Title

alpha-Aminoorganostannanes to alpha-aminoorganolithiums: Kinetic, mechanistic and structural studies

Date of Award

2004

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Robert E. Gawley - Committee Chair

Abstract

Lithiation and substitution of tertiary amines are an important gateway to functionalized amine compounds. A brief overview of the reactions of alpha-aminoorganolithiums is presented by way of introduction.As representative precursors to a-aminoorganolithiums, N-Boc and N-methyl-2-tributylstannyl-piperidines and pyrrolidines were selected and the kinetics of their reaction with n-butyllithium was studied. Using RINMR the rates of reaction of reaction of N-methylpiperidines were determined, and their activation parameters measured. The tin-lithium exchange was shown to be a two step process with a strong dependence on preorganization in the transition state. The much faster reaction with the N-Boc-2-tributylstannyl-piperidine showed evidence of precomplexation when observed by React-IRRTM.Pyrrolidine-derived alpha-aminoorganolithiums were generated by tin-lithium exchange and their structures determined by 1D multinuclear NMR techniques. The dipole stabilized N-Boc-2-lithiopyrrolidine did not show clear solution structure, consistent with a species undergoing dynamic solvent exchange or a solvent separated ion pair. The co-ordination stabilized N-methoxyethyl-2-lithiopyrrolidine was shown to be monomeric in THF solution, and the unstabilized N-ethyl-2-lithiopyrrolidine was shown to be a mixture of dimeric species.As part of a larger study on the kinetics and mechanism of racemization of alpha-aminoorganolithiums, the racemization of N-Boc-2-lithiopyrrolidine was studied. The barrier to enantiomerization at 240 K in ether was found to be 20 kcal.mol-1. The reaction was subject to a large positive entropy term which was attributed to the disruption of the solvation shell by the movement of the tert-butyl moiety of the carbamate.

Keywords

Chemistry, Organic

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3159150

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