Substituent effects in the Nicholas epimerization of glycosides. (14th November 2017)

• Record Type: Journal Article
• Authors: Tsou, Pei‐Kang; Lee, Yen‐Chun; Lankau, Timm; Isobe, Minoru; Yu, Chin‐Hui
• Is Part Of: Journal of physical organic chemistry. Volume 31:Number 3(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-11-14
• Subjects: Density functional theory -- epimerization -- glycoside -- Nicholas reaction -- mechanism -- substitution; Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.3780
• Languages: English
• ISSNs: 0894-3230

Abstract

Abstract: The Nicholas reaction is a proven and versatile tool in glycoside chemistry. Its application is less clear‐cut, if the intermediate Nicholas cation has two reactive sides that enable different reactions. Density functional theory (DFT) calculations are used to rationalize the observed difference in product yields for the Nicholas epimerization and substitution obtained from experiments with very similar glycosides. Substituents, which can increase the rigidity of the backbone, should be avoided in epimerization reactions as they can slow down reorientation of the intramolecular ion pair so that the substitution reaction dominates. Abstract : Comparative DFT calculation show that substituents increasing the rigidity of the backbone can prevent the Nicholas epimerization while having no significant influence on the Nicholas substitution reaction.