Glycosylation Using Hemiacetal Sugar Derivatives: Synthesis of O-(alpha)-D-Rhamnosyl-(1(right arrow)3)-O-(alpha)-D-rhamnosyl-(1(right arrow)2)-drhamnose and O-(alpha)-D-Tyvelosyl-(1(right arrow)3)-O-(alpha)-D-mannosyl-(1(right arrow)4)-L-rhamnose

O-(alpha)-D-Rhamnopyranosyl-(1(right arrow)3)-O-(alpha)-D-rhamnopyranosyl-(1(right arrow)2)-D-rhamnopyranose, a repeating trisaccharide of the O-specific polysaccharides (OPSs) of Pseudomonades, and O-(alpha)-D-tyvelopyranosyl-(1(right arrow)3)-O-(alpha)-D-mannopyranosyl-(1(right arrow)4)-L-rhamnopyranose, a trisaccharide composing the OPSs of Salmonella typhi, were synthesized by in-situ activating glycosylation reactions using hemiacetal sugar derivatives. Allyl 2,4-di-O-benzyl-(alpha)-D-rhamnopyranoside was prepared via the direct ditritylation of allyl (alpha)-D-mannopyranoside. 3-O-Acetyl-2,4-di-O-benzyl-D-rhamnopyranose was used as a precursor for the moiety of D-tyvelose (3,6dideoxy-D-arabino-hexose, 3,6-dideoxy-D-mannopyranose, 3-deoxy-D-rhamnose) of the salmonella trisaccharide.