Bicyclic anhydro structure

For our bicyclic anhydro structure 7, treatment with methanol and with 1.5 equivalents of A-iodosuccinimide (NIS) in acetonitrile gave an inseparable mixture of diastereomeric a-manno, p-manno, and p-gluco-2-deoxy-2-iodomethylglycosides 8a-c (1 1.5 5.2 by proton NMR integration) in a 93% yield (Scheme 12.4). Contrary... 

The failure of a compound to undergo periodate oxidation can not be regarded as positive proof that it contains no 1,2-glycol structures. If the glycol is securely locked in a trans position, oxidation has been shown not to occur. This resistance has been encountered in the bicyclic anhydro hexoses, for example, l,6-anhydro-/3-D-glucofuranoseM and 1,6-anhydro-a-D-galactofuranose.54 This work has already been summarized in this... 

Anhydro sugars have been of recurring interest for nearly a century. They were first obtained by alkaline1 and pyrolytic degradation2 of natural products and have since found varied uses. The rigid, bicyclic structures of some classes have made them useful in spectral investi-... 

The best approach to the structure of monomeric DHA was through H NMR and NMR studies. On the basis of H NMR, DHA was proposed to exist in aqueous solution as a bicyclic hydrated species, that is, 3,6-anhydro-L-xt/Zo-hexulono-l,4-lactone hydrate (53). We have made further studies on this structure using DHA prepared by oxygen oxidation in ethanol, or methanol or water using charcoal as a catalyst. The method is described earlier in this chapter. 

This compound was isolated by Diels and Meyer " on boiling o-glucose phenylosazone in methanol containing traces of sulfuric acid. They believed it to be identical with 3,6-anhydro- o-glucose phenylosazone, which had previously been prepared by other means." After observing differences in the physical properties of the two compounds, they suggested formula XVII, which they modified a year later " by proposing the pyrazole structure XVIII. This was found to be inadequate for several reasons, and the bicyclic formula XIX, or XX, was put forward by Percival." ... 

The fact that the formazan is formed ehminates structures XVII, XVIII, and XXI, which do not meet the conditions for this reaction. This fimiishes dired evidence in place of the indirect evidence on which Hardegger and Schreier had discarded structures XVIII and XXI. The bicyclic structure XIX, and XX, proposed by Percival" can be dismissed on comparison of the ultraviolet spectra. This compound, after coupling, should contain the two chromophoric groups of the simple formazans, whereas osazone formazans contain three of them. Anhydro- D-glucose phenylosazone formazan and its diacetate display practically the same maxima (maxima at 335 and 405 ran and 340 and 405 m/x, respectively) as does the indisputably-acyclic pyruvaldehyde phenylosazone formazan (maxima at 335 and 410 m/t), and these peaks differ substantially from the values for the simple sugar for-... 

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