Stereoselective Synthesis of β-D-Mannopyranosides with Reactive Mannopyranosyl Donors Possessing a Neighboring Electron-Withdrawing Group This work was supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie, and the European Community (Grant No. HPRN-CT-2000-00001/GLYCOTRAIN). A.A.H.A.R. and E. S. H. El Ashry are grateful to the Alexander von Humboldt Foundation for a fellowship and for the continued support, respectively.

An electron-withdrawing protecting group at the O-2 atom and a good anomeric leaving group at the mannopyranosyl donor are required for a new, practical approach to the production of β-linked mannopyranoside units (see scheme, MPM=para-methoxybenzyl, TDS=thexylmethysilyl, TMS=trimethylsilyl, All=β-D-allose, OTf=trifluoromethanesulfonate). Many attempts to solve this problem in a direct manner have failed. β-Mannopyranoside units are found, for instance, in N-glycopeptides.