An experimental evaluation of the geometry of transition structures for oxygen transfer reactions: Use of the endocyclic restriction test
Woods, Keith Warren
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https://hdl.handle.net/2142/20853
Description
Title
An experimental evaluation of the geometry of transition structures for oxygen transfer reactions: Use of the endocyclic restriction test
Author(s)
Woods, Keith Warren
Issue Date
1991
Doctoral Committee Chair(s)
Beak, Peter
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
Oxygen transfer reactions giving rise to epoxides from olefins have been the topic of numerous studies with both synthetic and mechanistic emphases. In spite of considerable effort, the issue of the transition structure geometry has been a fundamental unanswered question. Our research has focused on investigating the geometry of the oxygen transfer reaction between peroxy acids and olefins, and between N-sulfonyloxaziridines and olefins. We have made use of the endocyclic restriction test to probe these transition structure geometries. This approach involves constructing systems in which the functional group that provides the oxygen moiety is joined to an olefin through tethers of varying lengths. The endocyclic restriction test, in combination with double labelling techniques, distinguishes intermolecular from intramolecular reactivity and allows limits to be placed on the trajectory of the oxygen transfer.
In this investigation of transition structure geometries we have demonstrated that oxygen transfer from peroxy acids to olefins can occur intramolecularly through a 16.5-membered endocyclic transition structure but not through an 8.5-membered transition structure. The interpretation is that the necessary geometry can be achieved in the large endocyclic transition structure but not in the smaller ring. These results are consistent with the disposition of the olefin and the oxygen-oxygen bond of the peroxy acid at 180$\sp\circ$.
We have also determined that transfer of oxygen from N-sulfonyloxaziridines to olefins can proceed intramolecularly through both 7.5-membered and 5.5-membered endocyclic transition structures. Our results indicate a relatively wide reaction window and are inconsistent with approach of the olefin and the N-sulfonyloxaziridine through a strict S$\sb{\rm N}$2-like geometry.
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