Murahashi Cross-Coupling at −78 °C: A One-Pot Procedure for Sequential C−C/C−C,C−C/C−N,and C−C/C−S Cross-Coupling of Bromo-Chloro-Arenes

The coupling of organolithium reagents, including strongly hindered examples, at cryogenic temperatures (as low as −78 °C) has been achieved with high-reactivity Pd-NHC catalysts. A temperature-dependent chemoselectivity trigger has been developed for the selective coupling of aryl bromides in the presence of chlorides. Building on this, a one-pot, sequential coupling strategy is presented for the rapid construction of advanced building blocks. Importantly, one-shot addition of alkyllithium compounds to Pd cross-coupling reactions has been achieved, eliminating the need for slow addition by syringe pump.     

C3−C3′ and C6−C6′ Oxidative Couplings of Carbazoles

9-Substituted carbazoles are widely used units in materials science, and their oxidative reactions have been utilized for the synthesis and characterization of polymers. Though the oxidative mechanism of carbazoles has been known for a few decades, structural definition has remained difficult, because their polymers are generally insoluble with incomplete characterization and unknown dependence of the electrochemical potentials. The oxidative reactions of 9-substituted carbazoles should be carefully considered under specific oxidative conditions; otherwise, structure definitions could be wrong, because the IR and NMR spectra used previously cannot quantitatively analyze 3,3′-coupling and 6,6′-coupling of carbazoles. In this review, the best understanding of the C3−C3′ and C6−C6′ oxidative couplings of 9-substituted carbazoles is presented, and the benefit of these oxidative reactions from the viewpoints of electrochemical synthesis, film engineering, and the synthesis and processing of polymers is highlighted.     

C6, C7, and C8 perfluoroalkyl-substituted phosphinic acids

Reaction of red phosphorus with RfI in a 1:2 molar ratio at 230 degrees C led to the formation of a mixture of (Rf)2PI and (Rf)PI2 (Rf = C6F13, C7F15, C8F17) in about a 70:30 ratio, respectively. These mixtures were separated by vacuum distillation. (Rf)2PI (Rf = C6F13, C7F15) are yellow liquids whereas (C8F17)2PI is a yellow solid. Oxidation of (Rf)2PI with excess NO2 led to (Rf)2P(O)OH (Rf = C6F13, C7F15, C8F17) in > 90% isolated yields after aqueous hydrolysis of the anhydride intermediates. These highly fluorinated phosphinic acids are white solids with sharp melting points and are highly soluble in methyl sulfoxide (DMSO) and 1,1,2-trichlorotrifluoroethane. However, solubility in chloroform and methylene dichloride is low. These perfluoroalkylphosphinic acids were characterized by IR, NMR (1H, 19F, and 31P), and mass spectra and elemental analysis.     

Numerical simulation of C/C/C planar X-ray waveguides.

A numerical simulation was done to check the possibility of using planar C/C/C multilayers with density contrast 0.2 and 0.7 g/cm3 as an X-ray waveguide. After an optimization procedure, suitable waveguide layer thicknesses were found which provide a high degree of resonant standing wave field intensity enhancement in the core layer at incident beam energy of 13 keV. The obtained results were compared with those of the Mo/Be/Mo waveguide, whose high waveguiding capability at the same energy value was reported in the 1990s. The comparison shows that standing wave field intensity resonant enhancement provided by C/C/C planar multilayers is very high and, consequently, a guided beam can be well detected.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

Reducing ability of supramolecular C60 dianion toward C=O, C=C and N-N bonds

Different from C60 dianion which readily reacts with electrophiles, supramolecular C60 dianion (2) generated from gamma-cyclodextrin-bicapped C60 (1) and NaBH4 (or diborate) in DMSO-H2O (9:1, v/v) is able to reduce N-N+, C=C-EWG and C=O bonds to provide the respective dihydro derivatives; 1-mediated reduction of acetophenone with NaBH4 in the presence of (Me2N)2CH2 and EtONa gives turn over frequency (TOF)/h of 400.     

Incorporating C2 into C60 films

The material formed by depositing C(2)(-) anions onto/into thin C(60) films (on graphite) at room temperature has been studied by means of thermal desorption mass spectroscopy, ultraviolet photoionization spectroscopy, atomic force microscopy (AFM), and surface enhanced Raman spectroscopy. As-prepared, C(2)/C(60) films manifest thermal desorption behaviour which differs significantly from pure C(60) films. Whereas the latter can be fully sublimed, we observe decomposition of C(2)/C(60) films to a high-temperature-stable material while predominantly C(60), C(62), and C(64) are desorbed in parallel. Deposition of C(2)(-) also leads to significantly modified electronic and vibrational properties. Based on DFT model calculations of the Raman spectra, we suggest that as-prepared C(2)/C(60) films contain appreciable amounts of polymeric networks comprising -C(2)-C(60)-C(2)-C(60)- chains. Detection of sublimed C(62) and C(64) upon heating implies that thermal decomposition of C(2)/C(60) films involves addition/uptake of C(2) units into individual fullerene cages. Correspondingly, annealing films up to various intermediate temperatures results in significant modifications to valence-band UP spectra as well as to surface topographies as imaged by AFM. The novel carbonaceous material obtained by heating to T > 950 K has a finite density of states at the Fermi level in contrast to as-prepared C(2)/C(60). It comprises fused fullerene cages.     

Iminopropadienethiones, Ar=N=C=C=C=S

Aryliminopropadienethiones 9 have been generated by flash vacuum thermolysis of isoxazolones of the type 5 and characterized by mass spectrometry and matrix isolation IR spectroscopy in conjunction with DFT calculations and chemical trapping.     

