Force Triggered Cyclisations and Retrocycloadditions

Abstract

Mechanical force, with its ability to distort, bend and stretch chemical bonds, is unique in the way it activates chemical reactions. Early work in the area focussed on the destructive aspects of this remarkable source of energy, however, in recent years there has been a shift towards using mechanical force for productive chemistry. Polymers are used to transduce force, in a highly directional fashion, into the scissile bonds of a force-sensitive moiety, or mechanophore. Using this technique, chemical transformations which are not possible via other methods of activation have been demonstrated, along with the application of mechanophores as latent catalysts and force sensors. In this thesis, structural and geometric effects on mechanophore activation are probed, along with the attempted preparation of new mechanophores and the translation of mechanochemistry into a synthetic chemistry setting. Initial work focusses on the design and preparation of mechanophores which can undergo a force-induced Bergman cyclisation to produce intermediates for graphene nanoribbon synthesis. Three different macrocyclic enediyne mechanophores are designed and their attempted syntheses are detailed. The efficiency of activation of a mechanophore is dependent on the successful transduction of force into the scissile bonds. We investigate the effects of stereo- and regiochemistry on the reactivity of Diels-Alder mechanophores and, in doing so, switch off the mechanical susceptibility of one of the adducts. We further investigate the local environment around a mechanophore by varying the nature of the polymerisation initiator and introducing a second mechanophore in close proximity, assessing their effect on mechanical activation. Building on the idea of mechanically inert units, the application of mechanochemistry to the synthetic chemist is developed by using a polymer catalyst design. Optimisation and early stage development are demonstrated by way of orthogonal substrate binding and selective mechanical cleavage.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Guillaume De Bo (Supervisor) & Stephen Edmondson (Supervisor)