Synthesis of pyrazoles via CuI-mediated electrophilic cyclizations of α,β-alkynic hydrazones

Synthesis of pyrazoles via electrophilic cyclization of α,β-alkynic hydrazones by copper(I) iodide is described. When treated with copper(I) iodide in the presence of triethylamine in refluxing acetonitrile, α,β-alkynic hydrazones, prepared readily from hydrazines and propargyl aldehydes and ketones, undergo electrophilic cyclization to afford pyrazole derivatives in good to excellent yields. The reaction appears to be general for a variety of α,β-alkynic hydrazones and tolerates the presence of aliphatic, aromatic, and ferrocenyl moieties with electron-withdrawing and electron-donating substituents.     

Synthesis of β-tosylethylhydrazine and its use in preparation of N-protected pyrazoles and 5-aminopyrazoles

β-Tosylethylhydrazine (6) can be prepared efficiently in one step from commercially available p-tolyl vinyl sulfone (7) and hydrazine hydrate. This hydrazine reacts with both 1,3-diketones and conjugated ynones in glacial acetic acid to provide a variety of N-tosylethyl-protected (TSE) pyrazoles in good yields. The TSE group can be removed from the pyrazoles using potassium t-butoxide in THF at −30 °C-rt. In addition, hydrazine 6 condenses with β-ketonitriles and β-aminoacrylonitriles to afford 5-aminopyrazoles, which can be deprotected by brief treatment with NaOEt in EtOH/DMSO at 45 °C.     

Synthesis of BR2 complexes of α-pyrrolyl dipyrrins

A series of BR₂ complexes of α-pyrrolyl dipyrrin were synthesized from BF₂ complex of α-pyrrolyl dipyrrin (3-pyrrolyl BODIPY) by treating it with various alkyl- and aryl magnesium halides under mild Grignard reaction conditions. The BR₂ complexes were functionalized at α-position of the appended pyrrole ring with formyl, chloro and bromo functional groups and these functionalized BR₂ complexes were used further to prepare various novel derivatives of BR₂ complexes. The BR₂ complexes were characterized by HR mass, NMR, absorption, fluorescence, and electrochemical techniques. Two of the BR₂ complexes were structurally characterized by X-ray crystallography. Our studies revealed that the substitution of fluorine atoms at the boron center of 3-pyrrolyl BODIPYs with different alkyl/aryl groups significantly alters their structural, spectral and electrochemical properties. The DFT studies also support the alteration of the electronic properties of the BR₂ complexes.     

Solubility characteristics ofβ-cyclodextrin inclusion complexes

Some inclusion complexes of-cyclodextrin (cyclomaltoheptaose) have been investigated, particularly with respect to their solubility. The mathematical characterization of the equilibrated host-guest system containing both solid and solution phases is discussed (first of all those, which contain 1:1 or 1:1 + 2:1 species) and demonstrated by different examples.     

Comprehensive studies of Tolperisone·HCl-cyclodextrin complexes

Solid inclusion complexes of TolperisoneHCl with five various cyclodextrins were prepared by kneading and spray drying. The complex formation between the drug and the cyclodextrins were proven using thermoanalytical methods, X-ray diffraction, IR spectroscopy. The results of the solid state investigations were supported by the liquid phase investigations, such solubility and parition constant measurements and stability constant determination. Among all cyclodextrins used the - and -CD-s were found to be the best complexing agents.     

Inclusion complexes of alcohols with α-cyclodextrin

Calorimetric studies of the inclusion complexes of straight and branched alcohols and of diols with alpha-cyclodextrin (-CD) have been carried out in water solvent. The data suggest that straight and branched chain alcohols enter the cavity of -CD alkyl end first. The hydroxyl group hydrogen bonds to the outer oxygen ring of the cyclodextrin. For branched chain alcohols the longer alkyl part of the molecule penetrates the -CD cavity up to the hydroxyl group. Diols form two hydrogen bonds to the outer oxygen ring of the cyclodextrin with some penetration into its interior.     

Iron-catalyzed aminolysis of β-carbonyl 1,3-dithianes: synthesis of stereodefined β-enaminones and 3,4-disubstituted pyrazoles

A novel iron-catalyzed aminolysis of β-carbonyl 1,3-dithianes with various amines including ammonia, primary and secondary amines, as well as hydrazine hydrate has been developed, leading to the synthesis of stereodefined β-enaminones and 3,4-disubstituted pyrazoles in good to high yields.     

