Direct chemical synthesis of β-mannopyranosides and other glycosides via glycosyl triflates

Article abstract of DOI:10.1016/S0040-4020(98)00426-8

High yield, highly stereoselective methods for the synthesis of β- mannopyranosides primary, secondary, and tertiary alcohols are presented. Activation of mannosyl sulfoxides or mannosyl thioglycosides with trifluoromethanesulfonic anhydride or benzenesulfenyl triflate, respectively, leads to the efficient formation of α-mannosyl triflates at -78 °C in dichloromethane, in the presence of 2,6-di-tertbutyl-4-methylpyridine. These triflates then react S(N)2-like with alcohols to give the β-mannosides. The use of a 4,6-O-benzylidene protected mannose is required for high selectivity, as is the use of non-participating protecting groups on O-2 and O-3 of the donors. It is further demonstrated that the thioglycoside/benzensulfenyl triflate activation is applicable in the glucoside series, when both armed and disarmed protecting groups are tolerated.