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Article: Ruthenium-catalyzed alkylation of indoles with tertiary amines by oxidation of a sp3 CH bond and lewis acid catalysis

TitleRuthenium-catalyzed alkylation of indoles with tertiary amines by oxidation of a sp3 CH bond and lewis acid catalysis
Authors
KeywordsAlkylation
Indoles
Lewis acids
Oxidation
Ruthenium
Issue Date2010
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, 2010, v. 16 n. 19, p. 5723-5735 How to Cite?
AbstractRuthenium porphyrins (particularly [Ru(2,6-Cl2tpp)CO]; tpp = tetraphenylporphinato) and RuCl3 can act as oxidation and/or Lewis acid catalysts for direct C-3 alkylation of indoles, giving the desired products in high yields (up to 82% based on 60-95% substrate conversions). These ruthenium compounds catalyze oxidative coupling reactions of a wide variety of anilines and indoles bearing electron-withdrawing or electron-donating substituents with high regioselectivity when using tBuOOH as an oxidant, resulting in the alkylation of N-arylindoles to 3{[(N-aryl-N-alkyl)amino]methyl} indoles (yield: up to 82%, conversion: up to 95%) and the alkylation of N-alkyl or N-H indoles to 3-[p-(dialkylamino)benzyl]indoles (yield: up to 73%, conversion: up to 92%). A tentative reaction mechanism involving two pathways is proposed: an iminium ion intermediate may be generated by oxidation of an sp3 C-H bond of the alkylated aniline by an oxoruthenium species; this iminium ion could then either be trapped by an N-arylindole (pathway A) or converted to formaldehyde, allowing a subsequent three-component coupling reaction of the in situ generated formaldehyde with an N-alkylindole and an aniline in the presence of a Lewis acid catalyst (pathway B). The results of deuterium-labeling experiments are consistent with the alkylation of N-alkylindoles via pathway B. The relative reaction rates of [Ru(2,6-Cl 2tpp)CO] catalyzed oxidative coupling reactions of 4-X-substituted N,N-dimethylanilines with N-phenylindole (using tBuOOH as oxidant), determined through competition experiments, correlate linearly with the substituent constants o (R2=0.989), giving a ρ value of -1.09. This ρ value and the magnitudes of the intra- and intermolecular deuterium isotope effects (kH/kD) suggest that electron transfer most likely occurs during the initial stage of the oxidation of 4-X-substituted N,N-dimethylanilines. Ruthenium-catalyzed three-component reaction of N-alkyl N-H indoles, paraformaldehyde, and anilines gave 3-[p-(dialkylamino)benzyl] indoles in up to 82% yield (conversion: up to 95%). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.
Persistent Identifierhttp://hdl.handle.net/10722/134733
ISSN
2015 Impact Factor: 5.771
2015 SCImago Journal Rankings: 2.323
ISI Accession Number ID
Funding AgencyGrant Number
University of Hong Kong
Hong Kong Research Grants CouncilHKU7009/06P
Area of Excellence Scheme, University Grants Committee (HKSAR)AoE/P-10-01
Funding Information:

This work was supported by The University of Hong Kong (University Development Fund), the Hong Kong Research Grants Council (HKU7009/06P). and the Area of Excellence Scheme (AoE/P-10-01) established under the University Grants Committee (HKSAR).

References

 

