While alcohols have successfully undergone kinetic resolutions, amines pose achallenge due to their nucleophilic nature. Aziridines were identified as potential substrates as a result of their synthetic utility and reduced nucleophilicity. Using a helical aminopyridine catalyst, the kinetic resolutions of ketoaziridines were explored. Initial attempts revealed anomalous kinetic behaviour [slow conversion and non-first order]. Non-buffered noncatalytic control reactions demonstrated unexpected reaction dynamics, as gauged by HPLC and 1H NMR. Stopped-flow spectroscopy revealed photochemical sensitivity of the aziridine. As a result of this new information, the project evolved into a study of the photochemical behaviour of ketoaziridines and their spectroscopic properties.UV-vis absorbance and fluorescence spectroscopy were used to probe the photochemical reactivity of ketoaziridines. These studies suggested a two-step mechanism where an azomethine ylide formed a reactive intermediate, ultimately to form 2,5-diphenyloxazole. Kinetic analysis revealed the mechanism was autocatalytic with respect to oxazole formation. TD-DFT calculations suggested the mechanism proceeded via a diradical species upon irradiation. This mechanistic route was studied by investigating the presence of a magnetic field effect on the kinetics of absorption and emission changes, in collaboration with the Manchester Institute of Biotechnology. Further studies demonstrated a radical species, derived from the irradiation of aziridine, may be used as a photoinitiator in the polymerization of methyl methacrylate. This work also involved development of a synthetic platform to diphenyloxazoles, where functionality may be installed in the initial steps. Use of this strategy allowed for the synthesis of a natural product, texaline.
|Date of Award
|8 Jun 2016
|David Carbery (Supervisor) & Christopher Pudney (Supervisor)