Unsubstituted Carbon Atom Research Articles

Sequential Ring-Opening and Ring-Closing Reactions for Converting para-Substituted Pyridines into meta-Substituted Anilines.

Herein we report a method for converting para-substituted pyridine rings into meta-dialkylamino-substituted benzene rings through sequential ring-opening and ring-closing reactions. The nitrogen atom in the pyridine rings was replaced with a methine group, and a dialkylamino substituent was introduced onto the original unsubstituted carbon atom in the pyridine rings. This process can be formally regarded as a hybrid of the skeletal editing and C-H amination of pyridine rings.

Trans-stereochemistry from the insertion of alkynes into a ruthenium - carbon bond of a bridging-phenyl ligand

The reaction of Ru5(μ5-C)(CO)13(μ-η2-Ph)[μ-Au(NHC)], 1, NHC = 1,3-bis(2,6-diisopropylphenyl-imidazol-2-ylidene) with ethyne (C2H2) yielded the new compound Ru5(μ5-C)(CO)13[μ-η2-E-C(H)C(H)Ph][μ-Au(NHC)], 2 in 89 % yield. Compound 2 contains a square-pyramidal cluster of five ruthenium atoms with a carbido ligand in the base of the square pyramid and a bridging σ+π-coordinated 2-phenylvinyl ligand, μ−η2-E-CHCHPh, formed by an overall trans-insertion of the C2H2 into the Ru-C bond to the bridging η2-Ph ligand in 1. A similar reaction of 1 with phenylacetylene (PhC2H) yielded the new compound Ru5(μ5-C)(CO)13[μ-η2-Ε-C(Ph)C(H)Ph][μ-Au(NHC)], 3 in 96 % yield. Compound 3 contains a bridging σ+π-coordinated, η2-1,2-diphenylvinyl ligand, η2-E-C(Ph)C(H)Ph, formed by an overall trans-insertion of the molecule of PhC2H into the Ru-C bond of the bridging η2-phenyl ligand in 1. The phenyl ligand was shifted to the unsubstituted carbon atom of the PhC2H molecule.

Expanding the Reactivity of Donor-Acceptor Cyclopropanes: Synthesis of Benzannulated Five-Membered Heterocycles via Intramolecular Attack of a Pendant Nucleophilic Group.

Lewis-acid-induced domino transformations of donor-acceptor cyclopropanes, possessing a nucleophilic center embedded in a donor group, into functionalized 2,3-dihydrobenzo[ b]furans and 2,3-dihydrobenzo[ b]thiophenes are reported herein. An unusual switch of the electrophilic center in the three-membered ring, from the atom bearing a donor substituent to an unsubstituted carbon atom, was achieved by a judicious choice of Lewis acid, which induces the isomerization of a cyclopropane to an electrophilic alkene, and the length of linker, connecting a nucleophilic moiety and the small ring.

Ring Activation of Furanic Compounds on Ruthenium-Based Catalysts

We employed a combination of isotopic labeling experiments, density functional theory calculations, and first-principles microkinetic modeling to investigate the mechanism of H/D exchange of furanic platform molecules. Alkylated furans (e.g., 2-methylfuran (2-MF)) exhibit appreciable H/D exchange, but furan and oxygenated furanics (e.g., furfuryl alcohol) do not. Detailed mass fragmentation pattern analysis indicates H/D exchange only occurs at unprotected α-carbons. Simulations show that, in the presence of coadsorbed toluene (solvent), the most likely pathway involves Ru surface mediated scission of the C–O bond in the furan ring at the unsubstituted carbon atom, followed by dehydrogenation, deuteration, and ring-closure steps. The degree of H/D exchange reaction depends mainly on the adsorption strength of exchange intermediates: strongly bound compounds, e.g., furan and furfuryl alcohol, inhibit H/D exchange via site blocking and slow desorption, whereas alkylated furans are sterically repelled by the solvent freeing up catalyst sites for exchange at the unsubstituted α-carbon of the furan ring. The binding strength of exchange intermediates is governed by interaction of the substituent group both with the surface and with the coadsorbed solvent molecules. The proposed H/D exchange mechanism on metal catalysts, which involves the opening of furan ring, is in stark contrast to the Brønsted catalyzed ring activation and suggests a possible pathway for the formation of ring-opening products and for rational selection of solvents.

