An improved method for the synthesis of protected glycosyl fluorides from thioglycosides using N,N-diethylaminosulfur trifluoride (DAST).

The direct conversion of thioglycosides to glycosyl fluorides frequently used in oligosaccharide synthesis was examined using N,N-diethylaminosulfur trifluoride (DAST). Although the reaction proceeded without N-bromosuccinimide (NBS), in some cases it was found that the electrophilicity of the Vilsmeier-type electrophilic sulfinium cation species was not sufficient for the activation of certain less-reactive thioglycosides. Here, we report the results of fluorination reactions of a series of monosaccharides using DAST in the absence of NBS, and also discuss the acceleration of the reaction in the presence of dimethyl(methylthio)sulfonium trifluoromethanesulfonate (DMTST) resulting in excellent product yields.