One-pot synthesis of fluorinated terphenyls by site-selective Suzuki-Miyaura reactions of 1,4-dibromo-2-fluorobenzene

The Suzuki-Miyaura reaction of 1,4-dibromo-2-fluorobenzene with two equivalents of arylboronic acids gave fluorinated para-terphenyls. The reaction with 1 equiv of arylboronic acid resulted in site-selective formation of biphenyls. The one-pot reaction of 1,4-dibromo-2-fluorobenzene with two different arylboronic acids afforded fluorinated para-terphenyls containing two different terminal aryl groups.     

Electrophilic aromatic fluorination with fluorine: meta-Directed fluorination of anilines

Anilines are mainly or selectively fluorinated in the meta-position with F₂ when dissolved in triflic acid, sometimes in the presence of small quantities of antimony pentafluoride. The regioselectivity is increased when an electron-donating substituent is present at the para-position.     

Novel fluorinated amphiphilic cyclodextrin derivatives: Synthesis of mono-, di- and heptakis-(6-deoxy-6-perfluoroalkylthio)-β-cyclodextrins

A new series of fluorinated amphiphilic β-cyclodextrin derivatives has been synthesized. The strategy is based on the modification of the C-6 position of the mono-6-deoxy-6^A-para-tolylsulfonyl, di-6^A, 6^D-deoxy-6^A, 6^D-(para-tolylsulfonyl) and heptakis-(6-deoxy-6-iodo)-β-cyclodextrin precursors. The synthesis lead to mono-perfluoroalkylthio-, di-perfluoroalkylthio- and heptakis-perfluoroalkylthio-β-cyclodextrin in excellent yields (90-99%).     

An efficient Fe(III)-catalyzed 1,6-conjugate addition of para-quinone methides with fluorinated silyl enol ethers toward β,β-diaryl α-fluorinated ketones

Reported here is a highly efficient 1,6-conjugate addition of fluorinated silyl enol ethers to para-quinone methides, allowing facile access to a range of β,β-diaryl α-fluorinated ketones with good to high yields. Fe(OTf)₃ was identified as the optimal catalyst, with the loading of 3?mol%. Notably, this represent the first 1,6-conjugate addition with fluorinated silyl enol ethers. The synthetic potential of the resulting adducts is also demonstrated.     

Chloro-substituted Hoveyda-Grubbs ruthenium carbene: Investigation of electronic effects

A series of applications of cross and ring-closing metathesis has been made to investigate the application profile of the chloro-substituted Hoveyda-Grubbs ruthenium carbene in order to evaluate electronic effects resulting from the introduction of a chlorine atom para to the isopropoxy moiety of its parent catalyst.     

Fluorous aryl compounds by Matsuda-Heck reaction

Fluorous aryl compounds are obtained through the arylation of different electron-rich and electron-poor olefins with an arenediazonium salt bearing a fully fluorinated octyl-ponytail at the para position. The Matsuda-Heck reactions are catalyzed by Pd(OAc)₂ or 4-hydroxyacetophenone oxime-derived palladacycle as efficient sources of Pd nanoparticles, with loadings of 1 mol % Pd, at room temperature, in methanol and without the need to add external base.     

Regioselective Iodination of Chlorinated Aromatic Compounds Using Silver Salts

The iodination of chlorinated aromatic compounds using Ag₂SO₄/I₂, AgSbF₆/I₂, AgBF₄/I₂, and AgPF₆/I₂ offers access to iodoarenes that are valuable intermediates in organic synthesis. Specifically, iodination of phenols, anisoles, and anilines with a 3,5-dichloro substitution pattern preferentially yielded the ortho, para, and para iodinated product, respectively. In the case of chlorobenzene and 3-chlorotoluene, AgSbF₆/I₂, AgBF₄/I₂, and AgPF₆/I₂, but not Ag₂SO₄/I₂, selectively introduced the iodine in para position to the chlorine substituent.     

Synthesis of chloropolyfluoroarenes from polyfluoroarenethiols and PCl<Subscript>5</Subscript>

Replacement of the thiol group in polyfluoroarenethiols with chlorine was performed by treating with PCl₅ as chlorinating agent. By heating in ampules at 200–220°C polyfluoro- and polyfluorochloroarenethiols with PCl₅ mono- and dichloropolyfluoroarenes and also 1,2,4-trifluorotrichlorobenzene were synthesized. Dichloropolyfluoroarenes contain chlorine atoms in ortho- and para-positions.     

