Highly Regio- and Stereoselective Synthesis of Mannose-Containing Oligosaccharides with Acetobromo Sugars as the Donors and Partially Protected Mannose Derivatives as the Acceptors via Sugar Orthoester Intermediates

An orthoester formation/rearrangement sequence , in which 1,2-O-ethylidenated mannose or partially protected mannosides function as the glycosyl acceptors and simple acetobromo sugars as the glycosyl donors (see reaction scheme), provides an efficient and highly regio- and stereoselective route to mannose-containing 1→6, 1→3, and 3,6-branched oligosaccharides with exclusive 1,2-trans linkage.