Year

2019

Degree Name

Doctor of Philosophy

Department

School of Chemistry and Molecular Bioscience

Abstract

Cyclopropenes are unsaturated, three-membered ring systems that are highly strained and as a result, serve as highly useful building blocks in the field of synthetic chemistry. The electron rich double bond of cyclopropenes makes them ideal substrates for electrophilic Lewis acids, such as gold catalysts. Gold catalysts readily activate cyclopropenes towards ring-opening and given the strain of these ring systems, reactions are often highly facile and can result in substantial increases in molecular complexity. Thus, the gold-catalysed reactions of cyclopropenes represent a highly versatile field of chemistry, especially considering that substitution around the cyclopropene ring can be used to control regio-, diastereo- and enantioselectivity. Despite this potential however, research into gold-catalysed reactions of cyclopropenes remains relatively undeveloped compared to the gold-catalysed reactions of other C–C multiple bonds (i.e. alkynes, alkenes and allene). It has therefore been the aim of this thesis to help contribute to this field by investigating the rearrangements that occur when derivatives of cyclopropenyl carbinols are reacted with gold catalysts. Cyclopropenyl carbinols are a particularly useful class of cyclopropene given that the alcohol moiety serves as a tethering point for further functionalisation. It has been the discovery of this thesis that cyclopropenyl propargyl ethers, derived from C1-substituted cyclopropenyl carbinols, undergo initial ring-opening followed by a Claisen rearrangement in the presence of a gold catalyst, to form highly substituted furans. Cyclopropenyl allyl ethers can also undergo gold-catalysed ringopening and a Claisen rearrangement (followed by additional chemical transformations) to diastereoselectively form highly substituted tetrahydrofurans. Alternatively, cyclopropenyl sulfonamides obtained from the Mitsunobu coupling of C3-substituted cyclopropenyl carbinols, have also been reacted with gold catalysts. Cyclopropene–furan systems were found to undergo a [4C+3C] dearomative cycloaddition reaction to form 5,7-fused heterocyclic scaffolds with an oxa-bridge, while cyclopropene–indole (and pyrrole) systems were found to undergo a Friedel–Crafts cyclisation to generate tetrahydro-β-carboline scaffolds. All of these heterocyclic skeletons feature in a variety of natural and synthetic products which have numerous pharmacological, agricultural and industrial applications. The work presented in this thesis may therefore represent new methods for the synthesis of these compounds and provides valuable insight into the molecules that can be accessed through the gold-catalysed rearrangement of these unique three-membered carbocycles.

This thesis is unavailable until Monday, May 04, 2020

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.