Chiral Oxovanadium Research Articles

Chiral oxo-vanadium (+)-pseudoephedrine complex immobilized on magnetic nanoparticles: A highly efficient and recyclable novel nanocatalyst for the chemoselective oxidation of sulfides to sulfoxides using H2O2

The first chiral oxo-vanadium (+)-pseudoephedrine complex supported on magnetic nanoparticles Fe3O4 [VO(pseudoephedrine)@MNPs] as novel magnetically interphase nanocatalyst was designed and characterized using the most common techniques. VO(pseudoephedrine)@MNPs catalyzed the chemoselective oxidation of sulfides to sulfoxides using hydrogen peroxide as a green oxidant in high yields with 20–27% enantiomeric excesses under solvent-free conditions at room temperature. The catalyst was recycled up to 20 times with little loss of activity and enantioselectivity.

Synthesis, characterization and catalytic property of chiral oxo-vanadium (+)-pseudoephedrine complex supported on magnetic nanoparticles Fe3O4 in the cyanosilylation of carbonyl compounds

Vanadium complex of pseudoephedrine immobilized on magnetic nanoparticle Fe3O4[VO(Pseudoephedrine)@MNPs] was prepared and characterized by UV–vis, SEM, XRD, TGA, EDX, FT-IR, AGFM and elemental analysis techniques. VO(Pseudoephedrine)@MNPs was found to catalyze the cyanosilylation of carbonyl compounds using TMSCN in good yields with 8–25% enantiomeric excesses under solvent-free conditions at room temperature. The catalyst was recycled up to 15 times with little loss of activity and enantioselectivity.

ChemInform Abstract: Enantioselective Silylcyanation of Aldehydes Catalyzed by New Chiral Oxovanadium Complex.

Abstract Oxovanadium(V) complex 4 was prepared from VOSO 4 and tridentate Schiff base ligand, which was prepared from substituted salicylaldehyde and inexpensive ( S )-valine. Asymmetric silylcyanation of the aldehydes catalyzed by catalyst 4 afforded cyanohydrins with good enantioselectivities.

Enantioselective silylcyanation of aldehydes catalyzed by new chiral oxovanadium complex

Oxovanadium(V) complex 4 was prepared from VOSO 4 and tridentate Schiff base ligand, which was prepared from substituted salicylaldehyde and inexpensive ( S)-valine. Asymmetric silylcyanation of the aldehydes catalyzed by catalyst 4 afforded cyanohydrins with good enantioselectivities.

Preparation of chiral oxovanadium (IV) Schiff base complex functionalized by ionic liquid for enantioselective oxidation of methyl aryl sulfides

Abstract Chiral oxovanadium (IV) Schiff base complex covalently grafted with ionic liquid (IL: 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate) has been reported first time. The IL-functionalized complex was found to be an efficient catalyst in the enantioselective oxidation of methyl aryl sulfides to sulfoxides with hydrogen peroxide as an oxidant. Especially, the IL-functionalized complex could be recovered conveniently by simple precipitation with addition of hexane and reused at least six cycles without loss of activity and enantioselectivity.

Chiral oxovanadium(V) complexes with a 6-amino-6-deoxyglucopyranoside-based Schiff-base ligand: Catalytic asymmetric sulfoxidation and structural characterization

Two new chiral oxovanadium(V) complexes [VO(OMe)(L)] ( 1) and [VO(Osal)(L)] ( 2) derived from the Schiff-base ligand 6- N-[(3,5-di- tert-butyl-salicylidene)amino]-6-deoxy-1,2,3-tri- O-methyl-α- d-glucopyranose (H 2L) were synthesized via two different routes. The reaction of the Schiff-base ligand H 2L with ammonium metavanadate in hot methanol as well as with tris(isopropoxy)oxovanadium(V) in diethyl ether at room temperature leads to a mixture of complexes 1 and 2, which can be isolated by means of fractional crystallization. The complexes were characterized with elemental analysis, 51V, 1H and 13C NMR, IR spectroscopy, MS and in case of 1 by X-ray diffraction. Complex 1 crystalizes in the orthorhombic space group P2 12 12 1 with a distorted trigonal bipyramidal geometry at the vanadium center ( τ = 0.58). Under hydrolytic conditions 1 forms the cis-dioxovanadium(V) complex [VO 2(MeOH)(HL)] ( 3) which can be monitored by NMR spectroscopy. Complexes 1 and 2 were tested as catalysts for sulfoxidation of different sulfide substrates PhSR (R = Me, Bz) utilizing hydrogen peroxide or tert-butyl hydroperoxide (TBHPO) as oxidant in dichloromethane as solvent. The yield as well as the enantiomeric excess were found to strongly depend on the catalyst, substrate and oxidant used.

