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Radical additions to Arenes: Cyclisations, rearrangements and applications to natural product synthesis

Radical additions to Arenes: Cyclisations, rearrangements and applications to natural product synthesis
Radical additions to Arenes: Cyclisations, rearrangements and applications to natural product synthesis

The work described in this thesis concerns the intramolecular addition of an aryl radical to an arene tethered by differing linkages. Exposure of 2-iodoaryl benzyl ethers to tributyltin hydride and AIBN resulted in the formation of an aryl-aryl bond. Attack of the aryl radical occurred in a 5-exo-trig manner with a subsequent fragmentation and concomitant rearomatisation. A suitably placed radical acceptor or hydrogen atom donor was found to be bias the reaction pathway.

2-Iodostilbenes were subjected to tributyltin-mediated radical forming conditions with cyclisation occurring via a 6-exo/endo-trig pathway to give the corresponding phenanthrenes in good to excellent yield. 2-Iododihydrostilbenes gave poorer results with a mixture of dihydrophenathrene and direct reduction products observed. Mechanistic details of the reaction are also discussed. The methodology has been applied to the synthesis of [5]helicenes by an iterative radical cyclisation approach. Tandem radical cyclisations are described providing a three step synthesis of [5]helicenes.

Application of the methodology towards the synthesis of the macrocyclic biarylheptanoid acerogenin E is detailed. The first total synthesis of toddaquinoline is also described. Preliminary work on the use of tributyltin hydride in combination with tetrabutylammonium fluoride for the reduction of aryl halides is illustrated.

University of Southampton
Nunn, Michael Ian Thomas
Nunn, Michael Ian Thomas

Nunn, Michael Ian Thomas (2002) Radical additions to Arenes: Cyclisations, rearrangements and applications to natural product synthesis. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The work described in this thesis concerns the intramolecular addition of an aryl radical to an arene tethered by differing linkages. Exposure of 2-iodoaryl benzyl ethers to tributyltin hydride and AIBN resulted in the formation of an aryl-aryl bond. Attack of the aryl radical occurred in a 5-exo-trig manner with a subsequent fragmentation and concomitant rearomatisation. A suitably placed radical acceptor or hydrogen atom donor was found to be bias the reaction pathway.

2-Iodostilbenes were subjected to tributyltin-mediated radical forming conditions with cyclisation occurring via a 6-exo/endo-trig pathway to give the corresponding phenanthrenes in good to excellent yield. 2-Iododihydrostilbenes gave poorer results with a mixture of dihydrophenathrene and direct reduction products observed. Mechanistic details of the reaction are also discussed. The methodology has been applied to the synthesis of [5]helicenes by an iterative radical cyclisation approach. Tandem radical cyclisations are described providing a three step synthesis of [5]helicenes.

Application of the methodology towards the synthesis of the macrocyclic biarylheptanoid acerogenin E is detailed. The first total synthesis of toddaquinoline is also described. Preliminary work on the use of tributyltin hydride in combination with tetrabutylammonium fluoride for the reduction of aryl halides is illustrated.

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Published date: 2002

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Local EPrints ID: 464811
URI: http://eprints.soton.ac.uk/id/eprint/464811
PURE UUID: 45b8260f-ffeb-4b62-8a53-a4c9a17a119f

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Date deposited: 05 Jul 2022 00:02
Last modified: 05 Jul 2022 03:13

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Author: Michael Ian Thomas Nunn

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