Direct versus conjugate addition to a terphenyl substituted alkynyl difluoro silane

Alkynyl difluoro silanes can react with nucleophiles either directly at the silane unit by displacing the fluorine atoms (direct addition) or, in contrast, the nucleophile can attack the β -carbon of the adjacent alkynyl group (conjugate addition). By using this type of conjugate addition a number of fascinating unsaturated silicon and germanium compounds have been prepared in the past using alkyl substituted phenyl groups as substituents. Therefore we wanted to investigate which regioselectivity isobserved in the case of such an alkynyl difluoro silane shielded by a terphenyl substituent (Mes₂C₆H₃-, Mes =2,4,6-trimethylphenyl). Surprisingly, the reaction with phenyl lithium leads exclusively to direct displacement rather than conjugate addition, which we could prove by X-ray crystallography of 5. Moreover, the synthesis, spectroscopic data and crystal structures of important intermediates to the starting alkynyl difluoro terphenyl silane 2 are presented.     

Development of direct fluorination technology for application to materials for lithium battery

Direct fluorination of 1,3-dioxolan-2-one with elemental fluorine was successfully carried out to provide 4-fluoro-1,3-dioxolan-2-one, which was expected as an additive for lithium ion secondary battery. 4-Fluoro-1,3-dioxolan-2-one was also further fluorinated with elemental fluorine to give three isomers of difluoro derivatives by the same methodology. Another topic is the preparation of trifluoromethanesulfonyl fluoride, an intermediate of lithium battery electrolyte, by the reaction of methanesulfonyl fluoride with elemental fluorine. The use of perfluoro-2-methylpentane as a solvent gave satisfactory selectivity of trifluoromethanesulfonyl fluoride.     

Synthesis of new haloderivatives of benzo[<Emphasis Type="Italic">f</Emphasis>]quinoline and 4,7-phenanthroline

By condensations of 2-naphthylamine and 6-aminoquinoline with halogen-substituted benzaldehydes, 3-acetylpyridine and acetophenone derivatives new 1,3-diaryl(heteryl)benzo-[f]quinolines and 4,7-phenanthrolines were synthesized containing atoms of fluorine, bromine, and chlorine in the phenyl rings.     

Oxoketene-oxoketene, imidoylketene-imidoylketene and oxoketenimine-imidoylketene rearrangements. 1,3-Shifts of phenyl groups

Dibenzoylketene 5 undergoes degenerate 1,3-shifts of the phenyl group between acyl and ketene carbon atoms, thus interconverting it with 6 and 7. This 1,3-shift takes place in the gas phase under flash vacuum thermolysis (FVT) conditions, but not in solution at 110-145 degrees C. Imidoyl(benzoyl)ketene 13 undergoes degenerate 1,3-shift of the phenyl group on FVT, thus interconverting it with 14, but the ketenimine isomer 15 is not formed, and none of these shifts take place in the solid state at 250 degrees C. Imidoyl(p-toluoyl)ketene 21 undergoes a 1,3-p-tolyl shift, interconverting it with ketene 22 but not with ketenimine 23. The imidoyl(p-toluoyl)ketene rotamer 25 cyclizes to 4-toluoyloxyquinoline 28 and 4-quinolone 29. The cyclization of imidoyl(benzoyl)ketene 13 to 4-benzoyloxyquinoline 18, and of 25 to 28 involves 1,3-C-to-O shifts of benzoyl (toluoyl) groups. Calculations of the transition states for the transformations at the B3LYP/6-31G** level of theory are in agreement with the observed reaction preferences.     

Carboxyketenes from 4-hydroxy-1,3-oxazin-6-ones and Meldrum's acid derivatives

New 4-hydroxy-1,3-oxazin-6-ones 8 and 16 were prepared from chlorocarbonyl(phenyl)ketene and amides. The flash vacuum thermolysis (FVT) reactions of these compounds and the 4-methoxy derivative 17 were investigated by Ar matrix isolation IR spectroscopy and online mass spectrometry including MS/MS analysis. Carboxy(phenyl)ketene 10 is formed as the major product by thermal fragmentation of 4-hydroxy-1,3-oxazin-6-one 8. This takes place via the unstable 6-hydroxy tautomer 9. Another tautomer, the 5H-isomer 12, leads to the formation of benzoyl isocyanate 13 as a minor product together with phenylketene 14. Carboxy(phenyl)ketene 10 remains detectable at high FVT temperatures but undergoes thermal decarboxylation to phenylketene 14. The same carboxy(phenyl)ketene 10 is also produced in significant amounts by FVT of 5-phenyl-Meldrum's acid 18 via the unstable enol tautomer 19. A small amount of the unsubstituted carboxyketene 20 is observable on FVT of Meldrum's acid 1 itself.     

