ja025639c_si_001.pdf (90.13 kB)
C2-Hydroxyglycosylation with Glycal Donors. Probing the Mechanism of Sulfonium-Mediated Oxygen Transfer to Glycal Enol Ethers
journal contribution
posted on 2002-06-04, 00:00 authored by Eiji Honda, David Y. GinThe C2-hydroxyglycosylation reaction employing the reagent combination of a diaryl sulfoxide
and triflic anhydride offers a novel method for glycal assembly whereby a hydroxyl functionality is
stereoselectively installed at the C2-position of a glycal donor with concomitant glycosylation of a nucleophilic
acceptor. Mechanistic investigations into this reaction revealed a novel process for sulfonium-mediated
oxidation of glycal enol ethers in which the sulfoxide oxygen atom is stereoselectively transferred to the
C2-position of the glycal. 18O-labeling studies revealed that the S-to-C2 oxygen-transfer process involves
initial formation of a C1−O linkage followed by O-migration to C2, leading to the generation of an intermediate
glycosyl 1,2-anhydropyranoside that serves as an in situ glycosylating agent. These findings are consistent
with the initial formation of a C2-sulfonium−C1-oxosulfonium pyranosyl species upon activation of the glycal
donor with Aryl2SO·Tf2O.