Total synthesis of (±) maoecrystal V

A concise first total synthesis of (±) maoecrystal V (1) is reported. The synthesis features a Wessely oxidative dearomatization of a phenol, an intramolecular Diels-Alder reaction, and a Rh-catalyzed O-H bond insertion as key steps.     

V Centers and Hole-Photostimulated Luminescence of BaFCl Crystal

V centers (hole centers) and hole-photostimulated luminescence of BaFCl crystal are reported for the first time. The absorption bands of V1, V2 and V3 centers are peaking at 205, 238 and 355 nm respectively. V2 center creation by X-irradiation and decay during photostimulated luminescence process are synchronousl with that of F center. This indicates that V centers play the same roles as F centers in X-ray storage and photostimulated luminescence processes.     

Photochemical addition of methanol to V60:Formation of 1,4-dimethoxyfullerene

The addition of methanol to C60 in the presence of acetylglycine (AG) was carried out under irradiation.The novel compound,1,4-dimethoxyl-l,4-dihydrofullerene (1),was isolated and characterized by FTIR,UV-vis,1H and 13C NMR,and FDMS.     

Synthesis of a Phosphoantigen Prodrug that Potently Activates Vγ9Vδ2 T-Lymphocytes

1. Download : Download high-res image (202KB)
2. Download : Download full-size image

     

Role of the V(V)/ 1O2Complex in Oxidative Reactions in the H2O2/V(V)/AcOH System: Oxidation of Alkenes and Anthracenes

Anthracene and its alkyl derivatives undergo oxidation in the V^(V)/H₂O₂/AcOH system via a nonradical mechanism through the intermediate formation of the vanadium(V) complex with singlet dioxygen as a ligand. The ¹O₂molecule is transferred from this complex to an unsaturated substrate. The free singlet dioxygen ¹O₂(¹ _g ) is almost inactive toward anthracene in AcOH solution. Consequently, the vanadium(V) complex with singlet dioxygen is the only oxidant species active in the reaction. The ratio between the rate constant of the reaction of this complex with 2-ethylanthracene and the rate constant of its deactivation is an order of magnitude greater than the ratio between the rate constant of the reaction of dissolved free singlet dioxygen with the same substrate and the rate constant of its deactivation (physical quenching).     

Preparation of Single Crystalline V6O13 Nanobelts

Ultralong beltlike nanostructures was successfully synthesized for V6O13 crystal by a hydrothermal route. The products are characterized by means of X-ray powder diffraction, transmission electron microscopy and high-resolution transmission electron microscopy. The experimental results give the evidence that the V6O13 nanobelts are pure, structurally uniform and single crystalline, with typical widths of 50 to 300 nm and lengths of up to a few millimeters.     

2,2′-dipyridylamine complexes of rhenium(V)

The reactivity of oxorhenium(V) precursors with the potentially N,N-donor ligand 2,2′-dipyridylamine (dpa) has been investigated. Reaction of a two-fold molar excess of dpa with trans-[ReO(OEt)Cl₂(PPh₃)₂] in ethanol led to the isolation of [ReOCl₂(OEt)(dpa)] (1). Spectroscopic measurements indicate that dpa is coordinated as a bidentate in the equatorial plane cis to the oxo group, with the ethoxide in the trans position. Treatment of trans-[ReOCl₃(PPh₃)₂] with a tenfold molar excess of dpa in ethanol at reflux yielded the trans-dioxo complex [ReO₂(dpa)₂]Cl (2), but with a twofold molar excess (μ-O)[{ReOCl₂(dpa)}₂] (3a) was isolated. The latter reaction with (n-Bu₄N)[ReOCl₄] as starting material in ethanol at room temperature led to a dark green product, also with the formulation (μ-O)[{ReOCl₂(dpa)}₂] (3b). These compounds were characterised by common spectroscopic techniques, and the crystal structures of 2·3H₂O, 3a and 3b·2DMSO were determined. The structure of 3b presents a nearly linear O=Re–O–Re=O group, with the two [ReOCl₂(dpa)] halves of the dimer rotated by 180.0° about the Re–O–Re fragment away from an eclipsed conformation. In 3a, the two halves are only rotated by 61.4°.     

