A Route to 3-Deoxy-4-O-methyl-D-manno-oct-2-ulosonic Acid (4-O-Methyl-KDO) and Its D-gluco Isomer Derivatives.-Starting with the gluconic acid derivative (I) via the Barton ester the α,β-unsaturated ketoester (III) is prepared. Its methoxymercuration leads to the title compounds (V) and (VI). -(PAKULSKI