Acyldesilylation of 5-Trimethylsilyl-2-furancarboxaldehyde

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Reactivity of the tethered alkyl uranium bonds of (η5:κ1-C5Me4SiMe2CH2)2U

Uranium-carbon bond reactivity has been investigated with the bis(tethered silylalkyl) uranium metallocene (η⁵:κ¹-C₅Me₄SiMe₂CH₂)₂U, 1. Tert-butyl nitrile, ^tBuCN, inserts into both of the tethered U-C bonds to produce the bis(tethered ketimide) complex [η⁵:κ¹-C₅Me₄SiMe₂CH₂C(^tBu)N]₂U, 2, which has unusually bent U-N-C bond angles. Carbon dioxide also inserts into both U-C bonds of 1 yielding the bis(tethered carboxylate) (C₅Me₄SiMe₂CH₂CO₂)₂U, 3. Neither PhCCPh nor PhCCH insert into the U-C bonds, but PhCCH cleaves the silylalkyl tethers in 1 to generate (C₅Me₄SiMe₃)^1? ligands in the complex (C₅Me₄SiMe₃)₂U(CCPh)₂, 4.     

Synthesis of (2S)-isopropyl-5-alkynylpyrimidin-2-ones: precursors of β-aminoacids

The efficient palladium-catalyzed Suzuki-Miyaura cross-coupling reaction of (2S)-isopropyl-5-iodo-2,3-dihydro-4(H)-pyrimidin-4-one with, arylethynyl-, heteroarylethynyl-, and alkylethynyltrifluoroborate salts is reported. The standard protocol was evaluated and optimized in order to gain access to suitable precursors of enantiopure 2-substituted β-amino acids. The scope and limitations of this methodology are discussed.     

Application of Ultrasonic Waves: An Improved Synthesis of 5′-Deoxy-5′-cyano-2′,3′-isopropylidene Adenosine

The title compound is prepared in excellent yield by the reaction of sodium cyanide with 1 in the presence of ultrasonic waves.     

Synthesis of 4′-(4‴-benzo-15-crown-5)-methyloxy-2,2′:6′,2″-terpyridine (L) and the crystal structure of its complexes with cobalt(II) and zinc(II): [ML2](ClO4)2 · 3H2O

The synthesis of 4′-(4?-benzo-15-crown-5)-methyloxy-2,2′:6′,2″-terpyridine (L) and is complexes with cobalt(II) and zinc(II) [CoL₂](ClO₄)₂ · 3H₂O (I) and [ZnL₂](ClO₄)₂ · 3H₂O (II) was described. For L and its complexes, the parameters of electronic absorption spectra in acetonitrile were determined and ¹H NMR signals were assigned. The structures of I and II were determined by X-ray crystallography. Compounds I and II are isostructural and consist of complex cations [ML₂]²⁺ (M = Co, Zn), ClO ₄ ^? anions, and crystal water molecules. The M atoms are located in special positions on twofold axes. The M atoms are surrounded by six N atoms of the terpyridine moieties of two organic molecular ligands. The M-N distance for the N(2) atoms of the central rings of the terpyridine moieties in both structures is shorter than for the side rings. The coordination polyhedra of the M atoms can be described as severely distorted octahedra. The major distortion of the octahedra is that the N…N distances in a terpyridine moiety are considerably shorter than those between the atoms of different moieties. The maximal deviation of the terpyridine atoms from the mean-square planes through these atoms is observed for the C(2) atom: 0.103(3) and 0.106(4) Å in I and II, respectively. The Co(1) and Zn(1) atoms are at a distance of, respectively, 0.1682(14) and 0.1415(17) Å from the corresponding planes.     

Studies on Kinetic Properties of Active Oxygen on the Surfaces of V_2O_5/SiO_2, V_2O_5-MoO_3/SiO_2 and V_2O5-P_2O5/SiO_2 Catalysts

Applying the TPD-MS with a high sensitivity of determination, the TPD spectrum of surface oxygen of V2O5/SiO2, V2O5-MoO3/SiO2 and V2O6-P2O5/SiO2 catalysts was obtained. The surface oxygen of these catalysts can be divided into three groups according to the desorption temperature. O2- desorbs mainly from 373K. to 423K, O- from 673K to 873K and O2- at above 873K. The activation energy and frequency factor of all the three kinds of oxygen species were calculated. Based on these results, the mechanism of oxygen desorption and the influence of P2O5 and MoO3 on the properties of oxygen supply of V2O5/SiO2 catalst were investigated. MoO3 and a small amount of P2Os increase the number of supplying oxygen and increase the activity of O- species. A large amount of P2O5 increases the number of supplying oxygen and restrains the activity of O- species.     

