Development of New Methods in Catalytic Dehydrative Synthesis

Abstract

This thesis is focused on the development of new methodologies in catalytic dehydrative synthesis. Through the course of the thesis three different dehydrative reactions are explored, using a range of catalytic methods.
Firstly, in Chapter 1 the importance of green chemistry and sustainable synthesis is discussed and the concept of dehydrative synthesis is outlined in this context.
In Chapter 2 the development of a boronic acid-catalysed reductive etherification is described. The procedure allows for the synthesis of ethers from aldehydes and alcohols using a commercially available arylboronic acid catalyst in combination with oxalic acid as a ligand. The procedure uses dimethylphenylsilane as a reducing agent and requires only mild reaction conditions. A broad range of aldehydes were successful substrates; however only simple alkyl alcohols were high yielding, primarily due to the competing homoetherification of the aldehyde. The nature of the catalytic mechanism was explored through a series of control experiments.
In Chapter 3 a Lewis acid-catalysed Lossen rearrangement is explored. Zinc chloride catalyses the synthesis of ureas from hydroxamic acids and amines via the Lossen rearrangement. Once optimised, the procedure was applied to the synthesis of a range of ureas with the majority of substrates giving moderate to high isolated yields of up to 82%. While multiple amine substrates could be used for the reaction, the use of alcohols for the synthesis of carbamates was not possible under the previously optimised conditions. Based on experimental observations and previously reported literature, possible catalytic mechanisms are discussed.
Finally, in Chapter 4, investigations are made into the development of an electrochemically driven deoxydehydration using oxo-vanadium catalysts. Three oxo-vandium(V) complexes were synthesised, two of which had been previously reported as catalysts for deoxydehydration, and their electrochemical behaviour studied by cyclic voltammetry. The development of an electrochemical deoxydehydration was then attempted using the vanadium complexes as catalysts. This was however unsuccessful with a maximum yield of <10% of the desired alkene product despite full conversion of the starting material.

Date of Award	22 Jan 2025
Original language	English
Awarding Institution	University of Bath
Supervisor	James Taylor (Supervisor) & Frank Marken (Supervisor)