The fluorinations of pentafluoronitrobenzene and pentafluorobenzaldehyde by cobalt(III) fluoride

The nitro-group survived in the fluorination of pentafluoronitrobenzene by cobalt(III) fluoride at 135–150°, the major products being undecafluoronitrocyclohexane and nonafluoro-4-nitrocyclohex-1-ene. 2H- Tetrafluoronitrobenzene similarly afforded $\text{cis-}$ and $\text{trans}$-2H-1-nitrodeca- fluorocyclohexane and 5H/4-nitro-octafluorocyclohex-l-ene. Pentafluoro- benzaldehyde was fluorinated to give undecafluorocyclohexanecarbonyl fluoride and nonafluorocyclohex-3-enecarbonyl fluoride. Nonafluoro-4- nitrocyclohex-1-ene was oxidized to 3-nitroheptafluorohexan-1,6-dioic acid, and undecafluoronitrocyclohexane was hydrogenated over a palladium catalyst at low pressure to give decafluorocyclohexanone oxime and 1H-decafluoro- cyclohexanamine, accompanied by 1-aminononafluorocyclohex-1-ene.     

Catalytic ring expansion, contraction, and metathesis-polymerization of cycloalkanes

Tandem dehydrogenation-olefin-metathesis catalyst systems, comprising a pincer-ligated iridium-based alkane dehydrogenation catalyst and a molybdenum-based olefin-metathesis catalyst, are reported to effect the metathesis-cyclooligomerization of cyclooctane and cyclodecane to give cycloalkanes with various carbon numbers, predominantly multiples of the substrate carbon number, and polymers.     

Stretching vibrations of the methylene group and ring strain in the cycloalkanes

A normal coordinate treatment shows that the observed frequency differences for the stretching vibrations of the methylene group in the cycloalkanes are due to force constant changes. The effect of change in geometry on these vibrations is quite small.     

Fluorinations with complex metal fluorides Part 8. Ring rearrangement in the fluorinations of quinoline with caesium tetrafluorocobaltate and with cobalt(III) fluoride

Fluorination of quinoline by caesium tetrafluorocobaltate at ca. 350° afforded mainly a mixture of pentadecafluoro-2-azabicyclo[4,4,0]dec-1(2)- ene (E), and heptadecafluoro-1-azabicyclo[5,3,0]decane (F), arising by skeletal rearrangement. Minor products were six polyfluorocyclohexa[b]- pyridines (G–L) all with carbocyclic rings having the -(CF₂)4 - moiety. Compound F was unreactive, but E was highly susceptible to nucleophiles, e.g. water and methanol. Isoquinoline was fluorinated similarly, but the only new product isolated was tridecafluoro-3-azabicyclo[4,4,0]deca- 1(6)-2-diene (R). The rearrangement occurring with quinoline prompted a re-examination of its fluorination by cobalt(III) fluoride. At ca. 350°, compound F was the major product, with very little E: there were some ring-opened materials, the most important being tetradecafluoro-4-pentafluoroethyl- 2-azaoct-2(Z)-ene (N).     

Detailed kinetic study of the ring opening of cycloalkanes by CBS-QB3 calculations

This work reports a theoretical study of the gas-phase unimolecular decomposition of cyclobutane, cyclopentane and cyclohexane by means of quantum chemical calculations. A biradical mechanism has been envisaged for each cycloalkane, and the main routes for the decomposition of the biradicals formed have been investigated at the CBS-QB3 level of theory. Thermochemical data(DeltaHf(o), S(o), Cp(o)) for all the involved species have been obtained by means of isodesmic reactions. The contribution of hindered rotors has also been included. Activation barriers of each reaction have been analyzed to assess the energetically most favorable pathways for the decomposition of biradicals. Rate constants have been derived for all elementary reactions using transition-state theory at 1 atm and temperatures ranging from 600 to 2000 K. Global rate constant for the decomposition of the cyclic alkanes in molecular products have been calculated. Comparison between calculated and experimental results allowed us to validate the theoretical approach. An important result is that the rotational barriers between the conformers, which are usually neglected, are of importance in decomposition rate of the largest biradicals. Ring strain energies (RSE) in transition states for ring opening have been estimated and show that the main part of RSE contained in the cyclic reactants is removed upon the activation process.     