Catalytic behavior of MnMCM-48 and WMnMCM-48 ordered mesoporous catalysts in a reductive environment: a study of the conversion of methylcyclopentane

Direct hydrothermal synthesis (HT), template ion-exchange (TIE) and molecular dispersion (MD) approaches were used to introduce manganese species into MCM-48-type mesoporous materials. The tungsten was highly dispersed within the channels of mesoporous MnMCM-48 samples by chemical grafting (CG) via a liquid–solid reaction. The prepared manganesosilicate and tungstenomanganesosilicate MCM-48-type mesoporous materials were characterized by physico-chemical techniques, including TEM, N2 sorption, XRD, XPS, UV-Vis and elemental analysis. The physico-chemical characterization revealed that all of the samples retained a high surface area, a regular cubic mesoporosity and that the Mn and W were highly dispersed. The higher unit cell parameter/pore wall thickness values of the MnMCM-48 and WMnMCM-48 samples relative to that of pure MCM-48 indicate the incorporation of Mn and W into the framework/channels of MCM-48. The Mn and W species existed as isolated sites in the framework/extra-framework or as monomolecular species. No bulk manganese or tungsten was observed outside the MCM-48-type mesoporous materials. The coexistence of Mn2+, Mn3+ or/and W6+ was evidenced by XPS and UV-Vis spectroscopic measurements. The catalytic activities of these samples were studied with respect to the conversion of methylcyclopentane (MCP) in reductive media as a function of Mn loading and reaction temperature (200–500 °C). Whatever the manganese content and irrespective of the temperature of reaction, the MnMCM-48 mesoporous samples did not exhibit catalytic activity, which suggests that the electrophilic manganese oxygen species, operative over all the samples, were inactive sites for the conversion of MCP. The addition of tungsten favored catalytic activity. When the WMnMCM-48 was not calcined, only the methane (C1) cracking product was observed to be formed by successive rupture of C–C bonds starting at 400 °C. When the WMnMCM-48 was calcined, ring-opening products formed by the C–C rupture, at substituted and unsubstituted carbon atoms, were observed starting at 400 °C. This behavior is associated with a symbiotic process between the MnMCM-48 support and the W nanoparticles.

The trisubstituted-triazole approach to extended functional naphthalocyanines

Recently, a novel modular approach to octatriazole-derived phthalocyanines (Pcs; 1) was developed and optimized in our group; herein, the pool of the functional Pc materials was expanded for an additional candidate (2), a fused derivative of 1. Compared with 1, the aromaticity in 2 is extended by an additional four benzene and eight triazole rings and, in addition, the triazole units and the Pc core co-create four functional, in-plane cavities. Various methods to link the unsubstituted carbon atoms of the neighboring triazoles in 1 to afford atomically flat naphthalocyanine (Nc) analogs (2), containing eight fused triazole moieties, were studied. Several synthetic routes were designed, among them the trisubstituted-triazole approach, which was found to be the most suitable route. The crucial steps of this approach, the copper-catalyzed azide-haloalkyne cycloaddition and the intramolecular homocoupling reactions, were first studied on a model system; subsequently, this methodology was applied in the synthesis of the desired Nc 2. The increased core size and the π-electron deficient structure predict this class of Ncs to possess very strong aggregation properties. Moreover, owing to the presence of four tridentate half-cavities, the final properties of the molecule or the assembly can, in principle, be further tuned by doping with metals or guest molecules.

Reactions of 1,2,4,5-tetrazines with S-nucleophiles

The reactions of 3,6-disubstituted and azoloannulated 1,2,4,5-tetrazines containing heterocyclic leaving groups with S-nucleophiles were studied. The methods of introduction of functionalized thiols, including thiol derivatives of 1,7- and 1,2-dicarba-closo-dodecaboranes, into the tetrazine ring were developed. It was established for the first time that, instead of replacement of a leaving group in the tetrazine ring, the attack of S-nucleophile at the unsubstituted carbon atom occurs in the case of imidazo[1,2-b][1,2,4,5]tetrazines to form previously unknown products of nucleophilic substitution of the hydrogen atom.

