A mixture that consists of 34.83 g (100 mmol) of 2,3,4,6-tetra-O-acetyl-mannopyranose, 1.7 g (5 mmol) of tetrabutylammonium hydrogen sulfate and 82.93 g (600 mmol) of fine-powder potassium hydroxide in 350 ml of diethoxymethane is cooled to 0° C. At 0° C., 32.26 g (150 mmol) of 2-benzyloxy-ethylbromide is added in drops over 30 minutes while being stirred vigorously. It is stirred for two hours at 0° C. 300 ml of benzene is added, solid is filtered out, and the filtrate is evaporated to the dry state in a vacuum. The residue is taken up in 500 ml of ethanol. 5 g of palladium (10%) on activated carbon is added thereto and hydrogenated until hydrogen absorption is completed. Then, catalyst is suctioned out, it is rewashed with a little ethanol and evaporated to the dry state in a vacuum. The residue is chromatographed on silica gel (mobile solvent: dichloromethane/nhexane/ethanol=20:8:2). The product-containing fractions are concentrated by evaporation.
