Glycosyl acceptors, 1-thioglycosides

An alternative could be steric activation-deactivation at the anomeric centers of the donor and acceptor. An example using this concept is shown in Scheme 12. In the electronic activation-deactivation concept, deactivated p-nitrophenyl thioglycosides can, after functioning as glycosyl acceptors, be transformed into... 

Several other examples have been reported in which thioglycosides were used as glycosyl acceptors. Thus, thioglycosides containing free hydroxyls can be coupled chemoselectively with glycosyl bromides and chlorides in the presence of silver triflate or tin(II) chloride-silver perchlorate as the promoter system [12,53,56,162,218-221]. 

To a solution of thioglycoside (1.0 equiv), 1-benzenesulfinyl piperidine (1.0 equiv), TTBP (2.0 equiv), and freshly activated 3 A powdered molecular sieves in dichloromethane (25.0 ml mmol-1) was added trifluoromethanesulfonic anhydride (1.1 equiv) at —60 °C under an argon atmosphere. The reaction mixture was stirred for 5 min, after that a solution of the glycosyl acceptor (1.5 equiv) in dichloromethane (4.0 ml mmol-1) was added. The reaction mixture was stirred at — 60 °C for 2 min, after that it was slowly warmed to room temperature and quenched by the addition of saturated aqueous NaHC03. The organic layer was washed with brine, dried (MgS04), filtered and the filtrate was concentrated to dryness. Purification of the crude product by column chromatography over silica gel afforded the product. 

Y. Ito and T. Ogawa, Sulfenate esters as glycosyl acceptors A novel approach to O-glycosides from thioglycosides and sulfenate esters, Tetrahedron Lett. 25 4701 (1987). 

The ability to arm and disarm thioglycosides in a manner similar to the NPG glycosyl acceptors has been reported. As with n-pentenyl glycosyl acceptors, the use of an electron-withdrawing substituent at C-2 was reported to inactivate... 

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