Aromaticity of ring carbo-mers of [N]annulenes and [N]cycloalkanes

Maps of current density induced by a perpendicular external magnetic field are calculated at the ipsocentric CTOCD-DZ/6-31G**//B3PW91/6-31G** level for ring carbo-mers of [N]-annulenes (closed-shell singlet states of C(3N)H, N = 3 to 7, with q = -1, 0, +1, 0, -1, respectively, and also the triplet ground state for N = 4) and of [N]-cycloalkanes (C(3N)H(qN), N = 3, 4, 5). Strong four-electron diatropic ring currents indicate conventional pi aromaticity for all the singlet and triplet carbo-[N]annulenes studied, with the exception of C(12)H(4), where instead the strong two-electron paratropic ring current is the signature of pi antiaromaticity. The carbo-[N]cycloalkanes (also known as [N]pericyclynes) show only localized pi currents, consistent with non-aromaticity. There is no indication of a 'homo-aromatic' ring current attributable to the in-plane pi orbitals of the inserted C2 units in any of the maps. Consequences for the interpretation of ELF (electron localisation function) populations are discussed.     

The photomediated reaction of alkynes with cycloalkanes

In the presence of a photomediator such as benzophenone, alkynes with electron-withdrawing groups react with cycloalkanes to give vinyl cycloalkanes. The reaction involves the regiospecific addition of a photochemically generated cycloalkyl radical to the beta-carbon of the alkyne. The stereochemical outcome of the reaction depends on the nature of the photomediator and alkyne used.     

Unprecedented directing group ability of cyclophanes in arene fluorinations with diaryliodonium salts

For the first time it is shown that exceptionally electron-rich arene rings can be fluorinated exclusively during the reductive elimination reactions of diaryliodonium fluorides. The 5-methoxy[2.2]paracyclophan-4-yl directing group simultaneously reduces unproductive aryne chemistry and eliminates ligand exchange reactions by a combination of steric and electronic effects. Use of the cyclophane directing group permits an unprecedented degree of control in fluorination reactions of diaryliodonium salts.     

Reactivity of cycloalkanes in hydrogen abstraction with different acceptors

The reactions of some acceptors (^?CH₃, ^?OOH, ^?CCl₃, O₃, and Br^?) with saturated cyclic hydrocarbons, viz., cyclohexane, cycloheptane, and cyclooctane were studied by the DFT methods based on B3LYP and PBE0 functionals, the method based on the double hybrid functional B2PLYP, a combined ONIOM approach (CCSD:B3LYP)) and the coupled-cluster method (CCSD) using the 6-31+G**, aug-cc-pVDZ, Midi-X, and SVP basis sets. A specific feature of these reactions is that their rates depend on the excess ring energy, although no ring opening occurs in all cases.     

Novel ring expansion of cyclopentanones to seven membered rings

By treatment with BF₃/ethyleneglycol, cyclopentanones with the carbonyl function at the C₃-position of α-side chain undergo the ring cleavage to build up the seven membered rings, and this novel ring expansion was applied to the synthesis of bulnesol.     

Synthesis of 1,2-Bis[propargyl(or allyl)oxy]cycloalkanes

Reactions of cyclic olefins with propargyl and allyl alcohols in the presence of crystalline iodine and a catalytic amount of Ag₃PW₁₂O₄₀ afforded in one step trans-1,2-bis[propargyl(allyl)oxy]cycloalkanes.     

Redox mediators of hydrogen sulfide oxidation in reactions with cycloalkanes

An indirect electrochemical method for thiolation of cycloalkanes C₅–C₇ has been suggested. The method is based on a new approach to activation of hydrogen sulfide by redox mediators.     