Behavior of 10-(perfluorohexyl)-decanol, a partially fluorinated analog of hexadecanol, at the air-water interface

10-(Perfluorohexyl)-decanol is a partially fluorinated analog of hexadecanol, an important detergent alcohol. With a melting point of T=48.82 °C and a melting enthalpy of ΔH=53.96 J/g, the intermolecular interactions of the fluorinated alcohol are weaker compared to hexadecanol (T=52.67 °C, ΔH=244.41 J/g). The behavior of this fluorinated alcohol at the air-water interface was studied on five different subphases, namely, water, NaCl (150 mM), CaCl₂ (2 mM), HCl (pH=2.0), and urea (0.5 M). Similar to other partially fluorinated amphiphiles, the compression isotherms of the fluorinated alcohol on all subphases are more expanded compared to the hydrocarbon alcohol with a limiting area of 32-36 Å² per molecule and a temperature-dependent phase transition at 5.6-8.2 mN/m (37 °C, compression rate of 10 mm/min). The dependence of the compression isotherms of 10-(perfluorohexyl)-decanol on subphase composition and temperature follows the trends reported for tetra- and hexadecanol. In particular, a shift to smaller molecular areas with increasing temperatures was observed on all five subphases. The shift to smaller molecular areas on urea indicates that in the case of 10-(perfluorohexyl)-decanol the effect is largely due to a loss of material from the air-water interface during compression of the monolayers. However, a squeezing-out of water molecules from the hydration sphere of the polar headgroup may still occur but can not be unambiguously proven.     

Reactions of fluoronitrobenzenes with MTBD strong base in acetonitrile in the presence of water molecules

Products of the reactions between three fluorinated nitrobenzenes (2,3,4,6-tetrafluoronitrobenzene, mNF4; 2,3,4,5-tetrafluoronitrobenzene, oNF4; pentafluoronitro-benzene, NF5) and 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) in the presence of the water molecules in acetonitrile were isolated and identified by analytical and spectroscopic methods. The reaction products included ortho- and para-substituted nitro-compounds. The kinetics of these reactions is independent of the substrates studied. The rate-determining step of these reactions is the hydrolysis of one ring of the MTBD molecule after the fast formation of the Meisenheimer complex. The mechanism of these reactions and the structures of the products are discussed.     

Assessment of the intramolecular C–H⋯X (X=F,Cl, Br) hydrogen bonding of 1,4-diphenyl-1,2,3-triazoles

The intramolecular six-membered C–H?X (X=F, Cl, Br) hydrogen bonding motif of halogen-substituted 1,4-diphenyl-1,2,3-triazole compounds has been assessed. Twelve triazole derivatives have been designed and prepared, which bear fluorine, chlorine or bromine atoms on the ortho- and/or para-positions of the benzene rings. ¹H NMR, X-ray crystallography, and DFT calculation investigations revealed that the ortho-fluorine, chlorine, and bromine atoms of the benzene ring on the C-4 of the triazole unit all can form six-membered C–H?X hydrogen bonding. In contrast, only fluorine forms similar, relatively stable intramolecular hydrogen bonding on the N-1 side of the triazole unit.     

Shape-selective para-chlorination of phenol using sulfuryl chloride with the aid of microporous catalysts

Aluminum-pillared montmorillonite clay, and partially cation-exchanged L type zeolites, efficiently catalyze the selective para-chlorination of phenol using SO₂Cl₂ in 2,2,4-trimethylpentane at 25 °C. A conversion of ∼96%, a para-selectivity of ∼89%, and a para/ortho ratio of 8.0, were achieved with H⁺, Al³⁺, Na⁺, and K⁺-L zeolite. This heterogeneous zeolite-catalyzed process is the first example, which shows a pronounced shape-selectivity in the chlorination of phenol.     

Structure and stability of halogenated polymers: Part 1—Ring-chlorinated polystyrene

Ring-chlorinated polystyrene has been prepared by reaction between polymer and chlorine at −20°C in the presence of iodine, using a 1·2:1 molar ratio of chlorine to styrene units. Although the product has a composition corresponding precisely to 1 Cl atom per styrene unit and the predominant site of chlorination is the para position in the aromatic ring, some ortho chlorination, backbone chlorination and unchlorinated structures have been shown to be present by characterisation spectroscopically and from degradation experiments.The chlorinated polymer loses the backbone chlorine readily as HCl at temperatures from 200°C. The resulting unsaturation in the backbone appears to destabilise the polymer towards chain scission and the main breakdown process, which resembles that of polystyrene in consisting of depolymerisation and transfer reactions, occurs over a wider temperature range and at lower temperatures than the decomposition of polystyrene. Products have been identified and estimated quantitatively.     

Fluorination of aromatic compounds with xenon difluoride in the presence of boron trifluoride etherate

Fluorination of benzene with the XeF₂—BF₃?Et₂O system in acetonitrile at low temperatures affords fluorobenzene in 18% yield, the conversion of benzene being 92%. The rest products are di-, tri-, tetra-, and polyphenyls with different fluorination pattern. Toluene and chloro- and bromobenzenes are fluorinated predominantly at the ortho and para positions. Fluorination of 4-nitroanisole affords 2-fluoro-4-nitroanisole in 73% yield.     

