Mannose reaction with bromine

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... 

Condensation of D- and L-arabinose, D-ribose, D-xylose, D-galactose, D-glucose and D-mannose with 2-hydrazino-6-methyl-4-oxopyrimidine afforded intermediate sugar (6-methyl-4-oxo-2-pyrimidinyl)hydrazones. Treatment of the latter in one pot with bromine-acetic acid-sodium acetate then acetic anhydride (to effect a cyclization-acetylation reaction) gave, after purification and de-O-acetyla-tion, derivatives 19 (n = 3 or 4, stereochemistry as defined by the starting aldose). ... 

Arabinose reacted with HCN to give two monocarboxylic acids (A and B in reaction 2.3) that were mirror images. When (H-)-mannose was oxidized with bromine-water, the product was found to be identical to one of the monocarboxylic acids (B) that was formed by reaction of (H-)-arabinose with HCN. 

C. O. Obenland,/. Chem. Ed., 41,566 (1964) procedure submitted to Org. Syn. Bromine-Sliver acetate. Lemieux and Fraser-Reid found a route to 2,5-anhydro-sugars in the reaction of methyl 2-desoxy-2-iodo-/3-D-glucopyranoside triacetate with a large excess of bromine and silver acetate to give in high yield an anomeric mixture of 1,3,4,6-tetra-0-acetyl-2,5-anhydro-l-methoxy-D-mannoses. 

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