Glycosylation, iodine-promoted

Preliminary studies show that iodine-promoted glycosylation of sugar alcohols with a mnnno-configured sulfoxide at room temperature gives rise to disaccharides in moderate to good yield (unoptimized). The stereochemical outcome of these... 

Iodine promotes glycosylation reactions of perbenzylated thioglycosides [222]. The interhalogen compounds of iodine, IBr and ICl are more active, capable of promoting... 

Kartha, K P R, Field, R A, Glycosylation chemistry promoted by iodine monobromide efficient synthesis of glycosyl bromides from thioglycosides, and 0-glycosides from disarmed thioglycosides and glycosyl bromides, Tetrahedron Lett., 38, 8233-8236, 1997. 

M. Adinolfi, B. Gaspare, A. Iadonisi, and M. Schiattarella, Iodine/triethylsilane as a convenient promoter system for the activation of disarmed glycosyl tri-chloro- and /V-(phenyl)trifluoroacetimidates, Synlett, 2 (2002) 269-270. 

Another popular promoter for glycosylation with thioglycosides is the reagent dimethyl(methylthio)sulfonium triflate (DMTST).60 A comparison between DMTST and NIS/TfOH for the formation of sialoglycoconjugates demonstrated that the iodine system provided superior yields and anomeric selectivity in nearly all cases.61 The yields and stereoselectivity also increased with an increase in solvent polarity, suggesting that enhanced stabilization of the oxacarbenium intermediate, the rate-limiting step in glycosylation, was responsible for the increased... 

In our hands iodine was indeed found to be an effective promoter of the alcoholysis of unprotected thioglycosides.18 Acetylated, disarmed 19 thioglycosides proved unreactive toward iodine, whereas benzylated, armed 19 thioglycosides were found to undergo efficient glycosylation of both simple and sugar alcohols in the presence of iodine (Fig. 7).18... 

Originally used in catalytic amounts in combination with silver oxide and silver carbonate in Koenigs-Knorr reactions, iodine was shown to promote glycosylations either alone or in combination with DDQ [74]. Iodine bromide was reported to be a more efficient promoter [75]. 

Triflic anhydride in the presence of a base such as DTBMP is the most frequently used promoter with sulfoxides. It has also been used with lanthanide triflates as coactivators [215]. Promoters other than triflic anhydride for the activation of sulfoxides for glycosylation include TfOH [249,250], TMSOTf in the presence of triethylphosphite [251], the heteropolyacid H3PW12O40 [252], the zirconocene reagent Cp2ZrCl2-AgC104 [253] and iodine and iodine monobromide [254,255]. 

These glycosylation reactions are promoted by NBS, iodonium dicollidine perchlorate (IDCP) or the corresponding triflate (IDCT) [353]. Iodine has also been reported to promote the reaction [254]. NIS, in combination with catalytic amounts of a protic acid such as TfOH [213], or Lewis acids such as TESOTf [17], Sn(OTf>2 [354] or BF3-Et20 [355], was introduced as a more active catalyst. Recently, glycosylation with NIS under microwave irradiation has been developed [356]. 

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