title: C2-hydroxyglycosylation with glycal donors. Probing the mechanism of sulfonium-mediated oxygen transfer to glycal enol ethers.
abstract: The 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. (18)O-labeling studies revealed that the S-to-C2 oxygen-transfer process involves initial formation of a C1[bond]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[bond]C1-oxosulfonium pyranosyl species upon activation of the glycal donor with Aryl(2)SO x Tf(2)O.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors.forename: Eiji
authors.initials: E
authors.lastname: Honda
authors.forename: David Y
authors.initials: DY
authors.lastname: Gin
mesh_terms: D000812:Anhydrides / Q000737:chemistry; D004987:Ethers / Q000737:chemistry; D006031:Glycosylation; D009844:Oligosaccharides / Q000138:chemical synthesis* / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D013237:Stereoisomerism; D013454:Sulfoxides / Q000737:chemistry*
chemical_list: D000812:Anhydrides; D004987:Ethers; D009844:Oligosaccharides; D013454:Sulfoxides; D010100:Oxygen