Anhydro Sugars as Intermediates in the Interconversion of Configurational Isomers

Anhydro Sugars as Intermediates in the Interconversion of Configurational Isomers 

Another example is provided by the observation of Ohle and Wilcke that whereas 3-tosyl-l,2-i8opropylidene-D-glucofuranose (XXXV) is saponified without anhydro ring formation and without Walden inversion, the triacetate of methyl S-tosyl-iS-n-glucofuranoside (XXXVI) is 

The inference is that the hydrofuranol ring of XL can never be directly formed by the saponification of a 3-tosyl ester of n-glucose, but only indirectly by the intermediate formation and scission of an anhydro ring of the ethylene oxide type. The sequence of reactions involved in the conversion of methyl 3-tosyl-j3-D-gIucoside into methyl 3,6-anhydro-D-glucoside is shown by XXXVI to XL. 

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 Wiggins who were able to isolate derivatives of no less than three anhydro sugars, one of which was 3,6-anhydro-D-glucoae, from the 

When this paper was published (in 1938), the evidence indicated that the hydrofuranol ring compound isolated was the pyranoaide form (XLVI). The later work of Haworth, Owen, and Smith, which is discussed in section V-1, corrected this impression and proved that the compound actually isolated by Peat and Wiggins was methyl 3,6-anhydro-/3-D-glucofuranoside (XLVIII). This correction does not invalidate the above argument, for it is known that XLVI is unstable and a trace of acid suffices to transform it into the stable furanoside. 

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