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.     

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.     

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.     

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.     

C50富勒烯及其二聚物C100、C101的光学性质

运用B3LYP方法在6-31G*基组水平上对C50富勒烯以及它的两个不同二聚物C100、C101的几何构型进行了全优化. 在优化所得构型的基础上, 采用TDB3LYP方法在3-21G*基组水平上对其激发态性质、电子吸收光谱进行了研究, 根据计算得到的态态间跃迁偶极矩和跃迁能等数据, 结合使用态求和公式进一步计算得到了它们不同光学过程中的三阶非线性极化率. 结果表明, 当C50富勒烯二聚以后, 其电子吸收光谱的最大波长吸收峰发生了明显的红移, 三阶非线性极化率有了较大的提高. 其中, [5,5]-[5,5]哑铃型二聚物C101有着比[2+2]闭环型二聚物C100更大的三阶非线性极化率.     

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.     

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.     

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.     

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.     

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.     

C,C- and C,N-Chelated Organocopper Compounds

Copper-catalyzed and organocopper-involved reactions are of great significance in organic synthesis. To have a deep understanding of the reaction mechanisms, the structural characterizations of organocopper intermediates become indispensable. Meanwhile, the structure-function relationship of organocopper compounds could advance the rational design and development of new Cu-based reactions and organocopper reagents. Compared to the mono-carbonic ligand, the C,N- and C,C-bidentate ligands better stabilize unstable organocopper compounds. Bidentate ligands can chelate to the same copper atom via η²-mode, forming a mono-cupra-cyclic compounds with at least one acute C-Cu-C angle. When the bidentate ligands bind to two copper atoms via η¹-mode at each coordinating site, the bimetallic macrocyclic compounds will form nearly linear C-Cu-C angles. The anionic coordinating sites of the bidentate ligand can also bridge two metals via μ₂-mode, forming organocopper aggregates with Cu-Cu interactions and organocuprates with contact ion pair structures. The reaction chemistry of some selected organocopper compounds is highlighted, showing their unique structure–reactivity relationships.     

Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

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.     

Rydberg electron transfer to C60 and C70

Experimental results are reported for the attachment of Ar* * (nl) Rydberg electrons to C₆₀ and C₇₀ over the range n = 19–270. In agreement with other Rydberg work we find that the rate coefficient for C ₆₀ ^? formation remains large (around 2·10^-8 cm³ s^-1) towards high n and is essentially constant for n > 40, thereby indicating the presence of an s-wave attachment process in contrast to interpretations of free electron attachment data postulating p-wave threshold behaviour. The rate coefficients for C ₇₀ ^? formation show a similar n-dependence as those for C ₆₀ ^? , but they are significantly larger. Possible mechanisms for s-wave attachment including formation of polarization-bound negative ion states are discussed. Regarding the threshold behaviour for the attachment of free electrons to C₆₀ we propose — based on an analysis of available free electron data — the presence of an s-wave (possibly resonance type) contribution near zero energy.     

Semiempirical vibrational and electronic structures of C60 and C70

The electronic and vibrational structures of C₆₀ and C₇₀ have been calculated at the PM3 semiempirical level. C₆₀ has a partially delocalized structure, while C₇₀ has both a localized set and a delocalized set of MOs. As with AM1 and MNDO, PM3 predicts the heat of formation of C₇₀ to be greater than that of C₆₀, and that C₇₀ is the thermodynamically more stable species. Calculation of the normal modes was accelerated over 40 times by limited use of symmetry theory.