Synthesis and features of thermolysis of fluorine-containing aromatic 1-hydroxy-1-hydroperoxides and 1,1′-dihydroperoxides

Aromatic fluorine-containing 1-hydroxy-1-hydroperoxides and 1,1′-dihydroxyperoxides were obtained and their thermolysis features were studied. The fluorine atoms incorporation into the aromatic ring of 1-hydroxy-1-hydroperoxides was found to lead to their thermal stability increase. 1,1′-Dihydroxyperoxides are the less thermal stable than 1-hydroxy-1-hydroperoxides. Compared to the fluorine atoms, incorporation of fluoroalkyl groups into the aromatic ring exerts greater effect on the stability of the peroxide.     

An experimental study of 19F-19F and 13C-19F spin-spin coupling in molecules of difluoro(fluorosulfonyl)- and difluoro(fluorosulfonyloxy)acetyl fluorides

High-resolution ¹⁹F and ¹³C NMR spectra of difluoro(fluorosulfonyl)- and difluoro(fluorosulfonyloxy) acetyl fluorides were studied, and specific features of complex spin-spin coupling of fluorine and carbon nuclei were characterized. The mechanisms of ¹⁹F and ¹³C coupling were interpreted.     

Unexpected Pt(II) migration between the calixarene oxygen atoms

Reaction between the 1,3-bis(trimethylsilyl) ether of calix[4]arene and platinum(II) difluoro complexes unexpectedly results in the formation of the 1,2-bridging platinum(II) calixarene complex, which, upon treatment with 2 equiv of acyl chloride, reinstates the 1,3-disubstitution pattern in the calixarene moiety.     

Effect of fluorine substitution on stretching vibrations of the azoxy group in azoxybenzenes

The IR and Raman spectra of azoxybenzene (I) and a number of its fluoroderivatives have been analysed, including the ¹⁵N and ¹⁸O labelled samples and complexes of some azoxybenzenes with SbCl₅. On the basis of the calculated frequencies and forms of normal vibrations of compound (I) in the valence force field, the vibration spectrum has been interpreted. The presence and number of fluorine atoms in the phenyl fragments of azoxybenzenes have practically no effect on the stretching frequencies of the azoxy group but considerably decrease the band intensity of vibrations of the azoxy and phenyl groups in the Raman spectra. Introduction of fluorine into the aromatic rings of azoxybenzenes considerably complicates complex formation with SbCl₅ at oxygen of the azoxy group.     

Five-Membered 2,3-Dioxo Heterocycles: XLV. Thermolysis of 5-Aryl-4-phenyl-2,3-dihydrofuran-2,3-diones in the Absence of Other Partners and in the Presence of Carbonyl Compounds

Aroyl(phenyl)ketenes generated by thermolysis of 5-aryl-4-phenyl-2,3-dihydrofuran-2,3-diones undergo [4+2]-cyclodimerization to 3-aroyl-6-aryl-3,5-diphenyl-3,4-dihydro-2H-pyran-2,4-diones. Heating of the latter leads to rearrangement with formation of 4-aroyloxy-6-aryl-3,5-diphenyl-2H-pyran-2-ones. Thermolysis of 5-aryl-4-phenyl-2,3-dihydrofuran-2,3-diones in the presence of carbonyl compounds yields 6-aryl-5-phenyl-4H-1,3-dioxin-4-ones.     

