On the application of a new benzannulation reaction to the synthesis of polycyclic aromatic hydrocarbons

UoM administered thesis: Phd

  • Authors:
  • Mohamad Elarfi

Abstract

ABSTRACT Due to their unique biological and physical properties PAHs are widely researched and applied in many fields of science and technology. Some PAHs are used as fluorescent emitters 104, 105, 105 and fluorescent probes for the study of biological processes such as carcinogen models107, organic conductors, dyes106, and solar cell research 116, 117 and as biosensors in many medical, pharmaceutical, and environmental applications. A new benzannulation reaction (the BHQ reaction), which has considerable synthetic potential, has been utilised in the synthesis of hindered polycyclic aromatics (PAHs). A library of linear and non-linear PAHs have been synthesized using an operationally robust, four-step, BHQ sequence (involving the allylation of a dihydroxyaromatic; ortho-Claisen rearrangement, trichloroacetylation of the resultant bis-phenol, and finally a copper-catalysed ATRC-benzannulation cascade). Specifically, 4,9-dichlorobenzophenthracene 134 and dichlorotriphenylene 129 were prepared successfully using our newly developed Atom Transfer Radical Cyclisation methodology. 4,9-Dichlorobenzophenthracene 134 has been prepared by way of a two-directional benzannulation reaction starting from bis-(trichloroacetate) 133 whilst 129 has been prepared by benzannulation reaction starting from trichloroacetate 128 (Scheme 1.39). The Atom Transfer Radical Cyclisation (ATRC) of o-diallylnaphthyl trichloroacetates 133 and 128 was accomplished in the presence of a CuCl catalyst and afforded 134 and 129 respectively in good yields: such reactions can be promoted by thermal or microwave activation. Unfortunately, this methodology is not applicable to 122, as attempted Claisen rearrangement lead to the generation of a spiroycle that has been fully characterised by single crystal X-ray crystallography. This outcome provides a potentially useful method for the desymmetrization of BINOL derivatives, which could find application in the development of new ligands for transition metals or the synthesis of scaffolds for pharmaceutical research. A small library of linear and non-linear dichloro-PAHs was successfully functionalized via a regioselective, iridium-catalysed, aromatic C-H borylation reaction. The synthesis and reactivity of “A2B3” penta-substituted 1,8-dichloro triphenylene 140 and of penta-substituted 4,9-diclorobenzophenathrene 141 has also been accomplished, affording access to 1,8- 4,9- and 2,6,11-substituted triphenylenes and benzophenathrenes respectively. The synthesis of “A2B2”, tetrasubstituted, aromatics was also accomplished via the application of regioselective, iridium- 10 catalyzed, C-H borylation reaction of 5,5'-dichloro-2,2'-binaphthalene 139 and 4,10-dichlorochrysene 39 and palladium catalysed cross-coupling strategies. Here orthogonal, sequential, Suzuki cross-coupling reactions have been utilised for the synthesis of a series of PAHs derived from 140 and 141 which have unique substitution patterns. In addition to the above-mentioned work the synthesis of a series of pyrene-derived anthracenes and anthraquinones is also presented. The interaction between these “molecular tweezers” and nitro-aromatics is briefly discussed. Such systems have potential application in analytical chemistry for the detection of high energy, nitro-containing, aromatics.

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Original languageEnglish
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Award date1 Aug 2019