DC FieldValueLanguage
dc.contributor.authorWang, MZen_HK
dc.contributor.authorZhou, CYen_HK
dc.contributor.authorWong, MKen_HK
dc.contributor.authorChe, CMen_HK
dc.date.accessioned2011-07-13T04:46:53Z-
dc.date.available2011-07-13T04:46:53Z-
dc.date.issued2010en_HK
dc.identifier.citationChemistry - A European Journal, 2010, v. 16 n. 19, p. 5723-5735en_HK
dc.identifier.issn0947-6539en_HK
dc.identifier.urihttp://hdl.handle.net/10722/134733-
dc.description.abstractRuthenium porphyrins (particularly [Ru(2,6-Cl2tpp)CO]; tpp = tetraphenylporphinato) and RuCl3 can act as oxidation and/or Lewis acid catalysts for direct C-3 alkylation of indoles, giving the desired products in high yields (up to 82% based on 60-95% substrate conversions). These ruthenium compounds catalyze oxidative coupling reactions of a wide variety of anilines and indoles bearing electron-withdrawing or electron-donating substituents with high regioselectivity when using tBuOOH as an oxidant, resulting in the alkylation of N-arylindoles to 3{[(N-aryl-N-alkyl)amino]methyl} indoles (yield: up to 82%, conversion: up to 95%) and the alkylation of N-alkyl or N-H indoles to 3-[p-(dialkylamino)benzyl]indoles (yield: up to 73%, conversion: up to 92%). A tentative reaction mechanism involving two pathways is proposed: an iminium ion intermediate may be generated by oxidation of an sp3 C-H bond of the alkylated aniline by an oxoruthenium species; this iminium ion could then either be trapped by an N-arylindole (pathway A) or converted to formaldehyde, allowing a subsequent three-component coupling reaction of the in situ generated formaldehyde with an N-alkylindole and an aniline in the presence of a Lewis acid catalyst (pathway B). The results of deuterium-labeling experiments are consistent with the alkylation of N-alkylindoles via pathway B. The relative reaction rates of [Ru(2,6-Cl 2tpp)CO] catalyzed oxidative coupling reactions of 4-X-substituted N,N-dimethylanilines with N-phenylindole (using tBuOOH as oxidant), determined through competition experiments, correlate linearly with the substituent constants o (R2=0.989), giving a ρ value of -1.09. This ρ value and the magnitudes of the intra- and intermolecular deuterium isotope effects (kH/kD) suggest that electron transfer most likely occurs during the initial stage of the oxidation of 4-X-substituted N,N-dimethylanilines. Ruthenium-catalyzed three-component reaction of N-alkyl N-H indoles, paraformaldehyde, and anilines gave 3-[p-(dialkylamino)benzyl] indoles in up to 82% yield (conversion: up to 95%). © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.en_HK
dc.languageeng-
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.subjectAlkylationen_HK
dc.subjectIndolesen_HK
dc.subjectLewis acidsen_HK
dc.subjectOxidationen_HK
dc.subjectRutheniumen_HK
dc.subject.meshAlkylation-
dc.subject.meshAmines - chemistry-
dc.subject.meshIndoles - chemistry-
dc.subject.meshOxidation-Reduction-
dc.subject.meshRuthenium - chemistry-
dc.titleRuthenium-catalyzed alkylation of indoles with tertiary amines by oxidation of a sp3 CH bond and lewis acid catalysisen_HK
dc.typeArticleen_HK
dc.identifier.openurlhttp://library.hku.hk:4550/resserv?sid=HKU:IR&issn=0947-6539&volume=16&issue=9&spage=5723&epage=5735&date=2010&atitle=Ruthenium-catalyzed+alkylation+of+indoles+with+tertiary+amines+by+oxidation+of+a+sp3+C-H+bond+and+Lewis+acid+catalysis-
dc.identifier.emailZhou, CY:cyzhou@hku.hken_HK
dc.identifier.emailChe, CM:cmche@hku.hken_HK
dc.identifier.authorityZhou, CY=rp00843en_HK
dc.identifier.authorityChe, CM=rp00670en_HK
dc.description.naturelink_to_subscribed_fulltext-
dc.identifier.doi10.1002/chem.200902387en_HK
dc.identifier.pmid20391566-
dc.identifier.scopuseid_2-s2.0-77952222923en_HK
dc.identifier.hkuros172893-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-77952222923&selection=ref&src=s&origin=recordpageen_HK
dc.identifier.volume16en_HK
dc.identifier.issue19en_HK
dc.identifier.spage5723en_HK
dc.identifier.epage5735en_HK
dc.identifier.isiWOS:000278349700026-
dc.publisher.placeGermanyen_HK
dc.identifier.scopusauthoridWang, MZ=24328900000en_HK
dc.identifier.scopusauthoridZhou, CY=35742480200en_HK
dc.identifier.scopusauthoridWong, MK=7403908449en_HK
dc.identifier.scopusauthoridChe, CM=7102442791en_HK

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