Abstract
The work presented in this thesis regards: 1) the development of a base free dehydrative cross-coupling process, utilising palladium(0) nanoparticles formed in situ under acidic conditions, 2) the development of synthetic protocols using the bio-available solvent Cyrene™ as a replacement dipolar aprotic solvent and 3) the use of Cyrene™ as a chiral scaffold.1) The use of sugars for the in situ formation of palladium nanoparticles has been previously developed in the Camp group. Building upon this work, a base free Mizoroki-Heck cross-coupling process for the synthesis of substituted stilbenes was developed and optimised, whereby glucose performed a dual role: stabilisation of the palladium(0) nanoparticles and regeneration of the active catalyst species. Due to the base free nature of this process, the reaction mixture becomes acidic. Relatively few protocols have been developed in which the feedstock of the Mizoroki-Heck reaction has changed from the standard alkene substrates. Typically, alkenes are reacted with aryl or alkyl halides in order to cross-couple and form a new C-C bond. Herein, a dehydrative method for the in situ formation of styrene and tandem cross-coupling process in a base free, H2O/MeCN solvent system has been developed, taking advantage of the acidic nature of the reaction mixture. After optimisation, the steric, electronic and substrate scope of the reaction conditions were investigated. The molar efficiency (Mol. E%) was calculated and evaluated against similar methods for the synthesis of substituted stilbenes.
2) The need for a green replacement dipolar aprotic solvents has become crucial due to the placement of N,N-dimethylformamide (DMF) and N-methylpyrrolidine (NMP) on the REACH list of restricted chemicals. In recent years, the chemical Cyrene™ has been investigated as a bio-available replacement for the dipolar aprotic solvents. The synthesis of ureas, amides and carbamates in Cyrene™ was developed and optimised from either isocyanates or acid chlorides with amines or alcohols. The synthesis of carbamates was monitored by in situ 19F NMR to determine the rate of the reaction in several solvents including Cyrene™. Additionally the large scale reaction, recycling of solvent and reuse was successfully performed.
3) Chiral scaffolds are useful tools as they allow the synthesis of several compounds of similar structure. The use of Cyrene™ as a chiral scaffold was investigated by several academic groups including the Camp group. Aldol condensation reactions were performed on Cyrene™ with a variety of aryl aldehydes in the presence of a strong base. Nine examples of condensation products were synthesised in very poor to moderate yields. X-ray crystallography was used to confirm the structure of the compounds synthesised.
Interestingly, a bis-addition product was detected in one of the Aldol examples, efforts to synthesise this along with generality afforded two of these dimers as sole products.
| Date of Award | 2023 |
|---|---|
| Original language | English |
| Supervisor | Duncan Gill (Co-Supervisor) & Karl Hemming (Co-Supervisor) |