First total synthesis of (±)-abyssinoflavanone V

The total synthesis of (±)-abyssinoflavanone V was first achieved through C-prenylation, selective protection of phenolic hydroxyl group, aldol condensation, cyclization and deprotection starting from cheap 4-hydroxybenzaldehyde and 2,4,6-trihydroxyacetophenone, with total yield 24%. All structures of new compounds were confirmed by IR, 1H NMR and MS.     

First total synthesis of （±）-abyssinoflavanone V

The total synthesis of （±）-abyssinoflavanone V was first achieved through C-prenylation, selective protection of phenolic hydroxyl group, aldol condensation, cyclization and deprotection starting from cheap 4-hydroxybenzaldehyde and 2,4,6- trihydroxyacetophenone, with total yield 24%. All structures of new compounds were confirmed by IR, 1^H NMR and MS.     

Study of thermal properties of potassium μ-hydroxo-bis(oxo-diperoxovanadate)(V)

The thermal decomposition of K₃[OH{VO(O₂)₂}₂]·H₂O was studied under dynamic conditions up to 350°C and also isothermally at 150°±3°C in self-generated atmosphere. K₄[V₂O₆(O₂)] is formed as the reaction intermediate. The final products of thermal decomposition of K₃[OH{VO(O₂)₂}₂]·H₂O are KVO₃ and K₄V₂O₇.

---

Zusammenfassung Unter dynamischen Bedingungen bis 350°C und isotherm bei 1503°C in selbsterzeugter Atmosphäre wurde die thermische Zersetzung von K₃[OH{VO(O₂)₂}₂]H₂O untersucht. Als Zwischenprodukt der Reaktion wird K₄[V₂O₆(O₂)] gebildet. Die Endzersetzungsprodukte von K₃[OH{VO(O₂)₂}₂]H₂O sind KVO₃ und K₄V₂O₇.

     

Evaluation of ‘east-to-west’ ether-forming strategies for the total synthesis of maoecrystal V

Model systems that evaluated different approaches to construct the central ether ring of maoecrystal V are described. Our first model systems attempted the ether formation using C–H functionalization reactions, which led to interesting rearrangements but none of the desired ether product. An intramolecular conjugate addition strategy was then explored that successfully formed the targeted C–O bond but resulted in the undesired stereochemistry.     

Cluster and Heterometallic Alkoxide Derivatives of Rhenium and d-Elements of V–VI Groups

The paper represents a listing of results obtained by developing the original methods of controlled synthesis of cluster and mono-, bi- and trimetallic oxo-alkoxide derivatives of rhenium and d-elements of V–VI groups. The developed techniques of the synthesis of metal alkoxides include: (1) anodic dissolution of the metals in the alcohol media; (2) direct reaction of the rhenium (VII) oxide with alkoxide derivatives of the transition elements. By such techniques were obtained: Re₄O₄(OEt)₁₂, Re₄O₆(OⁱPr)₁₀; individual rhenium alkoxocomplexes: Re₄O₂(OMe)₁₆, Re₄O₆(OMe)₁₂, Re₄O_6−y(OMe)_12+y; bimetallic ReMoO₂(OMe)₇, Re_4−xMo_xO_6−y(OMe)_12+y, Re_4−xW_xO_6−y(OMe)_12+y; Nb₂(OMe)₈(ReO₄)₂, Ta₂(OMe)₈(ReO₄)₂, Nb₄O₂(OMe)₁₄(ReO₄)₂, Ta₄O₂(OMe)₁₄(ReO₄)₂, Nb₄O₂(OEt)₁₄(ReO₄)₂, Ta₄O₂(OEt)₁₄(ReO₄)₂, alkoxocomplexes: Nb_2−xTa_x(OMe)₈(ReO₄)₂, Nb_4−xTa_xO₂(OMe)₁₄(ReO₄)₂, Nb_4−xTa_xO₂(OEt)₁₄(ReO₄)₂. All compounds mentioned above are characterized with X-ray single crystal study, IR-spectroscopy, DTG. It has been shown, that thermal decomposition of alkoxide derivatives in inert or hydrogen atmosphere leads to formation nano-size powders of individual rhenium and its alloys at low temperature. Thermal decomposition in air leads to formation individual metal oxides or its solid solutions. It has been demonstrated that the alkoxide derivatives could be promising precursors for next generation catalysts manufacturing.     

