Showing papers on "Intramolecular force published in 2013"
TL;DR: The scavenging behavior of a series of phenolic and anilines compounds toward H2O2 and DPPH was examined in this paper, where wide differences among compounds in each series and between the two series were observed.
409 citations
TL;DR: A strategy based on intramolecular hydrogen-binding interactions in 2D covalent organic frameworks (COFs) is shown to improve the crystallinity, porosity, and chemical stability of the material.
Abstract: A strong bond: A strategy based on intramolecular hydrogen-binding interactions in 2D covalent organic frameworks (COFs) is shown to improve the crystallinity, porosity, and chemical stability of the material. The concept is validated by removing the hydrogen-bonding interaction in the methoxy analog which showed a lower stability and crystallinity.
370 citations
TL;DR: In this paper, photoinduced electron transfer from benzene to the singlet-excited state of the 3-cyano-1-methylquinolinium ion has enabled the oxidation of benzene by dioxygen with water to yield phenol selectively.
Abstract: Selective photocatalytic oxygenation of various substrates has been achieved using organic photocatalysts via photoinduced electron-transfer reactions of photocatalysts with substrates and dioxygen under visible light irradiation. Photoinduced electron transfer from benzene to the singlet-excited state of the 3-cyano-1-methylquinolinium ion has enabled the oxidation of benzene by dioxygen with water to yield phenol selectively. Alkoxybenzenes were obtained when water was replaced by alcohols under otherwise the same experimental conditions. Photocatalytic selective oxygenation reactions of aromatic compounds have also been achieved using an electron donor–acceptor linked dyad, 9-mesityl-10-methylacridinium ion (Acr+–Mes) acting as a photocatalyst and dioxygen as an oxidant under visible light irradiation. The oxygenation reaction is initiated by intramolecular photoinduced electron transfer from the mesitylene moiety to the singlet-excited state of the acridinium moiety of Acr+–Mes to afford an extremely long-lived electron-transfer state. The electron-transfer state can oxidize and reduce substrates and dioxygen, respectively, leading to selective oxygenation and halogenation of substrates. C–C bond formation of substrates has also been made possible by using Acr+–Mes as a photocatalyst.
322 citations
TL;DR: Mechanistic investigations of this reaction cascade uncovered a new photoredox catalyzed C-C bond cleavage reaction which resulted in the formation of tetrahydroquinoline derivatives in good yields under mild reaction conditions.
Abstract: Visible light photoredox catalyzed inter- and intramolecular C–H functionalization reactions of tertiary amines have been developed. Oxygen was found to act as chemical switch to trigger two different reaction pathways and to obtain two different types of products from the same starting material. In the absence of oxygen, the intermolecular addition of N,N-dimethyl-anilines to electron-deficient alkenes provided γ-amino nitriles in good to high yields. In the presence of oxygen, a radical addition/cyclization reaction occurred which resulted in the formation of tetrahydroquinoline derivatives in good yields under mild reaction conditions. The intramolecular version of the radical addition led to the unexpected formation of indole-3-carboxaldehyde derivatives. Mechanistic investigations of this reaction cascade uncovered a new photoredox catalyzed C–C bond cleavage reaction.
313 citations
TL;DR: This reaction provides the first example of enantioselecctive C-H functionalizations through Pd(II)/Pd(IV) redox catalysis, which activates phenylacetic acids followed by an intramolecular C-O bond formation afforded chiral benzofuranones.
Abstract: Pd(II)-catalyzed enantioselective C–H activation of phenylacetic acids followed by an intramolecular C–O bond formation afforded chiral benzofuranones. This reaction provides the first example of enantioselecctive C–H functionalizations through Pd(II)/Pd(IV) redox catalysis.
288 citations
TL;DR: The reaction of a trinuclear titanium polyhydride complex with dinitrogen, which induces dinitrogens cleavage and partial hydrogenation at ambient temperature and pressure is reported.
