Chiral oxovanadium complex catalyzed enantioselective oxidative coupling of 2-naphthols

Chu, Chih‐Peng; Hwang, Der-Ren; Wang, Shengkai; Uang, Biing‐Jiun

doi:10.1039/b101670i

Cited by 132 publications

(48 citation statements)

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“…We initially reasoned that the stereocontrol would be improved by introducing another suitable chiral center close to the naphthoxy or phenoxy in the complex 4. 14,15 On the basis of this idea, we have designed novel oxovandium complexes 1 and 5, which contain two chiral centers in amino acids and an axial chirality in the binaphthyl unit (Figure 2). The complexes 1 and 5 differ in the absolute configuration of the axial chirality of the binaphthyl moiety.…”

Section: Resultsmentioning

confidence: 99%

“…The best result for the oxidative coupling of 6-substitued 2-naphthols was seen in the case of 6-bromo-2-naphthol, which gave rise to the product with 90% ee (entry 12). Also conducted were symmetric oxidative couplings of 2-naphthols bearing two substituents at C6 and C7, respectively-(entries [13][14][15][16][17][18][19][20][21]. The size of the substituent at C7 somewhat affects the enantioselectivity.…”

Section: Entioselective Oxidative Couplings Of 2-naphthols a R T I C mentioning

confidence: 99%

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Highly Enantioselective Oxidative Couplings of 2-Naphthols Catalyzed by Chiral Bimetallic Oxovanadium Complexes with Either Oxygen or Air as Oxidant

et al. 2007

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Abstract:The chiral bimetallic oxovanadium complexes have been designed for the enantioselective oxidative coupling of 2-naphthols bearing various substituents at C6 and/or C7. The chirality transferring from the amino acid to the axis of the biphenyl in oxovanadium complexes 2 was found to occur with the use of UV and CD spectra and DFT calculation. The homo-coupling reaction with oxygen as the oxidant was promoted by 5 mol % of an oxovanadium complex derived from L-isoleucine and achiral biphenol to afford binaphthols in nearly quantitative yields with high enantioselectivities of up to 98% ee. An oxovanadium complex derived from L-isoleucine and H8-binaphthol is highly efficient at catalyzing the air-oxidized coupling of 2-naphthols with excellent enantioselectivities of up to 97% ee. 51 V NMR study shows that the oxovanadium complexes have two vanadium(V) species. Kinetic studies, the cross-coupling reaction, and HRMS spectral studies on the reaction have been carried out and illustrate that two vanadium(V) species are both involved in catalysis and that the coupling reaction undergoes a radical-radical mechanism in an intramolecular manner. Quantum mechanical calculations rationalize the importance of the cooperative effects of the axial chirality matching S-amino acids on the stereocontrol of the oxidative coupling reaction. The application of the transformation in the preparation of chiral ligands and conjugated polymers confirms the importance of the current process in organic synthesis.

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Section: Resultsmentioning

confidence: 99%

Section: Entioselective Oxidative Couplings Of 2-naphthols a R T I C mentioning

confidence: 99%

Highly Enantioselective Oxidative Couplings of 2-Naphthols Catalyzed by Chiral Bimetallic Oxovanadium Complexes with Either Oxygen or Air as Oxidant

et al. 2007

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“…These complexes exhibit attractive promise as orally available treatments for diabetes mellitus and also have a number of applications as catalysts in various oxidation reactions [1][2][3][4][5][6][7][8][9][10]. Recently, some oxovanadium complexes, especially bimetallic oxovanadium complexes of chiral Schiff bases reported by Gong's group, were shown to provide high enantioselectivity for the oxidative coupling of 2-naphthols, which play very important roles in the history of asymmetric synthesis [11][12][13][14][15][16][17].…”

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Electrospray mass spectrometry and tandem mass spectrometry of bimetallic oxovanadium complexes

Luo

et al. 2008

J. Am. Soc. Mass Spectrom.

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A series of six bimetallic oxovanadium complexes (1-6; only one was purified) were investigated by electrospray quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) in negative-ion mode. Radical molecular anions [Ml-were observed in MS mode. Fragmentation patterns of [Ml-were proposed, and elemental compositions of most of the product ions were confirmed on the basis of the high-resolution ESI-CID-MS/MS spectra. A complicated series of low-abundance product ions similar to electron impact (EI) ionization spectra indicated the radical character of the precursor ions. Fragment ions at m/z 214, 200, and 182 seem to be the characteristic ions of bimetallic oxovanadium complexes. These ions implied the presence of a V-D-V bridge bond, which might contribute to stabilization of the radical. To obtain more information for structural elucidation, three representative bimetallic oxovanadium complexes O xovan ad iu m complexes have played active roles in the fields of pharmaceutical research and organic synthesis. These complexes exhibit attractive promise as orally available treatments for diabetes mellitus and also have a number of applications as catalysts in various oxidation reactions [1][2][3][4][5][6][7][8][9][10]. Recently, some oxovanadium complexes, especially bimetallic oxovanadium complexes of chiral Schiff bases reported by Gong's group, were shown to provide high enantioselectivity for the oxidative coupling of 2-naphthols, which play very important roles in the history of asymmetric synthesis [11][12][13][14][15][16][17].Structural characterization of the bimetallic oxovanadium complexes is key to the further development of their functions. Nuclear magnetic resonance (NMR) spectroscopy eH and SlV) can provide abundant information for structural analyses of bimetallic oxovanadium complexes. Unfortunately, NMR measurements Address reprint requests to Dr. Z.-J. Wu, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China. E-mail: wuzhijunyinger@ 163.com require pure samples, which are difficult to obtain for most bimetallic oxovanadium complexes [17]. X-ray crystallographic analyses require the production of monocrystals, which limits the applicability of this technique for structural characterization. Furthermore, UV, IR, and ESR spectroscopy offer only limited structural information [18]. Obviously, a method that provides abundant structural information without laborious purification would be highly desirable for the structural characterization of the bimetallic oxovanadium complexes.Mass spectrometry (MS) has greatly benefited from the development of electrospray ionization (ESI) and has been applied successfully in various fields. A series of simple oxovanadium complexes has been studied by . Recently, Zeng et al. reported the fragmentation study of monometallic oxovanadium Schiff base complexes by ESI-IT-MS n [25]. However, it seems not to obtain the information of uniform fragmentation patterns, except for the loss of CO 2 , Surprisingly, in our recent work, the [Ml...