Polymerization of α-olefins promoted by zirconium complexes bearing bis(phenoxy-imine) ligands with ortho-phenoxy halogen substituents

New fluorinated bis(phenoxy-imine)zirconium complexes bearing halogen substituents in the ortho and para positions of the phenolate rings, bis[N-(3,5-dibromosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (1) and bis[N-(3,5-dichlorosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (2) have been synthesized and used as precatalysts in the polymerization of propylene and 1-hexene. Their catalytic behaviour was compared with that of the analogous fluorinated zirconium complexes bearing alkyl groups in the same positions of the phenolate rings to investigate the effects produced by the introduction of additional electron-withdrawing halogen substituents. Complexes 1 and 2 produce stereoirregular, slightly syndiotactic enriched polypropylenes showing enhanced catalytic activities and an improved primary regioselectivity. Both catalysts promote efficiently the oligomerization of 1-hexene to atactic and regioregular oligomers. Interestingly for both the studied monomers it is possible to control the molecular weights and the structures of end groups of the produced polymeric chains by an appropriate choice of the cocatalyst. Functionalization reactions of the unsaturated polymeric chains selectively produced are also reported.     

DFT calculations for the structure and properties of polychlorodibenzo-<Emphasis Type="Italic">para</Emphasis>-dioxine anion-radicals

Calculations for molecules and anion-radicals (ARs) of polychlorodibenzo-para-dioxines (PCDDs) in gas phase have been performed by Becke-Lee-Yang-Parr (B3LYP) hybrid method. The peculiarity of PCDD AR structure consists in the fact that one of C-Cl bonds is approximately by 0.75 Å longer than the other C-Cl bonds and is about 2.6 Å. A symmetric structure of 2,3,7,8-tetrachlorodibenzo-para-dioxine (TCDD) AR is the local minimum on the potential energy surface, which is higher than the absolute minimum by 2.76 kcal/mol. The electron affinity values were computed. PCDDs with one or two chlorine atoms have negative values of the electron affinity, while those with three or more chlorine atoms have positive ones.     

Substituent effects on the stability of copper(II) chelates with some Neville Winter's azo dyes

The effect of substituents on the stability of the complexes formed by reaction of Neville Winter's acid para-substituted azo dyes (p-chloro, methoxy, nitro, and sulfonic) is studied. Log K values for the complexes were determined spectrophotometrically. The p-methoxy and p-chloro chelates exhibited maximum and minimum stabilities, respectively, the methoxy group being electron repelling and chlorine electron withdrawing. Calculations applying Hammett and linear free energy equations indicate that copper in these chelates acts as a π-electron accepter and that such chelates exhibit coplanarity.     

5-Amino-Substituted Derivatives of 4-Nitrofurazane: Synthesis,Structure, and Biological Activity

New amination reactions of 5-chloro-4-nitrobenzofurazane with different amines were studied. The reactions of 5-chloro-4-nitrobenzofurazane with 2,4,6-trichloro-, para-acetyl-, and para-carboxyethylanilines gave the products of aromatic nucleophilic substitution of the chlorine substituent in the nitrogenous heterocycle, the composition and structure of which was established by chemical, physical, and physicochemical methods and X-ray diffraction analysis. The thermal stability was studied by synchronous thermogravimetry and differential scanning calorimetry (TG?DSC). The synthesized compounds showed a high antibacterial and antimycotic activity against human and animal pathogenic microflora.     

Molecular recognition of a self-assembled monolayer of a polydithiocarbamate derivative of β-cyclodextrin on silver

The synthesis and molecular recognition properties of a new sulfur containing β-cyclodextrin (β-CD) derivative chemisorbed on a silver surface are described. Hepta-6-amino-6-deoxy-β-CD was allowed to react with CS₂ in the presence of ammonia to give a mixture of partially substituted dithiocarbamate derivatives with an average degree of substitution of 4.5. A modified silver electrode with this derivative is capable of discriminating between the three positional isomers of nitrobenzoate ion and nitrophenol, as determined by cyclic voltammetry. Only the meta- and para-isomers give a signal corresponding to the reduction of the nitro group. This is attributed to the different orientations of the nitro group with respect to the silver surface after inclusion in the CD cavity. Experiments in the presence of cyclohexanol showed a decrease in signal intensity of the meta- and para-isomers which is associated with the competitive complexation of this guest, suggesting that the electroactive probe is complexed to the cavity.     

Halogenation regioselective en serie aromatique—I: Chloration des phenols et de leurs ethers a l'aide de reactifs mettant en jeu des interactions donneur-accepteur

An efficient regiospecific route for the chlorination of phenol involving hexachlorocyclohexadienones is described. The selectivity is attained by using a reagent tailored in such a way that it is able to participate in charge transfer interactions and hydrogen bonding with the substrate. This recognition between substrate (phenol) and 2, 3, 4, 4, 5, 6-hexachlorocyclohexa 2, 5-dien 1-one 1 which we have called “réactif p” allows the chlorination of phenol in the para position. The use of 2, 3, 4, 5, 6, 6-hexachlorocyclohexa 2,4-dien-1 one 2 we have called “reactif o” permits the chlorination in the ortho position. These two reagents are stable and inexpensive materials, synthetized from pentachlorophenol and chlorine. The chlorination of anisole with these two reagents, gives solely the parachloro derivative, under steric control.