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Flow system for heterocyclic synthesis

Hayes, Simon Jonathan. 2007. Flow system for heterocyclic synthesis. PhD Thesis, Cardiff University.

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The potential of the silver-catalysed cyclisation has been illustrated by the synthesis of furans, pyrroles and pyrazole-N-oxides. With yields predominantly being >95%, and ubiquitous high purity, the results herein show the compatibility of many substituents including alkyl, aryl and silyl, to name but a few. Extended investigations have improved our understanding of reaction rates, the effect of stereochemistry and the use of protection strategies as well as identifying a handful of limitations. With the above results in hand, and a desire to recognise the practical advantages of a metal-catalysed procedure, we have further described two continuous flow systems for heterocyclic synthesis. The first, a trickle-bed reactor, produces heterocycles in excellent yields (>95% except where volatile products were produced) and has been shown to exhibit < 1 ppm silver leaching. Our understanding of the optimal flow rates, catalyst loading and practical attributes associated with such a reactor is then described. The second, a supercritical carbon dioxide : ionic liquid system, has been shown to produce furans in excellent yields (>95%), when used in batch mode, and in slightly lower yield (>70%) when used in a continuous fashion. Once again silver leaching was seen to be <1 ppm. The success of these two systems, and the speed in which their success was achieved, clearly demonstrates the ease of working with silver-catalysed cyclisations. In a further brief foray, the use of heat and microwave irradiation is discussed in view of potential applications to other continuous systems. Finally, several specific applications of the silver-catalysed cyclisation have been shown. It is seen that this procedure is suitable for the synthesis of scented furans and has uses in the preparation of heterocyclic substrates, which can be used for bigger and better things. One such example, which is described in Chapter 6, is the formation of oxepan-4-ones, oxepin-4-ones and oxocins-5-ones from their corresponding furyl alcohols.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303210044
Funders: EPSRC, GSK
Date of First Compliant Deposit: 30 March 2016
Last Modified: 31 Jan 2020 07:30

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