A synthetic route to 4-C-methyl-xylo-furanose

3-O-benzyl-1,2-isopropylidene-α-D-xylo-pentodialdofuranose could not be α-methylated by direct or indirect methods. The aldol product from reaction of the dialdofuranose with formaldehyde could not be trapped, but underwent a Cannizzaro reaction to give the C-4-bis-hydroxymethyl product. The latter can be regioselectively sulfonated at the pro-(S) hydroxymethyl group. Reduction with lithium aluminum hydride then affords 3-O-benzyl-1,2-isopropylidene-4-C-methyl-α-D-xylo-furanose as the major isomer, the configuration of which is proved by transformation into an oxetane.