Aglycon delivery method

The sulfoxide method has been applied to the concept [319,374] of intramolecular aglycone delivery for the formation of [1-mannosidcs by means of a silylene linker. In the original work, the acceptor and a thioglycoside donor were joined by means of a silylene group before the oxidation to the sulfoxide [141]. However, it was later found that the preformed sulfoxide was tolerated by the chemistry for the introduction of the linker [286,375]. The intramolecular aglycone delivery step was shown to function effectively for the transfer of the donor to the 2-, 3- and 6-position of glucopyr-anosides, as exemplified in Scheme 4.64. 

As a conclusion, the internal aglycon delivery approach works well in furano-sidic systems and provides a convenient stereospecific route to )3-fructofurano-sidic disaccharides. The scope and limitations of this method will be further evaluated in the synthesis of larger oligosaccharides structures containing -fructofuranosyl residues. 

The use of the p-methoxybenzyhdene acetal tethered intramolecular aglycone delivery was extended to polymer-supported oligosaccharide synthesis [77]. The method also proved to be successful in the synthesis of other difficult linkages, such as (3-D-fructofuranosides [78], (3-D-arabinofuranosides [79-81] and a-D-fucofuranosides [82]. 

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