Neighboring group participation in glycopyranosylation reactions is probed for esters at the 3-Oaxial and equatorial, 4-O-axial and equatorial, and 6-O-sites of a range of donors through the use tert-butoxycarbonyl esters. The anticipated intermediate cyclic dioxanyl cation is interrupted for the axial 3-O-derivative leading to the formation of a 1,3-O-cyclic carbonate ester, with loss of a tertbutyl cation, providing convincing evidence of participation by esters at that position. However, no evidence was found for such a fragmentation of carbonate esters at the 3-O-equatorial, 4-O axial and equatorial and 6-O positions indicating that neighboring group participation from those sites does not occur under typical glycosylation conditions. Further probes employing a 4-O-(2-carboxy) benzoate ester and a 4-O-(4-methoxybenzoate) ester, the latter in conjunction with an 18 O quench designed to detect bridging intermediates, also failed to provide evidence for participation by 4-Oesters in galactopyranosylation.

2-(2-Pyridyldithio-3-butenyl) glycosides react with carbohydrate-based thiols in a two step process involving sulfenyl transfer followed by desulfurative 2,3-allylic rearrangement, promoted by either triphenylphosphine or silver nitrate, to give novel saccharide mimetics. In an alternative embodiment of the same chemistry anomeric thiols are coupled with carbohydrates derivatized in the form of 2-(2-pyridyldithio-3-butenyl) ethers. This new method of glycoligation does not require protection of hydroxyl groups and is compatible with the presence of acetamides, azides, trichloroethoxycarbamates, and thioglycosides. Variations on the general theme enable the preparation of mimetics of reducing and non-reducing oligosaccharides as well as of non-glycosidically linked systems.

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