Neighboring-Group Participation by C-2 Ether Functions in Glycosylations Directed by Nitrile Solvents

• Published in: Chemistry : a European journal 2011-10, Vol.17 (43), p.12193-12202
• Main Authors: Chao, Chin-Sheng, Lin, Ching-Yu, Mulani, Shaheen, Hung, Wei-Cheng, Mong, Kwok-kong Tony
• Format: Article
• Language: English
• Subjects: arabinans; Chemistry; glycosylation; neighboring-group effects; nitrile solvents; oligosaccharides; Participation; Solvents
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201100732

Ether‐protecting functions at C‐2 hydroxy groups have been found to play participating roles in glycosylations when the reactions are conducted in nitrile solvent mixtures. The participation mechanism is based on intramolecular interaction between the lone electron pair of the oxygen atom of the C‐2 ether function and the nitrile molecule when they are positioned in a cis configuration. A 1,2‐cis glycosyl oxazolinium intermediate is formed. This participation, in conjunction with the anomeric effect of the glycosyl donor, confers high 1,2‐trans selectivities on glycosylations. Further application of this concept has led to efficient preparations of α‐(1→5)‐arabinan oligomers. Highly selective: C‐2 ether‐protecting functions have been found to play participating roles in glycosylations when the reactions are conducted in alkyl nitrile solvent mixtures (see scheme). The mechanism involves a Ritter‐like interaction of the C‐2 ether oxygen with an alkyl nitrile molecule. Together with the anomeric effect, this results in a high 1,2‐trans selectivity in glycosylations and in an efficient preparation of α‐(1→5)‐arabinan oligomers.