Hydrofluoroarylation of alkynes with fluoroarenes

A combination of Ni(cod)(2) and PCyp(3) is found to be an effective catalyst for chemoselective activation of the C-H bond of fluoroarenes over C-F bonds followed by insertion of alkynes to allow direct alkenylation of the electron-deficient arenes. The characteristics of the reactions are: a C-H bond ortho to a fluorine substituent is selectively activated; the reactivity of fluorobenzenes is roughly proportional to the number of fluorine atoms. The reaction conditions tolerate a broad range of both alkynes and fluoroarenes containing both electron-withdrawing and -donating groups, thus allowing efficient synthesis of a variety of substituted ethenes containing a fluoroaryl motif in high regio- and stereoselective manners. Mechanistic studies including both labeling experiments and stoichiometric reactions reveal that oxidative addition of C-H bonds in fluoroarenes to nickel(0) is kinetically highly facile whereas that of C-F bonds is thermodynamically favoured.     

Emission spectra of the radical cations of hexa-, penta-, tetra-, and tri-fluorobenzenes

Emission spectra of the radical cations of the title fluorobenzenes were excited in the gaseous phase by electron impact. The spectra, vibrational fine structure discernible and the threshold energy of the emission are discussed in relation to the photoelectron spectra of the fluorobenzenes.     

Hydrodefluorinations by low-valent niobium catalyst

Catalytic hydrodefluorinations of organofluorine compounds by low-valent niobium catalyst were developed. In the presence of niobium(V) chloride (typically, 5 mol%), fluorobenzenes, α,α,α-trifluorotoluenes and (trifluoromethyl)pyridines were hydrodefluorinated with lithium aluminum hydride to give the corresponding benzenes, toluenes and methylpyridines in good yields, respectively.     

Chemoselectivity of cobalt-catalysed carbonylation—A reliable platform for the synthesis of fluorinated benzoic acids

The cobalt-catalysed methoxycarbonylation of polysubstituted bromo,fluoro- and chloro,fluorobenzenes and 1,2,4-trichlorobenzene with emphasis on the chemo- and regio-selectivity of the reaction is described. The structures of isolated products of 1,4-dichloro-2-fluorobenzene carbonylation were determined by single-crystal X-ray diffraction. The fact that the fluorine substituents in the studied compounds remain intact indicates in favor of the anion-radical activation of aryl halides by a cobalt catalyst. For the first time, a universal method of preparation of the various fluorobenzoic acid derivatives from available raw materials with a good yield has been elaborated.     

Reactions of some bromofluorobenzenes with copper(I) benzenethiolate

The reactions of copper(I) benzenethiolate with some bromofluorobenzenes have resulted in the replacement of the bromine by a phenylthio group. Combinations of this method and the reactions of sodium thiolates with fluorobenzenes have enabled various isomeric phenylthio substituted fluorobenzenes C₆H_xF_y(SR)_z to be prepared. The new products have been characterized by elemental analyses, mass, infrared, and fluorine NMR spectroscopy.     

Aromatic polyfluoro-compounds—V The preparation of highly fluorinated benzenes by defluorination of polyfluorocyclohex-anes, -enes, and -dienes

Hexa-, penta- and tetra- fluorobenzenes are formed from appropriate polyfluorocyclohexanes, -enes and -dienes by passage in vapour form over heated iron gauze.     

Ortho effect in fluorobenzenes: cross-correlated relaxation and quantum chemical studies

An early solid-state NMR study of the shielding tensors in substituted fluorobenzenes had indicated the presence of the 'ortho effect'. This was confirmed recently in the liquid state from a study of cross-correlated relaxation, which gives a handle on the shielding tensor. We report here a combined experimental and computational study on substituted fluorobenzenes where the ortho substituent is varied systematically. Experimental measurements of the longitudinal relaxation of 19F indicate the cross-correlation between the chemical shift anisotropy (CSA) of fluorine and its dipolar interaction with the ortho proton, and provide a measure of the CSA orientation parameter. This parameter is obtained also from quantum chemical calculations of the 19F CSA tensor. We establish a correlation between the CSA orientation parameter and linear free energy parameters by resorting to a multi-parameter regression analysis. Excellent correlation is obtained for most of these substituents only when a parameter for the ortho effect is included.     

