Mannose methyl hemiacetal

Lemieux and Fraser-Reid174 have reported that the reaction of methyl 3,4,6-tri-0-acetyl-2-deoxy-2-iodo-j3-D-glucopyranoside (137) with bromine and silver acetate in acetic acid containing potassium acetate gives an almost quantitative yield of 1,3,4,6-tetra-O-acetyl-2,5-anhydro-D-mannose methyl hemiacetal (139), obtained as an... 

Anomeric ediyl hemiacetals of the methyl ester of aldehydo-D-galacturonic acid tetraacetate were prepared by Dimler and Link. In chloroform, these isomers mutarotated to an intermediate value over a period of several hours, and the mutarotation was complex. Solvent-free oldehydo-D-galactose pentaacetate was obtained in crystalline form, and did not show mutarotation in 1,1,2,2-tetrachloro-ethane. " In the presence of water, the corresponding crystalline aldehydrols of aZde/tydo-D-galactose pentaacetate and aldehydo-T>-mannose pentaacetate were obtained. 

This strategy was also used in the stereoselective synthesis of L-xylo-heptulosonic acid [79] as well as D-ma/wooctulosonic acid (KDO) [80]. It is worth to note that the mannose derivative when used in hemiacetal form, failed to react with methyl dihaloacetate [80b]. 

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