An elegant convergent synthetic strategy has been developed for the preparation of the 4,6-O-(R)-pyruvate acetal containing pentasaccharide repeating unit of the cell wall O-antigen of Escherichia coli O156 using stereoselective [2 + 3] block glycosylation. Stereoselective 1,2-cis glycosylation of the judiciously functionalized monosaccharide intermediates led to the formation of the desired pentasaccharide in satisfactory yield.