Synthesis of 2-bromo-8-methyltetracene and investigation into C-Br functionalisation in tetracene precursors

Shine, Jonathan (2017) Synthesis of 2-bromo-8-methyltetracene and investigation into C-Br functionalisation in tetracene precursors. MSc(Res) thesis, University of Nottingham.

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Abstract

The research project reported in this thesis describes the synthesis of novel compound 2-bromo-8-methyltetracene. The synthetic method developed in the Woodward laboratory for the straightforward and efficient synthesis of 2 and 2,8-substituted tetracenes is adapted for the difficult Bradsher cyclisation of an electron poor phenylene ring. Treatment with 4 equivalents of neat TiCl4 left to stir at room temperature for 48 hours yielded the compound at 4% yield after purification. This protocol was extended to attempt to synthesise 2,8-dibromotetracene, however this treatment only gave monocyclised product 6-bromo-3-(4-bromobenzyl)-2-naphthaldehyde.

The next stage of the project was the attempted C-Br functionalisation of tetracene precursors, to enable the quick application of structural complexity. The Suzuki, Stille and Buchwald-Hartwig cross coupling reactions were investigated, as well as methylation with a trimethylaluminum adduct. These all led to undesirable results halting any further investigation. Lithium-halogen exchange and electrophilic substitution with dimethyl disulfide did provide the functionalised product in unseparable mixtures with the hydrodebromination product. More promising was the Negishi coupling utilising a highly active palladium N-heterocyclic-carbene catalyst. On some occasions the coupling provided the coupling product at high purity and yield. Unfortunately in other cases the reaction would not initiate, leading to the conclusion that this reaction is capricious. An attempt to optimise the procedure was carried out by coupling to the iodinated analogue, however, this failed to yield the product cleanly.

Further work resulted in the successful scale up of the synthesis of parent tetracene and tetracene derivative tetrathiotetracene. Upon alteration of the quenching procedure the synthesis of tetracene was successfully carried out on a 2 g scale. Tetrathiotetracene synthesis was scaled up to 1 g without purity or yield deterioration.

The potentially novel reaction of tetrathiotetracene with nitric acid was then investigated. Initial suggestions of the production of nitrated tetrathiotetracene could not be replicated, only a trace amount of this compound was detected with the major product having different analytical data. Attempts to identify the major product failed to resolve the issue.

Item Type: Thesis (University of Nottingham only) (MSc(Res))
Supervisors: Woodward, Simon
Subjects: Q Science > QD Chemistry > QD241 Organic chemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 48135
Depositing User: Shine, Jonathan
Date Deposited: 11 Jan 2018 14:13
Last Modified: 11 Jan 2018 14:14
URI: http://eprints.nottingham.ac.uk/id/eprint/48135

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