Iodine and its interhalogen compounds: Versatile reagents in carbohydrate chemistry v. synthesis of 1,2-trans-linked 1-thioglycosides from the per-o-acetylated glycoses

Treatment of per-O-acetylated mono- and di-saccharides with (alkyl/arylthio)trimethylsilane and iodine at ambient temperature results in the formation of the corresponding 1,2-trans-1-thioglycosides in very high yield. In the case of higher boiling thiols such as ethanethiol, the reaction can be effectively carried out in the presence of the thiol itself instead of the silylated derivative, but the reaction is not stereospecific. Moreover, in the latter reactions a portion of the starting material remains unchanged even on prolonged reaction. With β-D-glucose pentaacetate (11) as the starting material, its epimerisation occurred during the reaction and therefore the recovered starting material was of α-D-configuration. In addition, the methyl disulphide-hexamethyldisilane system has been found to serve as an effective and cheaper alternative to the expensive (methylthio)-trimethylsilane.