Approaches to the study of the geometry and mechanism of nucleophilic reactions at sulfur(II)
Reif, Lee Alvin, Jr.
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Permalink
https://hdl.handle.net/2142/21304
Description
Title
Approaches to the study of the geometry and mechanism of nucleophilic reactions at sulfur(II)
Author(s)
Reif, Lee Alvin, Jr.
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
Approaches to the study of the required reaction trajectory and geometry of nucleophilic attack at two different sulfur(II) species is reported. Systems designed to investigate the reaction trajectory involving nucleophilic attack at sulfur(II) by use of the endocyclic restriction test are discussed.
Treatment of 2-iodoaryldithioesters, 150 and 170, with tert-butyllithium provide, by halogen-lithium exchange, a reactive intermediate which adds carbophilically to the thiocarbonyl group generating indanone products, 161, 177, and 178. It was demonstrated that a phenyl anion would add thiophilically with these systems therefore suggesting that the required reaction trajectory for thiophilic addition could not be obtained in the formation of a six-membered ring. This reaction appears to provide the first evidence that a required reaction geometry exists for a thiophilic addition process. Formation of the indanone products provides evidence against the involvement of a radical process in thiophilic addition. It is reasonable to assume that if a radical is involved, it would close to the six-membered ring in our system. This was not observed, suggesting that a single electron process is unlikely.
A system, 198, containing a protected amine and a sulfenate was developed which may allow the study of the reaction geometry involved in nucleophilic substitution at bivalent sulfur. It was demonstrated that cleavage of the protecting group on the amine lead to conversion of the sulfenate to the sulfenamide, 199. Double labelling crossover studies were carried out with this system. Conditions could not be found for the deprotection of the amine which did not lead to scrambling of the sulfenamide product. Dilution studies with this system did not provide a clear choice between an intermolecular or intramolecular process. A by-product, 200, which arises from an intermolecular reaction is formed while the amount of sulfenamide product, 199, generated relative to starting material conversion, showed no change upon dilution suggesting an intramolecular process. No clear conclusion could be drawn on the bivalent sulfur system.
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