Insight into the Mechanism of the Asymmetric Ring-Opening Aminolysis of 4,4-Dimethyl-3,5,8-trioxabicyclo[5.1.0]octane Catalyzed by Titanium/BI NOLate/Water System: Evidence for the Ti(BINOLate)2-Bearing Active Catalyst Entities and the Role of Water.
The mechanism of the enantioselective ring-opening aminolysis of 4,4-dimethyl-3,5,8- trioxabicyclo[5.1.0]octane with benzylamine, catalyzed by the titanium-BINOLate species generated in situ from a mixture of enantiopure BINOL (1,1′-bi-2-naphthol), Ti(OiPr), and HO in the presence of benzylamine in...
| Publicado en: | Journal of the American Chemical Society Vol. 130; no. 31; pp. 10116 - 10128 |
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| Autores principales: | , , , , , |
| Formato: | Artículo |
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American Chemical Society
8/6/2008
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| Materias: | |
| Acceso en línea: | Ver este registro en EBSCOhost |
| fields | @attributes: recordID: 1 pdfLink: plink: https://search.ebscohost.com/login.aspx?direct=true&db=hlh&AN=34123719&site=ehost-live header: @attributes: shortDbName: hlh uiTerm: 34123719 longDbName: Humanities International Complete uiTag: AN controlInfo: bkinfo: jinfo: jid: 00027863 ACS jtl: Journal of the American Chemical Society issn: 00027863 maglogo: N pubinfo: dt: 8/6/2008 vid: 130 iid: 31 pid: 997 pub: American Chemical Society artinfo: ui: 34123719 10.1021/ja801847r ppf: 10116 ppct: 12 formats: tig: atl: Insight into the Mechanism of the Asymmetric Ring-Opening Aminolysis of 4,4-Dimethyl-3,5,8-trioxabicyclo[5.1.0]octane Catalyzed by Titanium/BI NOLate/Water System: Evidence for the Ti(BINOLate)2-Bearing Active Catalyst Entities and the Role of Water. aug: au: Hongli Bao Jing Zhou Zheng Wang Ylniong Guo Tianpa You Kuiling Ding affil: State Key Laboratory of Organometallic Chemistry and Shanghai Mass Spectrometry Center Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, P. R. China, and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, China su: Cyclic compounds Catalysis Alkanes Titanium Catalysts Water Ring formation (Chemistry) sug: subj: Cyclic compounds Catalysis Alkanes Titanium Catalysts Water Ring formation (Chemistry) ab: The mechanism of the enantioselective ring-opening aminolysis of 4,4-dimethyl-3,5,8- trioxabicyclo[5.1.0]octane with benzylamine, catalyzed by the titanium-BINOLate species generated in situ from a mixture of enantiopure BINOL (1,1′-bi-2-naphthol), Ti(OiPr), and HO in the presence of benzylamine in toluene, was investigated in detail using a combination of reaction profile measurements, nonlinear effect (NLE) studies, solution ¹H NMR analysis, electrospray ionization mass spectrometry (ESI-MS), as well as the results obtained from screening of dynamic catalyst library of complexes L/TI/L (L or L = chiral diol ligands). The BINOL-to-titanium ratio and the presence or absence of water in the catalytic system were found to exert profound influences on both reactivity and enantioselectivity of the reaction. The NLE studies revealed that the titanium species involved in the catalysis should contain more than one BINOL unit, either within or at the periphery of the catalytic cycle. ESI-MS analysis of the catalytic systems provided strong support in favor of the mechanistic proposal that titanium complexes bearing the Ti(BlNOLate) moiety should be the active species responsible for the catalysis, which was further confirmed by the observation of synergistic effect of the heteroligand combinations during screening of the dynamic catalyst library. ESI-MS analysis of the reaction system indicated that water does not take part in the catalyst generation, which is an unprecedented finding in contrast to the previous mechanistic understandings in the titanium catalytic chemistry involving the participation of water. Most probably, water functions as a proton shuttle in the catalysis, facilitating the proton transfer between the reactants. Furthermore, the origin of (+)-NLE observed in the present catalytic system is rationalized on the basis of the ESI-MS analysis of the catalyst system prepared from a 1:1 pseudoracemic mixture of (S)-BINOL and (R)-3,3′,6,6′-D-BINOL. Finally, the reactivity differences between several couples of epoxide/amine combinations were tentatively rationalized on the basis of the arguments on their relative coordination preferences, and several other aliphatic amines were also found to efficiently ring-open the titled epoxide in excellent enantioselectivities. The results from this study are expected to shed some light on the often elusive chemistry of Ti(IV)-based catalytic systems where water or molecular sieves (or alcohols, etc.) are found to play an important yet inexplicable role and may help the search for effective asymmetric Ti(IV) catalysts for other types of reactions. pubtype: Academic Journal doctype: Article src: R language: English refInfo: copyright: @attributes: flag: Y dt: @attributes: year: 2008 holdings: @attributes: islocal: N |
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