Lerma, I.C.; (2007) Transformations mediated by palladium-(n-heterocyclic)carbene complexes. Doctoral thesis , University of London.

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Abstract

The synthesis of 3-substituted benzofurans by the intramolecular Heck cyclisation of 2-chlorophenyl allyl ethers has proved unsuccessful using a palladium/imidazolium salt protocol previously developed in our group. A palladium deallylation process was at play in this case, although both 2-iodo- and 2-bromophenyl derivatives do react under similar conditions. Similarly, the synthesis of indoles has been achieved with the same pattern of reactivity shown by benzofurans. The mild amination of aryl iodides with a palladium/imidazolium system has been achieved using the hindered base lithium hexamethyldisilazide (LHMDS). In the first instance, only secondary amines were found to react, whilst a limited selection of primary amines investigated, either failed or needed more forcing conditions with concomitant formation of bisarylated by-product. Further optimisation studies were conducted with the aid of computer software for statistical design of experiments (DoE). A sterically hindered aryl iodide and a less demanding substrate were studied against N-methylbenzylamine. The resulting optimum conditions have benefited this protocol by allowing a primary amine, N-hexylamine, to react under mild conditions, although bisarylation was still observed.

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