Thesis-2008-Allart.pdf (6.02 MB)
Metal-promoted [3+2] and [4+2] cycloaddition reactions
thesis
posted on 2018-06-29, 11:36 authored by Eric A. AllartDicobalt complexes have been extensively used in synthetic chemistry to protect triple
bonds, to form new carbon/carbon bonds using the Nicholas reaction and to form polycyclic
molecules using the Pauson-Khand reaction. Using these dicobalt complexes, the formation
of new carbon-heteroatom bonds was developed through [3+2] and [4+2] cycloaddition
reactions via a stabilised dipole intermediate. Initial work carried out makes use of
cyclopropanes substituted with a metal-alkyne complex towards the synthesis of
tetrahydrofurans and pyrrolidines in good yields and with acceptable diastereoselectivity.
The initial aim of the work described hereafter was to improve and expand the previous
work carried out within the group. An alternative route using dihydrofurans as a
cyclopropane surrogate was explored as well as other methods to form the cyclopropane in
a-position to the alkyne. To extend the scope of the methodology, [4+2] cycloaddition
reactions have been explored, using Nicholas carbocation. Various precursors have been
prepared using a Knoevenagel condensation or an ene reaction. For the first time in synthetic
chemistry, a novel [4+2] dipolar cycloaddition reaction from a cyclobutane has been
developed. This reaction has opened a new way for the synthesis of six-membered
heterocycles in a totally diastereoselective fashion using cyclobutane cores as precursors. A
wide range of aldehydes was used as trapping reagents to form tetrahydropyrans in good
yields up to 95% and with a good to total diastereoselectivity proven by nOe and X-Ray
analyses. The use of other reagents such as ketones, imines and alkenes has been
investigated· towards the formation of new six-membered rings as an extension of the
methodology.
History
School
- Science
Department
- Chemistry
Publisher
© Eric AllartPublisher statement
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/Publication date
2008Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy at Loughborough University.Language
- en