Pd-catalyzed Suzuki-Miyaura Cross-coupling Reactions Research Articles

Pd-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction in Glycerol Using KOH as Base and Glycerol-Triethanolamine Deep Eutectic Solvent under Inorganic Base‑Free Conditions

Glycerol and glycerol-triethanolamine deep eutectic solvent are both environmentally benign, cost-effective, and practical solvents for the Pd-catalyzed Suzuki-Miyaura cross-coupling of aryl halides with arylboronic acids. Utilizing KOH as base, the reaction in glycerol proceeded smoothly with low catalyst loadings (up to 0.5 mol% of PdCl2(PPh3)2) providing excellent yields (up to 99%) of the cross-coupling products, which can be readily extracted with hexane. However, the recyclability of the glycerol medium containing the catalyst is limited to a few cycles. Furthermore, it was explored the use of chlorodiphenylphosphine as a pre-ligand. Although glycerol phosphinite was not generated in situ, PPh2Cl proved to be an excellent pre-ligand, yielding the coupling product with a 98% yield. Compared to glycerol, glycerol-triethanolamine deep eutectic solvent (TEOA:G DES) proves to be a superior solvent for the cross-coupling reaction. In addition, the presence of amine group in the solvent allowed to obtain an inorganic base-free cross-coupling protocol. Aryl bromides and aryl boronic acids containing both electron releasing and attracting functional groups can be coupled without requiring the addition of any further base, affording the biphenyl products in moderate to good yields. The cross-coupling products can be easily isolated by extraction with hexane. Moreover, we observed the formation of triethanolamine phenylboronate during the reaction. The triethanolamine boronate was subsequently synthesized through the condensation of phenylboronic acid with triethanolamine and fully characterized. 11B nuclear magnetic resonance (NMR) spectroscopy confirmed the coordination of the nitrogen to the boron atom of the triethanolamine boronate.

Synthesis of Functionalized Hexahydrocarbazoles by Beckmann Elimination and Nucleophile-Intercepted Beckmann Fragmentation.

The Beckmann elimination and nucleophile-intercepted Beckmann fragmentation (NuBFr) of oximes starting from regioisomeric indolinyl bicyclic ketones lead to products that are subjected to further synthetic manipulations and ultimately result in the stereospecific formation of densely functionalized hexahydrocarbazoles. The Pd-catalyzed Suzuki-Miyaura cross-coupling reaction of a key alkenyl bromide intermediate with various boronic acids gives arylated products.

De Novo Diastereoselective Synthesis of 1-Hydroxyl Allogibberic Methyl Ester en Route to Diverse Bioactive Molecules.

The first de novo synthesis of 1-hydroxyl allogibberic methyl ester, en route to pharbinilic acid and other bioactive molecules, is accomplished in diastereoselective manner. Key reactions of the synthesis include a Pd-catalyzed Suzuki-Miyaura cross-coupling reaction, a Lewis acid-catalyzed reductive Prins cyclization reaction, and a SmI2-mediated transannular pinacol coupling reaction. The synthesis provides a new avenue to access diverse relevant bioactive molecules.

In Situ Monitoring of Palladium-Catalyzed Chemical Reactions by Nanogap-Enhanced Raman Scattering using Single Pd Cube Dimers

The central dilemma in label-free in situ surface-enhanced Raman scattering (SERS) for monitoring of heterogeneously catalyzed reactions is the need of plasmonically active nanostructures for signal enhancement. Here, we show that the assembly of catalytically active transition-metal nanoparticles into dimers boosts their intrinsically insufficient plasmonic activity at the monomer level by several orders of magnitude, thereby enabling the in situ SERS monitoring of various important heterogeneously catalyzed reactions at the single-dimer level. Specifically, we demonstrate that Pd nanocubes (NCs), which alone are not sufficiently plasmonically active as monomers, can act as a monometallic yet bifunctional platform with both catalytic and satisfactory plasmonic activity via controlled assembly into single dimers with an ∼1 nm gap. Computer simulations reveal that the highest enhancement factors (EFs) occur at the corners of the gap, which has important implications for the SERS-based detection of catalytic conversions: it is sufficient for molecules to come in contact with the "hot spot corners", and it is not required that they diffuse deeply into the gap. For the widely employed Pd-catalyzed Suzuki-Miyaura cross-coupling reaction, we demonstrate that such Pd NC dimers can be employed for in situ kinetic SERS monitoring, using a whole series of aryl halides as educts. Our generic approach based on the controlled assembly into dimers can easily be extended to other transition-metal nanostructures.