1,3,3-Trimethyl-5-nitro-1-phenylindane

In the title compound, C18H19NO2, the five-membered ring of the indane fragment adopts an envelope conformation with the unsubstituted carbon atom at the flap displaced by 0.412 (3) Å from the plane formed by the other four atoms. The nitro group forms a dihedral angle of 5.3 (2)° with the indane benzene ring while the dihedral angle between the phenyl ring and the indane benzene ring is 76.74 (9)°.

Molecular Complexes of Simple Anions with Electron‐Deficient Arenes: Spectroscopic Evidence for Two Types of Structural Motifs for Anion–Arene Interactions

Anion-pi interactions between a pi-acidic aromatic system and an anion are gaining increasing recognition in chemistry and biology. Herein, the binding features of an electron-deficient aromatic system (1,3,5-trinitrobenzene (TNB)) and selected anions (OH-, Br-, and I-) are examined in the gas phase by using the combined information derived from collision-induced dissociation experiments at variable energy, infrared multiple-photon dissociation spectroscopy, and quantum chemical calculations. We provide spectroscopic evidence for two different structural motifs of anion-arene complexes depending on the nature of the anion. The TNB-OR- complexes (R=H, or alkyl groups which were studied earlier) adopt an anionic sigma-complex structure whereby RO- attacks the aromatic ring with covalent bond formation, and develops a tetrahedral ring carbon bound to H and OR. The halide complexes rather conform to a structure in which the TNB moiety is hardly altered, and the halogen is placed on an unsubstituted carbon atom over the periphery of the ring at a C-X distance that is appreciably longer than a typical covalent bond length. The ensuing structural motif, previously characterized in the solid state and named weak sigma interaction, is now confirmed by an IR spectroscopic assay in the gas phase, in which the sampled species are unperturbed by crystal packing or solvation effects.

Effects of substituents in the cationic and anionic η3-allylpalladium complexes according to data from 13C NMR spectroscopy and quantum chemical calculations

A linear correlation of chemical shifts (δ) of signals in the 13C NMR spectra of the unsubstituted terminal carbon atom of the allyl ligand in [(1-R-η3-C3H4)Pd]NO3 (R = Me, CH2OMe, CO2Me, COMe, CHO) with the substituent constants σ+ and σs- in acetone solutions was found. A considerable deviation from linearity was observed for R = Ph. The 13C nuclear magnetic screening constants were calculated by the DFT method in the GIAO approximation for equilibrium geometries of the cations [(1-R-η3-C3H4)Pd(Me2C=0)2]+ and anions [(1-R-η3-C3H4)PdCl2]s-. In the latter case, the theoretical and experimental δ values are consistent. The influence of the substituent R on the geometric parameters and charges on atoms in the neutral, anionic, and cationic η3-allylpalladium complexes is discussed.

Correlations between 13C NMR chemical shifts of [(1-R-η3-C3H4)PdCl]2 and Na[(1-R-η3-C3H4)PdCl2] and substituent constants

Linear correlations between 13C NMR chemical shifts of unsubstituted terminal carbon atom of the allylic ligand in [(1-R-η3-C3H4)PdCl]2 and Na[(1-R-η3-C3H4)PdCl2] and the modified Hammett constants were established. Two-parameter correlations using the Swain-Lupton parameters R+, R−, and F were obtained.

