Coupling Route Research Articles

Chemoselective functionalization of α-carbolines at the C-2, C-3, C-4, and C-6 positions using Suzuki–Miyaura reactions

The synthesis of 2-, 3-, 4-, and 6-substituted pyrido[2,3-b]indoles (α-carbolines) by palladium-catalyzed cross-coupling reactions from the corresponding halopyrido[2,3-b]indoles is described. A sequential and a one-pot chemoselective double Suzuki–Miyaura coupling route is presented for the synthesis of symmetrically and unsymmetrically disubstituted pyrido[2,3-b]indoles.

Matrix Effects on the Triplet State of the OLED Emitter Ir(4,6-dFppy)2(pic) (FIrpic): Investigations by High-Resolution Optical Spectroscopy

The sky-blue emitting compound Ir(4,6-dFppy)(2)(pic) (iridium(III)bis[2-(4',6'-difluorophenyl)pyridinato-N,C(2')]-picolinate), commonly referred to as FIrpic and representing a well-known emitter material for organic light emitting diodes (OLEDs), has been investigated in detail by optical spectroscopy. Studies at temperatures from T = 1.5 K to T = 300 K were carried out in CH(2)Cl(2) and tetrahydrofuran (THF). In CH(2)Cl(2), two discrete sites were observed at cryogenic temperatures and studied by site-selective, high-resolution spectroscopy. The investigations reveal that the molecules located at the two sites exhibit distinctly different photophysical properties. For example, the three substates I, II, and III of the emitting triplet state T(1) of the low-energy site A show a distinctly larger zero-field splitting (ZFS) and exhibit shorter individual decay times than observed for the high-energy site B. The vibrational satellite structures in the emission spectra of the substates I(A) and I(B) exhibit clear differences in the ranges of metal-ligand (M-L) vibrations. For the compound studied in a polycrystalline THF host, giving only strongly inhomogeneously broadened spectra, the ZFS parameters and substate decay times vary in a similar range as observed for the two discrete sites in the CH(2)Cl(2) matrix. Thus, the amount of ZFS, the emission decay times, and also the intensities of the M-L vibrational satellites are affected by the matrix cage, that is, the host environment of the emitting complex. These properties are discussed with respect to variations of spin-orbit coupling routes. In particular, changes of d-orbital admixtures, that is, differences of the metal-to-ligand charge transfer (MLCT) character in the emitting triplet, play an important role. The matrix effects are expected to be also of importance for FIrpic and other Ir(III) compounds when applied as emitters in amorphous OLED matrixes.

Two-Element PIFA Antenna System With Inherent Performance of Low Mutual Coupling

This letter presents and demonstrates a new technique for reducing mutual coupling between closely packed antenna elements. Just locating the antenna element near the edge of ground plate and without adding any additional baffler between elements, the inherent performance of low mutual coupling is attained in the two-element antenna system. Furthermore, this inherent characteristic does not depend on element orientation arrangement and element form, but the coupling routes of the electromagnetic energy. The operation mechanism is explored and explained based on electromagnetic wave propagation theory. The proposed technique has a good application potential to integrate multiantenna elements into a space-limited platform.

Kumada–Corriu Cross Coupling Route to the Anti-Cancer Agent Combretastatin A-4

A short and efficient synthesis of the anticancer agent combretastatin A-4 was accomplished from inexpensive starting materials using the iron-catalyzed cross-coupling of a Grignard reagent and a bromostilbene as the key step.

Thermo-responsive monolithic materials

One of the recent major improvements of HPLC was the introduction of monolithic silica columns, which have the advantage of faster separation and lower back pressure as compared to common silica beads. Here, we present an interesting alternative to such reversed-phase monolithic columns by a convenient coupling route of a thermo-responsive polymer to hydrophilic silica monoliths. Poly( N-isopropylacrylamide) (PNIPAM) was polymerized in solution via a reversible addition fragmentation chain transfer (RAFT) polymerization technique and coupled then in situ onto an amino-modified silica monolithic column. These columns were compared with RP-18 monolithic columns in the separation of steroids under isocratic condition in aqueous mobile phase. Separation is optimized just by changing the temperature, instead of changing the mobile phase composition.

Steam cracking and methane to olefins: Energy use, CO2 emissions and production costs

While most olefins (e.g., ethylene and propylene) are currently produced through steam cracking routes, they can also possibly be produced from natural gas (i.e., methane) via methanol and oxidative coupling routes. We reviewed recent data in the literature and then compared the energy use, CO2 emissions and production costs of methane-based routes with those of steam cracking routes. We found that methane-based routes use more than twice as much process energy than state-of-the-art steam cracking routes do (the energy content of products is excluded). The methane-based routes can be economically attractive in remote, gas-rich regions where natural gas is available at low prices. The development of liquefied natural gas (LNG) may increase the prices of natural gas in these locations. Oxidative coupling routes are currently still immature due to low ethylene yields and other problems. While several possibilities for energy efficiency improvement do exist, none of the natural gas-based routes is likely to become more energy efficient or to lead to less CO2 emissions than steam cracking routes do.

