Synthetic and Mechanistic Investigation of Alpha-Amido Carbanions
Zajdel, William John
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Permalink
https://hdl.handle.net/2142/70208
Description
Title
Synthetic and Mechanistic Investigation of Alpha-Amido Carbanions
Author(s)
Zajdel, William John
Issue Date
1982
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 removal of an sp('3) proton from a carbon adjacent to nitrogen followed by reaction with an electrophile to effect substitution at that site provides umpolung of the customary amine polarity. This thesis reports the use of a carbonyl moiety to aid in the stabilization of negative charge adjacent to nitrogen. The syntheses of ten different N,N-dialkyl amide systems are reported, five of which have been successfully substituted via an (alpha)-amido carbanionic intermediate.
The triethylcarbinyl moiety of N,N-dialkyl-2,2-diethylbutyramides was found to be sufficiently bulky to protect the carbonyl group from nucleophilic attack during metalation, but not too bulky to prevent subsequent cleavage of the electrophilically substituted amides to amines. Thus, diethylamine was alkylated and hydroxyalkylated to afford N-(1-methyl)tridecyl-N-ethylamine and N-(1-hydroxybenzyl)ethyl-N-ethylamine. The alkylation and hydroxyalkylation of cyclic amines was also effected, as demonstrated by the conversion of 4-phenylpiperidine to 2-butyl-4-phenylpiperidine and 2-hydroxybenzyl-4-phenylpiperidine.
The metalation appears to proceed via an (alpha)-azolithio intermediate with the carbanion electron pair in an equatorial sp('3) orbital on the carbon syn to the carbonyl oxygen. This geometry is consistent with a combination of electrostatic stabilization by the dipole of the amide group and metal ion chelation of the lone-pair electrons on the carbanion carbon and the carbonyl oxygen in stabilizing the generation of a trappable (alpha)-amido carbanionic intermediate. This result is consistent with ab initio calculations. In addition, a stereochemical investigation of the cleavage of hydroxyalkylated piperidyl-2,2-diethylbutyramides indicates that the equatorial-threo stereoisomer is obtained exclusively.
Finally, this thesis reports the possibility of electrophilically substituting the carbon adjacent to the nitrogen of an imidate derived from a primary amine.
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