Abstract: Both the Haber-Bosch and biological ammonia syntheses are thought to rely on the cooperation of multiple metals in breaking the strong N≡N triple bond and forming an N–H bond. This has spurred investigations of the reactivity of molecular multimetallic hydrides with dinitrogen. We report here the reaction of a trinuclear titanium polyhydride complex with dinitrogen, which induces dinitrogen cleavage and partial hydrogenation at ambient temperature and pressure. By 1 H and 15 N nuclear magnetic resonance, x-ray crystallographic, and computational studies of some key reaction steps and products, we have determined that the dinitrogen (N 2 ) reduction proceeds sequentially through scission of a N 2 molecule bonded to three Ti atoms in a μ-η 1 :η 2 :η 2 -end-on-side-on fashion to give a μ 2 -N/μ 3 -N dinitrido species, followed by intramolecular hydrogen migration from Ti to the μ 2 -N nitrido unit.
284 citations
TL;DR: For the first time the N-H-imidates are demonstrated to be good directing groups in C-H activation, also capable of undergoing intramolecular N-N bond formation.
Abstract: Substituted 1H-indazoles can be formed from readily available arylimidates and organo azides by RhIII-catalyzed C–H activation/C–N bond formation and Cu-catalyzed N–N bond formation. For the first time the N-H-imidates are demonstrated to be good directing groups in C–H activation, also capable of undergoing intramolecular N–N bond formation. The process is scalable and green, with O2 as the terminal oxidant and N2 and H2O formed as byproducts. Moreover, the products could be transformed to diverse important derivatives.
273 citations
TL;DR: This Perspective provides a historical context for these methods and describes recent contributions, as well as the remaining challenges to intramolecular C(sp3)–H amination.
Abstract: Increasing interest in C(sp3)–H bond functionalization has led to a multitude of recent advances in intramolecular C(sp3)–H amination. Direct, intramolecular C(sp3)–N bond-forming processes provide expedient access to a range of azacycles without the need for prefunctionalized amine precursors such as aminoaldehydes, aminoalkyl halides or aminoalkenes. Some of these methods have been successfully applied to the synthesis of complex natural products. This Perspective provides a historical context for these methods and describes recent contributions, as well as the remaining challenges to intramolecular C(sp3)–H amination.
263 citations
TL;DR: Two inkjet pigments, epindolidione and quinacridone, that break this design rule are explored and afford intermolecular π-stacking reinforced by hydrogen-bonding bridges, and air-stable organic field effect transistors are reported.
Abstract: Extensive intramolecular π-conjugation is considered to be requisite in the design of organic semiconductors. Here, two inkjet pigments, epindolidione and quinacridone, that break this design rule are explored. These molecules afford intermolecular π-stacking reinforced by hydrogen-bonding bridges. Air-stable organic field effect transistors are reported that support mobilities up to 1.5 cm(2)/Vs with T80 lifetimes comparable with the most stable reported organic semiconducting materials.
221 citations
TL;DR: In this article, the structure of Aristolochic acid (AA1) has been resolved at the MPWPW91 density functional theory method in combination with Aug-cc-pVDZ basis sets.
200 citations
TL;DR: A novel synthesis of azepinone derivatives by using a Rh-catalyzed intramolecular annulation reaction of N-substituted benzamides and α,β-unsaturated aldehydes and ketones is developed.
Abstract: A novel synthesis of azepinone derivatives by using a Rh-catalyzed intramolecular annulation reaction of N-substituted benzamides and α,β-unsaturated aldehydes and ketones is developed.
TL;DR: Several common variations of Prins-type cyclizations and their applicability to the total synthesis of natural products and analogs have been discussed in this article, and a microreview of these reactions can be found in Section 2.
TL;DR: A series of HPIPs are developed as new ESIPT fluorescent compounds and shown to be rationally tuned using quantum chemical methods, which can rationalize the effect of the substituent and its position on the IPT state.
