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Memorial University - Electronic Theses and Dissertations 5
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TitleStudies on guanidinyl pyrrolidine catalyzed conjugate additions and synthesis of (-)-pancracine and (+)-ipalbidine
AuthorLingampally, Rajinikanth
DescriptionThesis (Ph.D.)--Memorial University of Newfoundland, 2011. Chemistry
Paginationxviii, 243 leaves : ill.
SubjectAlkaloids--Synthesis; Asymmetric synthesis; Pyrrolidine; Catalysts
Degree GrantorMemorial University of Newfoundland. Dept. of Chemistry
NotesIncludes bibliographical references.
AbstractThe organocatalytic, asymmetric conjugate addition of carbon nucleophiles and heteroatom nucleophiles to enones is of interest because the products are useful synthetic intermediates. We have observed that these reactions are catalyzed by proline-derived guanidines. The present study examines the enantioselective addition of malonates, nitroalkanes and heteroatom nucleophiles to a variety of enones in order to provide the corresponding Michael adducts. The observations from this study provide some insight into the reactivity of amine-guanidine bifunctional catalyst motifs and lay the foundation for designing second generation catalysts having modulated nucleophilic and basic character. -- Enantiomerically pure y-nitroketones and their derivatives are an important class of organic compounds due to their utility as building blocks for the asymmetric synthesis of natural products and biologically active molecules. In the present study, the organocatalytic Michael addition of a monoprotected cyclohexane 1, 3-dione and selected β-nitro styrenes in the presence of a proline-derived triamine catalyst provided the conjugate addition products in good yield (83-90%), with high enantiomeric excess (89-99%) and high diastereoselectivity (≥19/1). These Michael adducts were utilized in a stereoselective synthesis of cis and trans-3-aryloctahydroindoles. Application of this methodology is presented in a short formal total synthesis of the methanomorphanthridine alkaloid (-)-pancracine. -- Enantiomerically enriched y-nitroketones obtained from the triamine catalyzed organocatalytic Michael addition were also utilized as starting materials in an efficient synthesis of indolizidines. The utility of this methodology is highlighted by its application in a short total synthesis of the arylindolizidine alkaloid (+)-ipalbidine. The synthetic strategy has potential applications in the preparation of congeners and analogs of several arylindolizidine alkaloids.
Resource TypeElectronic thesis or dissertation
FormatImage/jpeg; Application/pdf
SourcePaper copy kept in the Centre for Newfoundland Studies, Memorial University Libraries
RightsThe author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
CollectionElectronic Theses and Dissertations
Scanning StatusCompleted
PDF File(6.92 MB) --
CONTENTdm file name24285.cpd