Epimerization of 2‘-Carbonylalkyl-C-Glycosides via Enolation, β-Elimination and Intramolecular Cycloaddition
Citations Over TimeTop 21% of 2003 papers
Abstract
Treatment of 2'-carbonyl-alpha-C-glycopyranosides of gluco, galacto, manno, 2-deoxy, and 2-azido sugars with 4% NaOMe resulted in anomeric epimerization to give their respective beta-anomers in good to excellent yields. The epimerization of the 2'-aldehyde of alpha-C-galactopyranoside (10) in deuterium methanol, which afforded the beta-anomer with exclusive deuterium replacements at the 1'-position, excluded the possibility of the exo-glycal as being involved as an intermediate. When 2'-aldehyde (36) and 2'-ketone (41) of 2,3-di-O-benzyl-alpha/beta-l-C-arabinofuranoside were used as substrates we were able to obtain the respective equatorial alpha-C-arabinopyranosides (37 and 42). These observations confirmed that the epimerization involves an acyclic alpha,beta-unsaturated aldehyde or ketone, which is formed by the enolation of 2'-carbonyl-alpha-C-glycoside with subsequent beta-elimination. Thereafter an intramolecular hetero-Michael cycloaddition occurs, leading to the formation of thermodynamically controlled stable products, which were exclusively the equatorial C-glycopyranosides, except in the case of 2'-carbonyl-C-furanosides, where a mixture of two anomers was obtained.
Related Papers
- → Anomeric configuration-dependence of the Lattrell-Dax epimerization from D-glucose to synthetically useful D-allose derivatives(2020)12 cited
- → New Carbohydrate-DerivedS,S-Dioxothiochroman Derivatives and Their Unexpected Easy Epimerization at the Anomeric Position(2013)8 cited
- → Switchable reactivity of 2-benzoyl glycals towards stereoselective access of 1-3 and 1-1 S/O linked disaccharides(2023)1 cited
- → Novel C-3 Epimerization of Glycals by Metal Chlorides(1991)17 cited
- → New synthesis of (±)-meroquinene aldehyde and its epimer from (±)-norcamphor(1979)10 cited