ABSTRACT
Nucleophilic substitution reactions are an important part of synthetic carbohydrate chemistry as they allow for the installation at a specically activated position a variety of different functional groups, usually with inversion of stereochemistry. The
Experimental ............................................................................................................ 55 General Methods ................................................................................................. 55 General Reaction Conditions .............................................................................. 55
Method A ........................................................................................................ 55 Method B ........................................................................................................ 55 3-O-(Imidazole-1-sulfonyl)-1,2:5,6-di-O-isopropylidene-α-dglucofuranose ................................................................................................. 55 Benzyl 4-O-(imidazole-1-sulfonyl)-2,3-O-isopropylidene-α-lxylopyranoside ............................................................................................... 56
Acknowledgments .................................................................................................... 56 References ................................................................................................................ 58
activation of alcohols in carbohydrate chemistry usually involves one of two different methods. The rst involves a direct conversion from the alcohol through a transient species, usually an alkoxyphosphonium salt (e.g., Mitsunobu reaction). The second, a more general method, is through the initial formation of a sulfonate, which is an excellent leaving group. The best-known examples of these leaving groups are the methanesulfonates, p-toluenesulfonates, and triuoromethanesulfonates. A related functional group that has only seen limited use in the carbohydrate literature is the imidazole-1-sulfonate (imidazylate), despite the group allowing preparation of a variety of carbohydrate-based molecules.1-10 The imidazylate group has advantages over common sulfonates as they are more stable and amenable to chromatographic purication and they can be prepared from readily available and inexpensive reagents. Also, upon substitution they result in the formation of sulfate and imidazole as byproducts, which are not classied as genotoxic, in contrast to methanesulfonate, p-toluenesulfonate, and triuoromethanesulfonate.11