Five-Membered 2,3-Dioxo Heterocycles: XLVII. Reaction of 5-Aryl-4-phenyl-2,3-dihydrofuran-2,3-diones with Compounds Containing C = N and C≡N Bonds

Thermal decarbonylation of 5-aryl-4-phenyl-2,3-dihydrofuran-2,3-diones gives rise to intermediate aroyl(phenyl)ketenes which react with nonactivated Schiff bases, N,N'-dicyclohexylcarbodiimide, and p-di-methylaminobenzonitrile according to the [4 + 2]-cycloaddition pattern with formation of 6-aryl-5-phenyl-4H-1,3-oxazin-4-ones. Reactions of 5-aryl-4-phenyl-2,3-dihydrofuran-2,3-diones with activated Schiff bases at a temperature below the thermolysis temperature lead to 4-aroyl-4-phenyltetrahydropyrrole-2,3-diones.     

BODIPY Dyes Bearing Multibranched Fluorinated Chains: Synthesis,Structural, and Spectroscopic Studies

A small series of boron-dipyrromethene (BODIPY) dyes, characterized by the presence of multibranched fluorinated residues, were designed and synthesized. The dyes differ in both the position (para-perfluoroalkoxy-substituted phenyl ring or boron functionalization) and number of magnetically equivalent fluorine atoms (27 or 54 fluorine atoms per molecule). Photophysical and crystallographic characterization of the synthesized BODIPYs was carried out to evaluate the effect of the presence of highly fluorinated moieties on the optical and morphological properties of such compounds.     

Die chemie der schweren carben-analogen R2M,M = Si,Ge, Sn: IX. Eigenschaften und thermolyse von neuen 7-silabicyclo[2.2.1]heptadienen

Factors governing the ease and mechanism of 7-silabicyclo[2.2.1]heptadienes thermolysis in order to generate free silylenes and the corresponding benzene derivatives are investigated. For this purpose, 29 new compounds of the types VII–X have been prepared. No indications for a polar mechanism or an intermediate biradical could be found. The degradation is exactly of first order in all cases investigated sofar, and is enhanced by phenyl groups at the bridgehead C atoms, if a conformation coplanar with the basic ring is allowed by the neighbouring substituents, but is not enhanced by phenyl groups at the Si. The X-ray structure of two typical derivatives is discussed with this respect. A special mechanism is operating in the easy thermolysis of carbomethoxy-substituted compounds leading to cyclic sila enolether intermediates.     

A Study of Competitive Coordination of Benzochalcogenazole Ligands by Heteronuclear NMR Spectroscopy

Complexes of 2-methyl(phenyl)benzo-1,3-tellurazole and 2-methyl(phenyl)benzo-1,3-selenazole with tungsten pentacarbonyl and boron trifluoride were studied by heteronuclear NMR spectroscopy (¹H, ¹³C, ⁷⁷Se, and ¹²⁵Te). The coordination mode of the ambident ligand can be determined from the coordination shifts of the ¹²⁵Te and ⁷⁷Se NMR signals: upfield at coordination via Te and Se atoms and downfield at N coordination.     

Electron-impact and thermal fragmentation patterns of some perfluoroalkylene-linked aromatic and heteroaromatic compounds

The pyrolysis of some perfluoroalkylene-linked aromatic and heteroaromatic polymer precursors and a poly(1,3-phenylenehexafluorotrimethylene) has been studied using a combined pyrolysis-gas chromatographic-mass spectrometric method. Whereas the electron-impact induced fragmentations of the polymer precursors are almost exclusively controlled by cleavage β to the aromatic or heteroaromatic ring, thermolysis of these compounds yields products whose formation is consistent with the occurrence of primary cleavage processes that are not confined β to the ring.     

Transition states of strain-promoted metal-free click chemistry: 1,3-dipolar cycloadditions of phenyl azide and cyclooctynes

Density functional theory (B3LYP) calculations on the transition states for the Huisgen 1,3-dipolar cycloadditions of phenyl azide with acetylene, cyclooctyne, and difluorocyclooctyne are reported. The low activation energy of the cyclooctyne "strain-promoted" cycloaddition (DeltaE = 8.0) compared to the strain-free acetylene cycloaddition (DeltaE = 16.2) is due to decreased distortion energy (DeltaEd) of cyclooctyne (DeltaDeltaEd = 4.6) and phenyl azide (DeltaDeltaEd = 4.5) to achieve that cycloaddition transition state. Electronegative fluorine substituents on cyclooctyne further increase the rate of cycloaddition by increasing interaction energies.     