Abstract: 2-(2′-Hydroxyphenyl)imidazo[1,2-a]pyridine (HPIP, 1) and its derivatives are synthesized, and their fluorescence properties are studied. Although all the compounds show faint dual emission (Φ ≈ 0.01), which is assigned to the normal and excited-state intramolecular proton transfer (ESIPT) fluorescence in a fluid solution, they generally display efficient ESIPT fluorescence (Φ up to 0.6) in a polymer matrix. The introduction of electron-donating and electron-withdrawing groups into the phenyl ring causes blue and red shifts of the ESIPT fluorescence emission band, respectively. On the other hand, the introduction of such groups into the imidazopyridine part results in fluorescence shifts in the opposite directions. The results of ab initio quantum chemical calculations of the intramolecular proton-transferred (IPT) state are well in line with the ESIPT fluorescence energies. The plots of the calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels ag...
TL;DR: It is found that the substitution of a single atom leads to strong variations of the adsorption height, as predicted by state-of-the-art density-functional theory, including van der Waals interactions with collective substrate response effects.
Abstract: We measured the adsorption geometry of single molecules with intramolecular resolution using noncontact atomic force microscopy with functionalized tips. The lateral adsorption position was determined with atomic resolution, adsorption height differences with a precision of 3 pm, and tilts of the molecular plane within 0.2 � . The method was applied to five � -conjugated molecules, including three molecules from the olympicene family, adsorbed on Cu(111). For the olympicenes, we found that the substitution of a single atom leads to strong variations of the adsorption height, as predicted by state-ofthe-art density-functional theory, including van der Waals interactions with collective substrate response effects.
TL;DR: An efficient Cu-catalyzed synthesis of quinazolines via the C-N bond formation reactions between N-H bonds of amidines and C(sp(3))-H bonds adjacent to sulfur or nitrogen atoms in the commonly used solvents, followed by intramolecular C-C bond formation reaction was developed for the first time.
TL;DR: Air-stable precatalysts, very mild conditions, and an easy protocol allow rapid access to medicinally useful aryl thioethers, as demonstrated in the facile synthesis of (±)-chuangxinmycin as a key step.
TL;DR: Iron(II) bromide catalyzes the transformation of ortho-substituted aryl azides into 2,3-disubstituting indoles through a tandem ethereal C-H bond amination [1,2]-shift reaction.
Abstract: Iron(II) bromide catalyzes the transformation of ortho-substituted aryl azides into 2,3-disubstituted indoles through a tandem ethereal C-H bond amination [1,2]-shift reaction. The preference for the 1,2-shift component of the tandem reaction was established to be Me < 1° < 2° < Ph.
TL;DR: A new synthesis of substituted 1,3-diaryl-substituted indazoles and 1H-pyrazoles from arylhydrazones via FeBr(3)/O(2) mediated C-H activation/C-N bond formation reactions is reported.
Abstract: A new synthesis of substituted 1H-indazoles and 1H-pyrazoles from arylhydrazones via FeBr3/O2 mediated C–H activation/C–N bond formation reactions is reported. The corresponding 1,3-diaryl-substituted indazoles and trisubstituted pyrazoles were obtained in moderate to excellent yields under mild conditions.
TL;DR: By adjusting the length of C-tracts, the i-motif-functionalized DNA nanocircles may serve as a versatile tool for the formation of larger interlocked dsDNA nanostructures, like rotaxanes and catenanes, to achieve diverse mechanical operations.
Abstract: The folding of various intra- and intermolecular i-motif DNAs is systematically studied to expand the toolbox for the control of mechanical operations in DNA nanoarchitectures We analyzed i-motif DNAs with two C-tracts under acidic conditions by gel electrophoresis, circular dichroism, and thermal denaturation and show that their intra- versus intermolecular folding primarily depends on the length of the C-tracts Two stretches of six or fewer C-residues favor the intermolecular folding of i-motifs, whereas longer C-tracts promote the formation of intramolecular i-motif structures with unusually high thermal stability We then introduced intra- and intermolecular i-motifs formed by DNAs containing two C-tracts into single-stranded regions within otherwise double-stranded DNA nanocircles By adjusting the length of C-tracts we can control the intra- and intermolecular folding of i-motif DNAs and achieve programmable functionalization of dsDNA nanocircles Single-stranded gaps in the nanocircle that are fu
TL;DR: The combination of polarization-resolved mid-infrared spectroscopy of marker modes and time-dependent density functional theory (TD-DFT) provides key insights into the transient structures of the molecular chromophore during ultrafast isomerization dynamics.
