Development of a flow electrochemical method for effecting reductive radical and radical–polar crossover reactions with non–sacrificial electrodes

Abstract

Organic electrosynthesis has proven to be a powerful technique for effecting reactions that otherwise require harsh reducing reagents or oxidants. In this thesis, we employ electrosynthesis to form aryl radicals from aryl halides. It begins with a study to identify effective reaction conditions through optimisation. We then sought to delineate the range of substrates applicable to the chemistry to determine the similarities and differences compared with other synthetic methods. Our first foray examined the synthesis of spirodienes from iodophenyl benzyl ethers involving a reductive dearomatisation. This led us to consider how the transfer of a second electron to the substrate could switch reactions from the radical domain to the polar domain. This radical–polar crossover was investigated further through collaborative work examining the synthesis of 2,3–dihydrobenzofurans from iodophenyl allyl ethers. Our experimental results were investigated by colleagues to gain a fuller understanding of the mechanism through theoretical calculations. Finally, an examination of the electrochemistry of iodobenzyl phenyl ether led us to observe a dichotomous pathway whereby the reaction mechanism changes if the substrate had two ortho substituents on the acceptor ring. When these positions were unsubstituted, the reaction formed a biaryl phenol. By contrast, when they each carried a substituent, 2– arylbenzyl alcohols were formed. We attribute this change to a difference in the relative rates for transfer of the second electron to the substrate which changes the point at which the reaction crosses into the polar domain.

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Identifiers

ORCID for James, Edward Pearce: orcid.org/0000-0002-8401-2417

ORCID for David Harrowven: orcid.org/0000-0001-6730-3573

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