Stereoselective glycosylation reactions

Mukaiyama, T, Matsubara, K, Stereoselective glycosylation reaction starting from 1-0-trimethylsilyl sugars by using diphenyltin sulfide and a catalytic amount of active acidic species, Chem. Lett., 1041-1044, 1992. 

Kim J-H, Yang H, Boons G-J (2005) Stereoselective glycosylation reactions with chiral auxiliaries. Angew Chem hit Ed Engl 44 947-949... 

This synthesis demonstrated that the neighboring-group participation effect on the stereoselectivity of glycosylation reactions can be extended to sohd-phase processes. In this case, milder and more practical cleavage conditions than previously discussed were established. The use of /V- bromosuccinimide as the thiophilic reagent in acetone/water or tetrahydrofuran/methanol permitted the release of oligosaccharides in form of lactols or 1-0-Me glycosides, respectively. The tetrasaccharide derivative was isolated in 34% yield from thiol resin 3 (80% yield per step). 

The synthesis and application of glycosyl dimethylthiophosphate donors has also been reported.52 These donors were prepared from the reducing sugars in moderate to good yield and exhibit considerable shelf stability. Glycosylation reactions with a variety of primary and secondary glycosyl acceptors suffered from poor stereoselectivity and required silver triflate as promoter to achieve reasonable coupling yields (Scheme 6.16). 

Besides stereoselective synthesis of various monosaccharides, stereoselective reaction for the preparation of glycosides is an important problem in the synthetic field of carbohydrate chemistry. However, the classical methods, which require the assistance of heavy metal salts or drastic reaction conditions, are still employed by and large in the synthesis of such compounds. Taking these disadvantages into consideration, new glycosylation reactions, which proceed under mild reaction conditions with high selectivity, have been developed and exploited. 

In C-glycosylation reactions a new stereocenter is formed, and in general only one of the two stereoisomers is desired. Therefore, it is quite important to develop stereoselective C-glycosylation procedures, in which the stereochemical outcome can be predicted... 

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