Rhoda-Electrocatalyzed C−H Methylation and Paired Electrocatalyzed C−H Ethylation and Propylation

The use of electricity over traditional stoichiometric oxidants is a promising strategy for sustainable molecular assembly. Herein, we describe the rhoda-electrocatalyzed C−H activation/alkylation of several N-heteroarenes. This catalytic approach has been successfully applied to several arenes, including biologically relevant purines, diazepam, and amino acids. The versatile C−H alkylation featured water as a co-solvent and user-friendly trifluoroborates as alkylating agents. Finally, the rhoda-electrocatalysis with unsaturated organotrifluoroborates proceeded by paired electrolysis.     

Transition metals catalyzed C–C and C–O bonds formation: facile synthesis of flavans and benzoxepines

A simple and practical method has been developed based on intermolecular [Pd]-catalyzed C–C and an intramolecular [Cu]-catalyzed C–O bond formations for the synthesis of flavans and benzoxepines. Interestingly, the method is amenable for the synthesis of a wide variety of flavans and benzoxepines with dense functionalities on aromatic moieties. Significantly, flavans and benzoxepines are present as core/part-structures in many biologically active natural products.     

Stereoselective synthesis of C15C24 and C25C30 fragments of dolabelides

The stereocontrolled synthesis of a C15C24 fragment of dolabelides is reported. The C19 and C21 hydroxyl-bearing stereocenters were installed using ruthenium-mediated asymmetric hydrogenations of cyclic hemiketal 4 and β-keto ester 7. The C25C30 portion of dolabelides was prepared as well by ring opening of chiral epoxy alcohol 12 to set up the C27 stereogenic center.     

Cobalt-catalyzed direct C–C bond formation between tetrahydrofuran and alkynes

We aimed to describe an efficient CoCl₂-catalyzed direct C–C bond formation of tetrahydrofuran (THF) with various alkynes in the presence of tert-butyl hydroperoxide and catalytic amount of acid to obtain vinyl-substituted THFs. Mono- and di-substituted alkynes were suitable for this transformation.     

Recent advances in radical-mediated fluorination through C–H and C–C bond cleavage

The C–H and C–C bonds are abundant in organic compounds, yet generally inert in chemical transformations. Therefore, direct functionalization of inert chemical bonds remains challenging. The fluorine-containing compounds are of special interest for their uses in medicinal chemistry. Direct fluorination of C–H and C–C bonds undoubtedly represents one of the most ideal and attractive approaches to incorporate fluorine atom into complex molecules. Herein, we summarize the recent advances in radical-mediated C–H and C–C bond fluorination. Three types of transformations are discussed: (1) direct C–H abstraction/fluorination of alkanes; (2) decarboxylative fluorination of alkyl carboxylic acids; (3) ring-opening fluorination.     

Divergent Coupling of Benzocyclobutenones with Indoles via C−H and C−C Activations

Highly selective divergent coupling reactions of benzocyclobutenones and indoles, in which the chemoselectivity is controlled by catalysts, are reported herein. The substrates undergo C2(indole)–C8(benzocyclobutenone) coupling to produce benzylated indoles and benzo[b]carbazoles in the Ni- and Ru-catalyzed reactions. A completely different selectivity pattern C2(indole)–C2(benzocyclobutenone) coupling to form arylated indoles is observed in the Rh-catalyzed reaction. Preliminary mechanistic studies suggest C−H and C−C activations in the reaction pathway. Synthetic utility of this protocol is demonstrated by the selective synthesis of three different types of carbazoles from the representative products.     

Electronic structures of C36 fulleride anions: C36− and C362−

Electronic structures for mono- and dianionic species of two promising C₃₆ fullerene isomers, 14 and 15, are investigated by means of the hybrid Hartree–Fock (HF)/density functional (DF) method. Structural deformations, charge distributions, and spin densities upon one- or two-electron reduction are explained in light of the lowest unoccupied molecular orbitals (LUMOs) of each neutral isomer. First electron affinities for the neutral isomers 14 and 15 are predicted to be 2.3 and 2.5 eV, respectively, facilitating n-type doping for C₃₆ solids. The degrees of local aromaticity of the isomers 14 and 15 tend to decrease with reduction in contrast with C₆₀.     

