Addition of Phosphites to N,N-Diferrocenylidene-1,3-phenylenedimethylamine and N,N-Diferrocenylidene-1,3-cyclohexylenedimethylamine: Synthesis of Corresponding Model Bis-Aminophosphonates

The preparation of tetraalkyl 1,3-phenylene-di(methylamino)-di-ferrocenylmethyl-phosph onates (4a–c) and tetraalkyl 1,3-cyclohexylene-di(methylamino)-di-ferrocenylmethylphosph onates (5a–c) by the addition of dialkyl phosphites to N,N-diferrocenylidene-1,3-phenylenedimethylamine 1 and N,N-diferrocenylidene-1,3-cyclohexylenedimethylamine 2 is described. The diastereoselectivity, which was observed in both cases, is consistent with that observed in other cases.     

Potentiometric Liquid Membrane Sensors That Discriminate Linear Homologs and Geometrical/Positional Isomers of Dicarboxylates

Abstract

Potentiometric discrimination of series of linear homologs (4-7), geometrical isomers (8,9), and positional isomers (10-12) of dicarboxylate guests by a liquid membrane sensor containing Iipophiiic macrocyclic polyamine 1 as a sensory element is described. the pH conditions were carefully set so that the potentiometric response to the dianionic forms of the guests could be specifically observed. Whereas only small discrimination was observed for the flexible linear homologs (4-7), marked discrimination was observed, for the geometrical isomers (8,9) and positional isomers (10-12) having rigid structures. the selectivities of the potentiometric response were found to correlate well with the reported selectivities of host-guest complexation in water displayed by macrocyclic polyamines having the structures related to 1.     

The molecular and crystal structures of two diastereomeric 3,4-dihydropyrromethenones

The molecular and crystal structures of the two racemic diastereomeric 3,4-dihydropyrromethenone derivatives1 and2 of configurations (Z) and (E) were determined at 93 K (1, 2) and at room temperature (1). From an analysis of the crystallographically observed temperature coefficients a pseudorotation flexibility of the pyrrolidinone ring in the crystal is deduced. In both compounds a nearly orthogonal arrangement between the two heterocyclic ring systems is observed, which is ascribed to the steric bulk of the substituents in positions 1 and 3 of the pyrrolidinone ring.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet.     

In situ Polypropylene Nanocomposites: Gas‐Phase Polymerization of Propylene in the Presence of Nanofillers using Nanosilica‐Supported‐Zirconocene Catalyst

This work concentrates on using the gas‐phase polymerization technique for the production of highly loaded nanocomposites. Filler loading levels near the vicinity of 40 wt% have been obtained using different nanofillers. Three different in situ Polypropylene (PP) nanocomposites, i.e., Cloisite‐20A filled polypropylene (CFPP), Kaolin filled polypropylene (KFPP) and nanosilica filled polypropylene (SFPP) have been prepared by gas‐phase polymerization. The catalyst used is Nanosilica‐Supported‐Zirconocene. The fillers used are Closite‐20A, Kaolin and nanosilica, respectively. These were pre‐treated with MAO (Methylaluminoxane) to inhibit their deactivating action on the catalyst because of the presence of either acidic or basic groups on their surfaces; in this way MAO acts as a co‐catalyst for the three polymerization reactions being discussed. Significantly higher molecular weight polypropylene was formed with nanosilica as the filler. The melting temperature and enthalpy is also observed to be comparatively higher in this case. However, in the case of other fillers, the molecular weights, as well as melting points, are comparatively lower. With the catalyst used, a mixture of crystalline and amorphous polypropylene was observed to form. Comparatively lesser amounts of crystalline polypropylene are also observed.     

