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A-aryl quaternary centres via asymmetric vicarious nucleophilic substitution

Davies, Christopher Alan 2005. A-aryl quaternary centres via asymmetric vicarious nucleophilic substitution. PhD Thesis, Cardiff University.

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This dissertation first describes a new method for the formation of a-aryl lactams based on the Vicarious Nucleophilic Substitution reaction. The route involves the three-component coupling of a nitroarene, an a-phenylsulfanyl lactam and an electrophile. The process incorporates various electrophiles and various-substituted cyclic amides and has been developed for the most part using nitrobenzene. The process was also applied to a-phenylsulfenyl pyrazolidinones. The process also includes examples of amides possessing a removable nitrogen protecting group to give access to functionalised amides with a free NH group. Secondly, an asymmetric version of the VNS reaction is described. The diastereoselectrvity of the VNS-alkylation reaction of lactones was studied. For example using an a-phenylsulfanyl-Y-substituted butyrolactone, nitrobenzene and an alkyl halide, diastereoselectivities of greater than 7:1 were observed in some cases. The stereogenic centre at the y position is clearly able to exert considerable control in the generation of the new stereogenic centre at the a-position. The third area of research described involves capture of the intermediate VNS anion with aryl electrophiles. Activated electrophiles react in this way via an SnAt process. The VNS and SnAt reactions were combined to form an efficient one-pot three-component coupling process to give easy access to functionalised diarylmethanes. Reduction of the nitro group of selected products gave a quick and easy route to the oxmdole structural motif. The final chapter describes our attempts to react the intermediate VNS anion with unactivated aryl halides in a transition metal cross-coupling process. Unfortunately, we did not find conditions to effect the coupling of the anion derived from a VNS process with aryl halides. Nevertheless, the anion of nitrophenylacetates prepared via deprotonation participates in cross-coupling reactions with ease and provides an alternative way to prepare diarylmethanes. This has the potential to be extremely useful due to the lack of reports of nitroarenes in cross-coupling processes.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303203718
Funders: EPSRC, GlaxoSmithKline
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 Oct 2017 15:24

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