Reversing Reactivity: Stereoselective Desulfurative 1,2- trans-O-Glycosylation of Anomeric Thiosugars with Carboxylic Acids under Copper or Cobalt Catalysis
Résumé
We have discovered a new mode of reactivity of 1-thiosugars in the presence of Cu(II) or Co(II) for a stereoselective O-glycosylation reaction. The process involves the use of a catalytic amount of Cu(acac) 2 or Co(acac) 2 and Ag 2 CO 3 as an oxidant in α,α,α-trifluorotoluene (TFT). Moreover, this protocol turned out to have a broad scope, allowing to prepare a wide range of complex substituted O-glycoside esters in good to excellent yields with an exclusive 1,2-trans-selectivity. The late-stage modification of pharmaceuticals by this method was also demonstrated. To get a closer insight into the reaction mechanism, cyclic voltammetry (CV) was performed.
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