Synthesis of New Chiral N-Heterocyclic Carbenes and Abnormal Carbenes
Author(s)
Levy, Jean-Noel
Type
Thesis
Abstract
Chapter 1
Carbenes have fascinated organic chemists ever since the first evidence of their existence. The
isolation and first crystallographic analysis of a stable NHC by Arduengo, in 1991, has had a major
impact on the application of NHCs in chemistry. NHCs are widely used as ligands for transition
metals, but also as catalysts in their own right.
The aim of this project is to synthesise novel monodentate chiral NHCs 1 in order
to induce a high level of stereocontrol in a selection of asymmetric reactions. The
rigid ring structure, C2 symmetry and the presence of bulky groups (R) that
project directly toward the reactive centre are important concepts in the design of
our molecules.
During the first part of my thesis, we developed a one-pot synthesis of allylic chlorides from
benzaldehyde. A mechanistic study was carried out, as well as studying the scope of the reaction.
We then achieved the synthesis of the desired NHCs precursors in 13 or 14 steps and carried out
studies of their coordination and application in asymmetric α-arylation and allylic alkylation.
Chapter 2
Recently novel coordination modes have been noted for NHCs. The so-called “abnormal” NHCs, due
to their isomeric relationship between C2- and C4-bound imidazolylidene ligands are one type of
relatively unexplored ligand. We have therefore developed a strategy to access chiral abnormal
NHCs.
Two
different chiral abnormal NHC precursors: 1,2,3-triazolidinenes 2 and isomeric Hartwig’s NHCs 3
were synthesised via a short synthesis (2 or 3 steps) and metallated with a transition metal.
Carbenes have fascinated organic chemists ever since the first evidence of their existence. The
isolation and first crystallographic analysis of a stable NHC by Arduengo, in 1991, has had a major
impact on the application of NHCs in chemistry. NHCs are widely used as ligands for transition
metals, but also as catalysts in their own right.
The aim of this project is to synthesise novel monodentate chiral NHCs 1 in order
to induce a high level of stereocontrol in a selection of asymmetric reactions. The
rigid ring structure, C2 symmetry and the presence of bulky groups (R) that
project directly toward the reactive centre are important concepts in the design of
our molecules.
During the first part of my thesis, we developed a one-pot synthesis of allylic chlorides from
benzaldehyde. A mechanistic study was carried out, as well as studying the scope of the reaction.
We then achieved the synthesis of the desired NHCs precursors in 13 or 14 steps and carried out
studies of their coordination and application in asymmetric α-arylation and allylic alkylation.
Chapter 2
Recently novel coordination modes have been noted for NHCs. The so-called “abnormal” NHCs, due
to their isomeric relationship between C2- and C4-bound imidazolylidene ligands are one type of
relatively unexplored ligand. We have therefore developed a strategy to access chiral abnormal
NHCs.
Two
different chiral abnormal NHC precursors: 1,2,3-triazolidinenes 2 and isomeric Hartwig’s NHCs 3
were synthesised via a short synthesis (2 or 3 steps) and metallated with a transition metal.
Date Issued
2011-01
Date Awarded
2011-04
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Fuchter, Matthew
Creator
Levy, Jean-Noel
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)