Arylcarboxylic acids have been recognised as useful substrates for various chemical transformations either for their directing behaviour or decarboxylative activation. They have gained a lot of attention because they are readily available, low cost and bench stable reagents. This thesis illustrates the development of carboxylic acid directed Ru-catalysed C-H arylation of benzoic acids and indole carboxylic acids with aryl halides. We first detail out the first phosphine-free Ru-catalysed C-H arylation of benzoic acids with readily available aryl halides (Chapter 2). This protocol has also been applied to indole carboxylic acids and aryl iodides as coupling partners. We then exploit the decarboxylation activity of the carboxyl group towards iodination. The procedure of transition-metal free decarboxylative iodination has been discussed in the corresponding chapter (Chapter 3). This thesis also outlines the application of decarboxylative iodination in one-pot cross-coupling process. Various Pd-catalysed cross-coupling reactions require Ag as halide abstractor where iodoarenes are mostly employed as coupling partners, to prevent catalyst inhibition. Additionally, Ag additives have commonly been utilised as oxidants and decarboxylating agent. Very recently, it was found that phosphine-ligated Ag-carboxylates are able to perform C-H bond cleavage in electron deficient/hetero-arenes in Pd/Ag or Au/Ag catalytic system. We then looked into the role of silver additive in near-room temperature alpha- arylation of benzo[b]thiophenes with aryl iodides (Chapter 4). It was envisioned that the reaction proceeds through Ag mediated C-H activation of benzo[b]thiophene which was supported by reaction progress kinetic analysis (RPKA) and variable time normalisation analysis (VTNA). Further, it was previously discovered that quaternary ammonium salt could be used for halide abstraction, as an alternate to Ag source in Pd- and Ru-catalysed direct arylation. This allowed us to envisage that Ag salt could be used in catalytic amount. We developed a novel Pd/Ag co-catalysis methodology for the construction of biaryls, using fluoroarene-chromium tricarbonyl complexes and bromoarenes (Chapter 5). Preliminary to all chapters, a brief overview with examples of different works carried out in carboxylic acid-directed arylation and iodo-decarboxylation of arylcarboxylic acids and roles of Ag additives in Pd catalysis areas has been outlined in Chapter 1.
|Date of Award
|1 Aug 2020
- The University of Manchester
|Igor Larrosa (Supervisor) & Daniele Leonori (Supervisor)
- C-H activation