1,2-anhydro-3,4,6-tri-O-benzyl-β-D-mannopyranose

1,2-Anhydro pyranosides are useful intermediates for the preparation of O-glycosides, N-glycosides, and C-glycosyl compounds. The epoxides can be activated under Lewis acidic conditions to give a cyclic cation. The cation captures nucleophiles to give glycosides. Danishefsky demonstrated the utility of 1,2-anhydro pyranosides in solid-phase oligosaccharide synthesis. Since 1,2-epoxides are extremely sensitive to the acid, the typical epoxidation conditions of olefins using m-chloroperbenzoic acid‡ cannot be used. The neutral oxidation reagent 3,3-methyldioxirane was successfully used for preparation of 1,2-anhydro pyranosides from glycals. The disadvantage of the latter method for epoxidation is the instability of the reagent. Furthermore, the concentration of the reagent is limited. The disadvantage of the latter method for epoxidation is the instability of the reagent, which can be used only in limited concentration. For large-scale preparation, the method involving epoxide formation by nucleophilic attack of alkoxide generated in situ is reliable.