Abstract: We characterize the structural and electronic changes during the photoinduced enol-keto tautomerization of 2-(2'-hydroxyphenyl)-benzothiazole (HBT) in a nonpolar solvent (tetrachloroethene). We quantify the redistribution of electronic charge and intramolecular proton translocation in real time by combining UV-pump/IR-probe spectroscopy and quantum chemical modeling. We find that the photophysics of this prototypical molecule involves proton coupled electron transfer (PCET), from the hydroxyphenyl to the benzothiazole rings, resulting from excited state intramolecular proton transfer (ESIPT) coupled to electron transfer through the conjugated double bond linking the two rings. The combination of polarization-resolved mid-infrared spectroscopy of marker modes and time-dependent density functional theory (TD-DFT) provides key insights into the transient structures of the molecular chromophore during ultrafast isomerization dynamics.
TL;DR: Alkyne tethered benzamides undergo rhodium(III)-catalyzed intramolecular annulations to give tricyclic isoquinoline derivatives in good yields.
Abstract: Alkyne tethered benzamides undergo rhodium(III)-catalyzed intramolecular annulations to give tricyclic isoquinoline derivatives in good yields. DFT calculations suggest that the reaction mechanism involves a migratory insertion of the alkyne into the rhodium–nitrogen bond of the rhodacycle intermediate that results from the initial C–H activation. This contrasts with the pathway proposed for intermolecular cases, which considers an insertion into the rhodium–carbon instead of the rhodium–nitrogen bond. The annulation is also effective with acrylamides; and, while anilides fail to participate in the process, naphthylamides do undergo the intramolecular annulation, albeit the chemoselectivity is different than for the intermolecular reactions.
TL;DR: In this article, a review of recent developments in hypervalent organoantimony and -bismuth complexes with bidentate (C,E )- and tridentate( E,C, E )-ligands is presented.
TL;DR: A xanthene-based fluorescent probe 1, in which tightly held acylguanidine and aldehyde groups engage in multiple intramolecular hydrogen bonds within the concave side of the molecule, provided compelling experimental evidence for the functional role of HBD-HBA interactions in the "remote" control of chemical reactivity.
Abstract: Hydrogen-bonding promoted covalent modifications are finding useful applications in small-molecule chemical synthesis and detection. We have designed a xanthene-based fluorescent probe 1, in which tightly held acylguanidine and aldehyde groups engage in multiple intramolecular hydrogen bonds within the concave side of the molecule. Such an interdigitated hydrogen bond donor–acceptor (HBD–HBA) array imposes significant energy barriers (ΔG‡ = 10–16 kcal mol–1) for internal bond rotations to assist structural preorganization and effectively polarizes the electrophilic carbonyl group toward a nucleophilic attack by CN– in aqueous environment. This covalent modification redirects the de-excitation pathways of the cyanohydrin adduct 2 to elicit a large (>7-fold) enhancement in the fluorescence intensity at λmax = 440 nm. A remarkably faster (> 60-fold) response kinetics of 1, relative to its N-substituted (and therefore “loosely held”) analogue 9, provided compelling experimental evidence for the functional rol...
TL;DR: In this paper, the authors examined the nature of halogen bonding via experimental and computational characterizations of a series of associates between electrophilic bromocarbons R-Br and bromide anions.
Abstract: The nature of halogen bonding is examined via experimental and computational characterizations of a series of associates between electrophilic bromocarbons R-Br (R-Br=CBr3F, CBr3NO2, CBr3COCBr3, CBr3CONH2, CBr3CN, etc.) and bromide anions. The [R-Br, Br(-)] complexes show intense absorption bands in the 200-350 nm range which follow the same Mulliken correlation as those observed for the charge-transfer associates of bromide anions with common organic π-acceptors. For a wide range of the associates, intermolecular R-Br···Br(-) separations decrease and intramolecular C-Br bond lengths increase proportionally to the Br(-)→R-Br charge transfer; and the energies of R-Br···Br(-) bonds are correlated with the linear combination of orbital (charge-transfer) and electrostatic interactions. On the whole, spectral, structural and thermodynamic characteristics of the [R-Br, Br(-)] complexes indicate that besides electrostatics, the orbital (charge-transfer) interactions play a vital role in the R-Br···Br(-) halogen bonding. This indicates that in addition to controlling the geometries of supramolecular assemblies, halogen bonding leads to electronic coupling between interacting species, and thus affects reactivity of halogenated molecules, as well as conducting and magnetic properties of their solid-state materials.
