Anomerization of Methyl Glycosides by Acid-Catalysed Methanolysis: Trapping of Intermediates

Autor:	Karl-Jonas Johansson, Bengt Lindberg, Per J. Garegg, Peter Konradsson
Rok vydání:	1999
Předmět:	chemistry.chemical_classification Reducing agent Organic Chemistry Oxocarbenium Glycoside chemistry.chemical_element Protonation Borane Ring (chemistry) Cleavage (embryo) Biochemistry Medicinal chemistry Oxygen chemistry.chemical_compound chemistry Organic chemistry
Zdroj:	Journal of Carbohydrate Chemistry. 18:31-40
ISSN:	1532-2327 0732-8303
DOI:	10.1080/07328309908543976
Popis:	Intermediate oxocarbenium ions or other intermediates produced during acid catalyzed anomerization of some methyl glycosides were trapped by reduction with 4-methylmorpholine borane. The glycosylium ion intermediate formed on anomerization of methyl 4-O-methyl-α-D-glucopyranoside gave, as expected, only a mixture of the α- and β-D-glucopyranosides, as this reaction is slow compared to the degradation of the reducing agent. The more reactive methyl 2-deoxy-4-O-methyl-α-D-arabino-hexopyranoside gave two reduction products, namely, 1,5-anhydro-2-deoxy-4-O-methyl-D-arabino-hexitol and 2-deoxy-1,4-di-O-methyl-D-arabino-hexitol, indicating alternative reaction pathways, involving either exo or endo C-O cleavage. The aldofuranosides, when necessary methylated on O-5 in order to avoid formation of pyranosides, gave 1-O-methylalditols, indicating protonation of the ring oxygen, followed by endo C-O cleavage. The methyl 2-deoxy-5-O-methyl-α-D-arabino-hexofuranosides, however, gave a mixture of the 1,5-di-O...
Databáze:	OpenAIRE
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