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.     

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.     

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.     

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.     

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.     

Classification of 486 isomerizations among 7212C/13C isotopomers of cyclic C7

Isotopic rules are studied for calculated vibrational frequencies of all possible 72¹²C/¹³C isotopomers of the C₇ cluster of the C_2v symmetry. The isotopomers can undergo 486 isomerizations which are decomposed into 27 subclasses using properties of sums of the squares of the vibrational frequencies.     

Structure and stability of the defect fullerene clusters of C60: C59, C58, and C57

We have performed density functional calculations for the structures and stabilities of various isomers of the defect fullerene clusters of C(60): C(59), C(58), and C(57). The C(59_)5-8, C(58_)5-5-7, and C(57_)4-5-9 clusters were calculated to be the most stable isomers of the C(59), C(58), and C(57) clusters, respectively. There are obvious relationships between structure and stability of the defect fullerene clusters. First, an unsaturated carbon atom favors being located at a 6-membered ring rather than a 5-membered ring. Second, the most stable isomers prefer to have newly formed 5-membered rings, rather than newly formed 4-membered rings.     

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.     

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).     

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.     

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.     

Optical gain characteristics of C 460 and C 450

Dye concentration dependent gain spectra for Coumarin 460 (C 460) and Coumarin 450 (C 450) in ethanol have been studied using Amplified Spontaneous Emission (ASE) technique under Nitrogen laser (337.1 nm) excitation in the concentration range 10(-2)-10(-5) m/l. The dependence of lasing wavelength and peak gain on concentration have been understood in terms of variation of fluorescence lifetime, which is due to photo-physical processes such as radiation trapping and concentration-quenching. Pump intensity dependence of efficiency is also explained in terms of fluorescence lifetime. A comparison of the stability of the two dyes has also been made on the basis of the functional groups at different positions of the basic coumarin.