Inapplicability of the Antiperiplanar Lone Pair Hypothesis to C-P Bond Breaking and Formation in Some S-C-P(+) Systems

Both C(2)-P bond breaking and formation in the S-C-P(+) system do not occur according to the antiperiplanar lone pair hypothesis. Experiments using 2-phosphonio derivatives of 5-tert-butyl-1,3-dithiane and cis-4,6-dimethyl-1,3-dithiane are against the participation of higher-energy boat conformers as reactive intermediates. The results obtained support a possibility of conformational adjustment in the course of the reaction. Stereoelectronic control of the C(2)-P bond breaking and formation results from interplay of several factors. The role of the n(S)-sigma(C(2))(-)(P) and sigma(C(4,6))(-)(S)-sigma(C(2))(-)(P) hyperconjugation, as well as of the repulsive interactions between lone electron pairs pi(S) of endocyclic sulfur atoms and pi-electrons of the phenyl ring(s) connected with phosphorus, is discussed.     

Lewis Acid Catalyzed Condensation–Cyclization Cascade: Direct Synthesis of Di/Trifluoromethyl‐1,2,3,4‐tetrahydroquinazolines

Condensed heterocycles such as quinazolines constitute the framework of many promising drugs. The great impact of the dramatic fluorine effect in pharmaceuticals prompted a great surge in the quest for fluorinated drug design resulting in over 20 % fluorine‐containing drugs in the market today. Therefore, finding an efficient and cost‐effective method for the direct synthesis of fluorine‐tagged quinazoline systems is of great significance in the pharmaceutical arena. For the first time, a one‐pot sequential condensation–cyclization reaction to form selectively the difluoro/trifluoromethylated tetrahydroquinazolines from simple components difluoro/trifluoroacetaldehyde hemiacetal and aromatic amines is reported. Our recent studies using difluoro/trifluoroacetaldehyde hemiacetal as simple and elegant difluoro/trifluoromethyl synthons and metal triflates such as gallium triflate as safe and stable Lewis acid catalysts led us to this direct synthesis protocol for the expedient and convenient synthesis of fluorinated quinazolines. DFT calculations at PCM/B3LYP/6‐31++G** were carried out for evaluating a possible reaction mechanism for this cyclization. According to the DFT calculations, product stereochemistry is thermodynamically driven, favoring the cis isomer as the major product, which is also confirmed experimentally.     

9‐Phenyl‐3,4,4a,9a‐tetrahydrotri­ptycene and 9‐phenyl‐1,2,3,4,4a,9a‐hexa­hydro­triptycene

The structure of 9‐phenyl‐3,4,4a,9a‐tetra­hydro­triptycene, C₂₆H₂₂, (I), exhibits regiochemistry consistent with a stepwise mechanism for its formation from photo­cyclo­addition of 1,3‐cyclo­hexa­diene and 9‐phenyl­anthracene. Bond distances involving the bridgehead C atoms are similar in (I) and the hydrogenated derivative, 9‐phenyl‐1,2,3,4,4a,9a‐hexa­hydro­triptycene, C₂₆H₂₄, (II), with bonds to the quaternary‐C atoms exhibiting significant elongation [1.581 (2) Å in (I) and 1.585 (2) Å in (II)]. The molecular geometry precludes significant σ–π overlap between the phenyl groups and the interannular bonds in both compounds, indicating that the origin of the bond lengthening is steric in nature.     

Effect of lateral substitution by fluorine and bromine atoms in ferroelectric liquid crystalline materials containing a 2-alkoxypropanoate unit

Two homologous series of ferroelectric liquid crystalline compounds with 2-alkoxypropanoate chiral unit containing biphenyl benzoate core laterally substituted by fluorine and bromine have been synthesized and studied. All compounds possess the ferroelectric smectic C* phase over a broad temperature range. For bromine-substituted compounds values of spontaneous polarization reach high values up to 250 nC cm^-2. The effects of the lateral substitution on the phenyl ring far from the chiral centre by methyl and methoxy groups, fluorine, chlorine and bromine atoms on mesomorphic properties and on values of the spontaneous polarization are discussed.