Vanadium-Salan Catalyzed Enantioselective Ring Opening of meso-Epoxides with Aromatic Amines

The first example of enantioselective ring-opening of meso-epoxides catalyzed by chiral oxovanadium(V)-salan complexes is reported. The reaction furnished 1,2-aminoalcohols in good yields and moderate to high enantioselectivities (up to 87%).

Asymmetric Synthesis and Characterization of Chiral 2,2′‐Diamino‐3,3′‐diethoxycarbonyl‐8,8′‐diphenyl‐1,1′‐biazulene

rac‐2,2′‐Diamino‐3,3′‐diethoxycarbonyl‐8,8′‐diphenyl‐1,1′‐biazulene was synthesized from diethyl 2‐aminoazulene‐1,3‐dicarboxylate and was optically resolved into two enantiomers of S‐form and R‐form. The enantioselective oxidative couplings with two chiral amines [(−)‐sparteine and (R)‐(+)‐α‐methylbenzylamine] and ferric chloride catalyst, and the asymmetric couplings with two chiral oxovanadium(IV) complexes of ethyl 2‐amino‐4‐phenylazulene‐1‐carboxylate, easily yielded chiral 2,2′‐diamino‐3,3′‐diethoxycarbonyl‐8,8′‐diphenyl‐1,1′‐biazulene. Therefore, the introduction of two phenyl groups at the 8‐ and 8′‐postions of each azulene ring using phenyl magnesium bromide via an addition–oxidation–decarboxylation mechanism resulted in 1,1′‐biazulene forming a chiral C2 axis.

Novel Achiral Biphenol‐Derived Diastereomeric Oxovanadium(IV) Complexes for Highly Enantioselective Oxidative Coupling of 2‐Naphthols.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic enantioselective coupling of 2-naphthols by new chiral oxovanadium complexes bearing a self accelerating functional group

New chiral oxovanadium complexes containing an extra phenolic hydroxyl group were found to enhance the catalytic enantioselective coupling of 2-naphthols in moderate to good enantioselectivity.

Novel achiral biphenol-derived diastereomeric oxovanadium(IV) complexes for highly enantioselective oxidative coupling of 2-naphthols.

Optically pure 1,1’-binaphthol and its derivatives have been evaluated as versatile chiral auxiliaries and ligands in asymmetric transformations. Research in this area has provided many efficient and useful methods for the preparation of key chiral building blocks, some of which have been used for the construction of complex natural products.[1] They have also been extensively applied to the preparation of chiral organic materials.[2] The wide-ranging and important applications of such compounds in organic synthesis have stimulated great interest in developing efficient methods for their preparation.[3] Compared to the well-established resolution of racemic binaphthol for the preparation of optically pure BINOL,[3a±f] catalytic asymmetric preparation of chiral binaphthols has developed much more slowly. The discovery of efficient catalysts for the highly enantioselective formation of optically active binaphthol and its derivatives is an attractive target. The oxidative coupling of 2-naphthols in the presence of a catalytic amount of a copper complex of a chiral amine has provided several promising results, but high enantioselectivity has been achieved only for the coupling of 3carboalkoxyl-2-naphthols (93% ee).[4] A photo-activated chiral [RuII(salen)(NO)] complex catalyzes the aerobic oxidative coupling of 2-naphthols with 33±71% ee.[5] Chen et al. and Uang et al. independently designed similar oxovanadium(iv) complexes of chiral Schiff bases for the asymmetric oxidative coupling of 2-naphthols with moderate enantioselectivities of up to 62% ee.[6] We developed the catalyst (R,S)-1c for the oxidative coupling of 2-naphthol with high enantioselectivity, and found that the chiral centers on the amino acid part and the axially chiral binaphthyl unit are both crucial to stereocontrol by the catalyst.[7] However, a drawback is that the chiral oxovanadium complex must be prepared from an optically pure 3,3’diformyl-2,2’-dihydroxy-1,1’-binaphthol and (S)-amino acid. The catalyst is only highly enantioselective when the two COMMUNICATIONS

