Glycosyl xanthates

Scheme 4.72 Synthesis of S-glycosyl dithiocarbonates (glycosyl xanthates).

Transformation of 2-deoxysugar derivatives into glycosyl xanthates can be performed by the treatment of O-benzyl-protected hemiacetal derivative with diphe-nylphosphoryl chloride, followed by the reaction with O-ethyl potassium xanthate in the presence of a base (NaOH, PTC reaction or NaH in appropriate organic solvent). High yields and selectivities in such reactions were observed when using sodium hydride in anhydrous THF [401],... 

Scheme 4.73 Glycosyl xanthates in stereoselective synthesis of galactosamine-containing oligosaccharides [399],...

Scheme 4.95 Stereoselective synthesis of oligosaccharides via glycosyl xanthate [399].

The standard conversion of alcohols into their xanthate esters through reaction with carbon disulphide and an alkylating agent is improved by the addition of a quaternary ammonium salt [69]. Excellent yields (>90%) are obtained in relatively short reaction times under mild conditions. The formation over relatively short reaction times of O-glycosyl xanthates from partly protected glycosides has been described using a stoichiometric amount of the quaternary ammonium salt [70]. 

A. Marra and P. Sin3y, A novel stereoselective synthesis of N-acetyl-a-neuraminosyl-galactose disaccharide derivatives, using anomeric S-glycosyl xanthates, Carbohydr. Res. 795 303 (1990). 

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). 

W. Szeja and J. Bogusiak, Synthesis of glycosyl xanthates from reducing sugar derivatives under phase-transfer conditions, Carbohydr. Res., 170 (1987) 235-239. 

A 2-thio-neuraminic acid glycosyl xanthate gives good yields of a-linked disaccharides when used in conjunction with phenylselenyl triflate. ... 

Sodium alcohol Glycosyl mercaptides from glycosyl xanthates... 

---