Gas phase electronic spectra of the carbon chains C5, C6, C8, and C9

Three electronic absorption systems for C5 at 511, 445, and 232 nm and one for C6, C8, and C9 centered at 228, 259, and 288 nm have been observed in the gas phase. The C5 chain was produced in both discharge and ablation sources and detected using resonant two-color two-photon ionization spectroscopy involving 10.5 eV photons. The decay of the excited singlet electronic states indicates fast intramolecular processes on a subpicosecond time scale. The internal energy is assumed to be trapped in a triplet state for at least 15 micros. Hole-burning experiments on the 2 (3)Sigma(u)- <-- X (3)Sigma(g)- transition of C6, C8, and (1)Sigma(u)+ <-- X (1)Sigma(g)+ of C9 confirm the predissociative nature of the excited electronic states.     

Gentamicin C: Separation of C1, C1a,C2, C2a and C2b components by HPLC using lsocratic ion-exchange chromatography and post-column derivatisation

Summary A HPLC system, using a strong cation exchanger and isocratic elution, was developed for the separation of the main, components of gentamicin (C₁, C_1a, C₂, C_2a) and C_2b (sagamicin) in less than 20 minutes. The detection was performed by post-column derivatisation with o-phthalaldehyde and a fluorescence detector. The detection limit was 10ng for gentamicin C₁. Some commercial gentamicin samples were analyzed.     

Catalytic C–C coupling through C–H arylation of arenes or heteroarenes

The present review refers to catalytic methods to arylate arene or heteroarene compounds. The resulting compounds are ubiquitous in biology and in pharmaceuticals or fine chemicals production. Until a few decades ago they were prepared according to laborious procedures often involving a series of steps all requiring product isolation. Catalytic methods are much simpler and convenient and often consist of one-pot procedures leading to highly selective reactions. The reaction types described here encompass intermolecular as well as intramolecular reactions. Assistance by chelating groups, heteroatoms and metallacycles are considered for metal-catalyzed reactions not involving the use of oxygen or stoichiometric oxidants.     

Energy of the C = C Double Bond

Determination of the bond energy as the difference between the experimental energy of the double bond and standard value of the C-C bond energy does not take into account changes in the energy of the C-C bond as it becomes shorter. The change in the single bond energy upon its shortening by 0.2 Å was evaluated from the compressibilities of diamond and polyethylene, and also by quantum-chemical calculations. With this value taken into account, the energies of the and bonds in ethylene become close, which proves the equivalence of the traditional and banana models of the C = C bond.     

Pulchellin C and inuchinenolide C from Inula caspica

The pseudoguaianolide inuchinenolide C and the eudesmanolide pulchellin C have been isolated for the first time from the flower heads and leaves ofInula caspica Blume, and their spatial structures have been established by an x-ray structural experiment as 2,6-diacetoxy-6-hydroxy-1,7(H),8,10(H)-pseudoguai-11(13)-en-8,12-olide and 2,3-dihydroxy-5,7,8(H)-eudesma-4(15),11(13)-dien-8,12-olide, respectively.Institute of Organic Synthesis and Coal Chemistry, Academy of Sciences of the Kazakh SSR, Karaganda. A. N. Nesmeyanov Institute of Organometallic Compounds, Academy of Sciences of the USSR, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 748–757, November–December, 1990.     

Ionization and excitation of C60, C70, and C80 fullerenes

Good agreement of E_SCF results for the ionization potentials with the corresponding one-electron levels in C₆₀, C₇₀, and C₈₀ fullerenes, as well as with generalizations of the Koopmans theorem to cases considering various one-electron transitions in ions, was observed. Both are in good agreement with the available experimental data. An explanation is given both for the agreement and for the existing deviations, according to which the dispersions of the results for the ionization potentials obtained in a number of studies of the Koopmans theorem should be ascribed to differences in the parametrization and methods of construction of the semiempirical Fockian for acceptable methods of calculation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 29, No. 6, pp. 501–513, November–December, 1993.     

Chemistry of stable iminopropadienones, RN=C=C=C=O

The synthesis, spectroscopic properties, and chemical reactions of the stable (neopentylimino)-, (mesitylimino)-, and (o-tert-butylphenylimino)propadienones (6) are reported. Nucleophilic addition of amines affords the malonic amidoamidines 7 and 8. 3,5-Dimethylpyrazole reacts analogously to form 9b. Addition of 1,2-dimethylhydrazine produces pyrazolinones 10-12. Addition of N,N'-dimethyldiaminoethane, -propane, and -butane gives diazepine, diazocine, and diazonine derivatives 13-15, respectively (X-ray structures of 13c, 14a, and 15a are available). The mesoionic pyridopyrimidinium olates 18 are obtained by addition of 2-(methylamino)pyridine (X-ray structure of 18b available). Primary 2-aminopyridines afford the pyridopyrimidininones 20-29 and 31 (X-ray structure of 21a available), and 2-aminopyrimidines and 2-aminopyrazine afford pyrimidopyrimidinones and pyrazinopyrimidinones 33-35. Pyrimidoisoquinolinone 36 results from 1-aminoisoquinoline and pyridoquinolinone 40 from 8-aminoquinoline. 2-Aminothiazoline and 2-aminothiazole afford thiazolopyrimidinone derivatives 41-43 (X-ray structure of 43a available).     

Pulchellin C and inuchinenolide C from Inula caspica

The pseudoguaianolide inuchinenolide C and the eudesmanolide pulchellin C have been isolated for the first time from the flower heads and leaves ofInula caspica Blume, and their spatial structures have been established by an x-ray structural experiment as 2α,6β-diacetoxy-6α-hydroxy-1α,7α(H),8β,10β(H)-pseudoguai-11(13)-en-8,12-olide and 2α,3β-dihydroxy-5β,7α,8α(H)-eudesma-4(15),11(13)-dien-8,12-olide, respectively.