38791-30-9Relevant academic research and scientific papers
Mechanism of anomerization of permethylated methyl D-glycopyranosides by trimethylsilyl trifluoromethanesulfonate
Lee, Chang Kiu,Kim, Eun Ju,Lee, In-Sook Han
, p. 243 - 250 (1998)
Anomerization of permethylated methyl D-glycopyranosides catalyzed by trimethylsilyl trifluoromethanesulfonate was examined by NMR spectroscopy and gas-liquid chromatography. The initial-rate analysis showed that the rates of anomerization of β to α were faster than those of the opposite at various concentrations of the catalyst. The overall rates of disappearance of the substrates were faster than the rates of appearance of the opposite anomers because of the formation of a pyrylium-type of compound. The structure of the latter was proposed based on 1H and 13C NMR spectra, although it was not isolable. Both cyclic and acyclic oxonium ions appear to be intermediates in the anomerization. The former seems to be the key intermediate for the formation of the pyrylium-type of compound as well as the anomerization of α-glycosidic linkages. β-Glycosidic linkages, on the other hand, appear to undergo anomerization mostly via acyclic oxonium ions.
Anomerization and transglycosylation reactions of permethylated methyl D-glycopyranosides
Lee,Kim,Lee
, p. 197 - 206 (2007/10/02)
The anomerization reactions of permethylated methyl D-glycopyranosides in the presence of various Lewis acid catalysts, such as Me3SiOTf, Me3SiOMs, BF3 · OEt2, or TiCl4 were examined in dichloromethane solution. β Anomers of the glycosides anomerized to the α anomer very rapidly, but the anomerizations in the opposite direction were slower. Transglycosylation reactions of the glycosides in the presence of similar catalysts and ethanol gave preferably the α anomers with most substrates employed. No anomerization was observed in the case of the α-mannoside, probably because the α anomer is strongly favored at equilibrium. Nevertheless, transglycosylation took place. The anomerization reactions of permethylated methyl D-glycopyranosides in the presence of various Lewis acid catalysts, such as Me3SiOTf, Me3SiOMs, BF3·OEt2, or TiCl4 were examined in dichloromethane solution. β Anomers of the glycosides anomerized to the α anomer very rapidly, but the anomerization in the opposite direction were slower. Transglycosylation reactions of the glycosides in the presence of similar catalysts and ethanol gave preferably the α anomers with most substrates employed. No amerization was observed in the case of the α-mannoside, probably because the α anomer is strongly favored at equilibrium. Nevertheless, transglycosylation took place.
