under neutral conditions. The reactions are highly efficient, giving alpha glycosides even with sterically demanding glycosyl accepters. Glucosyl iodides react with allyl alcohol slowest and require refluxing conditions. Galactosyl iodides are intermediate in reactivity, providing the allyl glycoside in 3 h at room temperature, whereas glycosylation of fucosyl iodides occurs in less than 1 h under similar conditions. The scope and limitations of the reactions were demonstrated with a variety of accepters, including an anomeric hydroxyl group, to give trehalose analogs, beta-Selective glycosylation of glucosyl iodides, in the absence of C-2 participation, could be achieved by simply changing the solvent from benzene to acetonitrile. (C) 1999 Elsevier Science Ltd. All rights reserved.