Facile one-pot synthesis of 5-substituted isoxazoles and pyrazoles through microwave-promoted intramolecular cyclization of γ-hydroxyalkynal oximes and hydrazones

Simple and efficient one-pot synthesis of 5-substituted isoxazoles and pyrazoles has been developed. The formation of the target isoxazoles and pyrazoles is initiated by 1,2-nucleophilic addition of generated in situ hydroxylamine or hydrazine to α-acetylenic γ-hydroxyaldehydes with further intramolecular cyclization of the adducts. The protocols are associated with readily available substrates, simple procedure, short reaction time, and moderate to high yields.     

Inclusion complexes of β-cyclodextrin with dihydroxyphenols of various nature

The ways for the practical preparation of stable inclusion complexes of β-cyclodextrin with dihydroxyphenols of various nature are developed. Mutual orientation of hydroxy groups and the nature of the bridge in the bisphenols are shown to affect considerably their ability to the complex formation.     

Molecular complexes of quinones: I. π-π complexes of p-chloranil with benzene and its derivatives

The relation between the position of the charge transfer band of molecular complexes formed by p-chloranil with benzene derivatives and ionization potentials of the donor molecule was analyzed. Electronic absorption spectra of p-chloranil complexes with donor molecules possessing degenerate molecular orbitals were examined. Unlike complexes with other acceptors, such as 1,3,5-trinitrobenzene and 1,3-dinitrobenzenea, molecular complexes of p-chloranil with analogous donors were classed within a single group.     

synthesis and properties of β-brominated metal complexes of meso-triphenylcorrole

Spectral properties and chemical stability of Mn(III), Mn(IV), Fe(III), Fe(IV), and Cu(III) complexes of β-octabromotriphenylcorrole [(β-Br)₈(ms-Ph)₃Cor], synthesized from β-unsubstituted compounds by their reaction with molecular bromine, were studied. Cyclic voltammetry, electron microscopy, and X-ray spectral microanalysis were used to obtain electrochemical characteristics of metal corroles M(β-Br)₈(ms-Ph)₃Cor and gain insight into the surface texture of active catalysts on the basis of metal corroles. The electron-acceptor β-bromine substitution in the MCor macrocycle shifts the equilibrium in electron-donor solvents to lower oxidation states of the metals and also stabilizes manganese and destabilizes copper complexes in the protondonor medium HOAc-H₂SO₄. The electrocatalytic activity of the complexes in the reduction of molecular oxygen depends on the nature of the ligand and increases in the order Mn ≤ Cu ? Fe in the case of β-octabrominated macrocycles. The character of distribution of active centers on the surface of the catalysts was established for the first time.     

Microwave-assisted synthesis of novel cyclodextrin–cucurbituril complexes

Microwave irradiation was successfully used in order to obtain stable supramolecular aggregates between cyclodextrins and cucurbiturils, without the participation of any long-chain common ‘molecular thread’ guest. These aggregates were characterised by means of various different techniques, namely NMR, thermogravimetry, polarimetry and ESI-MS. Cross-analysis of experimental data allowed us to obtain insights on the stoichiometries of the composites and their thermal stabilities. The possible structures of the composites are briefly discussed, as well as the actual nature of their intrinsic stability.     

Structure and properties of polymeric ethyne-hexacarbonyldicobalt π complexes

A polymeric ethyne-hexacarbonyldicobalt π complex was prepared by the reaction of poly-p-diethynylbenzene with Co₂(CO)₈. The conformations in which the polymer chains can exist and the conformations in which the ?C≡CH and-Ph-groups can form π complexes with Co₂(CO)₈ were revealed by analysis of Stuart-Briegleb molecular models. The IR spectra of the polymeric complexes were analyzed, and their thermal degradation in air was examined.     

