Stereoselective C-glycosylation reactions of ribose derivatives: electronic effects of five-membered ring oxocarbenium ions.
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.
Larsen
Catharine H
CH
Department of Chemistry, University of California-Irvine, Irvine, CA 92697-2025, USA.
Ridgway
Brian H
BH
Shaw
Jared T
JT
Smith
Deborah M
DM
Woerpel
K A
KA
D006031:Glycosylation; D007477:Ions; D012266:Ribose / Q000737:chemistry*; D013237:Stereoisomerism
D007477:Ions; D012266:Ribose