Novel bicyclic donors for the synthesis of 2-deoxy-β-glycosides

Novel bicyclic glycosyl donors have been prepared by the cycloaddition reaction of glycals with 3-thiono-2,4-pentanedione 17 followed by methylenation of the resulting ketone. Treatment of the heterocyclic donors with triflic acid in the presence of a variety of alcohol accepters leads to the formation of beta-glycosides in good yields and with excellent stereoselectivities. Desulfurization of the C-2 carbon-sulfur bonds gives the corresponding 2-deoxy-beta-glycosides. This method has been extended to the synthesis of glycosidic linkages found in the aureolic acid antibiotics. Tetra-N-butylammonium triflate proved to be a useful additive in these glycosylation reactions, suggesting an important role for triflate anion in stabilizing intermediates which are formed.