Arene complexes of transition metals in reactions with nucleophilic reagents: XXX. Reaction of π-halomesitylene [Tetramethyl(ethyl)cyclopentadienyl]rhodium(II) complexes with anions derived from CH acids

Reactions of fluoro-and chloromesitylene π-complexes [(η6-1-Hlg-2,4,6-Me3C6H2)(η5-C5EtMe4)Rh]-(BF4)2 (Hlg = F, Cl) with diethyl malonate anion in THF or acetone-d6 at 20°C initially (within the first 5–30 min) involve nucleophile addition at unsubstituted carbon atom in the arene ligand with formation of π-cyclohexadienyl complexes {[η5-1-(EtOCO)2CH-1-H-3-Hlg-2,4,6-Me3C6H2](η5-C5EtMe4)Rh}(BF4). The subsequent replacement of the halogen atom yields {[η6-1-(EtOCO)2CH-2,4,6-Me3C6H2](η5-C5EtMe4)Rh}(BF4)2, where the arene ligand is readily withdrawn from π-coordination by the action of chloride ion or the solvent. Dimethyl mesitylmalonate was isolated in 76% yield. Likewise, the reactions with anions derived from malononitrile and ethyl cyanoacetate gave 25–38% of the corresponding derivatives 1-R-2,4,6-Me3C6H2 where R = (NC)2CH or EtOCO(NC)CH.

Activation of Metal Hydride Complexes by Tri-tert-butylphosphine-Platinum and -Palladium Groups

The compounds HM(CO)4SnPh3, M = Os (10), Ru (11) are activated in the presence of Pt(PBut3)2 and Pd(PBu(t)3)2 toward the insertion of PhC2H into the M-H bond. The compounds PtOs(CO)4(SnPh3)(PBu(t)3)[mu-HCC(H)Ph], 12, and PtOs(CO)4(SnPh3)(PBu(t)3)[mu-H2CCPh], 13, were obtained from the reaction of 10 with PhC2H in the presence of Pt(PBu(t)3)2. Compounds 12 and 13 are isomers containing alkenyl ligands formed by the insertion of the PhC2H molecule into the Os-H bond at both the substituted and unsubstituted carbon atoms of the alkyne. Both compounds contain a Pt(PBu(t)3) group that is bonded to the osmium atom and a bridging alkenyl ligand that is pi-bonded to the osmium atom. The reaction of 11 with PhC2H in the presence of Pt(PBu(t)3)2 yielded the products PtRu(CO)4(SnPh3)(PBu(t)3)[mu-HC2(H)Ph], 14, and PtRu(CO)4(SnPh3)(PBut3)[mu-H2C2Ph], 15, which are also isomers similar to 12 and 13. The reaction of 11 with PhC2H in the presence of Pd(PBu(t)3)2 yielded the product PdRu(CO)4(SnPh3)(PBu(t)3)[mu-H2C2Ph], 16. Compound 16 contains a Pd(PBu(t)3) group bonded to the ruthenium atom and a bridging H2C2Ph ligand that is pi-bonded to the palladium atom. Compound 10 reacted with Pt(PBu(t)3)2 in the absence of PhC2H to yield the compound PtOs(CO)4(SnPh3)(PBu(t)3)(mu-H), 17. Compound 17 is a Pt(PBu(t)3) adduct of 10. It contains a Pt-Os bond with a bridging hydrido ligand. Compound 17 reacted with PhC2H to yield 12. Compound 12 reacted with PhC2H to yield the compound PtOs(CO)3(SnPh3)(PBu(t)3)[mu-HCC(Ph)C(H)C(H)Ph], 18. Compound 18 contains a bridging 2,4-diphenylbutadienyl ligand, HCC(Ph)C(H)C(H)Ph, that is pi-bonded to the osmium atom and sigma-bonded to the platinum atom. Fenkse-Hall molecular orbitals of 17 were calculated. The LUMO of 17 exhibits an empty orbital on the platinum atom that appears to be the most likely site for PhC2H addition prior to its insertion into the Os-H bond.