Statistical-mechanical calculation of the thermodynamic characteristics of the adsorption of fluorobenzenes and fluorotoluene on graphite

Conclusions At low (zero) occupancies, the thermodynamic characteristics for the adsorption of fluorobenzenes and fluorotoluenes may be calculated using the semiempirical statisticalmechanical theory.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 223–224, January, 1986.     

Prediction of vtbrational spectra by the CNDO/2 force method: I. Out-of-plane vibrations of benzene and fluorobenzenes

The out-of-plane force constants of benzene and 12 fluorobenzenes have been calculated by the CNDO/2 force method. Two empirical scaling factors had to be applied to obtain good agreement. The mean deviation between the 88 calculated and experimental frequencies is 16 cm^?1.     

Theoretical investigation of in-plane hydrogen-bonded complexes of ammonia with partially substituted fluorobenzenes

Systematic investigation of in-plane hydrogen-bonded complexes of ammonia with partially substituted fluorobenzenes has revealed that fluorobenzene, difluorobenzene, and trifluorobenzene favor formation of cyclic complexes with a C-H...N-H...F-C binding motif. On the other hand, tetrafluorobenzene and pentafluorobenzene favor formation of linear C-H...N hydrogen-bonded complexes. The complete absence of exclusively linear N-H...F hydrogen-bonded complexes for the entire series indicates that C-F bond in fluorobenzenes is a reluctant hydrogen-bond acceptor. However, fluorine does hydrogen bond when cooperatively stabilized with C-H...N hydrogen bonds for the lower fluoro analogues. The propensity of fluorobenzenes to adapt to the C-H...N-H...F-C binding motif decreases with the progressive fluorination of the benzene ring and disappears completely when benzene ring is substituted with five or more fluorine atoms.     

The additivity of substituent effects upon J(FF) in polysubstituted fluorobenzenes: An update

Substituent effects upon ³J(FF) are demonstrated to be additive, and a previous analysis of ⁴J(FF) and ⁵J(FF) in polysubstituted fluorobenzenes is updated.     

Ab initio evaluation of bond orders and valence numbers in some substituted benzenes

Mayer's definition of bond order and valence number of an atom in a molecule in the ab initio SCF theory have been applied to calculate bond orders and valence numbers using different ab initio methods for some fluorobenzenes. The results have been discussed in the light of Mulliken population analysis. The traditional view that the valency of an atom is directly related to the atomic charge is found to be invalid in the present ab initio calculations.     

Palladium‐Catalyzed Carbonylative Reactions of 1‐Bromo‐2‐fluorobenzenes with Various Nucleophiles: Effective Combination of Carbonylation and Nucleophilic Substitution

A systematic study on the carbonylative transformation of 1‐bromo‐2‐fluorobenzenes with various nucleophiles has been performed. Different types of double nucleophiles, such as N?N, N?C, O?C, and N?S, can be effectively applied as coupling partners. The corresponding six‐membered heterocycles were isolated in moderate to good yields.     

The electronic effect of butadienyliron tricarbonyl substituents

The effect of butadienyliron tricarbonyl substituents on the polarographic oxidation potentials of the ferrocenyl nucleus and the ¹⁹F NMR chemical shifts in m- and p-substituted fluorobenzenes is discussed. The data obtained by different physical methods enable us to conclude that all carbon atoms in the coordinated butadiene are sp² hybridized.     

