N-Trifluoromethylthiosaccharin/TMSOTf: A New Mild Promoter System for Thioglycoside Activation

This work[1] presents our continued efforts in the field of thioglycoside chemistry by finding new activation conditions and applying this procedure into a strategy for one-pot oligosaccharide synthesis. We describe our investigation into the application of N-trifluoromethylthiosaccharin,[2] a new electrophilic trifluoromethythiolating reagent, as a promoter for the activation of thioglycosides. The activation proceeds by the in situ activation of N-trifluoromethylthiosaccharin with TMSOTf, which then serves to activate thioglycosides for glycoside bond formation giving glycosidation products in high to excellent yields. The results show that the activated thioglycosides undergo glycosidation reactions with various glycosyl acceptors to give the corresponding glycosides in moderate to excellent yields.[1] In addition, orthogonal activation of ethyl thioglycoside in the presence of phenyl thioglycoside was achieved under the above conditions, as shown below. This chemoselectivity could potentially serve as an extension to our one-pot oligosaccharide strategy[3] with the hope of producing larger oligosaccharides in a more efficient way. The mildness of our promoter system will allow us to exploit the observed reactivity differences of α- and β- thioglycosides for the design of one-pot oligosaccharide synthetic strategies.