Non‐Innocent Behaviour of Imido Ligands in the Reactions of Silanes with Half‐Sandwich Imido Complexes of Nb and V: A Silane/Imido Coupling Route to Compounds with Nonclassical SiH Interactions

Reactions of imido complexes [M(Cp)(=NR')(PR''3)2] (M=V, Nb) with silanes afford a plethora of products, depending on the nature of the metal, substitution at silicon and nitrogen and the steric properties of the phosphine. The main products are [M(Cp)(=NR')(PR3)(H)(SiRnCl3-n)] (M=V, Nb; R'=2,6-diisopropylphenyl (Ar), 2,6-dimethylphenyl (Ar')), [Nb(Cp)(=NR')(PR''3)(H)(SiPhR2)] (R2=MeH, H2), [Nb(Cp)(==NR')(PR''3)(Cl)(SiHRnCl2-n)] and [Nb(Cp)(eta 3-N(R)SiR2--H...)(PR''3)(Cl)]. Complexes with the smaller Ar' substituent at nitrogen react faster, as do more acidic silanes. Bulkier groups at silicon and phosphorus slow down the reaction substantially. Kinetic NMR experiments supported by DFT calculations reveal an associative mechanism going via an intermediate N-silane adduct [Nb(Cp){=N(-->SiHClR2)R'}(PR''3)2] bearing a penta-coordinate silicon centre, which then rearranges into the final products through a Si--H or Si--Cl bond activation process. DFT calculations show that this imido-silane adduct is additionally stabilized by a Si--HM agostic interaction. Si--H activation is kinetically preferred even when Si--Cl activation affords thermodynamically more stable products. The niobium complexes [NbCp(=NAr)(PMe3)(H)(SiR2Cl)] (R=Ph, Cl) are classical according to X-ray studies, but DFT calculations suggest the presence of interligand hypervalent interactions (IHI) in the model complex [Nb(Cp) (==NMe)(PMe3)(H)(SiMe2Cl)]. The extent of Si--H activation in the beta-Si--HM agostic complexes [Cp{eta 3-N(R')SiR2--H}M(PR''3)(Cl)] (R''=PMe3, PMe2Ph) primarily depends on the identity of the ligand trans to the Si--H bond. A trans phosphine leads to a stronger Si--H bond, manifested by a larger J(Si--H) coupling constant. The Si--H activation diminishes slightly when a less basic phosphine is employed, consistent with decreased back-donation from the metal.

Synthesis and Nonlinear Optical Properties of a New A‐π‐A Two‐Photon Compound Utilizing Dibenzothiophene as Center

AbstractA new two‐photon material, 3E,6E‐bis(2‐pyrid‐4′‐ylvinyl)dibenzothiophene (BPVDBT), has been firstly synthesized by an efficient Pd‐catalyzed Heck coupling route. The single‐ and two‐photon fluorescence, quantum yields, lifetimes, solvent effects of the chromophore were studied in detail and the compound exhibited solvent‐sensitivity. The fluorescence intensity (Iout) and input excitation intensity (Iin) can fit in well with the quadratic parabolas, which indicates that the up‐converted fluorescence was induced by the two‐photon absorption (TPA). TPA cross‐section of BPVDBT has been measured using the two‐photon‐induced fluorescence method, whose value is 14.24×10−50 cm4·s·photon−1·molecule−1 at 750 nm. The experimental results confirm that BPVDBT is a good two‐photon absorbing chromophore with an A‐π‐A type.

Regioselective Suzuki Cross-Coupling Route to 3,4-Disubstituted Quinolin-2(1H)-ones

Reported is a regioselective method for the synthesis of 3,4-disubstituted quinolin-2(1H)-ones via Pd-catalyzed Suzuki cross-coupling reactions. The starting 3-bromo-4-tosyl-quinolin-2(1H)-one is easily synthesized from the commercially available 4-hydroxyquinolin-2(1H)-one. Selective Suzuki coupling occurs, as expected, at the more reactive bromo substituent to give 3-substituted products (route i). A second tosylate coupling (route ii) may be achieved under more vigorous conditions to afford 3,4-disubstituted quinolones. Alternatively, excess of a single boronic acid coupling partner leads to a 3,4-disubstituted product (route iii). The conditions for the tosylate coupling were extensively optimized and only the conditions shown provided the expected product. The reaction scope was moderately studied.

