Glycosyl donors protected with bulky silyl protective groups (
tert-butyldimethylsilyl, TBS), on the2-, 3-, and 4-OH groups were found to have superior reactivity compared with benzylated thioglucosides.The enhanced reactivity is explained by the stereoelectronic effects associated with the conformationalchange induced by the silylation. A TBS silylated thioglucoside donor has axial OR groups, whereas abenzylated thioglucoside has equatorial OR groups, leading to much more favorable charge-dipoleinteractions in the transition state. This concept could be used to create "super armed" glucosyl, mannosyl,rhamnosyl, and galactosyl donors, which could cross-couple with the armed acceptors, phenyl 2,3,4-tri-
O-benzyl-
![](/images/gifchars/beta2.gif)
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D-thioglucoside or phenyl 2,3,6-tri-
O-benzyl-
![](/images/gifchars/beta2.gif)
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D-thioglucoside, to give the corresponding armeddisaccharides in good to excellent yields.