Regioselective Oxidations, Regioselective Halogenations and Carbene Reactions of Sugar Derivatives Bearing a Thioether GroupRegioselective stoechiometrically controlled procedures are described for the oxidation of thiosugars either at the sulfur atom (to sulfoxides or sulfones) or at a hydroxymethylene group (to ketosugars). Ruthenium tetraoxide reacted at both sites. Chloration (SO2Cl2) of β‐ketothioether sugar derivative3took place exclusively at C(6). Evidence is given that a chlorosulfonium intermediateCwas formed when the dichloroketothiosugar derivative6was treated with SO2Cl2. The carbene generated from the tosylhydrazone16rearranged to the enoses17–20, the migrating group coming in equal proportions from C(4) and C(6). Some stereochemical aspects of these reactions are discu