Methyl 1,2-Orthoesters as Useful Glycosyl Donors in Glycosylation Reactions: A Comparison with n-Pent-4-enyl 1,2-Orthoesters

Mannopyranose‐derived methyl 1,2‐orthoacetates (R = Me) and ‐benzoates (R = Ph) can function as glycosyl donors – upon BF3·Et2O activation in CH2Cl2 – in glycosylation reactions with monosaccharide acceptors to afford disaccharides in good yields. In the process, glycosylation is preferred to acid‐catalyzed rearrangement leading to methyl mannopyranosides. Methyl 1,2‐orthoesters can be also used in regioselective glycosylation protocols with monosaccharide diols, in which they display good regioselectivity. Methyl 1,2‐orthoesters are useful glycosyl donors upon acid activation with boron trifluoride etherate. They react smoothly with monosaccharide alcohols or diols, leading to disaccharides in good to excellent yields. When monosaccharide diols are used as glycosyl acceptors, good regioselectivity in the glycosyl coupling is observed.