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Article: Stereo- and enantioselective alkene epoxidations: A comparative study of D4- and D2-symmetric homochiral trans-dioxoruthenium(VI) porphyrins

TitleStereo- and enantioselective alkene epoxidations: A comparative study of D4- and D2-symmetric homochiral trans-dioxoruthenium(VI) porphyrins
Authors
KeywordsAsymmetric oxidation
Epoxidation
Kinetics
Macrocycles
Ruthenium
Issue Date2002
PublisherWiley - V C H Verlag GmbH & Co KGaA. The Journal's web site is located at http://www.wiley-vch.de/home/chemistry
Citation
Chemistry - A European Journal, 2002, v. 8 n. 11, p. 2495-2507 How to Cite?
AbstractThe mechanism of stoichiometric enantioselective alkene epoxidations by the D4- and D2-symmetric homochiral trans-dioxoruthenium(VI) porphyrins, [RuVI(D4-Por*)O2] (1) and [RuVI(D2-Por*)O2] (2a), in the presence of pyrazole (Hpz) was studied by UV/ Vis spectrophotometry and analysis of the organic products. The enantioselectivity of styrene oxidations is more susceptible to steric effects than to substituent electronic effects. Up to 72% ee was achieved for epoxidation of 3-substituted and cis-disubstituted styrenes by employing 1 as the oxidant, whereas entantioselectivities of only 20-40 % were obtained in the reactions with 2-substituted and trans-disubstituted styrenes. Complex 2a oxidized 2-substituted styrenes to their epoxides in up to 88% ee. Its reactions with transalkenes are more enantioselective (67 % ee) than with the cis-alkenes (40 % ee). Based on a two-dimensional NOESY NMR study, 2a was found to adopt a more open conformation in benzene than in dichloromethane, which explains the observed solvent-dependent enantioselectivity of its reactions with alkenes. The oxidation of aromatic alkenes by the chiral dioxoruthenium(VI) porphyrins proceeds through the ratelimiting formation of a benzylic radical intermediate; the observed enantioselectivity (eeobs) depends on both the facial selectivity of the first C-O bond formation step and the diastereoselectivity of the subsequent epoxide ring closure. To account for the observed facial selection, "side-on" and "top-on" approach transition state models are examined (see: B. D. Brandes, E. N. Jacobsen, Tetrahedron Lett. 1995, 36, 5123).
Persistent Identifierhttp://hdl.handle.net/10722/69717
ISSN
2015 Impact Factor: 5.771
2015 SCImago Journal Rankings: 2.323
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorZhang, Ren_HK
dc.contributor.authorYu, WYen_HK
dc.contributor.authorSun, HZen_HK
dc.contributor.authorLiu, WSen_HK
dc.contributor.authorChe, CMen_HK
dc.date.accessioned2010-09-06T06:16:12Z-
dc.date.available2010-09-06T06:16:12Z-
dc.date.issued2002en_HK
dc.identifier.citationChemistry - A European Journal, 2002, v. 8 n. 11, p. 2495-2507en_HK
dc.identifier.issn0947-6539en_HK
dc.identifier.urihttp://hdl.handle.net/10722/69717-
dc.description.abstractThe mechanism of stoichiometric enantioselective alkene epoxidations by the D4- and D2-symmetric homochiral trans-dioxoruthenium(VI) porphyrins, [RuVI(D4-Por*)O2] (1) and [RuVI(D2-Por*)O2] (2a), in the presence of pyrazole (Hpz) was studied by UV/ Vis spectrophotometry and analysis of the organic products. The enantioselectivity of styrene oxidations is more susceptible to steric effects than to substituent electronic effects. Up to 72% ee was achieved for epoxidation of 3-substituted and cis-disubstituted styrenes by employing 1 as the oxidant, whereas entantioselectivities of only 20-40 % were obtained in the reactions with 2-substituted and trans-disubstituted styrenes. Complex 2a oxidized 2-substituted styrenes to their epoxides in up to 88% ee. Its reactions with transalkenes are more enantioselective (67 % ee) than with the cis-alkenes (40 % ee). Based on a two-dimensional NOESY NMR study, 2a was found to adopt a more open conformation in benzene than in dichloromethane, which explains the observed solvent-dependent enantioselectivity of its reactions with alkenes. The oxidation of aromatic alkenes by the chiral dioxoruthenium(VI) porphyrins proceeds through the ratelimiting formation of a benzylic radical intermediate; the observed enantioselectivity (eeobs) depends on both the facial selectivity of the first C-O bond formation step and the diastereoselectivity of the subsequent epoxide ring closure. To account for the observed facial selection, "side-on" and "top-on" approach transition state models are examined (see: B. D. Brandes, E. N. Jacobsen, Tetrahedron Lett. 1995, 36, 5123).en_HK
dc.languageengen_HK
dc.publisherWiley - V C H Verlag GmbH & Co KGaA. The Journal's web site is located at http://www.wiley-vch.de/home/chemistryen_HK
dc.relation.ispartofChemistry - A European Journalen_HK
dc.subjectAsymmetric oxidationen_HK
dc.subjectEpoxidationen_HK
dc.subjectKineticsen_HK
dc.subjectMacrocyclesen_HK
dc.subjectRutheniumen_HK
dc.subject.meshAlkenes - Chemistry-
dc.subject.meshCytochrome P-450 Enzyme System-
dc.subject.meshEpoxy Compounds - Chemical Synthesis - Chemistry-
dc.subject.meshModels, Molecular-
dc.subject.meshOrganometallic Compounds - Chemistry-
dc.subject.meshPorphyrins - Chemistry-
dc.subject.meshRuthenium - Chemistry-
dc.subject.meshStereoisomerism-
dc.titleStereo- and enantioselective alkene epoxidations: A comparative study of D4- and D2-symmetric homochiral trans-dioxoruthenium(VI) porphyrinsen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0947-6539&volume=8&issue=11&spage=2495&epage=2507&date=2002&atitle=Stereo-+and+enantioselective+alkene+epoxidations:++a+comparative+study+of+D4-+and+D2-symmetric+homochiral+trans-dioxoruthenium(VI)+porphyrinsen_HK
dc.identifier.emailSun, HZ:hsun@hkucc.hku.hken_HK
dc.identifier.emailChe, CM:cmche@hku.hken_HK
dc.identifier.authoritySun, HZ=rp00777en_HK
dc.identifier.authorityChe, CM=rp00670en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1002/1521-3765(20020603)8:11<2495::AID-CHEM2495>3.0.CO;2-Gen_HK
dc.identifier.pmid12180328-
dc.identifier.scopuseid_2-s2.0-0037013599en_HK
dc.identifier.hkuros72417en_HK
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0037013599&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume8en_HK
dc.identifier.issue11en_HK
dc.identifier.spage2495en_HK
dc.identifier.epage2507en_HK
dc.identifier.isiWOS:000176075400009-
dc.publisher.placeGermanyen_HK
dc.identifier.scopusauthoridZhang, R=7404865969en_HK
dc.identifier.scopusauthoridYu, WY=7403913673en_HK
dc.identifier.scopusauthoridSun, HZ=7404827446en_HK
dc.identifier.scopusauthoridLiu, WS=8121250200en_HK
dc.identifier.scopusauthoridChe, CM=7102442791en_HK

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