Synthesis and physical properties of K4[Fe(C5O5)2(H2O)2](HC5O5)2·4H2O (C5O5(2-) = croconate): a rare example of ferromagnetic coupling via H-bonds

The reaction of the croconate dianion (C(5)O(5))(2-) with a Fe(III) salt has led, unexpectedly, to the formation of the first example of a discrete Fe(II)-croconate complex without additional coligands, K(4)[Fe(C(5)O(5))(2)(H(2)O)(2)](HC(5)O(5))(2)·4H(2)O (1). 1 crystallizes in the monoclinic P2(1)/c space group and presents discrete octahedral Fe(II) complexes coordinated by two chelating C(5)O(5)(2-) anions in the equatorial plane and two trans axial water molecules. The structure can be viewed as formed by alternating layers of trans-diaquabis(croconato)ferrate(II) complexes and layers containing the monoprotonated croconate anions, HC(5)O(5)(-), and noncoordinated water molecules. Both kinds of layers are directly connected through a hydrogen bond between an oxygen atom of the coordinated dianion and the protonated oxygen atom of the noncoordinated croconate monoanion. A H-bond network is also formed between the coordinated water molecule and one oxygen atom of the coordinated croconate. This H-bond can be classified as strong-moderate being the O···O bond distance (2.771(2) ?) typical of moderate H-bonds and the O-H···O bond angle (174(3)°) typical of strong ones. This H-bond interaction leads to a quadratic regular layer where each [Fe(C(5)O(5))(2)(H(2)O)(2)](2-) anion is connected to its four neighbors in the plane through four equivalent H-bonds. From the magnetic point of view, these connections lead to an S = 2 quadratic layer. The magnetic properties of 1 have been reproduced with a 2D square lattice model for S = 2 ions with g = 2.027(2) and J = 4.59(3) cm(-1). This model reproduces quite satisfactorily its magnetic properties but only above the maximum. A better fit is obtained by considering an additional antiferromagnetic weak interlayer coupling constant (j) through a molecular field approximation with g = 2.071(7), J = 2.94(7) cm(-1), and j = -0.045(2) cm(-1) (the Hamiltonian is written as H = -JS(i)S(j)). Although this second model might still be improved since there is also an extra contribution due to the presence of ZFS in the Fe(II) ions, it confirms the presence of weak ferromagnetic Fe-Fe interactions through H-bonds in compound 1 which represents one of the rare examples of ferromagnetic coupling via H-bonds.     

Synthesis and conversions of metallocycles. 9. Synthesis of polycyclic aluminocyclopentanes with the participation of (η5-C5H5)2ZrCl2

The Cp₂ZrCl₂-catalyzed (Cp=⁵-C₅H₅) stereoselective cyclometalation of norbornenes and norbornadienes with AlEt₃ was carried out. It led in one stage to the preparation of polycyclic aluminocyclopentanes (ACP). It was shown that the ACP synthesized can be converted into polycyclic thiophanes under the action of elementary sulfur.For previous communication, see [1].Institute of Chemistry, Bashkir Scientific Center, Ural Branch, Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 386–391, February, 1992.     

2-(5-O-nitro-1,4:3,6-dianhydro-D-glucit-2-yloxy)-5-R-5-nitro-2-oxo-1,3,2-λ5-dioxaphosphorinanes: synthesis and structure

5,5-Disubstituted 1,3,2-dioxaphosphorinanes were synthesized by the reaction of (5-O-nitro-1,4:3,6-dianhydro-D-glucit-2-yl) phosphochloridate with 2-nitro-2-R-propane-1,3-diols in the presence of organic bases. The structure of 5-bromo-5-nitro-2-(5-O-nitro-1,4:3,6-dianhydro-d-glucit-2-yloxy)-2-oxo-1,3,2-λ⁵-dioxaphosphorinane was established by X-ray diffraction.     

