The methyl 2,3-anhydrolyxopyranosides and 3,4-anhydroarabinopyranosides

Abstract

Monotoluene-p-sulphonylation of methyl α-D-xylopyranoside gives mainly the 2-sulphonate, which yields a mixture of methyl 2,3-anhydro-α-D-lyxopyranoside and methyl 3,4-anhydro-α-D-arabinopyranoside on treatment with alkali. At equilibrium the anhydroarabinoside predominates in the ratio 71 : 29. Methyl 2,3-anhydro-β-L-lyxopyranoside and methyl 3,4-anhydro-β-L-arabinopyranoside have been prepared from methyl β-L-arabinopyranoside, and their equilibration has been studied; the anhydrolyxoside predominates in the ratio 68 : 32. These results are compared with other cases of epoxide migration. When the acetates of the four epoxides are hydrolysed by aqueous acetic acid, unidirectional opening of the oxide ring occurs owing to the presence of a neighbouring trans-acetoxy group.