Preparation, Photophysics, and Electrochemistry of Segmented Comonomers Consisting of Thiophene and Pyrimidine Units: New Monomers for Hybrid Copolymers

An efficient coupling route to novel pi-conjugated comonomers consisting of pyrimidine, thiophene, and bithiophene units was developed. The novel pi-donor-acceptor-donor and pi-donor-acceptor-acceptor-donor conjugated compounds were prepared by Suzuki heterocoupling and Ni(0)-mediated Ullman homocoupling reactions. Photophysical investigation of these alternating pi-donor and acceptor compounds indicated that the deactivation of their singlet excited state proceeds predominately by fluorescence and results in high fluorescence quantum yields. Intersystem crossing to the triplet state was also present in ca. 10%. Quantification of the triplet manifold by laser flash photolysis further revealed that bithiophene produced its triplet state in only 31%. Cyclic voltammetry studies showed that the comonomers undergo both oxidation and reduction leading to their radical cations and radical anions, respectively. The radical cations are highly reactive and undergo anodic polymerization resulting in mutual p- and n-type dopable polymers. The extended conjugation resulting from polymer formation was confirmed by both absorbance and fluorescence spectroscopy and by GPC. Ruthenium binding with the conjugated homocoupled ligand was also found resulting in a hybrid alternating copolymer with significantly different spectroscopic and electrochemical properties relative to its metal-free counterpart.

A highly active Cu-MgO-Cr 2O 3 catalyst for simultaneous synthesis of furfuryl alcohol and cyclohexanone by a novel coupling route—Combination of furfural hydrogenation and cyclohexanol dehydrogenation

A novel coupling route highlighting the combination of hydrogenation of furfural and dehydrogenation of cyclohexanol in vapor phase conditions over Cu-MgO-Cr 2O 3 catalyst is highly advantageous in terms of avoiding external pumping of H 2 and maintaining the formation of furfuryl alcohol and cyclohexanone, the desired products, respectively, in good amounts at atmospheric pressure. The catalytic activity of this catalyst is compared with a Cu-MgO coprecipitated catalyst and a copper chromite (commercial Cu-1800P supplied by M/s. Engelhard Corp., USA) catalyst. Cu-MgO-Cr 2O 3 catalyst is prepared by coprecipitation method using tetraethyl ammonium hydroxide as precipitating agent. All the catalysts are characterized by BET surface area, temperature programmed reduction, XRD and XPS. The BET surface area of Cu-MgO-Cr 2O 3 catalyst is higher indicating the presence of smaller Cu particles. XRD results also indicate the presence of smaller particles of Cu in Cu-MgO-Cr 2O 3 catalyst. XPS results indicate the presence of Cu species (Cu 0/Cu +) at the surface of Cu-MgO-Cr 2O 3 catalyst. The higher yields of the products over the Cu-MgO-Cr 2O 3 catalyst in independent and combined reactions compared to the other two catalysts may be attributed to the promotional effect of Cr 2O 3, smaller Cu particle size and more number of Cu 0/Cu + species at the surface.

A Cu-Catalyzed C-N Bond Coupling Route to Substituted Indazoles

A Cu-Catalyzed C-N Bond Coupling Route to Substituted Indazoles

Pd-Catalyzed Sequential C-N and C-C Coupling Route to 2-Vinylindoles

Pd-Catalyzed Sequential C-N and C-C Coupling Route to 2-Vinylindoles

Synthesis of SrAl 2O 4Eu 2+,Dy 3+ phosphors by the coupling route of microemulsion with coprecipitation method

Nano-sized SrAl 2O 4:Eu 2+,Dy 3+ phosphors with good monodispersity and narrow size distribution were synthesized by the coupling of water-in-oil (W/O) microemulsion with coprecipitation method. The phase composition, morphology, crystallinity, excitation spectra, emission spectra, and afterglow decay of SrAl 2O 4:Eu 2+,Dy 3+ nanophosphors were measured. It was found that the amount of surfactant that was used had an important effect on the shape and average size of the phosphor particles. SrAl 2O 4 phase of the phosphors showed an increase with the increase in calcination temperature. When the calcination temperature reached 1150°C, the fine crystal of SrAl 2O 4 was formed and the long afterglow luminescence could be obviously observed. In comparison with the samples prepared by the high-temperature solid-state method, the calcination temperature showed an obvious decrease and a clear blue shift occurred in the excitation and emission spectra of the sample. The afterglow time could be more than 8 h.