Synthesis and evaluation of antiviral activity of 2′-deoxyuridines with 5-methylene-2-thiohydantoin substituents in the 5-position

Summary 1-(2-Deoxy-3,5-bis-O-(4-methylbenzoyl)-D-erythro-pentofuranosyl)-5-formyluracil (4) was synthesized from 5-formyluracil and an appropriate methyl glycoside and condensed with 2-thiohydantoin (5a) and its corresponding 3-phenyl derivative5b to give 5-[1-(2-deoxy-3,5-bis-O-(4-methylbenzoyl)-D-erythro-pentofuranosyl)uracil-5-ylmethylene]-2-thiohydantoins7a and7b, respectively, in 65–70% yield. They were deprotected with sodium methoxide in methanol to give both anomers of the free nucleosides. In a different route 5-formyluracil (1) was condensed with5b and subsequently with an appropriate methyl glycoside to give7b.On leave from Chemistry Department, Faculties of Science and Education, Tanta University, Tanta, Egypt     

Low Temperature Sol-Gel Preparation of β-Al2TiO5 Thin Films: Spectroscopic Analysis of the Precursors

Two sol-gel syntheses allowed the preparation of -Al₂TiO₅ thin films on silicon substrates at 700°C, reacting aluminum and titanium alkoxides with and without acetylacetone as a chelating agent. Nuclear magnetic resonance (NMR) and mass spectra of the sols allowed identification of the intermediate species formed and to show the formation of an Al-Ti containing polymer establishing that the synthesis without acetylacetone leads to the most extensive polymerization. The formation of -Al₂TiO₅ at low temperatures is attributed to diffusion-limited crystallization process, which takes place in the conditions of high homogeneity at molecular level reached in the sol-gel synthesis. The crystallization of the films was studied as a function of the firing time and temperature and confirmed that -Al₂TiO₅ with better thermal stability was obtained with the synthesis without chelating agent.     

Application of electron-transfer chain catalysis: preparation of bridged 〚{(η5-C5H5)Fe(CO)2}2(μ-diphosphine)2+〛 complexes without chelated 〚(η5-C5H5)Fe(CO)(η2-diphosphine)+〛 byproducts

The ligand substitution by diphosphine L–L on (η⁵-C₅H₅)Fe(CO)₂I usually results in the chelated 〚(η⁵-C₅H₅)Fe(CO)(η²-L–L)⁺〛〚I^–〛 product exclusively. One could suppress the chelated complexes and selectively prepare the bridged 〚{(η⁵-C₅H₅)Fe(CO)₂}₂(μ-L–L)²⁺〛 complexes by application of the electron-transfer chain catalysis with a chemical initiation. Introducing a catalytic amount of reductant at low temperature to the mixture of 2:1 (η⁵-C₅H₅)Fe(CO)₂I/L–L in THF selectively produces the bridged complexes in 78–93% isolated yields where L–L is Ph₂P(CH₂)_nPPh₂, n = 1–4, or (η⁵-C₅H₄PPh₂)₂Fe.     

Base Stabilized σ-Borane Complex of Group 5 Metals: Synthesis and Structure of [(η5-C5Me5)Ta(H3BNC5H4) (C5H4NS)(η2-S2)]

Azametallacyclopropane-containing base stabilized borane complexes of group 5 transition metals have been synthesized and their structural aspects have been described. Treatment of Cp* based Ta and Nb chlorides, Cp*TaCl₄ and Cp*NbCl₄ with [LiBH₄ ⋅ THF] followed by addition of ligands, such as 2-mercaptobenzothiazole, MBT, (C₇H₅NS₂) and 2-mercaptobenzoxazole, MBO (C₇H₅NSO) led to the formation of complexes [Cp*M-[BHS(CH₂ENC₆H₄)(C₇H₄NSE)] ( 1 : M=Ta, E=S; 2 ; M=Nb, E=S; 3 : M=Ta, E=O; 4 ; M=Nb, E=O, Cp*=pentamethyl-η⁵-cyclopentadienyl). By means of UV-vis absorption spectra, the electronic properties of these complexes associated with central metal atoms and heteroatoms (S or O) have been evaluated. In contrast, treatment of Cp*TaCl₄ with 2-mercaptopyridine, MP, (C₅H₅NS) under the same reaction conditions yielded the agostic σ-borane Ta complex, [Cp*Ta(H₃BNC₅H₄) (C5H₄NS)(η²-S₂)], 5 . Unlike 1 – 4 , where the metals interact with boron through bridging sulphur, 5 shows a notable σ-B−H bond interaction with Ta. All spectroscopic data of 1 – 5 along with the X-ray diffraction studies suggest complexes 2 , 4 , and 5 are base (amine) stabilized borane species. Computational studies based on Density Functional Theory (DFT) also supported this conclusion.     

