2,3-Anhydrosugars in glycoside bond synthesis: mechanism of 2-deoxy-2-thioaryl glycoside formation.
A series of investigations probing the mechanism of the 2,3-anhydrosugar migration-glycosylation reaction were performed using a thioglycoside with the D-lyxo stereochemistry as the substrate. Among the work reported are the results of quantum mechanical calculations, NMR studies, the measurement of alpha-deuterium kinetic isotope effects, and the synthesis of a series of substrate analogues. All studies point to a consistent finding: that the reaction proceeds through an oxocarbenium ion intermediate, not an episulfonium ion as previously suggested. It is proposed that the high stereoselectivity of the reaction arises from a preferred "inside attack" of the nucleophile onto the oxocarbenium ion intermediate.
Hou
Dianjie
D
Alberta Ingenuity Centre for Carbohydrate Science and Department of Chemistry, The University of Alberta, Edmonton, Alberta, T6G 2G2 Canada.
Taha
Hashem A
HA
Lowary
Todd L
TL