Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.645124
Title: Pyrolytic syntheses and reactions of seven-membered heterocycles
Author: Crawford, Lynne A.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2001
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Abstract:
Flash vacuum pyrolysis (FVP) reactions of N-(4-chlorophenoxymethyl)pyridinone systems and their benzo-fused analogues were found to follow one of two pathways. The first pathway was followed by the pyridin-4-one, phenanthridinone, quinolin-2-one and quinolin-4-one systems which all gave the parent heterocycle (i.e. pyridine, phenanthridine or quinoline respectively). Ring-expanded azepinones were shown to be intermediates in such reactions by 13C labelling experiments. The second pathway was followed by the pyridin-2-one and isocarbostyril systems where p-chlorophenol and the initial heterocycle (i.e. pyridin-2-one or isocarbostyril respectively) were obtained. The 'missing' CH2 group was detected as ethylene by bromine trapping experiments, which suggests that these compounds act as carbene generators under pyrolytic conditions. 5-[3-(Substitutedthio)propylidene]-2,2-dimethyl-1,3-dioxan-4,6-dione derivatives were synthesised for the first time and their structures were fully analysed. When pyrolysed, these compounds did not give the expected thiepinone systems and only fragmented products were isolated. The related 2-(alkylthio)arylmethylene precursors were also successfully synthesised but again no cyclisation products were obtained on pyrolysis. Reaction of Meldrum's acid with 2-(dialkylamino)benzaldehydes did not give the expected condensation product but instead novel 1,2,3,4-tetrahydroquinoline derivatives were obtained via a facile low-temperature "tert-amino effect". FVP of 5H-dibenzo[b.f]azepine at 950°C gives 9-methylacridine. However, the corresponding N-allylated derivative undergoes an unusual radical ring-contraction reaction to give pyrrolo[3,2,1-jk]carbazole; the optimum yield (63%) was obtained at 950°C. Reactions of this pyrrolocarbazole with electrophiles (e.g. Vilsmeier formylation, halogenation, reaction with oxalyl chloride) gave 2-substitution products in each case. Pyrrolo[3,2,1-jk]carbazole was also formed by the cyclisation of 2-(indol-l-yl)phenyl radicals generated by FVP of allyl 2-indol-I-ylbenzoates or I-(2-nitrophenyl)indoles. This route was found to be synthetically versatile and in optimum cases provided two-step access to substituted pyrrolo[3,2,1-jk]carbazoles and indolo[3,3,1-jk]carbazole. In some cases the reaction path was diverted to other products. Thus, when the corresponding benzimidazole and indazole systems were pyrolysed, the expected tetracycle rearranged under the reaction conditions to give 1-cyanocarbazole as the only product. FVP of the corresponding 2-methylbenzimidazole and indole systems gave 10H-4b,9-diazaindeno[1,2-a]indene and 10H-indolo[1,2-a]indole respectively; preliminary deuterium labelling experiments suggest that a hydrogen-transfer mechanism is involved. Cyclisation of the 2-(2-phenylbenzimidazol-1-yl)phenyl radical took place on the 2-phenyl substituent to give benzo[4,5]imidazo[1,2-f]phenanthridine rather than I-phenyl-2,9b-diazacyclopenta[jk]fluorene.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.645124  DOI: Not available
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