Synthesis and Ion Selectivity of Tetrakis[(N,N-dialkylaminocarbonyl) methoxy]homocalix[4]arenes

An attempted O-alkylation of the flexible macrocycle 1 withN,N-dialkylchloroacetamides in the presence of NaH, K₂CO₃ or Cs₂CO₃ gave only one pure stereoisomer 1,4-alternate-2a–c, while other possible isomers were not observed. In contrast, only an intractable mixture was obtained when Na₂CO₃ was used as base. The structural characterization of these products is discussed. The two-phase solvent extraction data indicated that tetrakis(N,N-dialkylaminocarbonyl) derivatives 2b–c show strong alkali metal cation affinity and the extractabilities are much higher than that for the corresponding calix[4]arene tetraethyl ester 4 and homocalix[4]arene tetraethyl ester 3. High Li⁺ and Na⁺ extractabilities were observed for tetrakis[(N,N-diethylaminocarbonyl) derivative 2b. However, no significant high ion selectivity for alkali metal cations was observed in tetraamide 2b. ¹H-NMR titration of tetraamide 2b with KSCN clearly demonstrates that a 1:1 complex is formed with retention of theoriginal symmetry to be conformationally frozen on the NMR time scale.     

Structures of Mn(II) complexes of bis(2-pyridylmethyl)amine (bpa) and (2-pyridylmethyl)(6-methyl-2-pyridylmethyl)amine (Mebpa): geometric isomerism in the solid state

The crystal structures of [Mn(bpa)₂](ClO₄)₂ (1), [bpa?=?bis(2-pyridylmethyl)amine], and Mn(6-Mebpa)₂(ClO₄)₂ (2), [6-Mebpa?=?(6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amine] have been determined. In 1, two facial [Mn(bpa)₂]²⁺ isomers are observed in the same unit cell, one with C _i (1a) and the other with C₂ (1b) symmetries. In 2, only the isomer with C₂ symmetry is observed. The structure of [Mn(bpa)₂]²⁺ with only C₂ symmetry has been reported previously (Inorg. Chem., 31, 4611 (1992)). The bond length order Mn–N_amine?>?Mn–N_pyridyl, observed in the C₂ and the C _i isomers in the crystals of 1, is the reverse of the order observed in the structure of [Mn(bpa)₂](ClO₄)₂ which contains only the C₂ isomer in the unit cell. The structure of 2 in which only the C₂ isomer is found, also shows the bond length order Mn–N_pyridyl?>?Mn–N_amine. In cyclic voltammetric experiments in acetonitrile solutions, 1 and 2 show irreversible anodic peaks at E _p?=?1.60 and 1.90?V respectively, (vs. Ag/AgCl), assigned to the oxidation of Mn(II) to Mn(III). The substantially higher oxidation potential of 2 is attributable to a higher rearrangement energy in complex 2 due to the steric effect of the methyl substituent.     

A Two Step Synthesis of the Nucleoside Q Precursor 2-Amino-5-cyanopyrrolo[2,3-d]pyrimidin 4-one (PreQo)

PreQ_o (1) is prepared in a 70 % yield by the condensation of chloro(formyl)acetonitrile (2) with 2,6-diaminopyrimidin-4-one (3), and subsequently converted to its amide derivative 5. Isolation of the intermediate 4 in the condensation reaction was also observed giving further insight into the proposed mechanism.     

π-Facial Selectivity in the Cycloaddition of Nitrile Oxides to 5,6-Dideoxy-5-Enofuranoses

Abstract

Benzonitrile oxide and ethoxycarbonylformonitrile oxide cycloadd regiospecifically and diastereoselectively to α-methyl 5,6-dideoxy-2,3-O-isopropylidene-d-lyxo-hex-5-enofuranoside 7 to afford isoxazolines 10 and 11. The π-facial selectivity (ca. 7:1) is comparable with that observed for xylo-alkene 1, and much greater than that for its ribo-isomer 4. The structure of isoxazoline 10a was determined by X-ray crystallography.     

