Anhydro sugars 1,6-, formation

C. A. Johnson and P. H. Gross, Heterocyclic amino sugar derivatives. 6. Stabilization of a reactive intermediate by steric hindrance. Mechanism of 3,6-anhydro sugar formation, J. Org. Chem., 38 (1973) 2509-2512. 

Broadly speaking, two reactions are possible under those circumstances anhydro sugar formation and condensation with active amino compounds. Although both of these reactions probably occur, it appears that the first type is favored. n-Glucose, which under comparable conditions shows very little tendency to form an anhydride, is able to pro-... 

Mechanistic and stereoelectronic aspects of anhydro sugar formation are discussed in Ref. 7). 

The ease of anhydro sugar formation (22) from alkali treatment of the chalcogen isolog (1) decreases in the order X = Se > S > O. 

Another example of the formation of a 3,6-anhydro ring by the saponification of a 3-tosyl-D-glucose derivative is furnished by the work of Peat and Wiggins11 who were able to isolate derivatives of no less than three anhydro sugars, one of which was 3,6-anhydro-D-glucose, from the... 

The unusual formation of an anhydro sugar by the hydrolysis of a trityl derivative has been described.76 The treatment of 5-trityl-D-ribofuranose triacetate with hydrogen bromide in acetic acid gives a ribosan diacetate which is presumed to be 1,5-anhydro-D-ribofuranose diacetate. 

Comprehensive reviews of the chemistry of both the glycals [105-107] and anhydro sugars [108,109] have appeared in the recent literature. This chapter will attempt to summarize what is known about their preparation and reactivity in the formation of the glycosidic linkage and highlight recent examples to emphasize practical and strategic considerations in the choice of glycosyl donors. 

Anhydro ring formation in the sugar series takes place when certain derivatives are subjected to alkaline hydrolysis. These derivatives contain groups, the hydrolysis of which leads to the transitory formation of a... 

There are several instances where reactive intermediates present during the synthesis of septanosides have reacted intramolecularly to give ring-contracted or bicyclic products.91 Similar intramolecular reactions (such as the formation of 1,6-anhydro sugars) have precedents in the pyranose literature. Such cases of intramolecular reactivity described in the literature notably involve novel ethers or thioethers as the nucleophilic species in the ring contractions. 

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