TL;DR: In this tandem catalytic synthesis of 3-aroylindoles both C-C and C-O bonds are installed at the expense of two sp(3) C-H bond cleavages.
TL;DR: The design of a synthetic strategy for a copper-catalyzed aerobic oxidative/ dehydrogenative a-functionalization of tertiary amines with subsequent intramolecular sp C O bond formation is disclosed.
Abstract: The hydroxy functional group directs the α-functionalization of tertiary amines, synthesizing 1,3-oxazines by C—O bond formation.
TL;DR: The direct observation of intramolecular hydrogen atom transfer reactions (tautomerization) within a single porphycene molecule on a Cu(110) surface by scanning tunneling microscopy is reported and it is found that the tautomersization can be induced via inelastic electron tunneling at 5 K.
Abstract: We report the direct observation of intramolecular hydrogen atom transfer reactions (tautomerization) within a single porphycene molecule on a Cu(110) surface by scanning tunneling microscopy. It is found that the tautomerization can be induced via inelastic electron tunneling at 5 K. By measuring the bias-dependent tautomerization rate of isotope-substituted molecules, we can assign the scanning tunneling microscopy-induced tautomerization to the excitation of specific molecular vibrations. Furthermore, these vibrations appear as characteristic features in the dI/dV spectra measured over individual molecules. The vibrational modes that are associated with the tautomerization are identified by density functional theory calculations. At higher temperatures above ∼75 K, tautomerization is induced thermally and an activation barrier of about 168 meV is determined from an Arrhenius plot.
TL;DR: The surface bonding and ordering of free-base porphine (2H-P), the parent compound of all porphyrins, on a smooth noble metal support, is investigated, revealing a surprisingly rich and complex behavior, including intramolecular proton switching, repulsive intermolecular interactions, and density-driven phase transformations.
Abstract: We investigated the surface bonding and ordering of free-base porphine (2H-P), the parent compound of all porphyrins, on a smooth noble metal support. Our multitechnique investigation reveals a surprisingly rich and complex behavior, including intramolecular proton switching, repulsive intermolecular interactions, and density-driven phase transformations. For small concentrations, molecular-level observations using low-temperature scanning tunneling microscopy clearly show the operation of repulsive interactions between 2H-P molecules in direct contact with the employed Ag(111) surface, preventing the formation of islands. An increase of the molecular coverage results in a continuous decrease of the average intermolecular distance, correlated with multiple phase transformations: the system evolves from an isotropic, gas-like configuration via a fluid-like phase to a crystalline structure, which finally gives way to a disordered layer. Herein, considerable site-specific molecule–substrate interactions, fav...
TL;DR: Various (Z)-2-bromoacetophenone tosylhydrazones were converted into indazoles at room temperature in excellent yields and the yield was improved by photoisomerization with UV light when E/Z isomeric mixtures of the starting material were used.
Abstract: cules. For the synthesis of N-heterocyclic compounds, CN coupling reactions are highly valuable; consequently, they have quite frequently been used in the preparation of specific polymers, dyes, and biologically active molecules to be used as agrochemicals and drugs. They are most often catalyzed by Pd-, Ni-, or Cu-based complexes, often at elevated temperatures. [2] Especially if applied in the synthesis of pharmaceuticals, the use of such transition-metal catalysts is controversial, since they may remain in the products as trace impurities, which have to be removed in tedious additional steps. Hence, reaction protocols that enable the preparation of compounds through inter- or intramolecular CN coupling reactions in the absence of transition metals are attractive and considered sustainable. [3] In this context, we previously reported various base-mediated N-, O-, and S-arylation reactions, including intramolecular ring-closing reactions to give heterocyclic products. [4] We now wondered about a transition-metal-free