1-Thioglycosides xanthates

Sialidation Using 2-Thioglycosides, Xanthates, or Phosphites of Sialic Acids in Acetonitrile... 

The stereochemistry of the reaction depended on the substrate in some favourable cases a single stereoisomer was formed, whereas in others mixtures of a,/ -isomers were obtained. An increase in yield was noted when the phenyl group of the thioglycoside was replaced by the 4-chlorophenyl group. Another useful fluorination involved xanthate esters, ROCSSMe, readily obtained from alcohols these upon reaction with 4-(difluoroiodo)toluene were converted into alkyl fluorides in 48-75% yield [54],... 

Condensation of 1 in ethanol with potassium ethylxanthate gave210 the crystalline O-ethyl S-glycosyl xanthate 63 (R = Et) in high yield on treatment with cold methanolic ammonia, the compound underwent O- and S-deacetylation and 1 actonization, to give a hygroscopic product to which structure 64 has been ascribed. Treatment of 64 with diazomethane, followed by acetylation, resulted in the known201 1-thioglycoside derivative 61 (R = Me). 

Under the same conditions, glycals are also formed from l-thioglycoside-2-xanthates. Phenyl thioglycopyranosides easily undergo reductive lithiation with lithium naphtalenide in tetrahy-drofuran at low temperatures and subsequent elimination of C-2 substituents [85,86]. Such reaction conditions are compatible with labile acid- and base-protecting groups and yields... 

M. Sakata, M. Haga, and S. Tejima, Synthesis and reactions of glycosyl methyl- and benzyl xanthates. A facile synthesis of 1-thioglycosides, Carbohydr. Res., 13 (1970) 379-390. 

Other literature methods not described in detail here, utilise glycosyl sulfenate [41], thiopseudourea [42], xanthate [42, 43], thiocyanate [44, 45] and dithioacetal [44, 46] intermediates or rely on radical addition to thiohemiacetals [47, 48] or thermal decomposition of diazo compounds prepared by reacting 1-thioaldoses and aryl diazonium salts [44]. Some of these procedures have specific advantage in some specific cases, e.g. the dithioacetal to thioglycoside route is valuable for preparing 1-thio-hexofuranosides [46, 49]. 

Reductive desulfurization has been extended to the appropriate ethyl 1-xanthate or ethyl, phenyl, and naphthyl 1-thioglycosides to prepare the 1,5-anhydro derivatives of D-glucitol, D-mannitol, galactitol, cellobiitol, gentiobiitol, maltitol, lactitol, D-arabitol, ribitol, and xylitol (56). When a 1-thioaldofuranoside is reductively desulfurized, the product is the corresponding 1,4-anhydro alditol (57). 

The important role now played by thioglycosides as glycosyl donors is well established in Section 1 by the large number of disaccharides, in particular, whose syntheses have been effected by their use. Variations such as 5-pyridyl compounds and glycosyl xanthates were referred to and a further involves the use of acetylated glycosyl 1-piperidinecarbodithioates, eg (128), which have been assessed as suitable as glycosyl donors for the production of 1,2-rra/M-related glycosides. ... 

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