Syntheses of β- and γ-fluorophenyl cis- and trans-α-methylene-γ-butyrolactones

Preparation of a series of cis-γ-fluorophenyl-β-phenyl-α-methylene-γ-butyrolactones is reported via ‘allylboration’ of fluorobenzaldehydes with (E)-methyl 3-phenyl-2-((4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)methyl)acrylate. The corresponding trans-γ-fluorophenyl lactones were prepared either (i) via ‘allylboration’ using the (Z)-reagents or (ii) via an indium triflate-mediated isomerization of the cis-products. The difficulty in isomerizing difluorinated cis-products confirms the probable intermediacy of carbocations. Finally, the synthesis of cis-β-fluorophenyl-γ-phenyl-α-methylene-γ-butyrolactones was achieved via an indium-catalyzed allylation–lactonization of aldehydes with (Z)-2-(bromomethyl)-3-(fluorophenyl)acrylates.     

Structure and conductivity in CeNb3O9-δ

Abstract  

In the search of new materials for solid oxide fuel cells, a study of the structure and electrical conductivity of Mg-doped and nominally pure CeNb₃O_9-δ was undertaken. This material exhibits an orthorhombic crystal structure as determined by Rietveld refinement. Through a combined study of 4-point DC and AC impedance spectroscopy, it was determined that the material presents oxygen ion conductivity, electron conductivity and electron-hole conductivity according to the partial pressure of oxygen and temperature in agreement with a simple defect chemistry model. Finally, some experiments seem to indicate the presence of proton conduction.     

Synthesis of cis- and trans-(±)-3-mercaptoproline and pipecolic acid derivatives via thio-Michael addition

The reactivity of 2,3-dehydroproline and 2,3-dehydropipecolic acid methyl ester derivatives with S-nucleophiles in the thio-Michael addition reaction has been explored. The addition of triphenylmethanethiol and subsequent trityl cleavage led to the corresponding cis- and trans-(±)-3-mercaptoproline and pipecolic acid derivatives in good yields.     

Synthesis of (E)- and (Z)-α,β-difluorourocanic acid

Horner-Emmons fluoroolefination of an aryl aldehyde followed by introduction of a second fluorine via “FBr” addition provides an original approach to the preparation of 1-alkyl-2-aryl-1,2-difluoroethenes. The utility of this procedure is demonstrated by the preparation of (E and Z)-α,β-difluorourocanic acid.     

Kinetics and mechanism of thermal gas-phase elimination of α- and β- (N-arylamino)propanoic acid: experimental and theoretical analysis

2-(N-Phenylamino)propanoic acid 1a and 3-(N-phenylamino)-propanoic acid 2a together with four of their aryl analogues were pyrolysed in the gas-phase. The reactions were homogeneous and free from catalytic and radical pathways. Analysis of the pyrolysate of 1 showed the elimination products to be carbon monoxide, acetaldehyde and aniline, while the pyrolysate of 2 reveals the formation of acrylic acid in addition to aniline. Theoretical study of the pyrolysis of 2 using an ab initio SCF method lend support to a reaction pathway involving a 4-membered cyclic transition state.     

μ-η-s-trans-Butadieneoctacarbonyldiiron(0) - Structural and spectroscopic properties

The crystal structure of [{Fe(CO)₄}₂(μ-η^2:2-s-trans-C₄H₆)] was determined by single-crystal X-ray diffraction at 90 K. The complex is located on a center of symmetry in the triclinic space group P1‾. The central C-C bond of the s-trans-butadiene ligand is slightly longer compared to non-coordinated s-trans-butadiene. The Fe-C_ax bond lengths are slightly longer than d(Fe-C_eq) in agreement with marginally shorter d(C≡O_ax) compared to d(C≡O_eq). In addition, the title complex was characterized by IR and Raman as well as NMR spectroscopy and the data are interpreted by the aid of results of DFT calculations.     

Synthesis of 2α- and 2β-substituted-14-epi-previtamin D3 and their genomic activity

2α- and 2β-Substituted analogs of 14-epi-previtamin D₃ were synthesized and isolated after thermal isomerization of 14-epi-vitamin D₃ triene at 80 °C. The VDR binding affinity and transactivation activity of osteocalcin promoter in HOS cells were tested, and the 2α-methyl-substituted analog was found to have greater genomic activity than 14-epi-previtamin D₃. We found that modification at the C2 position of the seco-steroidal skeleton afforded interesting effects for biological genomic activity for the previtamin D form as well as the natural vitamin D form.     

