Sugars 3,6-anhydro-ring

The two main classes of anhydro sugars are therefore the ethylene oxide and the hydrofuranol types. Other anhydro ring systems are known but the number of representatives of such systems is not great. 

Another example of the formation of a 3,6-anhydro ring by the saponification of a 3-tosyl-D-glucose derivative is furnished by the work of Peat and Wiggins11 who were able to isolate derivatives of no less than three anhydro sugars, one of which was 3,6-anhydro-D-glucose, from the... 

Anhydro ring formation in the sugar series takes place when certain derivatives are subjected to alkaline hydrolysis. These derivatives contain groups, the hydrolysis of which leads to the transitory formation of a... 

Deoxyhalogeno sugars are susceptible to nucleophilic attack, leading either to displacement, elimination, or anhydro-ring formation. The ease of displacement decreases in the order I > Br> Cl > F the iodo and bromo derivatives have, therefore, been especially utilized in such reactions, although several reactions with chlorodeoxy sugars have now been reported as a result of the increased availability of these compounds. The approach delineated in Section 11,1 (see p. 227) for predicting the reactivity of sulfonic esters can be expected also to be applicable, in an approximate and qualitative way,... 

If an appropriately situated, unsubstituted hydroxyl group is available, anhydro-ring formation usually takes precedence over substitution or elimination. Thus, with alkali, the bromo-, chloro-, and iodo-deoxy sugars react analogously to sulfonic ester derivatives148 to afford epoxides in good yield.22,169 It has been established170 that l,2 5,6-dianhydro-D-mannitol is formed in aqueous solutions of... 

All of the crystalline pyranoses thus far examined adopt a chair conformation. A boat conformation has not yet been found for crystalline monocyclic compounds of sugars. Fused-ring systems seem to be required for part of the molecule to adopt a boat form, as in sedo-heptulosan (5) (where a chair form is also a part of a boat form (fused to the boat form)27 and l,6-anhydro-/3-D-glucopyranose. 

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