Glycosylation with glycosyl sulfoxides

Scheme 8.19. Glycosylation reactions with a glycosyl sulfoxide.

Figure 16.17. Glycosylation of polystyrene-bound alcohols with pyranosyl sulfoxides [189,193]. R piva-loyl.

M. Casillas, A. M. Gomez, J. C. Lopez, and S. Valverde, A simple entry to pyranoid glycals reaction of anomeric glycosyl sulfoxides with organolithiums, Synlett, (1996) 628-630. 

Crich and co-workers have demonstrated elegantly that the stereoselective synthesis of fi-mannosides with glycosyl sulfoxides proceeds via anomeric a-triflate intermediates (51). Crich... 

An additional version of the two-stage activation used glycosyl sulfoxides to glycosylate thioglycoside acceptors [25-28]. The thioglycosides are then readily activated as sulfoxides using oxidation with m-chloroperbenzoic acid. 

In a different version of the same concept. Stork [67,68] and Bols [69-72] introduced silylene type tethering with glycosyl sulfoxide [67,68] or thioglycoside [69-72] donors. The silicon-tethered acceptor approach was also extended to the synthesis of a-D-gluco- [70,72] and a-D-galactopyranosyl linkages in oligosaccharides [70,72]. 

Furthermore, these authors were also able to perform the -mannosylations with the thiogly-coside 35 under the action of PhSOTf [45] or 1-benzenesulfinyl piperidine (BSP)-Tf20 [46] (O Scheme 17). In the cases of both glycosyl sulfoxide and thioglycoside, protection of the 4- and 6-positions by a cyclic acetal is critical. The corresponding perbenzylated donors gave poor -selectivity [47]. 

---