Kinetics of the single-electron chemical oxidation of rhenium(V) meso-phenyl-β-octaethylporphyrinate

The states and reactions of rhenium(V) complexes with meso-monophenyl-β-octaethylporphines containing Cl^? and OPh^? as axial ligands O=Re(Cl)MPOEP and O=Re(OPh)MPOEP in concentrated sulfuric acid at 298–348 K are studied via spectral and kinetic methods. While stable along M-N bonds, O=Re(Cl)MPOEP is found to undergo slow oxidation after transforming into axial hydrosulfate complex O=Re(HSO₄)MPOEP. It is shown that the sole electron oxidizing agent is atmospheric oxygen (with the assistance of highly concentrated protons) and the sites of reduction are aromatic ligands. The reaction product was identified as π-radical cation O=Re(HSO₄)MPOEP^·+. Forward and inverse chemical kinetics solutions are used to obtain a full kinetic equation and the reaction rate parameters of elementary steps, and to establish the stoichiometric mechanism of the composite oxidation of the complex. Complex O=Re(OPh)MPOEP in the form O=Re(OPh)(O₂)MPOEP with coordinated oxygen is shown experimentally to be stable with respect to oxidation. The obtained results are important for identifying intermediates in processes catalyzed by stable metal porphyrins.     

Complexes of tetracyanobiimidazole—V. Self-association of Ir(I) complex anions

The self-association of the planar anion [Ir(CO)₂Tcbiim]⁻ where H₂Tcbiim is 4,4′,5,5′-tetracyano-2,2′-biimidazole has been studied in acetontrile solution by analysis of the charge-transfer spectra. At low concentrations (∼ 10⁻⁵ M) monomer units prevail. At intermediate concentrations (∼ 10⁻³ M) dimerization is evident and a very strong (ε = 18 500 M⁻¹ cm⁻¹) new absorption appears at 475 nm. A novel procedure was used to obtain this value and to estimate the equilibrium constant for dimerization, 13.2 M⁻¹ at 24.4°C. From the temperature dependence of the spectra, ΔH is calculated to be −28 to −30 kJ M⁻¹. At higher concentrations (∼ 10⁻² M) spectral changes consistent with further oligomerization are observed.     

Production and properties of polyacenaphthylene—V dilute solution properties

Polyacenaphthylene was synthesized by thermal bulk polymerization, fractionated into 11 fractions by fractional precipitation and characterized by gel permeation chromatography, light scattering and osmometry. Long chain branching was observed in polyacenaphthylenes with $\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{> 1 × 10}{}^6\text{g/mol}$. θ-temperatures of branched and linear polyacenaphthylenes were determined in 1,2-dichloroethane and are different in magnitude. Polyacenaphthylene undergoes chemical degradation in manufacturers' grade 1,2-dichloroethane. Intrinsic viscosities in benzene, toluene, tetrahydrofuran at 25°C, and in 1,2-dichloroethane at 41.1°C have been measured and the Mark-Houwink constants of the viscosity molar mass relationship evaluated.     

Effect of basic additives on properties of V?Sb?Bi oxide catalysts for ammoxidation of xylenes

The introduction of K₂O and Bao additives into supported V–Sb–Bi oxide catalysts enhances their activity in ammoxidation of xylenes. Bond energy and inhomogeneity character of surface oxygen, oxidation states and relative contents of metal cations remain practically unchanged, whereas the concentration of basic sites significantly increases.

---

V–Sb–Bi . , , .

