Synthesis and Reactivity of Difluoroaromatic Compounds Containing Heterocyclic Central Groups

The reaction of trichloroacetaldehyde with fluorobenzene, followed by a series of transformations, gave 4-fluorobenzil and 4,4'-difluorobenzil which were used in the synthesis of new difluoroaromatic compounds with a heterocyclic central group. The ¹H, ¹³C, and ¹⁹F NMR spectra of the newly synthesized difluoroaromatic compounds were studied. The charge densities on the carbon atoms attached to fluorine were calculated in terms of the PM3 and AM1 semiempirical approximations. A correlation was found between the charge on C(F) and the corresponding ¹³C and ¹⁹F chemical shifts. Using this correlation, the reactivity of difluoroaromatic compounds in nucleophilic substitution reactions was estimated.     

New unsymmetrical difluoroaromatic compounds and estimation of their reactivities in nucleophilic substitution

A series of previously unknown unsymmetrical difluoroaromatic compounds, viz., p-fluorobenzoylphenyl(p-fluorophenyl)-substituted imidazoles, pyrazines, and quinoxalines, were synthesized according to multistep procedures with the use of chloral as the key compound. The reactivities of the resulting difluoroaromatic compounds were estimated based on ¹⁹F and ¹³C NMR spectral data and the results of quantum-chemical calculations. The calculated charge densities on the C_ipso atoms correlate linearly with the experimental chemical shifts in the ¹⁹F and ¹³C NMR spectra. Difluoroaromatic compounds, which are characterized by _F > –110 and _C > 163 and by the charge density on the C_ipso atom higher than 0.08 e, are sufficiently activated to be used for the preparation of high-molecular-weight polyethers.     

Activated bis- and tetrafluoroaromatic compounds containing bis-phenylquinoxaline fragments

New activated bis- and tetrafluoroaromatic compounds containing the bis-phenylquinoxaline fragments, viz., methylene-bis-6(7),6"(7")-{2-(p-fluoro)phenyl-3[4-(p-fluorobenzoyl)phenyl]quinoxalines}, were prepared according to multistep procedures with the use of chloral as the starting compound. The presence of the activating carbonyl groups in the para positions with respect to two fluorine atoms opens up the possibility of the use of these monomers for the synthesis of high-molecular-weight aromatic quinoxaline-containing polyether ketones.     

New activated bisfluoroaromatic compounds

Bis (p-fluorophenylethynyl) derivatives were obtained by the reaction of bisbromoaromatic compounds withp-fluorophenylacetylene in the presence of a Pd catalyst. Subsequent oxidation of these products using an I₂-DMSO system led to new bis(p-fluorophenylglyoxaly)ketones, α-diketones, and heterocyclic compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 810–812, April, 1997.     

Evaluation of the reactivity of new activated difluoroaromatic compounds

To evaluate the reactivity of new difluroroaromatic compounds in nucleophilic substitution, the positive charges on carbon atoms of C−F bonds were calculated using the quantum-chemical semiempirical PM3 method. A correlation between the charges calculated and the chemical shifts in the¹⁹F NMR spectra was established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 623–625, April, 1998.     

New bis-tetraarylcyclopentadienones

Reactions of new bis(α-diketones) with 1,3-diphenylacetone resulted in new bis(tetraarylcyclopentadienones).     

2,5-diphenyl-3,4-bis[p-(phenylethynyl)phenyl]cyclopentadienone and product of its Diels-Alder homocondensation

A new monomer of the ABA type, 2,5-diphenyl-3,4-bis[p-(phenylethynyl)phenyl]-cyclopentadienone, was synthesized. The Diels-Alder homocondensation of the monomer resulted in a highly branched polyphenylene (M _w=160000), readily soluble in organic solvents. The polymer obtained is thermally stable up to 600 °C (in argon atmosphere) and has a glass transition of 280°C. The structure of the monomer and polymer was confirmed by¹H NMR,¹³C NMR, IR Fourier, and Raman Fourier spectroscopy. Max-Planck-Institut für Polymerforschung, Ackermann-Weg, 10, Mainz, Deutschland. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 953–958, May, 1999.     

Novel aromatic tetracarboxylic acid dianhydrides

The Diels-Alder reactions of 4,4′-bis(2,4,5-triphenylcyclopentadienon-3-yl)benzophenone with carboxylic anhydrides containing multiple carbon-carbon bonds afforded novel tetracarboxylic dianhydrides. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1966–1969, October, 1999.     

New Activated Difluoroaromatic Compounds Containing Internal Acetylenic Moieties

New activated difluoroaromatic compounds having an internal acetylenic moiety were synthesized by reaction of trichloroacetaldehyde with fluorobenzene, followed by reaction with iodobenzene and cross coupling with acetylene in the presence of palladium complexes. According to the results of quantum-chemical calculations and ¹⁹F NMR data, the products are highly reactive compounds which can be used for the preparation of high-molecular-weight aromatic polyethers.