Specific features of the behavior of α- and β-glycosylfluoride tetraacetates during chemical ionization in isobutane and tetramethylsilane

Abstract

Reactions of α- and β-glycosylfluoride tetraacetates with trimethylsilicenium ion in the gas phase during chemical ionization have been studied. The [M+SiMe₃]⁺ ions formed from the glycosylfluorides are more stable than the corresponding [M+H]⁺ ions. The cleavage of the weakest glycosidic bond leading to the generation of glycosidic ions is not dominant for the trimethylsilylated ions, as it has been observed in the corresponding protolytic reactions. The ratio of the intensities of the [M+SiMe₃]⁺ and [M−F]⁺ ions characterizes the probability of the initial localization of the trimethylsilyl ion at the glycosidic center; the equatorial orientation of fluorine at C(1) makes it possible for the electrophile to bond with this substituent. Generation of the glycosidic ions is rather weakly affected by increasing temperature, whereas [M-AcO]⁺ formation is significantly intensified.