Self-Assembling Peptide−Polymer Conjugates Comprising (d-alt-l)-Cyclopeptides as Aggregator Domains

The synthesis of peptide−polymer conjugates comprising (d-alt-l)-cyclopeptides as aggregator domains and their self-assembly into tubelike structures is described. By coupling two well-defined poly(n-butyl acrylate) blocks to opposite sides of a preformed cyclic (d-alt-l)-α-octapeptide, a coil−ring−coil bioconjugate was accessed. The applied solution-phase coupling route allowed a multigram scale synthesis of the conjugate and assured both a controlled synthesis and ease of analysis. The controlled self-assembly of the conjugate leads to uniform tube structures. Atomic force microscopy (AFM) of these aggregates deposited on mica revealed a height of 1.4 ± 0.2 nm, a width of 5 nm, and roughly estimated lengths of up to 200−300 nm. A model is proposed, explaining the structure dimensions. This includes the formation of a tubular peptide core build via stacking of the cyclopeptides and a poly(n-butyl acrylate) shell wrapping around the peptide tube. The model is consistent with infrared spectroscopy and elec...

The Asymmetric Suzuki Coupling Route to Axially Chiral Biaryls

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access the actual ChemInform Abstract, please click on HTML or PDF.

A Rhodium‐Catalyzed Route for Oxidative Coupling and Cyclization of 2‐Aminobenzyl Alcohol with Ketones Leading to Quinolines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Negishi Cross Coupling Route to N-Unsubstituted α,α-Difluorohomophthalimides

Negishi Cross Coupling Route to N-Unsubstituted α,α-Difluorohomophthalimides

Pd/C-Catalyzed Oxidative Alkylation of Secondary Alcohols with Primary Alcohols

Transition metal-catalyzed carbon-carbon coupling protocol has been widely used as a powerful tool in synthetic organic chemistry. In connection with this report, during the course of our studies directed towards a ruthenium-catalyzed carbon-carbon bond forming reaction, we recently found a new ruthenium-catalyzed coupling reactions between ketones (or secondary alcohols) and primary alcohols. The coupling of ketones A with primary alcohols B preferentially afforded coupled ketones C (Scheme 1, route a) or coupled secondary alcohols D (Scheme 1, route b) according to the molar ratio of B to A. In addition, secondary alcohols E were also found to be coupled with B to afford D (Scheme 1, route c). Under these circumstances, this report describes a new Pd/C-catalyzed coupling route between E and B leading to oxidative coupled products C (Scheme 1, route d). The results of several attempted oxidative alkylation of 1phenylethanol (1a) with butanol (2a) under several conditions are listed in Table 1. Treatment of 1a with 2 equiv. of 2a in the presence of a catalytic amount of 5% Pd/ C (5 mol%) along with KOH in dioxane for 40 h afforded oxidative coupled product 1-phenylhexan-1-one (3a), coupled secondary alcohol 1-phenylhexan-1-ol (4), and acetophenone (5) in 2%, 3%, and 2% yields, respectively, with low conversion of 1a (run 1). However, when 1-decene was further added as a sacrificial hydrogen acceptor, the reaction rate was enhanced toward 3a and 5 formation with complete conversion of 1a, whereas 4 remains nearly constant (run 2). It appears that 1-decene works as a sacrificial hydrogen acceptor for a faster regeneration of [Pd] from [Pd]H2 generated during the course of the initial oxidations of 1a to 5 and 2a to butyraldehyde. The molar ratio of 2a to 1a affects the product distribution (runs 3, 4). The oxidized product 5 was formed in preference to 3a and 4 under lower molar ratio ([2a]/[1a] = 1) (run 3) and a lower selectivity between coupled products was observed with higher molar ratio ([2a]/[1a] = 3) (run 4). In spite of further elaboration for the optimization of reaction conditions (run 5, 6), the best result in terms of the yield of oxidative alkylated product 3a and the selectivity of 3a to 4 is best accomplished under the standard set of condition shown in run 2 of Table 1. Given the controlled reaction conditions, various secondary alcohols 1 and primary alcohols 2 were employed to investigate the reaction scope. The representative results are summarized in Table 2. The reactions of 1a with various straight and branched primary alcohols 2a-i gave the corresponding oxidative alkylated ketones 3a-i in the range of 43-83% yields with the concomitant formation of a considerable amount of acetophenone on GLC analysis. The reaction yield and rate were increased with the increase of the straight alkyl chain length in 2. The reaction proceeds likewise with aryl(methyl) carbinols 1b-d to afford the corresponding coupled ketones 3j-l. On the other hand, with cyclic carbinol 1-tetralol (1e), which has methylene reaction

Cover Picture: The Asymmetric Suzuki Coupling Route to Axially Chiral Biaryls (Eur. J. Org. Chem. 20/2005)

AbstractThe cover picture shows the general scheme for the asymmetric biaryl Suzuki coupling, which is surrounded by examples of axially chiral biaryls attainable by this method (bioactive natural products and chiral metal ligands). Various diastereoselective approaches with planar‐to‐axial or central‐to‐axial chirality induction, as well as diastereo‐ or enantio stereoselective approaches with chiral palladium ligands were described in recent years and are presented in the Micro review by O. Baudoin on p. 4223 ff.