Nucleophilic substitution reactions of pyranose polytosylates.

The 2,3,4-tri-toluenesulfonate ester derivatives of the methyl pyranosides of l-arabinose, d-ribose, d-lyxose, and d-xylose have been prepared, and their substitution reactions with various nucleophiles have been examined. For arabinose, xylose, and ribose, highly regioselective monosubstitutions were observed with benzoate, nitrite, and azide anions. These reactions have led to short and simple routes from d-xylose to l-arabinose derivatives, from l-arabinose to d-xylose derivatives, and from d-ribose to l-lyxose derivatives. The tritosylate derived from methyl alpha-d-lyxopyranoside was unreactive toward nucleophilic substitution reactions, giving instead a dihydropyran product arising from an initial E2 elimination reaction of the 2-tosylate.