Synthesis of Anhydro-aldoses and -ketoses

The two best-known syntheses of anhydro sugars are clearly those of 1,6-anhydro-/3-D-glucopyranose by alkaline treatment of phenyl 

There appears to have been little effort expended to date on the synthesis of 1,6-anhydroglycofuranoses. They have usually been pre- 

Brimacombe and Tucker48 were able to prepare l,4-anhydro-6-deoxy-2,3-0-isopropylidene-/3-L-talopyranose by an uncomplicated ring-closure, with inversion, of 6-deoxy-2,3-0-isopropylidene-4-0- 

Quite analogous ring-closures occur when the 1-O-acetyl derivatives of the rhamnopyranose and talopyranose derivatives are treated with sodium azide in N,N-dimethylformamide. l-O-Acetyl-6-deoxy-2,3-0-isopropylidene-4-0-mesyl-a-L-mannopyranose is converted exclusively into l,4-anhydro-6-deoxy-2,3-0-isopropylidene-/3-L-talo-pyranose. In this instance, the azide nucleophile attacks the l-O-ace-tyl group, liberating an 0-1 oxide ion which reacts with inversion of C-4. The 4-epimeric, l-O-acetyl-6-deoxy-talose derivative gives 60% of the direct inversion product l,4-anhydro-6-deoxy-2,3-0-isopropyli-dene-a-L-mannopyranose, together with other products.50 

Similarly, various a-D-glucopyranose derivatives having a mesyloxy group at C-4 and an acetoxyl group at C-l are also converted into 1,4-anhydro-/3-D-galactopyranose derivatives on treatment with sodium azide in such aprotic solvents as N,N-dimethylformamide.51 The use of sodium azide in N,N-dimethylformam ide under forcing conditions originated in attempts at nucleophilic displacements to form azido, 

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