Atomic force microscopy observation of the condensates of the spermidine-DNA complexes

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Resolution of β-aminophosphines with chiral cyclopalladated complexes

Resolution of the racemic chiral β-aminophosphines Ph₂PCH₂CH(Ph)NH(Ar) (L¹ for Ar = C₆H₅ and L² for Ar = 2,6-C₆H₃ⁱPr₂) has been investigated by use of different cyclopalladated complexes as chiral agents. The resulting complexes afford diastereomeric adducts in a 1:1 ratio. After successive crystallizations from ethanol, a d.e. of 98% was achieved for one aminophosphine palladium complex, while no significant d.e. was obtained after crystallizations from chlorinated solvents. The X-ray structure analysis has pointed out intermolecular hydrogen interactions N-H?Cl between the P,N ligand and the chloride ion, which are responsible for the formation and stabilization of the diastereomeric adducts. Thus, the use of oxygenated solvents cancels such hydrogen interactions by their stronger donor character and makes the diastereomers separation possible, allowing to isolate the optically pure (R)-Ph₂PCH₂CH(Ph)NH(Ph) L¹ of which the absolute configuration has been determined from the X-ray structure analysis of the related palladium dichloride complex.     

Modeling and conformation analysis of β-cyclodextrin complexes

Summary A series of -cyclodextrin complexes containing various guest molecules was studied using computer-aided molecular modeling and conformation analysis techniques. The geometry of each complex was studied using crystallographic data. The positions of the glycosidic O4 atoms indicate that the -cyclodextrin molecules are elliptically distorted. This distortion can be related to the van der Waals volume of the guest molecules. This correlation is different for aromatic and non-aromatic guest compounds. Rigid body docking experiments demonstrated that in crystal structures the guest molecule occupies a position in the cavity of nearly minimum interaction energy when there are no other molecules having interactions with the guest molecule. From the crystallographic data several rules could be deduced which seem to determine the conformation of -cyclodextrin molecules in complexes. A procedure was developed to construct -cyclodextrin molecules that are able to encompass guest molecules having a given van der Waals volume.     

Paramagnetic GdIIIFeIII heterobimetallic complexes of DTPA-bis-salicylamide

The reaction between DTPA (diethylenetriaminepenta-acetic acid)-anhydride and p-aminosalicylic acid (PAS) affords a novel ligand, [DTPA(PAS)₂], able to form stable heterobimetallic complexes with Gd³⁺ and Fe³⁺ ions. The lanthanide ion occupies an internal coordination cage formed by three nitrogen atoms, two carboxylate and two carboxoamido groups of the ligand, whereas the outer salicylic moieties form stable chelate rings with Fe^III ions. The stoichiometry of the resulting heterobimetallic complexes, established by measurements of water proton relaxation enhancement, is [(H₂O)-Gd-DTPA(PAS)₂]₂-Fe(H₂O)₂ or [(H₂O)-Gd-DTPA(PAS)₂]₃-Fe depending on the pH of the aqueous solution. The individual contributions to the observed relaxation enhancement from Gd³⁺ and Fe³⁺ paramagnetic ions have been clearly distinguished and analysed.     

Ortho-metallation of η-pyrrolylmetal complexes with triosmium clusters

The cluster [O₃(CO)₁₀(MeCN)₂] reacts with (η-cyclopentadienyl)(η-pyrrolyl)iron [azaferrocene, Fe(C₅H₅)(C₄H₄N) under mild conditions to give the oxidative addition product [Os₃H{(C₄H₃N)Fe(C₅H₅)}(CO)₁₀]. The group (C₄H₃N)Fe(C₅H₅) acts as a three-electron donor through the ortho-metallated pyrrolyl ring. An analogous compounds, [Os₃H{(C₄H₃N)Mn(CO)₃}(CO)₁₀], is obtained by the reaction of [Os₃(CO)₁₀(MeCN)₂] with [Mn(η-pyrrolyl)(CO)₃].     

Exo-H- andendo-H-η4-pentamethylcyclopentadiene complexes of platinum

A mixture ofendo-H andexo-H isomers (1a and1b) of the (⁴-C₅Me₅H)PtCl₂ complex was prepared by the reaction of K₂PtCl₄ with C₅Me₅H in MeOH. The mixture of isomers reacts with CpTl in the presence of TiBF₄ to give a novel complex, [(⁴-C₅Me₅H)Pt(⁵-C₅H₅)]⁺BF₄ ^–, as a mixture ofendo-H- andexo-H-isomers (2a and2b). The data of¹H and¹³C NMR spectroscopy of the resulting complexes are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 514–517, March, 1994.