Permanent URL to this publication: http://dx.doi.org/10.5167/uzh-48898
Satoh, H; Manabe, S; Ito, Y; Luethi, H P; Laino, T; Hutter, J (2011). Endocyclic cleavage in glycosides with 2,3-trans cyclic protecting groups. Journal of the American Chemical Society, 133(14):5610-5619.
An endocyclic pathway is proposed as a reaction mechanism for the anomerization from the beta (1,2-trans) to the alpha (1,2-cis) configuration observed in glycosides carrying 2,3-trans cyclic protecting groups. This reaction occurs in the presence of a weak Lewis or Bronsted acid, while endocyclic cleavage (endocleavage) in typical glycosides was observed only when mediated by protic media or strong Lewis acids. To rationalize the behavior of this class of compounds, the reaction mechanism and the promoting factors of the endocleavage are investigated using quantum-mechanical (QM) calculations and experimental studies. We examine anomerization reactions of thioglycosides carrying 2,3-trans cyclic protecting groups, employing boron trifluoride etherate (BF3 center dot OEt2) as a Lewis acid. The estimated theoretical reactivity, based on a simple model to predict transition state (TS) energies from the strain caused by the fused rings, is very close to the TS energies calculated by the TS search along the C1-C2 bond rotation after the endo C-O bond breaking. Excellent agreement is found between the predicted TS energies and the experimental reactivity ranking. The series of calculations and experiments strongly supports the predominance of the endocyclic rather than the exocyclic mechanism. Furthermore, these investigations suggest that the inner strain is the primary factor enhancing the endocleavage reaction. The effect of the cyclic protecting group in restricting the pyranoside ring to a C-4(1) conformation, extensively discussed in conjunction with the stereoelectronic effect theory, is shown to be a secondary factor.
|Item Type:||Journal Article, refereed, original work|
|Communities & Collections:||07 Faculty of Science > Institute of Physical Chemistry|
|Deposited On:||04 Aug 2011 09:11|
|Last Modified:||23 Nov 2012 14:12|
|Publisher:||American Chemical Society|
|Additional Information:||This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of the American Chemical Society, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/ja201024a.|
|Other Identification Number:||ISI:000289829100064|
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