Activation of propane C–H and C–C bonds by a diplatinum cluster: potential energy surfaces and reaction mechanisms

The activation mechanism of C₃H₈ catalyzed by the homonuclear bimetallic Pt₂ cluster has been detailedly explored on the singlet and triplet potential energy surfaces at BPW91/aug-cc-pvtz, Lanl2tz level. The C–H bond cleavage channel (dehydrogenation and the release of propylene) is kinetically predominant, whereas the C–C bond cleavage channel (demethanation and the release of ethane) should be ruled out. Furthermore, the release of propylene channel is kinetically favorable, while the dehydrogenation channel is thermodynamically preferable. Besides, both the C–H cleavage intermediate (Pt₂H₂C₃H₆b) and the C–C cleavage intermediates (CH₃HPt₂CHCH₃ and CH₃PtPtHC₂H₄) are thermodynamically preferred. The C–H cleavage intermediate (Pt₂H₂C₃H₆b) is kinetically favored, while the C–C cleavage intermediates (CH₃HPt₂CHCH₃ and CH₃PtPtHC₂H₄) are kinetically hindered. The homonuclear bimetallic Pt₂ cluster toward propane exhibits higher reactivity than the Pt atom, which is in good agreement with the experimental observation.     

Vibrational Predissociation Spectra of C2N− and C3N−: Bending and Stretching Vibrations

We present infrared predissociation spectra of C₂N⁻(H₂) and C ₃N⁻(H₂) in the 300–1850 cm⁻¹ range. Measurements were performed using the FELion cryogenic ion trap end user station at the Free Electron Lasers for Infrared eXperiments (FELIX) laboratory. For C₂N⁻(H₂), we detected the CCN bending and CC−N stretching vibrations. For the C₃N⁻(H₂) system, we detected the CCN bending, the CC−CN stretching, and multiple overtones and/or combination bands. The assignment and interpretation of the presented experimental spectra is validated by calculations of anharmonic spectra within the vibrational configuration interaction (VCI) approach, based on potential energy surfaces calculated at explicitly correlated coupled cluster theory (CCSD(T)-F12/cc-pVTZ−F12). The H₂ tag acts as an innocent spectator, not significantly affecting the C_2,3N⁻ bending and stretching mode positions. The recorded infrared predissociation spectra can thus be used as a proxy for the vibrational spectra of the bare anions.     

Transition Metal-Free Aromatic C−H,C−N,C−S and C−O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.     

Facile and efficient protocols for C–C and C–N bond formation reactions using a superparamagnetic palladium complex as reusable catalyst

Research on Chemical Intermediates - Facile and efficient protocols for some multicomponent coupling reactions such as the Suzuki reaction and synthesis of polyhydroquinoline and...     

ESR spectra and electronic structure of the C120 ·+ radical cation and the paramagnetic C120O2+ dication and C120O2− dianion

Electronic structure of the C₁₂₀ ^·+ radical cation and the paramagnetic C₁₂₀O²⁺ dication and C₁₂₀O²⁻ dianion in the triplet state was calculated by the MNDO/PM3 method in the valence approximation. The density distributions of the unpaired electrons in these systems were found and the ESR spectra of the above species were interpreted. Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 7, pp. 1257–1260, July, 1999.     