A QM/MM study of fluoroaromatic interactions at the binding site of carbonic anhydrase II, using a DFT method corrected for dispersive interactions

The interaction of the fluorinated benzyl ring of a series of inhibitors of carbonic anhydrase II (CAII), fluorine-substituted N-(4-sulfamylbenzoyl)benzylamines (SBB), with nearby residues in the active site has been studied using a hybrid QM/MM model. To account for the important dispersive interactions between the fluorinated benzenes and these residues, a density functional method with an empirical dispersive term, (DFT-D), is used as the QM part of the model. The major interactions are found to be between the substituted benzenes and the aromatic ring of a nearby phenylalanine residue. However, the intermolecular separations between these two groups span a greater range than that found for comparable interactions between isolated molecules, showing the importance of interactions with other residues, which have been quantified. A decomposition of the interaction energy between the fluorobenzenes and each residue has been carried out which shows the dispersive interactions to be dominant. This work has shown that a QM(DFT-D)/MM model is a computationally feasible and accurate way of studying substrate-protein interactions.     

A Cu(I)-promoted one-pot ‘SNAr-click reaction’ of fluoronitrobenzenes

A one-pot two-step sequence involving a nucleophilic aromatic substitution (S_NAr) of activated fluorobenzenes with azide nucleophile and in situ Huisgen cycloaddition of the resulting aryl azides with alkynes has been developed for a rapid access to 1,4-substituted triazoles. Control experiments revealed that both the steps are catalyzed by Cu(I) and also the course of reaction as S_NAr followed by [3+2]-cycloaddition.     

Multipolar complexes–II The self association of -NO2 -CN and -COCN polar groups

Fluorine nuclear magnetic resonance (F-NMR) has been used to determine dissociation constants for multipolar complexes formed by several p-substituted fluorobenzenes in CCl₄ and cyclohexane at 25°. Data in CCl₄ were also obtained at ?20°. The results are interpreted in simplified terms as dipole-dipole interactions which lead to a complex of net zero dipole moment. Although the dissociation constants are not of high accuracy, the values obtained do indicate that both polarity and steric effects are important in the presumed multipolar complexes.     

Synthesis of 10‐Aryl‐ and 10‐(Arylmethyl)acridin‐9(10H)‐ones via the Reaction of (2‐Fluorophenyl)(2‐halophenyl)methanones with Benzenamines and Arylmethanamines

The reaction of 1‐fluoro‐2‐lithiobenzenes, generated from 1‐bromo‐2‐fluorobenzenes 1 and BuLi, with 2‐halobenzaldehydes and subsequent oxidation of the resulting alcohols 2 afforded (2‐fluorophenyl)(2‐halophenyl)methanones 3 , which, on treatment with benzenamines or arylmethanamines, followed by NaH, gave rise efficiently to 10‐aryl‐ or 10‐(arylmethyl)acridin‐9(10H)‐ones ( 5 or 7 ), respectively.     

Analysis of perfluoroalkanes and fluorobenzenes using an Al2 O3 porous-layer open-tubular column

Summary Many of the isomers of fluorocarbons have boiling points which are less than one degree different. Thus it is necessary to use some other basis for their separation on a chromatographic column. One such possibility is gas-solid chromatography. It has been demonstrated that an alumina porous-layer open-tubular (PLOT) column is especially well suited for the analysis of fluoroalkanes and fluorobenzenes. This column is useful for the specific application of the measurement of electron attachment properties of these molecules using the electron-capture detector because of thelack of column bleed.     

Reaction of fluorochlorocarbene with cyclopentadiene,indene, and their alkyl derivatives by phase transfer catalysis

Fluorohalocarbene, generated from CHCl₂F using phase transfer catalysis, reacts with indene, cyclopentadiene, and their alkyl derivatives to form 2-fluoronaphthalenes or fluorobenzenes in 9–60% yield. Reactions proceed through formation of unstable fluorochlorocyclopropanes, which rearrange selectively independently of their stereochemical configuration into the corresponding aromatic fluorides with elimination of HCl.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1609–1613, July, 1990.