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“…These vanadium catalysts showed good enantioselectivity for the coupling of 2-naphthol derivatives, although the catalytic activity was moderate. Chu and Uang found that catalytic activity could be improved by the addition of Lewis 64) or Brønsted acids, 65) resulting in the production of BINOL with moderate to good enantioselectivity. Barhate and Chen 63) also developed the vanadium(IV) catalysts derived from VOSO 4 , (ϩ)-ketopinic acid, and a-amino acids.…”

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confidence: 99%

“…Vanadium-mediated couplings, which occur via a favorable one-electron phenolic oxidation, proceed under mild reaction conditions and tolerate many functional groups, with the further advantage that only water is formed as side product. [62][63][64][65][66][67][68][69][70][71] In 2001, Chen and colleagues 62) and Uang and colleagues 64) independently reported the first efficient asymmetric vanadium(IV) catalysts for oxidative coupling of 2-naphthol molecules prepared from vanadium(IV) oxide sulfate (VOSO 4 ), aldehyde derivatives, and (S)-amino acids. Gong and colleagues [66][67][68] reported dinuclear vanadium catalysts which possess a V-O-V linkage with a maximum enantioselectivity of 98%.…”

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confidence: 99%

Development of Dinuclear Vanadium Catalysts for Enantioselective Coupling of 2-Naphthols via a Dual Activation Mechanism

Takizawa

2009

CHEMICAL & PHARMACEUTICAL BULLETIN

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Catalytic asymmetric reactions are among the most powerful synthetic methods to obtain optically active compounds.1,2) Recent challenges focus on the development of asymmetric catalysts for carbon-carbon bond-forming reactions with high activity and broad substrate generality, which lead to practical, efficient, and environmentally benign chemical syntheses. Dual activation systems for substrates such as nucleophiles and electrophiles lead to enhanced reaction rates and more specific control of the transition structure with respect to the catalyst's asymmetric environment. Dual activation catalyses can be classified into three categories ( Fig. 1): Type 1) dual activation using two different kinds of catalysts [3][4][5][6][7][8][9][10][11][12] ; Type 2) conjugated-type dual activation with a functional group such as a phosphate which has both acidic and basic sites in one functionality [13][14][15] ; and Type 3) dual activation by two catalytic sites in a single catalyst. For efficient dual activation of the substrates, a balance between these two functionalities in the catalyst is required. For example, in an acid-base type catalyst the selfquenching reaction of acidic and basic moieties on the catalyst can lead to its inactivation.We postulated that a chiral complex possessing two identical metal centers in a single molecule, which could activate two substrates simultaneously in a homolytic coupling reaction of 2-naphthol molecules, would enhance the reaction rate with high enantioselectivity. To achieve the new dual activation catalysis in an oxidative coupling reaction, we designed the catalyst (R a ,S,S)-1 42) bearing two active sites attached to a binaphthyl skeleton, taking advantage of the activation entropy (Fig. 2). Activation entropy strongly con- Development of Dinuclear Vanadium Catalysts for Enantioselective Coupling of 2-Naphthols via a Dual Activation MechanismShinobu TAKIZAWA This review describes our recent efforts in the development of chiral dinuclear vanadium complexes which work as dual activation catalysts for oxidative coupling of 2-naphthols. A chiral dinuclear vanadium(IV) complex (R a ,S,S)-1a possessing (S)-tert-leucine moieties at the 3,3 -positions of the (R)-binaphthyl skeleton was developed, and found to promote oxidative coupling of 2-naphthol to afford (S)-1,1 -bi-2-naphthol (BINOL) with 91% ee. To verify the dual activation mechanism, mononuclear vanadium(IV) complex (S)-10 was also prepared. Kinetic analysis revealed that the reaction rate of oxidative coupling of 2-naphthol promoted by (R a ,S,S)-1a is 48.3 times faster than that of (S)-10. In the coupling reaction, the two vanadium metals in the chiral complex activate two molecules of 2-naphthol simultaneously achieving a high reaction rate with high enantiocontrol. Since the dinuclear vanadium(IV) complex was found to be readily oxidized to afford a corresponding vanadium(V) species during preparation in air, a new synthetic procedure using VOCl 3 and a convenient one-pot procedure using VOSO 4 under O 2 have been applie...

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Chiral oxovanadium complex catalyzed enantioselective oxidative coupling of 2-naphthols

Cited by 132 publications

References 18 publications

Highly Enantioselective Oxidative Couplings of 2-Naphthols Catalyzed by Chiral Bimetallic Oxovanadium Complexes with Either Oxygen or Air as Oxidant

Highly Enantioselective Oxidative Couplings of 2-Naphthols Catalyzed by Chiral Bimetallic Oxovanadium Complexes with Either Oxygen or Air as Oxidant

Electrospray mass spectrometry and tandem mass spectrometry of bimetallic oxovanadium complexes

Development of Dinuclear Vanadium Catalysts for Enantioselective Coupling of 2-Naphthols via a Dual Activation Mechanism

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