Studies on directed lithiation: 1. Reactivity studies on alkoxide-directed lithiation reactions. 2. NMR spectroscopic characterization of the solution structure of an asymmetric lithiation reagent
Gallagher, Donald Joseph
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/20935
Description
Title
Studies on directed lithiation: 1. Reactivity studies on alkoxide-directed lithiation reactions. 2. NMR spectroscopic characterization of the solution structure of an asymmetric lithiation reagent
Author(s)
Gallagher, Donald Joseph
Issue Date
1992
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
A multifaceted approach to the study of the structure and reactions of organolithium aggregates is described. The lithiation of the cyclopropyl rings of a rigid bis-cyclopropylcarbinol has been shown to occur via two sequential lithiation steps. The first lithiation occurs very rapidly compared to the lithiation of other cyclopropane rings and appears to be the result of a favorable geometric orientation of the alkoxide directing group with respect to the proton being removed. The second lithiation is the only example of a bis-cyclopropyl compound undergoing dilithiation and appears to be the result of a complex-induced proximity effect.
Attempts at evaluating the transition structure of alkoxide-directed lithiation were unsuccessful due to translithiation occurring during competitive lithiation reactions. Methodology and control experiments are proposed for future studies.
The competitiveness of halogen-lithium exchange versus removal of an acidic hydrogen was studied by reinvestigating a literature case in which it was alleged that halogen-lithium exchange occurs prior to removal of an alcoholic hydrogen. It was found that the previously reported results that support this conclusion are inaccurate because of the use of NMR to determine deuterium incorporation and the use of D$\sb2$O as a low temperature trap. The corrected results suggest that halogen-lithium exchange does not occur prior to removal of an acidic hydrogen on a molecular scale.
An NMR study has shown that the aggregation state of i-Pr$\sp6$Li is very dependent on the solvent and added complexation agents. In hydrocarbon solvents i-Pr$\sp6$Li exists as a mixture of tetramer and hexamer, while in diethyl ether there exists a mixture of tetramer and dimer. In THF only a dimeric species is observed. Addition of TMEDA and PMDTA to ethereal solutions of i-Pr$\sp6$Li causes formation of complexed dimers and monomers respectively.
The structure of a 1:0.5:1 complex of i-Pr$\sp6$Li/sparteine/Et$\sb2$O was shown to be a non-symmetrically complexed dimeric species in which one lithium atom is $\eta\sb2$ complexed by sparteine and the other lithium is complexed by two ether molecules. This novel structure appears to be the result of the steric bulk of sparteine.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
