Glucofuranose, 1,6-anhydro oxidation

If the disposition of hydroxyl groups is such that either an ethylene oxide or a hydrofuranol ring could be formed, then it is the three-membered anhydro ring that is preferentially established. Thus, if 6-tosyl-isopropylidene-D-glucofuranose (XII), in which there are present free hydroxyls at C3 and C5, is submitted to alkaline hydrolysis, it is the 5,6-anhydride VI alone that is formed7 the 3,6-anhydride appears only if the hydroxyl at C5 is protected by substitution as in X. 

A few polymerizations leading to nonhydrolyzable polysaccharides have been reported. The first was a base-catalyzed polymerization of 5,6-anhydro-l,2-0-isopropylidene-3-0-methyl-a-D-glucofuranose.u The polymerization was initiated most successfully with solid potassium or cesium hydroxide, and the d.p. achieved was —25. Hydrolysis gave a free, methylated, nonhydrolyzable polysaccharide, which was oxidized with hypoiodite to the poly(D-gluconic acid.)... 

Peat and coworkers187 investigated the reversion products formed by the action of acid on D-glucose and found, by periodate oxidation, that the mixed anhydrides contain 18 to 47% of material having a furanoid structure. Some 1,6-anhydro-0-D-glucofuranose was isolated. Other sugars apparently give only pyranoside reversion products. 

These considerations may be applied to an interpretation of the resistance of the trans 1,2-diols in l,6-anhydro-/3-D-glucofuranose and 1,6-an-hydro-a-D-galactofuranose. The bond angle32 for these hydroxyl groups apparently is near 120°, as is true in general for trans 1,2-diols on furan rings. Several examples are available of the oxidative cleavage of trans... 

In a similar approach, treatment of methyl glycosides with camphorsulfonic acid (CSA) in toluene under Dean-Stark conditions provides a good route to functionalized 1,6-anhydro sugars. Heathcock and co-workers showed that oxidation of the difficult-to-separate mixture of the l,6-anhydro- 8-D-glucopyranose (6) and l,6-anhydro- 8-D-glucofuranose (7) allowed for easy isolation of the desired ketone (8), by either chromatography or direct crystallization, depending on the reaction scale (O Scheme 4) [21]. 

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