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