A Density Functional Study of the 13C NMR Chemical Shifts in Functionalized Single-Walled Carbon Nanotubes

The 13C NMR chemical shifts for functionalized (7,0), (8,0), (9,0), and (10,0) single-walled carbon nanotubes (SWNTs) have been studied computationally using gauge-including projector-augmented plane-wave (GIPAW) density functional theory (DFT). The functional groups NH, NCH3, NCH2OH, and CH2NHCH2 have been considered, and different sites where covalent addition or substitution may occur have been examined. The shifts of the carbons directly attached to the group are sensitive to the bond which has been functionalized and may, therefore, be used to identify whether the group has reacted with a parallel or a diagonal C-C bond. The addition of NH to a parallel bond renders the functionalized carbons formally sp3-hybridized, yielding shifts of around 44 ppm, independent of the SWNT radius. Reaction with a diagonal bond retains the formal sp2 hybridization of the substituted carbons, and their shifts are slightly lower or higher than those of the unsubstituted carbon atoms. The calculated 1H NMR shifts of protons in the functional groups are also dependent upon the SWNT-group interaction. Upon decreasing the degree of functionalization for the systems where the group is added to a parallel bond, the average chemical shift of the unfunctionalized carbons approaches that of the pristine tube. At the same time, the shifts of the functionalized carbons remain independent upon the degree of functionalization. For the SWNTs where N-R attaches to a parallel bond, the average shift of the sp2 carbons was found to be insensitive to the substituent R. Moreover, the shifts of the functionalized sp3 carbons, as well as of the carbons within the group itself, are independent of the SWNT radius. The results indicate that a wealth of knowledge may be obtained from the 13C NMR of functionalized SWNTs.

Direct C-C Coupling of meso-Octamethylcalix[4]pyrrole with 6-Nitroazolopyrimidines

It has been found that the reaction of meso-octamethylcalix[4]pyrrole with four equivalents of 6-nitroazolopyrimidine is accompanied by the C-C coupling of unsubstituted carbon atom in azines with P-position of pyrrole rings and results in the formation of tetrapyrimidine-substituted calix[4]pyrroles without introduction of any catalysts. Mono- and di-substituted calixpyrroles have been isolated.

Acid-promoted direct C-C coupling of 1,3-diazines and 1,2,4-triazines with aryl-containing macrocyclic compounds and their open-chain analogues

A method of direct C-C coupling of azahetarenes with macrocycles (calix[4]arene, benzo-12crown-4, 1,5-bis(2,6-dimethylphenoxy)-3-oxapentane), based on the nucleophilic addition to unsubstituted carbon atom in azines, has been developed.

Theoretical Study of NCO and RCCH (R = H, CH3, F, Cl, CN) [3 + 2] Cycloaddition Reactions

We carried out a theoretical study of the radical [3 + 2] cycloaddition reaction of NCO + RCCH (R = H, CH3, F, Cl, CN), which produced a five-membered ring heterocyclic oxazole. An asynchronous two-bond formation mechanism was found, which led to a certain regioselectivity in the products when the substituted alkyne was used as a reactant. The preferable reactive sites of RCCH in various substituents are calculated by employing the Fukui functions and HSAB theory, and the results are in good agreement (except R = F) with the calculated energy barriers of the transition states in the potential energy surfaces. The N atom of NCO attacks the unsubstituted carbon atom of RCCH first, followed by the ring closure of the O atom with the other carbon atom to form the substituted oxazole. The order of the calculated first transition barriers (uts1) in the substituted alkynes (RCCH) is R = H > F > CN > Cl > CH3, and that for the second transition barriers (uts2), R = H > CH3 > CN > Cl > F. The reason for the decreased transition barriers of the substituted alkynes is analyzed.

Nucleophilic Attack on the Unsubstituted Carbon Atom of Azines and Nitroarenes as an Efficient Methodology for Constructing Heterocyclic Systems

AbstractFor Abstract see ChemInform Abstract in Full Text.

Metabolism of dichloromethylcatechols as central intermediates in the degradation of dichlorotoluenes by Ralstonia sp. strain PS12.

