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Title: Novel pyrolytic routes to fused heterocyclic rings
Author: Milligan, Andrew Alexander
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2003
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Substituted benzo[b]thiophenes were synthesised from 2-(S-allyl)- or 2-(S-benzyl)-cinnamic ester derivatives utilising flash vacuum pyrolysis (FVP). Under these conditions the benzyl or allyl groups cleaved from the precursor to form a thiophenoxyl radical which then cyclised with the ejection of the ester function as a radical leaving group. A deuteriated precursor was also synthesised to investigate the breakdown pathway during electron impact mass spectrometry. The reactions of some indole-based radicals were investigated. Thus iminyl radicals were generated from 2-thiophenoxylindole-3-carbaldehyde oxime ethers and thiiyl radicals from the anil of 2-thiobenzylindole-3-carbaldehyde. These radicals produced the same products viz the corresponding carbonitrile and the unexpected formation of an aldimine derivative. The thiiyl radical can interconvert to the iminyl via a spirodienyl intermediate. In contrast to the corresponding benzo-fused system, no cyclised products were observed. Surprisingly, FVP of 1-allyl-2-phenylsulfanyl-1H-indole did not lead to indol-1-yl radicals. The major products (obtained in low yields) were 4-phenylsulfanyl-5,6-dihydrobenzo[b]azocine (via an unusual rearrangement mechanism) and 6H-benzo[b]thieno[2,3-b]indole (probably formed after initial sigmatropic shift of the allyl group). The formation of fused pyridine systems by cyclisation of heterocyclic iminyl radicals under FVP conditions was investigated. Aldehyde precursors were obtained by Vilsmeier formylation or by Suzuki coupling methodology; cyclisations proceeded in high yields. Previous work to form phenanthrene derivatives utilising FVP of 2-arylcinnamic esters was extended to investigate the effect of a fused heterocycle. The mechanism involves initial electrocyclisation followed by loss of the ester function; this protocol proved to be an extremely efficient route to heterocyclic phenanthrene analogues.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available