Blueish-white-light-emitting Nanographenes Developed by Pd-catalyzed Suzuki-Miyaura Cross Coupling Reactions

Abstract Top-down methods produce nanographenes with many carboxy groups on their edges. These functional groups can be utilized for developing multichromophoric systems. As proof of concept, pyrene is installed on the edges by Pd-catalyzed cross-coupling reactions. The lack of monomer emissions from the functionalized nanographenes indicates that the neighboring chromophores are sufficiently distant to form the excimer. The pyrene-installed nanographene emits bluish-white-light. Its lipophilic nature allows fabricating a nanographene-dispersed polymethyl methacrylate film emitting visible light.

Synthesis of Pharmacologically Relevant New Derivatives of Maleimides via Ligand-Free Pd-Catalyzed Suzuki–Miyaura Cross-Coupling Reactions

The Suzuki–Miyaura coupling reactions were applied for synthesis of pharmacological relevant derivatives of known 3,4-dibromo-1-methyl-1H-pyrrole-2,5-dione compound. Suzuki–Miyaura reactions of 3,4-dibromo-1-methyl-1H-pyrrole-2,5-dione with two equivalents of arylboronic acids gave vicinal diphenyl-substituted maleimide products. The reaction with one equivalent of arylboronic acid resulted in site-selective synthesis of N-methyl-2-aryl-3-bromomaleimide. The one-pot reaction of 3,4-dibromo-1-methyl-1H-pyrrole-2,5-dione with two different arylboronic acids afforded N-methyl-2-3-diaryl-maleimides containing two different aryl groups. Maleimide-resulting compounds have added a general interest in the fields of Pharmaceuticals, diagnostics, materials and catalysis. The synthesis of maleimide-substituted compounds via Suzuki–Miyaura cross-coupling protocols has increased extensive interest in the synthesis of heterocyclic compounds.

Palladium-Catalyzed [3+2] Annulation of Naphthalimide Acceptors and Thiophene Donors.

Donor-acceptor (D-A) dyes constitute one of the fundamental structural motifs of functional organic materials. In most cases, the donor and acceptor moieties are connected by a single bond, which could potentially be replaced by a fused aromatic ring to enhance the rigidity and conjugation of the dye moieties. However, there is still a lack of synthetic methodologies for such fused D-A systems. Here we report the synthesis of D-A and A-D-A dyes that possess fully annulated donor and acceptor moieties based on palladium (Pd)-catalyzed [3+2] annulation reaction between bromo-chloro-naphthalene dicarboximide and thiophene- and indole-based boronic esters. Thus, a series of fused D-A and A-D-A conjugated dyes were synthesized in good to high yields by a cascade of Pd-catalyzed Suzuki-Miyaura cross-coupling and direct arylation reactions. The newly synthesized fused D-A and A-D-A dyes with one or two naphthalimide units fused to five-membered electron-rich heterocyles were systematically investigated by ultraviolet-visible spectroscopy, cyclic and square wave voltammetry, and density functional theory calculations. These dyes possess desirable optical and electrochemical properties for application as organic electronic materials as they show absorption up to the near-infrared region, undergo up to 4-fold reduction processes, and have low-lying LUMO energy levels down to -3.62 eV.

A Bulky Chiral N-Heterocyclic Carbene Palladium Catalyst Enables Highly Enantioselective Suzuki-Miyaura Cross-Coupling Reactions for the Synthesis of Biaryl Atropisomers.

