title: Stereoselective C-glycosylation reactions of ribose derivatives: electronic effects of five-membered ring oxocarbenium ions.
abstract: The factors controlling the highly alpha-selective C-glycosylation of ribose derivatives were determined by examining the stereoselective reactions of 18 ribose analogues differing in substitution at C-2, C-3, and C-4. The lowest energy conformers of the intermediate oxocarbenium ions display the C-3 alkoxy group in a pseudoaxial orientation to maximize electrostatic effects. To a lesser extent, the C-2 substituent prefers a pseudoequatorial position, and the alkyl group at C-4 has little influence on conformational preferences. In all cases, the product was formed by stereoelectronically preferred inside attack on the lowest energy conformer.
authors.affiliation: Department of Chemistry, University of California-Irvine, Irvine, CA 92697-2025, USA.
authors.forename: Catharine H
authors.initials: CH
authors.lastname: Larsen
authors.forename: Brian H
authors.initials: BH
authors.lastname: Ridgway
authors.forename: Jared T
authors.initials: JT
authors.lastname: Shaw
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Smith
authors.forename: K A
authors.initials: KA
authors.lastname: Woerpel
mesh_terms: D006031:Glycosylation; D007477:Ions; D012266:Ribose / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D007477:Ions; D012266:Ribose