Ralstonia sp. strain PS12 is able to use 2,4-, 2,5-, and 3,4-dichlorotoluene as growth substrates. Dichloromethylcatechols are central intermediates that are formed by TecA tetrachlorobenzene dioxygenase-mediated activation at two adjacent unsubstituted carbon atoms followed by TecB chlorobenzene dihydrodiol dehydrogenase-catalyzed rearomatization and then are channeled into a chlorocatechol ortho cleavage pathway involving a chlorocatechol 1,2-dioxygenase, chloromuconate cycloisomerase, and dienelactone hydrolase. However, completely different metabolic routes were observed for the three dichloromethylcatechols analyzed. Whereas 3,4-dichloro-6-methylcatechol is quantitatively transformed into one dienelactone (5-chloro-2-methyldienelactone) and thus is degraded via a linear pathway, 3,5-dichloro-2-methylmuconate formed from 4,6-dichloro-3-methylcatechol is subject to both 1,4- and 3,6-cycloisomerization and thus is degraded via a branched metabolic route. 3,6-Dichloro-4-methylcatechol, on the first view, is transformed predominantly into one (2-chloro-3-methyl-trans-) dienelactone. In situ (1)H nuclear magnetic resonance analysis revealed the intermediate formation of 2,5-dichloro-4-methylmuconolactone, showing that both 1,4- and 3,6-cycloisomerization occur with this muconate and indicating a degradation of the muconolactone via a reversible cycloisomerization reaction and the dienelactone-forming branch of the pathway. Diastereomeric mixtures of two dichloromethylmuconolactones were prepared chemically to proof such a hypothesis. Chloromuconate cycloisomerase transformed 3,5-dichloro-2-methylmuconolactone into a mixture of 2-chloro-5-methyl-cis- and 3-chloro-2-methyldienelactone, affording evidence for a metabolic route of 3,5-dichloro-2-methylmuconolactone via 3,5-dichloro-2-methylmuconate into 2-chloro-5-methyl-cis-dienelactone. 2,5-Dichloro-3-methylmuconolactone was transformed nearly exclusively into 2-chloro-3-methyl-trans-dienelactone.

Model compounds and monomers for phenylene ether carboranylene ketone (PECK) polymer synthesis: preparation and characterization of boron-arylated ortho-carboranes bearing carboxyphenyl, phenoxyphenyl or benzoylphenyl substituents

Fourteen new derivatives of ortho-carborane, 1,2-C2B10H12, have been prepared containing functionalized aryl groups attached to one or both of the boron atoms (B9 and B12) antipodal to the carbon atoms, in order to test the suitability of such species for use in the preparation of new categories of phenylene ether carboranylene ketone (PECK) polymers. Model compounds prepared from 9-iodo-ortho-carborane 1 to test synthetic procedures and reactions included the mono-substituted carboranes 9-R1-1,2-C2B10H11 in which the boron attached group R1 was p-tolyl (2), p-HO2CC6H43, p-MeOC6H4COC6H44, p-PhOC6H45 or p-PhCOC6H4OC6H46 (C6H4 represents para-phenylene throughout). Formation of 3 from 2 by CrO3 oxidation showed the capacity of the boron–aryl link to withstand strongly oxidizing conditions. Formation of 4 from 3 and anisole, PhOMe, in trifluoromethane sulfonic acid (TFSA), and of 6 from 5 and benzoic acid, PhCO2H, in TFSA showed such systems could undergo the acylation reactions that would allow polymer formation from suitable diarylcarborane monomers. Compound 7, 9-(3-PhCO-4-PhO-C6H3)-1,2-C2B10H11 an isomer of 6, was also obtained during the synthesis of 6 from 5 and benzoic acid. The diarylcarboranes 9,12-R22-1,2-C2B10H10 with R2 = p-tolyl 9, p-HO2CC6H410 or p-MeOC6H4COC6H411, bearing identical functionalised aryl groups attached to both antipodal boron atoms, were prepared from 9,12-I2-1,2-C2B10H108. Further series of diarylcarboranes 1,9- and 1,12-R32-1,2-C2B10H10, bearing identical aryl groups R3 on one carbon atom (C1) and on the antipodal boron atom (B12), or on the boron atom (B9) antipodal to the unsubstituted carbon atom (C2), have also been prepared and characterized, with R3 = p-tolyl 12, 13, p-HO2CC6H414, 15 or p-MeOC6H4COC6H416, 17.