The trisaccharide α- d-Man p-(1→2)-α- d-Man p-(1→2)- d-Man was synthesised by using a stepwise method. A key reaction in the preparation of the intermediates was the selective hydrogenolysis of mannopyranoside derivatives having both dioxane- and dioxolane-type benzylidene acetals, resulting in the exclusive cleavage of the former acetal rings.