The synthesis of D-and L-glycero-alpha-manno-thioheptopyranosides, protected with 4,6-O-alkylidenetype acetals is described. In glycosylations carried out with preactivation with the 1-benzenesulfinylpiperidine/trifluoromethanesulfonic anhydride couple, both the D-and L-glycero series exhibit excellent, beta-selectivity with a range of glycosyl acceptors. In contrast, a 4,7-O-alkylidene acetal was found not to afford, beta-selectivity. With a 4,6-O-[1-cyano-2-(2-iodophenyl) ethylidene] acetal protected thioglycoside, excellent, beta-selectivity was obtained in glycosylation reactions, and subsequent treatment with tributyltin hydride and azoisobutyronitrile brought about clean fragmentation to the 6-deoxy-glycero-beta-D-manno-heptopyranosides. This chemistry was applied to the stereocontrolled synthesis of methyl alpha-L-rhamno-pyranosyl-(1 -> 3)-D-glycero-beta-D-manno-heptopyranosyl-(1 -> 3)-6-deoxy-glycero-beta-D-manno-heptopyranosyl-(1 -> 4)-alpha-L-rhamno-pyranoside, a component of the lipopolysaccharide from Plesimonas shigelloides.