Molecular Recognition by Cesium Tetrabenzo-24-Crown-8

Two crystal structures of cesium tetrabenzo-24-crown-8 complexes are reported. Solvent molecules 4-methylmorpholine (1) and ethylene glycol (2) are observed to coordinate cesium within two clefts created by the cation–crown ether complex. Careful examination of the structures suggests that while both complexes exhibit sterically crowded clefts, the binding of cesium to the crown ether is perturbed only in 2. C—H... hydrogen bonding is observed between the clefts and the included guests. The ethylene glycol complex 2 forms a complex O—H...O hydrogen bond network between free and bound glycol and nitrate.     

Synthesis of Vinyl Sulfones from Aryl Methyl Ketones Under Sonochemical Conditions and Formation of Allyl Sulfones

An efficient synthesis of vinyl sulfones 3a-o from aryl methyl ketones 2 bearing an electron withdrawing group and the phosphonic ester 1 under sonochemical conditions is reported. These compounds are generally obtained as an E/Z mixture. Formation of the allyl sulfones 4 is also observed.     

Deformation Electron-Density Distributions of Tetraazathiapentalenes with Hypervalent S-N Bonds

Abstract

The deformation electron-density distributions of 6a-thia-1,3,4,6-tetraazapentalene derivatives (I, II) and bis(phenylthio)dibenzothiophene (III) were investigated by the X-ray diffraction method. For I and II, a structure around the hypervalent S-N bonds is a trigonal bipyramid with equatorial sp² hybrid of S-C bond and lone-pair electrons and apical polarized S-N bonds. In 111 lone-pair electron densities are observed perpendicular to the thiophene ring and the C-S-C sulfide planes.     

Efficient and Convenient Pyridine Ring-E Formation of the Cytotoxic Marine Alkaloid Ascididemin and Related Analogues.

Conversion of tetracyclic quinone 1 to the cytotoxic pentacyclic alkaloid ascididemin (2) in 80% yield is achieved by reaction with paraformaldehyde and ammonium chloride in refluxing acetic acid. High yielding annelations are aiso observed for the related analogues N-8 deaza ascididemin (3) and kuanoniamine A (4).     

Synthesis and spectroscopic properties of furyl-phenyl-acrylates and naphthofurans and their interaction with ct- DNA

A series of novel substituted derivatives related to furyl-phenyl-acrylates and naphthofurans, was synthesized and characterized by UV/Vis and fluorescence spectroscopy. Acyclic compounds can undergo photochemical dehydrocyclization by visible light irradiation in order to obtain their cyclic derivatives. The interactions of the prepared compounds with calf thymus DNA was investigated by means of electronic absorption and fluorescence spectra. It is intriguing that addition of ct-DNA induced a fluorescence increase of acyclic derivatives, exactly the opposite of the strong fluorescence quenching observed for cyclic derivatives 10 and 12. Compound 11 showed decreasing fluorescence intensity for lower concentrations of ct-DNA, while increasing of fluorescence is observed for high excess of added ct-DNA.     

A Novel Synthesis of 3,4-Discubstituted-1H-pyrazolo[3,4-b]quinolines

A simple and efficient synthesis of pyrazolo[3,4-b] quinolines is described. The synthesis involves reaction of 2-amino-3-cyanoquinoline-4-carboxylates(1) with hydrazine hydrate to give regioselectively only pyrazolo[3,4-b]quinolines (2). No formation of pyridazino quinolines (3) is observed.     

Supramolecular structures of Mn2+, Co2+ and Zn2+ complexes containing 1,3-bis(4-pyridyl)propane and aminosalicylate anion

In this study, the synthesis, spectroscopic properties and crystal structures of three new supramolecular compounds named [Mn₂(bpp)₄(H₂O)₄](AS)₄·H₂O (1), [Co₂(bpp)₄(H₂O)₄](AS)₄·H₂O (2) and [Zn(bpp)(AS)₂] (3), have been described, where bpp is 1,3-bis(4-pyridil)propane and AS^?  is aminosalicylate anion. By analysing the similarities between the X-ray powder diffraction results, it has been observed that compounds 1 and 2 are isomorphous, exhibiting an orthorhombic system with space group Pccn; for compound 3, another orthorhombic system was observed, with space group Aba2, which displays coordination between the Zn²⁺ metal ion and the aminosalicylate anion; this can be considered the first case in the literature involving the direct coordination to the metal ion. The vibrational spectra of compounds 1 and 2 are very similar. In the Raman spectra, the main bands are observed at ca. 1625 and 1020 cm^? 1, referring to the ^? O–C = O and CC/CN stretching modes of AS^?  and bpp ligands, respectively.     

