DDQ-Mediated Oxidation of 4,6-O-Methoxybenzylidene-Protected Saccharides in the Presence of Various Nucleophiles: Formation of 4-OH, 6-Cl, and 6-Br Derivatives

Treatment of 4,6- O - p -methoxybenzylidene-protected pyranosidic mono- and disaccharides with 2,3-dichloro-5,6-dicyano- p -benzoquinone (DDQ), in the presence of a few equivalents of water, gave the corresponding 6- and 4- O - p -methoxybenzoates with unprotected hydroxyl groups in the 4- and 6-position in the ratio ∼4:1 and in 85−98% yield. Dry conditions in the presence of halide salts gave the 6-deoxychloro and -bromo 4- O - p -methoxybenzoates exclusively, in >90% yield.