Direct and stereoselective synthesis of β-d-mannosides using 4,6-O-benzylidene-protected mannosyl diethyl phosphite as a donor

A direct and practical method for the construction of β-mannosidic linkages is described. While β-selectivities in the TMSOTf-promoted glycosidation of 2,3,4,6-tetra-O-benzyl-d-mannosyl diethyl phosphite are found to be highly dependent on the reactivity of acceptor alcohols, 2,3-di-O-benzyl-4,6-O-benzylidene-d-mannosyl diethyl phosphite reacts with a wide range of acceptor alcohols in the presence of TMSOTf in CH2Cl2 at −45 °C to give β-mannosides in high yields with good to high β-selectivities.