Polymerization and decomposition of terephthaloyl chloride and p-phenylenediamine at 500 °C

In order to synthesize the high temperature solid lubricating film by gas-phase polymerization at 500?°C with two kinds of gasified monomers for use in airplane and rocket engines, the polymerizing activity of terephthaloyl chloride (TPC) and p-phenylenediamine (PPD) at 500?°C and their polymerized product poly-p-phenyleneterephthamide (PPTA) as well as its decomposed solid residues were researched. It was proved by FT-IR and ¹HNMR on the solid residues after the 10?min experiment of the both monomers in muffle furnace at 500?°C and PPTA synthesized by conventional method that at 500?°C the polymerization tendency of these monomers should trump their decomposition tendency. The solid residues after the 10?min experiment mainly consisted of polymerized products which would decline as the experimental period increases, while the content of decomposed and carbonized products would raise. FT-IR and elemental analysis revealed a similar structure of the solid residues after the both monomers or PPTA calcined for 60?min at 500?°C, which further demonstrated the polymerized products would degrade, decompose and carbonize after the prophase polymerization. Finally, effects of experimental temperature and monomers molar ratio on amounts and structures of the solid residues were discussed to propose preliminary mechanisms of polymerization and decomposition.     

C-H⋯O, O-H⋯C, and C-H⋯C interactions in complexes of carbocations and carboanions

Molecular complexes formed by different forms of carbocations (carbenium ions) and carboanions with water, acetylene, and methane molecules have been calculated by the MP2/6-311++G(2df,2pd) method. In complexes with water where the carbon atom of the carbocation (carboanion) acts as the proton donor (acceptor), the energies of the C-H?O and O-H?C hydrogen bonds turn out to be approximately the same being 13–20 kcal/mol for carbocation (carboanion) species differing in the valence state of the carbon atom. Two types of C-H?C interactions have been revealed depending on the charge at the bridging hydrogen atom, which is determined by the hybridization of the donor carbon atom. The C-H?C interaction energy in molecular complexes with the positively charged hydrogen atom (carboanion complexes with acetylene) is an order of magnitude higher than in the complexes where the bridging hydrogen atom has an excess of electron density (carbocation complexes with methane). In all the complexes under consideration, the covalent C-H bond involved in interaction is elongated, and the negative charge is transferred from the acceptor to the donor.     

A Relative Study on Two-photon Absorption Properties of C60 and C70

We have theoretically investigated the one- and two-photon absorption properties of C60 and C70 using the ZINDO method. From the results it is suggested that the one-photon absorption spectra are in agreement with the experimental observations. It is found that the maximum TPA cross section of C70 is more than twice that of C60,which is consistent with the experimental results. A notable point is that the TPA process of C60 is different from that of C70 as well as other ordinary conjugated molecules.     

CATALOGIC 301C model – validation and improvement

In Europe, REACH legislation encourages the use of alternative in silico methods such as (Q)SAR models. According to the recent progress of Chemical Substances Control Law (CSCL) in Japan, (Q)SAR predictions are also utilized as supporting evidence for the assessment of bioaccumulation potential of chemicals along with read across. Currently, the effective use of read across and QSARs is examined for other hazards, including biodegradability. This paper describes the results of external validation and improvement of CATALOGIC 301C model based on more than 1000 tested new chemical substances of the publication schedule under CSCL. CATALOGIC 301C model meets all REACH requirements to be used for biodegradability assessment. The model formalism built on scientific understanding for the microbial degradation of chemicals has a well-defined and transparent applicability domain. The model predictions are adequate for the evaluation of the ready degradability of chemicals.     

Cu(I) metal organic framework catalyzed C–C and C–N coupling reactions

DABCO (1,4-diazabicyclo[2.2.2]octane) based Cu(I) metal organic framework (here after represented as Cu(I)-MOF) catalyzed Sonogashira cross-coupling reaction of iodobenzene and phenylacetylene was conducted smoothly to afford diphenylacetylene in excellent yield under N₂ atmosphere. For comparative study, piperidine based Cu(I) clusters were also investigated. Among these catalysts, Cu(I)-MOF exhibited higher activity with good selectivity for the C–C cross-coupled product. Cu(I) catalysts investigated in this study exhibited similar activity in the C–C homo-coupling reaction of phenylacetylene in O₂ atmosphere. Application of these catalysts was extended in the C–N coupling reactions between phenylboronic acid and aromatic/aliphatic/heterocyclic amines. Cu(I)-MOF can be readily recovered from the reaction mixture and reused for several cycles without loss in the catalytic activity.