Activation of Glycosyl Halides by Halogen Bonding

Halogen bonding is the formation of a non-covalent interaction between an electrophilic halogen substituent and a Lewis base, for instance, a halide. These kinds of relatively weak interactions have found applications in crystal engineering and initial applications in solution-phase chemistry are starting to appear. We report on the exploration of bis(iodoimidazolium) compounds as halogen-based Lewis acids in the activation of glycosyl halides. We show that these dicationic halogen-bond donors can be used to activate glycosyl halides if the carbohydrate core is sufficiently reactive enough. Furthermore, we provide comparison experiments which indicate that the mode of activation is indeed based on halogen bonding. This represents the first glycosylation reaction mediated by a (carbon-backbone-based) halogen-bond donor.