Reactions of Anhydro Sugars

REACTIONS OF ANHYDRO SUGARS a. Effect of the Hydrofuran Anhydro Ring on Sugar Reactivities 

Introduction of the planar hydrofuran anhydro ring into a sugar structure may result in elements of strain that have a profound effect on the reactivities of the sugar lactol ring. Haworth, Owen, and Smith 72) concluded that the anhydro ring assumes the character of the principal ring while the pyranose or furanose lactol rings play a subsidiary role. 

Treatment of methyl 3,6-anhydro-j3-D-galactopyranoside with methanolic hydrogen chloride does not result in isomerization to the anhydro- 

The methyl 3,6-anhydroaldohexopyranosides (II) cannot be formed by the application of glycosidation conditions to the parent 3,6-anhydro sugars, the furanosides being formed exclusively. They can be prepared, however, by introducing the 3,6-anhydro ring through standard procedures into the normal methyl aldohexopyranoside structures (I). 

An extreme case of glycoside lability, promoted by the presence of the hydrofuran anhydro ring, is found in methyl or ethyl 2,5-anhydro-L-arabo-furanoside (74). These glycosides hydrolyze to, 5-anhydro- 

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A. Rosenthal and J. N. C. Whyte, Reaction of anhydro sugars with sodium cobalt tetra-carbonyl and carbon monoxide, Can. J. Chem., 46 (1968) 2239-2243. 

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