Glycosyl iodides preparation

Reaction of peracetylated sugars with iodine in the presence of hexamethyl-disilazane has been reported to afford the corresponding glycosyl iodide.29 Glycosyl iodides have also been prepared by treatment of glycosyl chlorides or bromides with substoichiometric amounts of iodine and DDQ.30 In this instance, DDQ acts to oxidize iodide remaining after the initial attack on the electrophilic iodine. The benefit of this approach is to limit the amount of free iodide is solution, as recycling of iodine at the expense of DDQ is clearly not cost-effective. 

Chervin, S M, Abada, P, Koreeda, M, Convenient, in situ generation of anhydrous hydrogen iodide for the preparation of a-glycosyl iodides and vicinal iodohydrins and for the catalysis of Ferrier... 

Over the past decade, our laboratory has been actively involved in developing methods for the preparation and applications of glycosyl iodide donors (36-49) including efficient a-stereoselective glycosylation protocols that work well with various sugars iodides (39-41). Recently, we have applied this methodology in the synthesis a-anomeric glycolipids. 

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

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