Stereoselective α-Glucosylations from Glycosyl Hemiacetals Mediated by Lithium Iodide and Synthesis of the Pentasaccharide Repeating Unit of FPS-1

A stereoselective synthesis of 1,2-cis-glucosides from glucosyl hemiacetals is reported herein. It proceeds through a one-pot chlorination (under Appel conditions), halide metathesis to iodide (with LiI), and glycosylation sequence. A range of glycosyl acceptors and donors is shown to be suitable under the reaction conditions. To demonstrate the utility of this method, a target pentasaccharide containing 4 α-glucosyl linkages was synthesized.