Methyl 4-deoxy-3-O-methyl-[alpha],[beta]-DL-threo-pentopyrano-side was prepared by a highly selective reaction of methanol with cis-, trans-, or cis-trans-3,4-epoxy-2-methoxytetrahydropyran in the presence of a catalytic amount of p-toluenesulfonic acid. The structure was supported by its conversion, after hydrolysis, to the phenylo-sazone and, by nitric acid oxidation, to O-methyl-DL-tartaric acid.