Basekatalysierte asymmetrische Induktion der Reaktion von Methyl(phenyl)keten mit 1‐Phenylethanol: Gewinnung von Hydratropasäure in hoher Enantiomerenreinheit

Abstract

Nach 30 min bei Raumtemperatur entsteht aus (3a) der N-deblockierte y-N-Glycosyl-asparagin-benzylester (4) kristallin rnit 67% Ausbeute. Unter den Bedingungen wird der primare Ester an C-6 des Glucosamins nicht angegriffen.Gegeniiber dem hlufig verwendeten Benzyloxycarbonyl(Z)-Rest bietet die Peoc-Schutzgruppe bei den Glycosyl-Peptiden drei Vorteile:

Supramolecular Clusters between Carbohydrates and Concave Pyridines. Detection in the Gas Phase by Resonance-Enhanced Multi-Photon Ionization Refectron Time-of-Fight Mass Spectrometry

“…For example, the formation of a hydrogen bond between a base and an alcohol increases the nucleophilicity of the alcohol and, thus, accelerates the addition to a cumulene like an isocyanate or a ketene. 6,7 By using well designed, sterically shielded bases, for example concave pyridines such as 1, not only can the rate of this reaction be enhanced, 8 it is also possible to differentiate between various alcohols. 9 An impressive example for such a selectivity is the selective acylation of a carbohydrate derivative 10 possessing two unprotected, secondary, equatorial OH groups.…”