Luminescence Properties and Analytical Figures of Merits of Benzo(a)Pyrene Guanosine Adduct Adsorbed on α- β- and γ-Cyclodextrin/NaCl,and Trehalose/NaCl Solid Matrices

Abstract

Several cyclodextrin/NaCl and trehalose/NaCl mixtures were investigated as solid matrices for obtaining room-temperature luminescence from a benzo(a)pyrene (B(a)P) guanosine adduct. Room-temperature fluorescence (RTF) and room-temperature phosphorescence (RTP) intensities from the B(a)P-guanosine adduct were compared for different solid matrices. These results showed that 25% trehalose/NaCl, 1% α-cyclodextrin/NaCl, and 1% γ-cyclodextrin/NaCl solid matrices yielded strong fluorescence signals and moderately strong phosphorescence signals at room temperature from the B(a)P-guanosine adduct. In addition, the luminescence properties of pyrene, guanosine, guanosine 3′ -monophosphate free acid and guanosine 3′-monophosphate sodium salt on 1% α-, β-, and γ- cyclodextrin/NaCl solid matrices were obtained.     

N-Heterocyclic carbenes: deducing σ- and π-contributions in Rh-catalyzed hydroboration and Pd-catalyzed coupling reactions

The effect of tuning the electronic properties of N-heterocyclic carbene (NHC) ligands was evaluated in multiple, mechanistically distinct, metal-mediated reactions. Hydroboration and Heck reactions, catalyzed by Rh-NHC and Pd-NHC complexes, respectively, were found to result in yields that were up to ten times lower when π-withdrawing substituents were incorporated into the NHC backbone relative to analogues bearing σ-withdrawing groups.     

Kinetics and thermodynamics of liquid phase isomerization of α- and β-pinene over Pd/C catalyst

The kinetics and thermodynamics of the liquid phase isomerization of an α- and β-pinene mixture on a Pd/C catalyst were studied. The effects of pinene concentration, catalyst particle size, stirring rate, reaction temperature (293–423 K) and hydrogen pressure (0.5–11 bar) on the rate of α- and β-pinene isomerization were investigated. The reaction rate of the α-pinene isomerization has the first order with respect to the α-pinene concentration and 0.5 order with respect to the hydrogen pressure. The thermodynamic parameters of the isomerization (Gibbs energy, reaction enthalpy and reaction entropy) and the equilibrium ratio of pinenes under the conditions studied were determined. The general scheme of the reaction mechanism of α- and β-pinene isomerization over the Pd/C catalyst was proposed.     

Anomeric DNA Strand Displacement with α-D Oligonucleotides as Invaders and Ethidium Bromide as Fluorescence Sensor for Duplexes with α/β-, β/β- and α/α-D Configuration

DNA strand displacement is a technique to exchange one strand of a double stranded DNA by another strand (invader). It is an isothermal, enzyme free method driven by single stranded overhangs (toeholds) and is employed in DNA amplification, mismatch detection and nanotechnology. We discovered that anomeric (α/β) DNA can be used for heterochiral strand displacement. Homochiral DNA in β-D configuration was transformed to heterochiral DNA in α-D/β-D configuration and further to homochiral DNA with both strands in α-D configuration. Single stranded α-D DNA acts as invader. Herein, new anomeric displacement systems with and without toeholds were designed. Due to their resistance against enzymatic degradation, the systems are applicable to living cells. The light-up intercalator ethidium bromide is used as fluorescence sensor to follow the progress of displacement. Anomeric DNA displacement shows benefits over canonical DNA in view of toehold free displacement and simple detection by ethidium bromide.     

Enantioselective synthesis of (2R,3R)- and (2S,3S)-β-hydroxyornithine

An efficient and short synthesis of (2R,3R)- and (2S,3S)-β-hydroxyornithine 1a-b is described using Sharpless asymmetric dihydroxylation and regioselective nucleophilic opening of a cyclic sulfite as the key steps.     

A modular approach to aryl-C-ribonucleosides via the allylic substitution and ring-closing metathesis sequence. a stereocontrolled synthesis of all four α-/β- and D-/L-C-nucleoside stereoisomers

Iridium(I)-catalyzed allylation of the enantiopure monoprotected copper(I) alkoxide, generated from (S)-5a, with the enantiopure allylic carbonates (R)-9a,b has been developed as the key step in a new approach to C-nucleoside analogues. The anomeric center was thus constructed via a stereocontrolled formation of the C-O rather than C-C bond with retention of configuration. The resulting bisallyl ethers 15a,b (≥90% de and >99% ee) were converted into C-ribosides 29a,b via the Ru-catalyzed ring-closing metathesis, followed by a diastereoselective dihydroxylation catalyzed by OsO(4) or RuO(4) and deprotection. Variation of the absolute configuration of the starting segments 5a and 9a,b allowed a stereocontrolled synthesis of all four α/β-D/L-combinations.     