Axially chiral biaryl scaffolds are essential structural units in chemistry. The asymmetric Pd-catalyzed Suzuki-Miyaura cross-coupling reaction has been widely recognized as one of the most practical methods for constructing atropisomers of biaryls. However, longstanding challenges remain in this field. For example, substrate scope is often narrow and specialized, functional groups and heterocycles can lead to reduced reactivity and selectivity, bulky ortho-substituents are usually needed, and reported methods are generally inapplicable to tetra-ortho-substituted biaryls. We have developed an unprecedented highly enantioselective N-heterocyclic carbene (NHC)-Pd catalyzed Suzuki-Miyaura cross-coupling reaction for the synthesis of atropisomeric biaryls. These reactions enable efficient coupling of aryl halides (Br, Cl) or aryl triflates with various types of aryl boron compounds (B(OH)2, Bpin, Bneo, BF3K), tolerate a remarkably broad scope of functional groups and heterocycles (>41 examples), employ low loading of catalyst (0.2-2 mol %), and proceed under mild conditions. The protocol provided general and efficient access to various atropisomeric biaryls and heterobiaryls in excellent enantioselectivities (up to99% ee) with no need of using bulky ortho-substituted substrates and was effective for the synthesis of tetra-ortho-substituent biaryls. Moreover, the method was successfully applied to the diastereo- and enantioselective synthesis of atropisomeric ternaphthalenes. Critical to the success of the reaction is the development and application of an extremely bulky C2-symmetric chiral NHC, (R,R,R,R)-DTB-SIPE, as the ligand for palladium. To the best of our knowledge, this is the first highly enantioselective (>90% ee) example of a chiral NHC-metal-catalyzed C(sp2)-C(sp2) cross-coupling reaction.

Salicylaldehyde-stabilized Palladium Nanoparticles for Highly Efficient Suzuki-Miyaura Reaction at Room Temperature

Pd-catalyzed Suzuki-Miyaura cross-coupling reactions promoted by simple and commercial salicylaldehyde-based ligands were investigated. The effect of the ligands was evaluated and the reaction cond...

Synthesis, crystal structure analysis, spectral IR, UV–Vis, NMR assessments, electronic and nonlinear optical properties of potent quinoline based derivatives: Interplay of experimental and DFT study

Quinoline and its derivatives are widely studied by both synthetic and computational chemists due to their exciting perspectives in biological and nonlinear optical (NLO) research. Herein, three novel arylated quinolines: 3-(4-acetylphenyl)quinoline (1), 3-(4-(methylthio)phenyl)-quinoline (2) and 3-(4-phenoxyphenyl)quinoline (3) were synthesized employing Pd catalyzed Suzuki–Miyaura cross-coupling reaction. The chemical structures of all compounds were resolved employing different analytical techniques like 1H-NMR, FT-IR, UV–Vis, EIMS, elemental analysis and finally confirmed by single crystal X-ray diffraction analysis. Synthesized compounds were further subjected to density functional theory (DFT) calculations at B3LYP level of theory in conjunction with 6-311 + G(2d,p) basis set to explore optimized geometry, natural bond orbital (NBO) analysis, FT-IR spectroscopic data, frontier molecular orbitals (FMOs) and NLO properties. Overall, a good agreement was found between DFT computed results and corresponding experimental findings. Vertical electronic transition states were computationally calculated using time-dependent DFT (TDDFT) at same B3LYP level of theory and 6-311 + G(2d,p) basis set combination. NBO calculations indicated the occurrence of intra-molecular charge transfer in synthesized compounds, hence enormous molecular stability owing to hyperconjugative interactions. Energy of FMOs was used to calculate the global reactivity descriptors which indicated that synthesized molecules are chemically hard compounds with greater kinetic stability and electron donating capability. NLO properties were found to be in the range 1830–2960 a.u and order of 2 > 1 > 3. Urea molecule comparative analysis and two-state model confirmed that synthesized molecules are excellent NLO candidates and may have prospective uses in the technology related applications.

Computationally Assisted Mechanistic Investigation and Development of Pd-Catalyzed Asymmetric Suzuki-Miyaura and Negishi Cross-Coupling Reactions for Tetra-ortho-Substituted Biaryl Synthesis.

