Synthesis of 4-O-α- -galactopyranosyl- -rhamnose and 4-O-α- -galactopyranosyl-2-O-β-glucopyranosyl- -rhamnose using dioxolane-type benzylidene acetals as temporary protecting-groups

The Halide ion-catalysed reaction of benzyl exo-2,3-O-benzylidene-α- -rhamnopyranoside with tetra-O-benzyl-α- -galactopyranosyl bromide and hydrogenolysis of the exo-benzylidene group of the product 2 gave benzyl 3-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-α- -galactopyranosyl)-α- -rhamnopyranoside (6). Compound 2 was converted into 4-O-α- -galactopyranosyl- -rhamnose. The reaction of 6 with tetra-O-acetyl-α- -glucopyranosyl bromide and removal of the protecting groups from the product gave 4-O-α- -galactopyranosyl-2-O-β- -glucopyranosyl- -rhamnose.