Remote Activation of Disarmed Thioglycosides in Latent-Active Glycosylation via Interrupted Pummerer Reaction.

S-glycosides, S-2-(2-propylthio)benzyl (SPTB) glycosides, were converted to the corresponding oxidized glycosyl donors, S-2-(2-propylsulfinyl)benzyl (SPSB) glycosides, by simple and selective oxidation. Treatment of disarmed SPSB donor and various acceptors with triflic anhydride provided the desired glycosides in good to excellent yields. Meanwhile, observation of thiosulfinate, thiosulfonate, and disulfide suggested that the leaving group was activated via an interrupted Pummerer reaction. The disarmed SPSB thioglycosyl donors could be selectively activated in the presence of various thioglycosides with remote activation mode. Finally, two natural hepatoprotective glycosides, Leonoside E and Leonuriside B, were efficiently synthesized in a convergent manner with this newly developed method.