Acid-Catalyzed Synthesis of C-6-Esterified Sugar Acceptors from Acetals/Ketals Using Esters as Acyl Donors

A H 2 SO 4 –silica/TfOH-catalyzed regioselective primary esterification of acetal/ketal-protected glycosides has been developed. 4,6- O -Benzylidene-protected glycosides reacted smoothly with esters, which served as both solvent and acylating agent, to afford C-6-esterified orthogonally protected sugar acceptors. This transformation was also effective for benzylidene-protected 2-deoxyphthalimido- d -glucosamine glycosides and hence was utilized in one-pot synthesis of disaccharide from the corresponding precursor and fucosyl donor. Selectivity was observed in the case of 2,3:5,6-di- O -isopropylidene- d -mannofuranoside and 3,4- O -isopropylidene- d -galatopyranosides affording corresponding 5- and 4-hydroxy-free derivatives as major products.