The mechanism of photo-induced Stevens rearrangement of sulfonium ylides, and exploration of the chemical properties of ylidions
Zhang, JianJian
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https://hdl.handle.net/2142/19352
Description
Title
The mechanism of photo-induced Stevens rearrangement of sulfonium ylides, and exploration of the chemical properties of ylidions
Author(s)
Zhang, JianJian
Issue Date
1989
Doctoral Committee Chair(s)
Schuster, Gary B.
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
The mechanism of the photo-induced Stevens rearrangement of sulfonium ylides has been investigated. The chemical properties of phenacylsulfonium ylidions generated by sensitization with dicyanoanthracene (DCA) have been experimentally explored.
Irradiation of 9-dimethylsulfoniumfluorenyl ylide at 350 nm in acetonitrile produces the Stevens rearrangement product, methyl-9-methylfluorenyl sulfide and a dimer, 9,9$\sp\prime$-bifluorenyl-dimethyl sulfide. The mechanism of the photo Stevens rearrangement has been carefully investigated by product studies, kinetics, laser flash photolysis and isotopic tracer techniques. It is believed that the mechanism of the photo-Stevens rearrangement is the same as the thermal Stevens rearrangement which involves a homolysis of carbon-sulfur bond to form a radical pair. A double labeling crossover experiment shows that the Stevens rearrangement takes place intramolecularly in the original solvent cage. Laser flash photolysis indicates formation of the 9-fluorenyl-methyl sulfide radical upon photolysis of 9-dimethylsulfoniumfluorenyl ylide.
The photo-Stevens rearrangement of dialkylsulfoniumphenacyl ylides depends on largely the alkyl group bound to the sulfur atom. The Stevens rearrangement product is observed only if a stable radical is formed upon photolysis.
The mechanism of sensitization of phenacylsulfonium ylides with DCA has been investigated by product studies, kinetic and trapping techniques. The chemical properties of the ylidions are controlled primarily by the nature of the alkyl groups bound to sulfur atom. DCA-sensitized photolysis of phenacylsulfonium ylides generates ylidions and DCA$\sp-\cdot$. When the ylidions cleave to form free stable radicals, 1,2-(dibenzoyl)vinylmethyl sulfide is obtained as the major product and trans-1,2,3-benzoylcyclopropane is a minor product. When the ylidions cannot cleave to give stable free radicals the trans-1,2,3-benzoylcyclopropane is the exclusive product.
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