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postgraduate thesis: Organocatalytic asymmetric synthesis of dihydrodibenzofurans and asymmetric aziridination of α-nitroalkenes

TitleOrganocatalytic asymmetric synthesis of dihydrodibenzofurans and asymmetric aziridination of α-nitroalkenes
Authors
Issue Date2012
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Wang, Z. [汪子玉]. (2012). Organocatalytic asymmetric synthesis of dihydrodibenzofurans and asymmetric aziridination of α-nitroalkenes. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4979914
AbstractThe synthesis of useful chiral skeletons from simple achiral starting materials is always the dream of organic chemists. In the past decades, organocatalysis has been rapidly developed and has become one of the most important methods in asymmetric catalysis. The aim of this thesis is to develop asymmetric methods for the construction of useful chiral skeletons based on organocatalytic chemistry. Many natural products and biologically important compounds contain the hydrogenated dibenzofuran (Figure 1) as a common sub-structure. In the first part of this thesis, the first amine-catalysed asymmetric synthesis of a dihydrodibenzofuran species from bisenal substrates has been demonstrated. After a systematic screening of various reaction parameters, the optimal conditions have been found to be as follows: 0.1 M of substrate in solution with toluene with 0.2 equiv of (S)-di(2-naphthyl)pyrrolinol TMS ether (C2.8) and 0.2 equiv of 2-nitrobenzoic acid at 50 ℃ for 7 h under an argon atmosphere (Scheme 1). The first step product, an aldehyde, can be reduced in one pot to an alcohol by NaBH4. This two-step protocol gives exclusive cis selectivity. Many chiral cis-dihydrodibenzofuran species have been synthesized from the corresponding bisenal substrates in moderate to good yield with good to excellent ee (Scheme 1). The resulting cis-dihydrodibenzofuran species have promising synthetic applications. As shown in Scheme 2, the less hindered face of the newly formed C ring is more reactive and highly regioselective functionalizations of the C ring have been achieved. In the second part of this thesis, the first asymmetric aziridination of trans-α-nitroalkenes via a phase-transfer catalysis strategy has been systematically studied. The chiral phase-transfer catalysts screened are derivatives of the cinchona alkaloids. The new cinchonidine-derived phase-transfer catalyst CD17 has been found to be optimal for the aziridination (Figure 2). Addition of a small amount of water is crucial to achieve complete conversion of the reaction. Both trans-1-nitro-2-arylalkenes and trans-1-nitro-2-alkylalkenes are suitable substrates (Scheme 3). The reaction can be run on the gram-scale without significant loss of efficiency and ee. Mechanistic studies have revealed that the aziridination proceeds through an aza-Michael addition followed by an intramolecular SN 2 type three-membered ring formation (Scheme 4).
DegreeDoctor of Philosophy
SubjectNitroalkenes
Organic compounds - Synthesis
Asymmetric synthesis
Dibenzofurans
Dept/ProgramChemistry
Persistent Identifierhttp://hdl.handle.net/10722/193388

 

DC FieldValueLanguage
dc.contributor.authorWang, Ziyu-
dc.contributor.author汪子玉-
dc.date.accessioned2013-12-20T23:10:46Z-
dc.date.available2013-12-20T23:10:46Z-
dc.date.issued2012-
dc.identifier.citationWang, Z. [汪子玉]. (2012). Organocatalytic asymmetric synthesis of dihydrodibenzofurans and asymmetric aziridination of α-nitroalkenes. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4979914-
dc.identifier.urihttp://hdl.handle.net/10722/193388-
dc.description.abstractThe synthesis of useful chiral skeletons from simple achiral starting materials is always the dream of organic chemists. In the past decades, organocatalysis has been rapidly developed and has become one of the most important methods in asymmetric catalysis. The aim of this thesis is to develop asymmetric methods for the construction of useful chiral skeletons based on organocatalytic chemistry. Many natural products and biologically important compounds contain the hydrogenated dibenzofuran (Figure 1) as a common sub-structure. In the first part of this thesis, the first amine-catalysed asymmetric synthesis of a dihydrodibenzofuran species from bisenal substrates has been demonstrated. After a systematic screening of various reaction parameters, the optimal conditions have been found to be as follows: 0.1 M of substrate in solution with toluene with 0.2 equiv of (S)-di(2-naphthyl)pyrrolinol TMS ether (C2.8) and 0.2 equiv of 2-nitrobenzoic acid at 50 ℃ for 7 h under an argon atmosphere (Scheme 1). The first step product, an aldehyde, can be reduced in one pot to an alcohol by NaBH4. This two-step protocol gives exclusive cis selectivity. Many chiral cis-dihydrodibenzofuran species have been synthesized from the corresponding bisenal substrates in moderate to good yield with good to excellent ee (Scheme 1). The resulting cis-dihydrodibenzofuran species have promising synthetic applications. As shown in Scheme 2, the less hindered face of the newly formed C ring is more reactive and highly regioselective functionalizations of the C ring have been achieved. In the second part of this thesis, the first asymmetric aziridination of trans-α-nitroalkenes via a phase-transfer catalysis strategy has been systematically studied. The chiral phase-transfer catalysts screened are derivatives of the cinchona alkaloids. The new cinchonidine-derived phase-transfer catalyst CD17 has been found to be optimal for the aziridination (Figure 2). Addition of a small amount of water is crucial to achieve complete conversion of the reaction. Both trans-1-nitro-2-arylalkenes and trans-1-nitro-2-alkylalkenes are suitable substrates (Scheme 3). The reaction can be run on the gram-scale without significant loss of efficiency and ee. Mechanistic studies have revealed that the aziridination proceeds through an aza-Michael addition followed by an intramolecular SN 2 type three-membered ring formation (Scheme 4).-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.subject.lcshNitroalkenes-
dc.subject.lcshOrganic compounds - Synthesis-
dc.subject.lcshAsymmetric synthesis-
dc.subject.lcshDibenzofurans-
dc.titleOrganocatalytic asymmetric synthesis of dihydrodibenzofurans and asymmetric aziridination of α-nitroalkenes-
dc.typePG_Thesis-
dc.identifier.hkulb4979914-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplineChemistry-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_b4979914-
dc.date.hkucongregation2013-

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