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Title: New pyrolytic routes to fused bridgehead nitrogen heterocycles
Author: Tyas, Richard G.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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Under flash vacuum pyrolysis (FVP) conditions C-unsubstituted imidazole N-propenoate ester derivatives give 78±5:22±5 mixtures of pyrrolo[1,2-a]amidazol-5-one and pyrrolo[1,2-c]imidazol-5-ones. The mechanism involves a cascade process initiated by 1,5-sigmatropic shift of the substituent. Substitution of the imidazole N-propenoate ester at the 2-position or 4,5-positons of the heterocycle allows exclusive access to the pyrrolo[1,2-c]imidazol-5-one and pyrrolo[1,2-a]amidazol-5-one systems respectively upon FVP. Ring-opening of the pyrrolo[1,2-c]imidazol-5-one system in THF/water readily affords cis-urocanic acids [formally cis-3-(imidazo-4-yl)-acrylic acids]. A number of novel pyrrolo[1,2-a]indol-3-ones and pyrrolo[1,2-a]benzimidazol-1-ones have been prepared by a similar strategy involving FVP of indole or benzimidazole propenoate or N-benzoate ester derivatives. Pyrrolo[1,2-a]indol-3-ones have been obtained by complementary pyrolyses of indole 3-propenoates and N-propenoates and pyrolyses of indole N-benzoates affords the isoindolo[2,1-a]indol-6-one system. The pyrrolo[1,2-a]indol-3-ones are stable at room temperature whereas pyrrolo[1,2-a]benzimidazol-1-ones are much less so. The reactions of the new heterocyclic systems were studied. Thus, hydrogenation of pyrrolo[1,2-a]indol-3-one at medium pressure affords largely 1,2-dihydropyrrolo[1,2-a]indol-3-one whereas pyrrolo[1,2-a]benzimidazol-1-one affords 1,2-dihydropyrrolo[1,2-a]benzimidazol-1-one and 2-ethylbenzimidazole.  High pressure hydrogenation of pyrrolo[1,2-a]indol-3-one gives a range of hydrogenation products although complete hydrogenation has been achieved over 8 h for 11-methylisoindolo[2,1-a]indol-6-one. Diels-Alder cycloaddition reactions of pyrrolo[1,2-a]indol-3-one and pyrrolo[1,2-a]benzimidazol-1-one with isobenzofuran and with cyclopentadiene afford exclusively the endo adduct in each case. The reaction of pyrrolo[1,2-a]indol-3-one with 4-methoxybenzyl azide gives a 1,2,3-triazolo-adduct with high regioselectivity. The reaction of pyrrolo[1,2-a]indol-3-ones with a range of nucleophiles has been studied.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available