Investigation of transition structure geometries for the transfer of oxygen from heteroatoms to phosphorus
Kurtzweil, Mitchell Lloyd
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https://hdl.handle.net/2142/21420
Description
Title
Investigation of transition structure geometries for the transfer of oxygen from heteroatoms to phosphorus
Author(s)
Kurtzweil, Mitchell Lloyd
Issue Date
1992
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
The deoxygenation of a functional group containing an oxygen-heteroatom bond by a trivalent phosphorus compound to give the corresponding deoxygenated substrate and oxidized phosphorus compound is a reaction of synthetic and mechanistic importance. The endocyclic restriction test was utilized in this research to investigate transition structure geometries in the transfer of oxygen from heteroatoms to trivalent phosphorus.
Several systems were investigated which contained a diphenylphosphino group tethered to the oxygen-heteroatom functionality through some number of intervening carbon atoms. The functionalities included a nitrone, a short and long chain hydroxylamine, an O-acetylhydroxylamine, and a sulfoxide. In each system, distinction between intramolecular and intermolecular oxygen transfer was made through double labeling experiments. This information, along with kinetics, $\sp{18}$O-labeling, and other techniques provided data to distinguish between alternative mechanisms of oxygen transfer.
The conversion of nitrone 95 to imine-phosphine oxide 96 is suggested to occur via an addition-elimination mechanism involving the 6-membered ring intermediate 109.
The conversion of hydroxylamine 24 to amine-phosphine oxide 26 is also considered to occur via an addition-elimination mechanism and involve a 6-membered ring intermediate 196. However, when the HCl salt of 24 is used or when 24 is treated in AcOH, competing processes occur and mechanistic alternatives are not readily distinguishable. By lengthening the hydroxylamine side chain in 153, conversion to amine-phosphine oxide 154 becomes at least partially intermolecular, indicating that intramolecular oxygen transfer is inhibited.
Treatment of O-acetylhydroxylamine 134 in AcOH gives a detectable intermediate 133 which is converted to 26 upon workup. Intermediate 133 is also observed in toluene, but further reaction gives acetamide-phosphine oxide 161.
The conversion of sulfoxide 174 to sulfide-phosphine oxide 175 apparently requires an electrophilic catalyst. Mechanisms involving both 5- and 6-membered ring intermediates, 191 and 197, are proposed depending on the catalyst.
We have found that oxygen transfer to trivalent phosphorus from functionalities containing a heteroatom-oxygen bond can occur through either 5- or 6-membered ring transition state structures involving valence expansion at phosphorus. These reactions are substrate and condition dependent, however.
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