Glycosylation with 2-Deoxy Glycosyl Phosphites

Several methods were reported for the selective synthesis of a-glycosides in the absence of a controlling group at C-2. The 2-deoxy sugar is first converted into a glycosyl donor by formation of phosphites,53 phophonodithioates,54 or phosphinothioates,55 which react with different acceptors and promoters. 

Usual activation of the Kahne phenyl sulfoxide glycosylation method is by use of triflic anhydride, trimethylsilyl triflate, or triflic acid and methyl propiolate. This, however, has been found to be unsatisfactory in cases of glycosylating agents which do not have 2-deoxy groups. It has now been reported that triethyl phosphite with catalytic amounts of triflic acid cause the reaction to give disaccharide products in variable yields. ... 

Several direct and stereoselective glycosylation methods using 2-deoxyglycosyl phosphates, phosphoramidites," and phosphites have been reported. An alternative approach to construct 2-deoxy-p-glycosides was developed by Hashimoto et al. (Scheme 38.3). In their smdy, the gly-cosylations of several 2-deoxyglycosyl diethyl phosphites with several glycosyl-acceptors including primary and... 

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