ChemInform Abstract: The Rational Design of Novel Chiral Oxovanadium(IV) Complexes for Highly Enantioselective Oxidative Coupling of 2‐Naphthols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The rational design of novel chiral oxovanadium(IV) complexes for highly enantioselective oxidative coupling of 2-naphthols.

Several novel chiral oxovanadium(IV) complexes have been designed and prepared for the asymmetric catalytic oxidative coupling of 2-naphthols with high enantioselectivities of 83-98% ee.

Enantioselective Radical Cross-Coupling Reactions of Silyl Enol Ethers Using Chiral Oxovanadium

Abstract Asymmetric induction was observed in radical cross-coupling reactions of silyl enol ethers using chiral oxovanadium generated in situ from 8-phenylmenthol and vanadium oxytrichloride in the presence of MS4A (molecular sieves-4A).

ChemInform Abstract: Chiral Oxovanadium Complex Catalyzed Enantioselective Oxidative Coupling of 2‐Naphthols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Catalytic Asymmetric Coupling of 2-Naphthols by Chiral Tridentate Oxovanadium(IV) Complexes

A series of chiral oxovanadium(IV) complexes derived from tridentate N-3,5-substituted and N-3,4-benzo- and N-5,6-benzo-salicylidene-alpha-amino acids can serve as efficient catalysts for the enantioselective oxidative couplings of various 3-, 6-, and 7-substituted 2-naphthols under O(2). The best scenario involves the use of a vanadyl complex arising from 2-hydroxy-1-naphthaldehyde and valine (or phenylalanine) in CCl(4), leading to BINOLs in good yields (75-100%) and with enantioselectivities of up to 68%.

Chiral oxovanadium complex catalyzed enantioselective oxidative coupling of 2-naphthols

The enantioselective oxidative coupling of 2-naphthols using 2 mol% chiral oxovanadium complex under mild conditions afforded chiral BINOLs in moderate enantioselectivity.

Dielectric study of the tilted columnar mesophase in three new chiral metallorganic discotic mesogens

Chiral oxovanadium(IV), copper(II) and palladium(II) beta-diketonates show a room temperature tilted columnar mesophase (rectangular P21). The dielectric response of these compounds was measured in the frequency range 10-2-109Hz. Three different relaxation processes have been observed in the columnar phase. One of them is only present in this mesophase and we suggest that it is a Goldstone-like mode, similar to the one present in the helical SmC* phases. In our case the presence of the helix was confirmed by circular dichroism studies.

Switchable Columnar Metallomesogens. New Helical Self-Assembling Systems

Chiral oxovanadium(IV), copper(II), and palladium(II) ‚-diketonates show a room-temperature columnar mesophase which undergoes ferroelectric switching. All the compounds were obtained as liquid crystals at room temperature, and crystallization or melting processes were not detected by differential scanning calorimetry carried out to -20 °C. The mesophase was investigated by optical microscopy, DSC and X-ray diffraction, and identified as a rectangular columnar ( P21). The flowerlike texture observed for all the compounds led us to deduce a high tilt angle (ca. 40°) of the molecules with respect to the column axis. Circular dichroism has confirmed the existence of a helical arrangement within the column. This result is in accordance with the so-called columnar mode found at low frequencies (ca. 10 -3 Hz) in dielectric spectroscopy studies. The electrooptical response of these materials has been examined by means of a photomultiplier. The results obtained can be explained by considering a strong influence of the high tilt angle found in the mesophase.