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Synthesis of nitrogen heterocycles via amidyl radical cyclisations
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Peacock, Joanne Linda (1998) Synthesis of nitrogen heterocycles via amidyl radical cyclisations. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3225963~S15
Abstract
Intramolecular radical additions to alkenes have become increasingly popular in synthetic organic chemistry as a means for constructing cyclic arrays. The majority of work has focused upon the reactions of carbon-centred radicals but nitrogen radical cyclisations can provide an effective route to forming a variety of N-heterocycles. Cyclisation of nucleophilic aminyl radicals can be problematic due to their potential reversibility so the more electrophilic amidyl radicals were used for this investigation.
O-Benzoyl hydroxamic acid derivatives proved to be suitable precursors for forming the desired amidyl radicals and all cyclisations were performed using these precursors. A stereoselectivity study was performed on 5-exo amidyl radical cyclisations. Hence, a range of methyl and phenyl 3-substituted N-alkyl-N-benzoyloxypent-4-enamides were prepared and cyclised by reaction with tributyltin hydride. A small preference for trans 5-exo cyclisation was observed (diastereomeric excesses ranging from 10-48%) with the 3-phenyl substituted precursors showing greater selectivity than the 3-methyl substituted precursors. The N-alkyl group was found to have little effect on the reaction. Systems capable of undergoing 5-exo, 5-exo tandem amidyl radical cyclisations were also studied. The presence of a methyl group at the 5-position of the second forming ring resulted in a change of regiochemistry with 5-exo, 6-endo cyclisation actually becoming the dominant pathway.
A range of N-alkyl-N-benzoyl-4-phenylbut-3-enamides were synthesised and cyclised in a 4-exo fashion to form β-lactams. Also produced in these reactions were 2- benzoyl substituted amides formed from rearrangement of the starting material. These rearrangement reactions were studied in more detail and were found to proceed smoothly when promoted by base. Use of stronger bases led to shorter reaction times. The rearrangements were also conducted thermally (with no added base) in excellent yields.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QD Chemistry | ||||
Library of Congress Subject Headings (LCSH): | Radicals (Chemistry), Heterocyclic compounds -- Synthesis, Ring formation (Chemistry) | ||||
Official Date: | March 1998 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Chemistry | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Clark, Andrew J. (Professor) | ||||
Sponsors: | Engineering and Physical Sciences Research Council | ||||
Format of File: | |||||
Extent: | xviii, 234 leaves : illustrations, charts | ||||
Language: | eng |
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