New 1,2,4‐ and 1,3,4‐oxadiazole materials: synthesis,and mesomorphic and luminescence properties

The synthesis and liquid crystalline properties of new series of 1,2,4‐ and 1,3,4‐oxadiazole derivatives (2a–f and 5a–f respectively) are reported. These compounds contain only one terminal flexible alkoxy chain, the other terminal substituent is a protecting benzyl group. All compounds of series 2 exhibit an enantiotropic nematic phase. The homologue with the longest chain (2f) displays an enantiotropic dimorphism smectic A– nematic. None of the compounds of series 5 shows mesomorphism and only crystal–isotropic transitions were observed. The liquid crystalline properties were investigated by differential scanning calorimetry, polarizing optical microscopy and X‐ray measurements. Luminescence properties, in chloroform solution, of 2f and the series 5 compounds were evaluated. Good photoluminescence quantum yields for compounds of series 5 were observed. Compound 2f, incorporating the 1,2,4‐oxadiazole ring shows a very strong reduction in emissive properties.     

The Conformation of Sterically Congested Seven-Membered Rings Containing Tetracoordinate Germanium(IV): A First X-Ray Crystallographic Structure Determination

The X-ray crystallographic analysis of 6,6-dimethyl-2,4,8,10-tetra-tert-octyl-dibenzo[d,f][1,3,2]dioxagermepin, 1 is reported. In the solid-state conformation of 1, the dihedral angle about the C─C sp²-sp ² σ bond connecting the two aryl rings is 50.1°. The observed C₂ symmetry in the solid-state conformation of 1 is consistent with the previously suggested solution conformation.     

Detection of relative dimer and rotamer concentrations of diacetamide in different solvents by FT-IR spectroscopy and DFT calculations

The relative rotamer, dimer and tautomer concentrations of diacetamide have been studied by means of infrared spectroscopy, with the recorded spectra being analyzed employing results from density functional theory calculations. It is observed that the cis–trans monomeric form of diacetamide (1) is found to be the most stable isomer in all studied solvents, with trans–trans diacetamide (2) being found to be 20% of total diacetamide in methanol. While the dimer form of diacetamide (3) is present only in carbontetrachloride (about 34% of the total), its tautomeric forms (4, 5) are not favorable in any of the studied solvents.     

Quinomethides versus unsymmetric hybrids: two variations of non-radicaloid SEM-states in four-electron redox systems of bis-4<Emphasis Type="Italic">H</Emphasis>-imidazoles

A series of bis-4H-imidazoles 1a-h has been synthesized and characterized. Due to the integration of rigid substructures, the first fluorescent 4H-imidazole 1h which possesses the substructure of pyrrolo-pyrrol was obtained. Upon protonation of bis-4H-imidazoles, a bathochromic shift of 100 to almost 200 nm was observed originating from the transformation of merocyanine chromophores into cyanines. All 4H-imidazoles were reduced chemically yielding bridged 1H-imidazoles which immediately reoxidize when exposed to air. Stable quinomethide-like species 3a,b which represent the SEM form in this four-electron redox system are only observed during the reduction of bis-4H-imidazoles 1a,b. Influenced by larger bridging elements in derivatives 1c–1h, the electronic communication between terminal 4H-imidazoles is impaired. Therefore, detection and isolation of neither quinomethide-like nor biradikaloid SEM forms succeeded. Most likely a very fast electron-transfer-step leads to unsymmetric hybrids, consisting of one 1H- and one 4H-imidazole. The new synthesized derivative 1k is not only such a stable hybrid molecule, but also may be an indication for the existence of non-quinoid SEM-forms.