SmI2-induced cyclization of optically active (E)- and (Z)-β-alkoxyvinyl sulfoxides with aldehydes

SmI₂-induced reaction of (E)-β-alkoxyvinyl (R)- and (S)-sulfoxides with aldehydes effected a highly stereoselective intramolecular cyclization to give 2,6-anti-2,3-cis- and 2,6-syn-2,3-trans-tetrahydropyran-3-ols, respectively. The reaction of (Z)-(R)-isomer gave 2,6-syn-2,3-cis-tetrahydropyran-3-ol and a ring-opened product, and that of (Z)-(S)-isomer yielded many products.     

Photochemistry of β-(4-sydnonyl)-o-divinylbenzene: competitive cis-trans isomerization and photolysis

New cis- and trans-3-aryl-4-[2-(2-vinylphenyl)ethenyl]sydnones 2, aryl = phenyl, p-tolyl were prepared and transformed on irradiation in the presence of acrolein to a pyrazoline derivative that aromatized during isolation to trans-1-tolyl-3-[2-(2-vinylphenyl)ethenyl]pyrazole 7 and trans-5-formyl-1-tolyl-3-[2-(2-vinylphenyl)ethenyl]pyrazole 8.     

Synthesis of О-2-(acyl)vinylketoximes and their unusual rearrangements into 2- and 3-acyl-substituted pyrroles

О-2-(Acyl)vinylketoximes (freshly prepared from ketoximes and acylacetylenes in the presence of Ph₃P as catalyst in up to 83% yields) rearrange upon heating (125-150 °C) to give 2- or 3-acylpyrroles, wherein the positions of the acyl substituents do not correspond to known O-vinyloxime rearrangements; the chemo- and regioselectivity of the rearrangements depend on the reaction conditions. The described rearrangement enables syntheses of previously inaccessible substituted 2- or 3-acylpyrroles.     

Experimental and ab initio infrared study of χ-, κ‐ and α-aluminas formed from gibbsite

χ-, κ- and α-alumina phases formed by dehydration of micro-grained gibbsite between 773 and 1573 K are studied using infrared spectroscopy (IR). The structural transitions evidenced by X-ray diffraction (XRD) were interpreted by comparing IR measurements with ab initio simulations (except for the χ form whose complexity does not allow a reliable simulation). For each phase, IR spectrum presents specific bands corresponding to transverse optical (TO) modes of Al-O stretching and bending under 900 cm⁻¹. The very complex χ phase, obtained at 773 K, provides a distinctive XRD pattern in contrast with the IR absorbance appearing as a broad structure extending between 200 and 900 cm⁻¹ resembling the equivalent spectra for γ-alumina phase. κ-alumina is forming at 1173 K and its rich IR spectrum is in good qualitative agreement with ab initio simulations. This complexity reflects the large number of atoms in the κ-alumina unit cell and the wide range of internuclear distances as well as the various coordinances of both Al and O atoms. Ab initio simulations suggest that this form of transition alumina demonstrates a strong departure from the simple pattern observed for other transition alumina. At 1573 K, the stable α-Αl₂Ο₃ develops. Its IR spectra extends in a narrower energy range as compared to transition alumina and presents characteristics features similar to model α-Αl₂Ο₃⋅ Ab initio calculations show again a very good general agreement with the observed IR spectra for this phase. In addition, for both κ- and α-Αl₂Ο₃, extra modes, measured at high energy (above 790 cm⁻¹ for κ and above 650 cm⁻¹ for α), can originate from either remnant χ-alumina or from surface modes.     

Host compounds (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (TETROL) and (2R,3R)-(−)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) with guests o-, m- and p- toluidine: A comparative investigation

In this work, we have compared the host abilities of closely related compounds (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (TETROL) and (2R,3R)-(?)-2,3-dimethoxy-1,1,4,4-tetraphenylbutane-1,4-diol (DMT) when these were recrystallized from single and mixed toluidine guests. Significant differences in host behaviour and selectivities were revealed and these were explained by means of single crystal diffraction experiments. Thermal analyses were used to determine the relative complex stabilities, and these data correlated exactly with the host selectivity orders for both TETROL and DMT.