Loughborough University
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A study of directed cleavage of azirinidylcarbinyl radicals

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posted on 2013-11-28, 13:21 authored by Richard C. Toon
The work described in this thesis is an investigation into the reactivity and possible synthetic applications of aziridinylcarbinyl radicals. These radicals rapidly rearrange via βcleavage, which can proceed by breakage of either the CoN or C-C bond. Cleavage of the latter has been found when the molecule has a phenyl stabilising group attached to the aziridine ring. Chapter I is a review of the known radical reactions involving aziridines whilst chapter 2 discusses the various methods of aziridine syntheses. Chapter 3 outlines the project aims with reference to the potential of directed cleavage of aziridinylcarbinyl radicals in synthesis. Chapter 4, the main body of the work, describes the synthetic routes to aziridines derived from 3-phenyl-2-cyclohexen-I-one and indenone. The radical mediated β-cleavage reactions of these is reported and the selectivity of C-C v. CoN bond homolysis has been investigated. Two successful approaches to the target aziridines were involved. I) Conversion of 3-azido-3-phenylcyclohexan-I,2-diol, derived from the epoxide of 3- phenyl-2-cyc1ohexen-I-ol, to the aziridine via reaction with triphenylphosphine. Subsequent methylation and formation of the thiocarbonylimidazolide gave the radical precursor Nmethyl- 5-[imidazol-I-yl(thiocarbonyl)oxy]-I-phenyl-7-azabicylo[4.1.0]heptane. In the course of this work, several unusual cyclic thiocarbonates resulting from the reaction of 3-azido-3- phenylcyclohexan-I,2-diol and 2-azido-3-phenylcyclohexan-I,3-diol with I, I 'thiocarbonyl diimidazole were isolated. 2) Formation of N-(2-ethylquinazolinonyl)-I-phenyl-7-azabicyclo[4.1.0]heptan-5-01 from the reaction of 3-amino-2-ethyl-4(3H)-quinazolinone with 3-phenyl-2-cyc1ohexen-I-ol in the presence of lead tetraacetate. These aziridines show interesting acid-catalysed rearrangements to diazadioxabicyclo[2.2.2]octanes. Formation of the thiocarbonylimidazolide then gave the radical precursor. A number of other aziridines have been prepared using this methodology. It has been found that in all cases the precursors undergo CoN bond homolysis under radical conditions. These results are discussed and conclusions are drawn. Suitable future work is also suggested.



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© Richard Clive Toon

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A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.


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