Synthesis,characterization, and crystal structure of 2′,2″-dihydroxy-3,3‴-bichalcone and its related chalcone–flavanone and biflavanone analogs

The synthesis of 3,3′-diformyl-1,1′-biphenyl 1 and its reaction in basic media with 2′-hydroxyacetophenone and paeonol, respectively, are described. The products, a bichalcone 2, it’s partially cyclized analog, a flavanone–chalcone 3 and the fully cyclized biflavanone 4, are reported as products for the first reaction, while only the chalcone 5 for the second. The crystalline and molecular structure, solved by X-ray diffraction analysis, for compounds 2 and 5 are also presented in this work.     

Synthesis and Structural Characterization of [(η~5-C_5Me_5)_2Mo_2Fe_2S_4Br_2]

1 INTRODUCTION We once reported a CS bond cleavage reaction of (h5-C5Me5)Mo(StBu)3, which led to a Mo(IV) thio/thiolate complex (h5-C5Me5)MoS2(StBu)[1]. This reaction was facilitated by oxidants such as S8, gray selenium, and FeCl3[2]. The reaction with FeCl3 gave rise to a cubane cluster [(h5-C5Me5)2Mo2Fe2S4Cl2], which served as an excellent building block to construct various Mo/Fe/S clusters[2]. In this paper, we report the crystal structure of [(h5-C5Me5)2Mo2Fe…     

Structure of GdMg（BO2）5 Crystal

1 INTRODUCTION With the development of diode-pumped solid-sta- te lasers, the research to find more efficient materials for these lasers is gaining more importance. The luminescent materials host LnMgB5O10 may become potential solid-state laser materials[1, 2]. Nd3 -doped GdMg(BO2)5 as a potential diode-pumped laser crystal has been grown in our lab and characterized by a very strong absorption at near 808 nm and intense emission. Although the previous work repor- ted LaMg(BO2)5 with…     

Reaction of 2-hydroxyethylhydrazine with a trifluoromethyl-β-diketone: Study and structural characterization of a new 5-hydroxy-5-trifluoromethyl-4,5-dihydropyrazole intermediate

The reaction of the β-diketone 4,4,4-trifluoro-1-pyridin-2-yl-butane-1,3-dione and the monosubstituted hydrazine 2-hydroxyethylhydrazine has been investigated. Two products have been identified, 2-(2-hydroxyethyl)-3-pyridin-2-yl-5-trifluoromethyl-4,5-dihydropyrazole (P) and 2-(3-pyridin-2-yl-5-trifluoromethylpyrazol-1-yl)ethanol (L) in proportion 2:8, when the reaction was done at room temperature in ethanol for 15 h. The preparation of P as a pure product was performed in ethanol at 0 °C for 7 h. P has been characterized by ¹H, ¹³C{¹H} and ¹⁹F{¹H} NMR spectroscopy and by other techniques as appropriate.     

2D-QSAR Studies on Phenoxybenzoic Acid Derivatives: A Novel Class of 5a-Reductase Inhibitors

The quantitative structure-activity relationship （QSAR） of 14 phenoxybenzoic acid derivatives was studied by ab initio method at the HF/6-31G level using Guassian03 software. The optimized structures together with some characteristic and electric parameters of the title compounds were obtained; some stereo-parameters were calculated by HyperChem software. Stepwise multiple regression and principal component regression methods are adopted to establish multi-parametric models between biological activity and parameters. The results indicated that the lager Ehomo, M, V and LogP, the smaller Etumo and S, and the higher biological activity. A theoretical direction was provided to synthesize some compounds with high activity.