Rearrangements initiated by trimethylsilyl iodide: the facile ring opening of some cyclobutanone derivatives

The powerful electrophile trimethylsilyl iodide in the presence of certain catalysts rapidly and cleanly initiates the ring opening of a variety of cyclobutanone derivatives in a highly regioselective fashion yielding ultimately β-iodoketones.     

Rearrangements of cyclobutenones. Electrocyclic ring closure and thermal ring expansions of 3-allenyl- and 3-alkynyl-2-dienyl-4,4-dimethoxycyclobutenones

Thermal rearrangements of 2-allenyl- and 2-alkynyl-3-(2-ethenylphenyl)-4,4-dimethoxycyclobutenones were studied. At ambient temperature, the allenyl compounds undergo an electrocyclic cascade to give bicyclo[4.2.0]octadienyl-fused cyclobutenones. These unusual tetracyclic cyclobutenones were shown to be viable synthetic precursors to benzo[a]anthracene-7,12-diones, compounds representing the framework of the angucycline group of naturally occurring antibiotics. In contrast, the 2-alkynylcyclobutenones are stable at ambient temperature but undergo a facile rearrangement at 110 degrees C (toluene) to give the previously unknown naphthalene derivatives, 1,2-dihydro-2,2-dimethoxy-1-(3-alkenylidene)naphtho[2,1-b]furans.     

Bioavailability of fluoride administered as sodium fluoride or monofluorophosphate to humans

A double-bind cross-over study was conducted on four healthy subjects, aged 19-29 years, in order to determine the relative bioavailability and other pharmacokinetics features of fluoride (F) after single oral administration in fasting conditions of 2 mg F as sodium F (NaF) or sodium monofluorophosphate (MFP). The bioavailability was evaluated on the basis of the plasma levels and of the urinary excretion of F. Blood was sampled before and during the 8 h after the administration of the test solutions. For F excretion urine was sampled 12 h before the study and over the 8 h after the administration. Data were tested for statistically significant differences by ANOVA and Tukey's post hoc tests, and also by Student's t-test (p < 0.05). For the two formulations, the pharmacokinetics of F in plasma was characterized by a rapid absorption and by a peak (C_max = 0.1 μg/mL) which was reached 20 min after administration, followed by a biphasic elimination. In the 8 h following the administration the urinary excretion of F accounted for 35-41% of the administered dose, without significant differences between the two formulations. The AUCs (±S.D.) for NaF and MFP were 21.15 (±0.58) and 19.04 (±1.75) min μg mL⁻¹, respectively, and were not significantly different (p = 0.079). Based on the AUC and C_max of F in plasma and on the urinary excretion of F during the 8 h following administration, the relative bioavailabilities of the two F formulations were equivalent.     

Formation of cobaltic complexes by oxidation with potassium peroxymonosulfate in spectrophotometric determination of cobalt

Summary The oxidation of cobaltous complexes of amino-polycarboxylic acids to their corresponding cobaltic complexes with potassium peroxymonosulfate has been studied for simple spectrophotometric determination of 10–100 ppm of cobalt. The color reactions for cobalt are highly selective. Their molar absorptivities (200–300) and reduction potentials (about 0.45 v.) have been determined. The reactions are similar to that with hydrogen peroxide as an oxidant reported previously, but the peroxymonosulfate method has advantages over hydrogen peroxide because of no disturbance of gas bubbles, better stable color reactions, and elimination of ferric ion interference. The use of peroxymonosulfate as an oxidant for cobalt complexes of other ligands is also discussed.