Metal-catalyzed cross-coupling reactions are extensively employed in both academia and industry for the synthesis of biaryl derivatives for applications to both medicine and material science. Application of these methods to prepare tetra-ortho-substituted biaryls leads to chiral atropisomeric products that introduces the opportunity to use catalyst-control to develop asymmetric cross-coupling procedures to access these important compounds. Asymmetric Pd-catalyzed Suzuki-Miyaura and Negishi cross-coupling reactions to form tetra-ortho-substituted biaryls were studied employing a collection of P-chiral dihydrobenzooxaphosphole (BOP) and dihydrobenzoazaphosphole (BAP) ligands. Enantioselectivities of up to 95:5 and 85:15 er were identified for the Suzuki-Miyaura and Negishi cross-coupling reactions, respectively. Unique ligands for the Suzuki-Miyaura reaction vs the Negishi reaction were identified. A computational study on these Suzuki-Miyaura and Negishi cross-coupling reactions enabled an understanding in the differences between the enantiodiscriminating events between these two cross-coupling reactions. These results support that enantioselectivity in the Negishi reaction results from the reductive elimination step, whereas all steps in the Suzuki-Miyaura catalytic cycle contribute to the overall enantioselection with transmetalation and reductive elimination providing the most contribution to the observed selectivities.

Modular Dihydrobenzoazaphosphole Ligands for Suzuki–Miyaura Cross-Coupling

A new family of dihydrobenzoazaphosphosphole ligands was prepared and shown to enable modification of the phosphine electronic character by variation of the N-substituent. This new family of phosphines was shown to be highly active in the Pd-catalyzed Suzuki–Miyaura cross-coupling reaction with hindered coupling partners.

SYNTHESIS AND CHARACTERIZATION OF NOVEL 4-CYNANOPHENYL-FUNCTIONALIZED N4,N4,N4′,N4′-TERAPHENYLBENZIDINE (TPB) AS HOLE TRANSPORTING MOLECULAR MATERIALS

In this study, a new cyanophenyl-functionalized N4,N4,N4′,N4′-tetraphenylbenzidine (TPB) containing employable hole-transporting components has been synthesized with Pd-catalyzed Suzuki-Miyaura cross coupling reaction. N4,N4,N4′,N4′tetrakis-(4′-cynobiphenyl-4-yl)-biphenyl-4,4′-diamine (TPB-CN) was well characterized by 1H NMR, 13C NMR and CHN elemental analysis. The compound TPB-CN exhibited good thermal stability and luminescence properties. Time Dependent Density Functional Theory (TDDFT) computation was carried out to investigate the structural parameters and to understand the photophysical properties of the novel TPB-CN compound. The experimental and theoretical calculations performed to calculate absorption maxima in DCM by UV-Vis and TD-B3LYP/6-31g(d,p) were compared with each other. To identify crystal structure and to determine optical band gap of TPB-CN compound, its film form, which was coated on the glass substrate by spin coating, was used. The band gap of TPB-CN compound both in film and in solution was determined from the optical absorption measurements.

Harnessing a p-Quinone Methide Intermediate in the Biomimetic Total Synthesis of the Highly Active Antibiotic 20-Deoxy-Elansolid B1.

The polyketide, 20-deoxy elansolid B1, was prepared by a convergent strategy that relied on a putative biomimetic intramolecular Diels-Alder cycloaddition (IMDA) via a vinylic p-quinone methide intermediate to furnish the key tetrahydroindane unit. The (Z,E,Z)-configured triene unit was constructed by Pd-catalyzed Suzuki-Miyaura and Stille cross-coupling reactions without isomerization of any of the olefinic double bonds. Formation of a p-methide quinone intermediate under basic conditions and subsequent Michael addition by water to this intermediate proceeded with high facial selectivity which terminated this total synthesis. Remarkably, the new elansolid derivative 2 c shows very good inhibitory effect against Bacillus subtilis and Staphylococcus aureus (including MRSA) similarly to the best elansolid derivatives reported so far. Consequently, the hydroxyl group at C20 is not essential for antibacterial activity.

A Concise Synthesis of (−)-Incrustoporin and its Analogues by Pd-catalyzed Suzuki-Miyaura Coupling fromγ-Vinyl-γ-butyrolactone

A highly efficient synthesis of C3-arylbutenolides by Suzuki-Miyaura coupling is described. We developed a simple protocol to accomplish scaffolds of C3-arylbutenolides which include antifungal agent (−)-incrustoporin and twelve analogues by Pd-catalyzed Suzuki-Miyaura cross coupling reaction between chiral 3-iodobutenolide and various aryl boronic acids under aerobic conditions in good to quantitative yields.

