The Geometry of Formal Nucleophilic Substitution at Nonstereogenic Atoms: Use of the Endocyclic Restriction Test
Loo, De-Kai
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https://hdl.handle.net/2142/70390
Description
Title
The Geometry of Formal Nucleophilic Substitution at Nonstereogenic Atoms: Use of the Endocyclic Restriction Test
Author(s)
Loo, De-Kai
Issue Date
1987
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
Abstract
The geometry of formal nucleophilic substitution at the nonstereogenic atoms, oxygen, nitrogen, and chlorine has been investigated by use of the endocyclic restriction test.
The reaction of N-alkylhydroxylamines with triphenylphosphine proceeds with oxygen transfer from nitrogen to phosphorus to provide N-alkylamines and triphenylphosphine oxide. The mechanism of this formal nucleophilic substitution at oxygen by phosphorus has been studied by kinetics, substituent effects, and a double labeling experiment in a formally endocyclic system. The reaction does not appear to proceed by a classical S$\sb{\rm N}$2 process, a biphilic addition, or a free radical chain process. The mechanism is suggested to involve initial addition of oxygen to phosphorus to form a six-membered ring intermediate which undergoes proton transfer and nitrogen-oxygen bond cleavage to give the product. This reaction appears to provide the first determination of geometry in a formal nucleophilic substitution at oxygen.
The reaction of organolithium reagents with lithium alkoxyamides leads to amination of the organolithium compounds by a formal nucleophilic substitution on the negatively charged nitrogen. A double-labeling experiment in a formally endocyclic system shows the reaction to be intermolecular. The mechanism is suggested to involve a complex in which a proximity effect plays a key role in providing juxtaposition between two negatively charged species for reaction via a S$\sb{\rm N}$2-like transition state.
The nucleophilic substitution at chlorine of N-chloroacetanilide by nitrogen of a secondary amine generated by hydrolysis of a trifluoroacetyl amide or tert-butoxy carbamate has been studied in a formally endocyclic reaction. It has been found by double labeling experiments that the substrate can be scrambled extremely rapidly under a variety of reaction conditions. Thus the mechanism of the chlorine transfer from the nitrogen of an amide to the nitrogen of an amine may involve an external nucleophile although direct nucleophilic attack cannot be excluded.
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