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Herstellung von Kobalt(III)-Komplexen durch Oxydation mit Kaliumperoxymonosulfat zur spektrophotometrischen Bestimmung von Kobalt

Zusammenfassung Die Oxydation von Kobalt(II)komplexen der Aminopolycarbonsäuren mit Kaliumperoxymonosulfat wurde zwecks spektrophotometrischer Bestimmung von 10–100 ppm Kobalt untersucht. Die Farbreaktionen sind sehr selektiv. Ihre molare Extinktion (200–300) und ihr Reduktionspotential (etwa 0,45 V) wurden bestimmt. Gegenüber dem früher verwendeten Wasserstoffperoxid hat das Peroxymonosulfat den Vorteil, daß es keine Gasblasen bildet, daß die Farbreaktionen stabiler sind und daß Fe(III) nicht stört. Seine Verwendung auch für andere Kobaltkomplexe wurde diskutiert.

     

Novel synthesis of monofluorocyclobutanes by the ring expansion- fluorination of cyclopropylmethanols with an amine-metal fluoride pyridinium poly(hydrogen fluoride)-complex

Various new 1-fluoro-1-alkyl(or aryl)-2-substituted cyclobutanes were synthesized stereoselectively from 1-alkyl(or aryl)cyclopropyl carbinols by the ring expansion-fluorination using (ⁱPr)₂-KHF₂-(HF)_n·Py, and 2-hydroxymethyl-1-fluorocyclobutanes were synthesized via a new rearrangement of (1-alkyl(or aryl)cyclopropyl) ethylene oxides.     

Topological indices based on vertex, distance, and ring: on the boiling points of paraffins and cycloalkanes

Vertex, distance, and ring (in cyclic compounds) are three essential structure elements of a molecular graph, based on which three new topological indices VDI, OEI, and RDI are proposed. Multiple regression analysis was carried out against the boiling points of 343 hydrocarbons(160 paraffins and 183 cycloalkanes) with VDI, OEI, RDI, and N(2/3)(N is the number of carbon atoms) together, and a good QSPR model was obtained: ln(577 - Bp) = 6.729609 - 0.154107N(2/3) + 2.285632 x 10(-2)VDI - 7.921410 x 10(-3)OEI - 1.821962 x 10(-2)RDI (F = 6455.09, r = 0.9935, rms = 6.44 degrees C, n = 343).     

Telomerization of vinylidene fluoride with alkyl (or aryl) trifluoromethanethiosulfonates

The photochemical‐induced telomerization of vinylidene fluoride (VDF) with cyclohexyl (or phenyl) trifluoromethanethiosulfonate (CF₃SO₂SR), leading to CF₃(VDF)_nSR telomers, where R stands for cyclohexyl or phenyl, is presented. These sulfurated transfer agents were synthesized by the reaction between sodium triflinate (CF₃SO₂Na) and disulfide in the presence of bromine. ¹⁹F NMR spectroscopy enabled an assessment of the average degrees of telomerization (DP_n) of these telomers with a neat CF₃ end group as the label. These DP_n values increased for higher [VDF]₀/[CF₃SO₂SR]₀ initial molar ratios. Interestingly, the normal/reversed ratio of VDF units in these telomers was low. Finally, the cotelomerization of VDF and hexafluoropropylene with these transfer agents was successfully achieved, leading to original ω‐CF₃ fluoroelastomers, the thermal properties of which were investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4538–4549, 2002     

Molecular conformation of cyclenes: Part VI. Cycloalkatrienes with seven to ten carbon atoms in the ring

The strain energy of cycloalkatrienes with seven to ten carbon atoms in the ring is calculated as a function of various geometrical parameters. The most stable conformations are the boat for 1,3,5,cycloheptatriene and 1,3,5,cyclooctatriene, the all-cisC₂ for 1,3,6,cyclooctatriene, the boat-chair for 1,3,5, cyclononatriene, the all-cis crown for 1,4,7,cyclononatriene, a cis-trans-cis form for 1,3,5,cyclodecatriene, a cis-cis-trans and a trans-cis-cis conformer for 1,3,7, and 1,4,8,cyclodecatriene respectively. Some interconversion barriers are also discussed and compared with available experimental data. Fair agreement is generally found.