Reactions of 1,6-Anhydrohexopyranoses

Methanolic hydrogen chloride at elevated temperatures causes the conversion of 1,6-anhydrohexopyranoses into mixtures of the corresponding methyl glycosides.86,188,282,442 Ethyl 2,3,4-tri-O-benzyl-l-thio-a-D-glucoside was similarly obtained on treatment of 24 with ethane-thiol and zinc chloride.516,517 The anhydro bridge of levoglucosan (6) 

Another kind of intervention in the anhydrohexose aldose equilibrium has been described for l,6-anhydro-/3-D-gulopyranose. The action of 40% aqueous hydrogen bromide and bromine at 80° causes simultaneous hydrolysis and oxidation to D-gulono-1,4-lactone.122 

Fuming nitric acid and phosphorus pentaoxide in chloroform convert the trimefhyl ether of levoglucosan into the 1,6-dinitrate.90,556 Similar reaction of 38 yields tri-O-acetyl-D-glucose 1,6-dinitrate.556 

Dichloromethyl methyl ether and zinc chloride cleave 38 to the 6-formate (41). With an excess of the reagent, the final product is 2,3,4-tri-0-acetyl-6-0-(dichloromethyl)-a-D-glucopyranosyl chloride.565,566 

Unsubstituted 1,6-anhydrohexopyranoses react with boron tribromide or trichloride, the end products of this cleavage being unspecified oligosaccharides and free aldoses.126,567 Products having a C-6—P bond (for example, 42) are formed in the reaction of levoglucosan568,569 

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