Formation and Preparation of 1,6-Anhydrohexopyranoses

As early as 1881, Schiff24 (see also, Refs. 25 and 26) prepared a glassy, levorotatory material having the empirical formula C6Hi0O5 by thermal 

This reaction was then successfully applied in different modifications (—10% aqueous potassium hydroxide is mostly used), especially on the phenyl glycosides of aldohexopyranoses28 43 and of the corresponding oligosaccharides (see Sect. X,l,a), and still remains one of the methods frequently used for the preparation of l,6-anhydro-/3-D-glucopyranose31 38,40 (6) (for example, specifically labelled with carbon-14 see Ref. 44) and of l,6-anhydro-)3-D-galactopyranose.30,37 41,45 45a 

If the aglycon has a more complicated structure, involving, for example, a heterocyclic ring of the pyridine, pyrimidine, purine, or 

Phenyl 3- or 4-O-alkyl-R-D-glucopyranosides yield substituted 1,6-anhydro-/3-D-glucopyranoses,32,48-52 whereas 2-O-alkyl derivatives do not react under those conditions.32,33,43,49 The phenyl glycosides of 2-, 3-, or 4-deoxyhexoses behave similarly (see Sect. VII,3). 

The kinetics and mechanism of the formation of the 1,6-anhydride ring during the alkaline cleavage of aromatic glycosides depend on both the nature of the glycosidic bond and the substitution of the aglycon.32,35,43,46,58,59,62-65 Provided that steric conditions enable the 

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