     

51V and 17O NMR studies of the mixed metal polyanions in aqueous V—Mo solutions

NaVO₃Na₂MoO₄ solutions acidified with HCl were studied at the atomic V/Mo ratios equal to 3 : 1, 1 : 1, 1 : 3, 1 : 6 and vanadium concentration [V] = 0.1, 0.04, 0.004 and 0.0004 M in the range pH 7-2. Their ⁵¹V NMR spectra (measured at H_ito = 7 T) were compared with those of VW solutions containing mixed metal complexes of known composition. The VMo₅O₁₉³⁻ (⁵¹V NMR chemical shift relative to VOCl₃, δ, −502 ppm), V₂Mo₄O₁₉⁴⁻ (δ −494), V₂Mo₄O₁₉³⁻ δ −507), V₉MoO₂₈⁵⁻ (δ −422, −492, −501, −512, −521.5) and HV₉MoO₂₈⁴⁻ polyanions (p.a.) have been found to be dominant mixed species in Na-V-Mo solutions. Along with them the V_itxMO_13-itxO^−itx−3₄₀ p.a.(x∼2–3) of the Keggin type (δ −496, −498, −516, −522) are supposed to be formed at pH < 4 in concentrated solutions ([V] > 0.01 M). The V₂Mo₆O₂₆⁶⁻ p.a., isolated at pH ∼ 5 as the sodium salt (solid state δ −482), seem to be present in concentrated Na-V-Mo solutions only as minor species. On dissolving the salt the V₂Mo₆O₂₆⁶⁻ p.a. mainly disproportionates into the complexes mentioned. From solutions containing mainly the V₉MoO₂₈⁵⁻ p.a. the sodium salt of V₁₀O₂₈⁶⁻ is crystallized. The V₉WO₂₈⁶⁻ p.a. are detected in VW solutions at V/W > 1. ¹⁷O and ⁹⁵Mo NMR spectra of some mixed complexes are described. The distribution diagrams for VMo and V-W solutions at [V] = 0.004 M and V/Mo(W) = 1:3, derived from their ⁵¹V NMR spectra, are given.     

Anticancer Drugs (V)─—Synthesis of Etoposide Derivatives

ＡｎｔｉｃａｎｃｅｒＤｒｕｇｓ（Ｖ）─—ＳｙｎｔｈｅｓｉｓｏｆＥｔｏｐｏｓｉｄｅＤｅｒｉｖａｔｉｖｅｓＴＩＡＮＸｕａｎ,ＹＡＮＺｅ－ｑｕｎ,ＬＩＪｉｎ－ｘｉｎａｎｄＣＨＥＮＹａｏ－ｚｕ（ＮａｔｉｏｎａｌＬａｂｏｒａｔｏｒｙｏｆＡｐｐｌｉｅｄＯｒｇａｎ...     

Oxidation of Two α-Hydroxy Acids by Vanadium(V)

The pathways for the oxidation of tartaric acid and citric acid by vanadium(V) in perchloric acid medium have been studied at 303K by following the formation of vanadium(IV) spectrophotometrically at 760nm. The oxidation reaction displays fractional order dependence with respect to both the -hydroxy acids concentrations as well as fractional (tartaric acid) and first order (citric acid) dependencies with respect to the perchloric acid concentration. It does not matter at all whether the ionic strength was varied or was maintained constant. The reaction rate remains essentially constant with increasing ionic strength in the tartaric acid oxidation, but decreases slightly in the citric acid case. A decrease of the dielectric constant of the reaction medium results in a rate decrease in the tartaric acid oxidation and in a rate enhancement in the citric acid reaction. The activation parameters were obtained from studies of the reactions at different temperatures (293 to 313K). Based on the experimentally determined rate laws oxidation mechanisms and theoretical rate laws were proposed.     

Oxidation of Two α-Hydroxy Acids by Vanadium(V)

Summary. The pathways for the oxidation of tartaric acid and citric acid by vanadium(V) in perchloric acid medium have been studied at 303K by following the formation of vanadium(IV) spectrophotometrically at 760nm. The oxidation reaction displays fractional order dependence with respect to both the -hydroxy acids concentrations as well as fractional (tartaric acid) and first order (citric acid) dependencies with respect to the perchloric acid concentration. It does not matter at all whether the ionic strength was varied or was maintained constant. The reaction rate remains essentially constant with increasing ionic strength in the tartaric acid oxidation, but decreases slightly in the citric acid case. A decrease of the dielectric constant of the reaction medium results in a rate decrease in the tartaric acid oxidation and in a rate enhancement in the citric acid reaction. The activation parameters were obtained from studies of the reactions at different temperatures (293 to 313K). Based on the experimentally determined rate laws oxidation mechanisms and theoretical rate laws were proposed.Received April 8, 2003; accepted May 10, 2003 Published online September 18, 2003