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New frontiers in borrowing hydrogen catalysis

Reed-Berendt, Benjamin 2020. New frontiers in borrowing hydrogen catalysis. PhD Thesis, Cardiff University.
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This thesis describes the exploration and development of new reactions in borrowing hydrogen chemistry. Borrowing hydrogen (or hydrogen-autotransfer) is a sub-category of transfer hydrogenation chemistry, whereby a catalyst is employed to oxidise a starting material, (typically an alcohol) by dehydrogenation, yielding a metal hydride species and a reactive intermediate (typically a carbonyl). An in situ reaction is then performed on this reactive intermediate, and the metal catalyst returns the “borrowed” hydrogen to the resultant species, effecting an alkylation. This transformation provides many advantages over classical alkylation methods, but principally that it allows alkylations to be performed without the use of toxic or harmful materials. Alcohols are a typical reagent for these reactions, hence via borrowing hydrogen catalysis, alkylation can be effected with an environmentally benign, widely available alkylating agent. Furthermore, these reactions typically yield water as sole by-product, thus this transformation is highly atom economic. Initial efforts described here were in the exploration of a new regime for enantioselective borrowing hydrogen catalysis. The second chapter describes how enamine and dienamine reactions were attempted, with limited success. Next, work was performed on a cleavage-SNAr isomerisation reaction, effecting the formation of diaryl ethers, as presented in the third chapter. Multiple examples were formed in high yields. Attention was then transferred to earth-abundant transition metal-catalysed borrowing hydrogen methods. The fourth chapter discusses a manganesecatalysed N-alkylation of sulfonamides. Sulfonamides are important moieties in biologically active molecules. A borrowing hydrogen method for efficient alkylation of sulfonamides with both benzylic and aliphatic alcohols of varied chain lengths was investigated. Multiple examples were formed in high yields. The final chapter discusses the work performed in the tandem reduction-N-methylation of nitroarenes, under manganese catalysis. The reduction of nitroarenes is a key reaction in the production of aniline derivatives. Several examples were formed in moderate yields.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Date of First Compliant Deposit: 13 November 2020
Last Modified: 13 Nov 2021 02:30

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