Structure of Sugar Phenylosazones

The structure of sugar phenylosazones, derivatives first prepared by Fischer in 1884, has remained undefined. Besides Fischer s open-chain structure, a tautomeric azo-hydrazone structure and ring structures have been proposed. Although work in the last two decades involving ultraviolet spectra studies - and examination of the acetylated - and 

The acyclic structure does not explain how the reaction stops at C2 instead of continuing to C3, and why the unino hydrogen of only one phenylhydrazone group is methylatable when each of the imino groups apparently should have the same value. 

In an attempt to explain the first of these observations, Baly, Tuck, Marsden and Gazdar, as early as 1907, advanced the assumption (open-chain form presumed) that, in the sugar phenylosazones, the two conjugated double bonds form a condensed system because of their inner linkage, which causes the reaction to stop at C2. 

Fieser and Fieser, on theoretical grounds, proposed for the structure of the phenylosazones the chelate tautomers VI and VII of the acyclic 

Hardegger and Schreier, i the latest workers to deal with the problem, considered that any attempt to define precisely the structure of the phenylosazones, on the basis of information at hand, would be immature. For this reason, insofar as possible, they used Fischer s open-chain formula for the phenylosazones and their derivatives. 

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