Synthesis of Piceatannol, an Oxygenated Analog of Resveratrol

Piceatannol (3,3',4,5'-tetrahydroxy-trans-stilbene, 2), an oxygenated analog of resveratrol (1), was synthesized. It is one of the naturally occurring polyphenolic stilbenoids contained in red wine, and possesses many kinds of beneficial effects such as anticancer activity. The trans-stilbene skeleton of 2 was constructed by Pd-catalyzed Suzuki-Miyaura cross coupling reaction of triflate 8 with (E)-alkenylboronoate 13. The key intermediate 13 was prepared diastereoselectively by acid-catalyzed hydroboration of pinacolborane 12 to alkyne 11.

Magnetic Core-Shell to Yolk-Shell Structures in Palladium-Catalyzed Suzuki-Miyaura Reactions: Heterogeneous versus Homogeneous Nature.

This study describes a comparative investigation on the heterogeneous versus homogeneous nature of the Pd-catalyzed Suzuki-Miyaura cross-coupling reaction mechanism with specific magnetic hierarchical core-shell and yolk-shell structures. The hierarchical core-shell Fe3 O4 @SiO2 -Pd@mCeO2 (m=mesoporous) catalyst contains a core of nonporous silica-sheltered magnetite (Fe3 O4 ) nanoparticles (NPs), a transition layer of active palladium (Pd) NPs, and an outer shell of porous ceria (CeO2 ). The magnetic yolk-shell Fe3 O4 @h-Pd@mCeO2 (h=hollow) catalyst was prepared by selectively etching the nonporous silica interlayers. Notably, the results of the hot-filtration heterogeneity test, the effect of Pd concentration, and solid-phase poisoning, indicate that the two kinds of catalysts function in Pd-catalyzed Suzuki-Miyaura cross-coupling reactions through different catalytic mechanisms. Moreover, both catalysts demonstrated better catalytic activity than the Fe3 O4 @SiO2 -Pd catalyst. This finding can be ascribed to the outermost CeO2 shell having a high concentration of trivalent cerium and oxygen vacancies, which gives rise to the increased electron density of Pd NPs, and a faster rate-determining step in the oxidative addition reaction for the Suzuki reaction. In addition, we propose a feasible mechanism elucidating the synergistic effect between the supporting CeO2 and active species.

Synthesis of β-Substituted Cyclic Enones via Phosphonium Salt-Activated, Palladium-Catalyzed Cross-Coupling of Cyclic 1,3-Diones.

Phosphonium salt-activated, Pd-catalyzed Suzuki-Miyaura and Sonogashira cross-coupling reactions of cyclic 1,3-diones in the synthesis of β-substituted cyclic enones are described. These transformations exhibit good isolated yield and high generality with respect to both substrates and coupling partners. Extension of the substrate scope to cyclic 1,3-dione equivalents, such as 2-cyanocyclohexanone (4), is also briefly examined.

Suzuki-Miyaura cross-coupling optimization enabled by automated feedback.

An automated, droplet-flow microfluidic system explores and optimizes Pd-catalyzed Suzuki-Miyaura cross-coupling reactions. A smart optimal DoE-based algorithm is implemented to increase the turnover number and yield of the catalytic system considering both discrete variables-palladacycle and ligand-and continuous variables-temperature, time, and loading-simultaneously. The use of feedback allows for experiments to be run with catalysts and under conditions more likely to produce an optimum; consequently complex reaction optimizations are completed within 96 experiments. Response surfaces predicting reaction performance near the optima are generated and validated. From the screening results, shared attributes of successful precatalysts are identified, leading to improved understanding of the influence of ligand selection upon transmetalation and oxidative addition in the reaction mechanism. Dialkylbiarylphosphine, trialkylphosphine, and bidentate ligands are assessed.

Organic/inorganic salting-in/salting-out agents as promoters of Pd-catalysed ligand free synthesis of biaryls in water

Biaryls were synthesized using Pd-catalyzed Suzuki–Miyaura cross coupling reactions of aryl halides with aryl boronic acids in water in the presence of organic/inorganic additives as promoters. The coupling reactions, carried out in absence of ligand, proceed in good to excellent yields with easy product isolation and in relatively shorter reaction time.