Glycosides and Disaccharides

A Review covering the formation, structures and chemical reactivities of free radicals at the anomeric centres of carbohydrate derivatives is of relevance to aspects of the chemistry covered in this Chapter. 

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R. R. Schmidt and J. Michel, Facile synthesis of a- and [3-f7-glycosyl imidates preparation of glycosides and disaccharides, Angew. Chem. Int. Ed. Engl. 79 731 (1980). 

The anomeric bromination can result from photosubstitution of other positions in the ring moiety. Very recenly, bromination of fully protected I-2-O-benzylidenated pyranoses with bromotrichloromethane and U.V. light or NBS yields 2-O-benzoyl glycosylbromides which may be converted in situ to glycosides and disaccharides in good yields (Scheme 2). These reaction conditions are compatible with protective groups like esters (acetates, benzoates, tosylates) and silyl ethers. 

Helferich reported that mercuric cyanide is sometimes superior to silver carbonate as base in the synthesis of glycosides and disaccharides. Thus the condensation of tetra-O-benzoylbromoglucose (1 equiv.) with benzyl alcohol (1 equiv.) in nitro-methane in the presence of mercuric cyanide (1 equiv.) gives tetra-O-benzoylbenzyl-/3-D-glucose in 90% yield. Zorbach used this general procedure, except that 1,2-dichloroethane was used as the solvent, in a successful synthesis of the cardiac-active... 

M. Kiso and L. Anderson, Protected glycosides and disaccharides of 2-amino-2-deoxy-D-glucopyr-anose by ferric chloride-catalyzed coupling, Carbohydr. Res., 136 (1985) 309-323. 

A variety of glycosides and disaccharides are synthesized by coupling of glycosyl... 

In order to minimize such possible side-reactions as anomerization of glycosides and acetolysis of acetal structures, alternative techniques of acetylation have been studied. Whereas basic catalysis leads to severe complications in certain nitro sugar derivatives (see Section IV,2a and c pp. 124, 129), boron trifluoride etherate has proved to be an excellent agent for satisfactory acetylation of glycosides, O-benzyl-idenated glycosides, and disaccharides that contain a deoxynitro function.148,149... 

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