Glycosyl 6-nitro-2-benzothiazoate. A highly efficient donor for β-stereoselective glycosylation

Highly β-stereoselective glycosylations of glycosyl acceptors having a primary hydroxyl group by using a novel glycosyl donor, α-glycosyl 6-nitro-2-benzothiazoate (3), proceeded smoothly in the presence of a catalytic amount of trifluoromethanesulfonic acid (TfOH) in CH₂Cl₂ at -78°C to afford the corresponding glycosides in high yields. The donor 3 gave β-saccharides more dominantly compared with those using other α-glycosyl donors such as thioform- and trichloroacet-imidates or fluoride under the same conditions.