Showing papers on "Heck reaction published in 2016"

Porphyrinic Metal–Organic Framework Catalyzed Heck-Reaction: Fluorescence “Turn-On” Sensing of Cu(II) Ion

Abstract: It is of great importance for the highly selective, rapid, and sensitive detection of Cu(II) ion, as copper is an essential element in the environment and the human body, and exposure to high concentrations of Cu(II) will potentially cause health issues. In this work, we have developed a novel catalytic Heck reaction system based on Pd(II)-porphyrinic metal–organic framework (MOF), PCN-222-Pd(II), to generate highly fluorescent product in the presence of Cu(II). In this system, the achieved signal enlargement toward Cu(II) with high sensitivity not only takes advantage of a stronger binding affinity of Cu(II) over Pd(II) to the nitrogen atoms in the porphyrin, but also a rapid Pd(0)-catalyzed Heck-reaction triggered by the addition of Cu(II) ion. Compared with the previous detection methods, the current fluorescence “turn-on” approach not only realizes highly selective and sensitive detection of Cu(II) in aqueous solution, but also is able to separate the Cu(II) from the system. This work would open up a ...

Controllable Synthesis of Ultrathin Transition-Metal Hydroxide Nanosheets and their Extended Composite Nanostructures for Enhanced Catalytic Activity in the Heck Reaction

Abstract: We report an effective and universal approach for the preparation of ultrathin single- or multiple-component transition-metal hydroxide (TMH) nanosheets with thickness below 5 nm. The unique synthesis benefits from the gradual decomposition of the preformed metal-boron (M-B, M=Fe, Co, Ni, NiCo) composite nanospheres which facilitates the formation of ultrathin nanosheets by the oxidation of the metal and the simultaneous release of boron species. The high specific surface area of the sheets associated with their ultrathin nature promises a wide range of applications. For example, we demonstrate the remarkable adsorption ability of Pb(II) and As(V) in waste water by the ultrathin FeOOH nanosheets. More interestingly, the process can be extended simply to the synthesis of composite structures of metal alloy hollow shells encapsulated by TMH nanosheets, which show excellent catalytic activity in the Heck reaction.

N-Acylsaccharins as Amide-Based Arylating Reagents via Chemoselective N-C Cleavage: Pd-Catalyzed Decarbonylative Heck Reaction.

Abstract: Palladium-catalyzed decarbonylative Heck reaction of amides by chemoselective N–C activation using N-acylsaccharins as coupling partners has been accomplished. These studies represent only the second example of amide-Heck reactions reported to date. A broad range of electronically diverse amide and olefin coupling partners is amenable to this transformation. Orthogonal site-selective Heck cross-couplings by C–Br/N–C cleavage and mechanistic studies are reported. This report introduces readily available, bench-stable, cheap, and benign N-acylsaccharins as aryl transfer reagents to access versatile aryl-metal intermediates.

Enantioselective Palladium-Catalyzed Alkenylation of Trisubstituted Alkenols To Form Allylic Quaternary Centers

Abstract: In this report, we describe the generation of remote allylic quaternary stereocenters β, γ, and δ relative to a carbonyl in high enantioselectivity. We utilize a redox-relay Heck reaction between alkenyl triflates and acyclic trisubstituted alkenols of varying chain-lengths. A wide array of terminal (E)-alkenyl triflates are suitable for this process. The utility of this functionalization is validated further by conversion of the products, via simple organic processes to access remotely functionalized chiral tertiary acid, amine, and alcohol products.

Direct Synthesis of Alkenyl Boronic Esters from Unfunctionalized Alkenes: A Boryl-Heck Reaction

Abstract: We report the first example of a boryl-Heck reaction using an electrophilic boron reagent. This palladium-catalyzed process allows for the conversion of terminal alkenes to trans-alkenyl boronic esters using commercially available catecholchloroborane (catBCl). In situ transesterification allows for rapid access to a variety of boronic esters, amides, and other alkenyl boron adducts.

Synthesis of Secondary Unsaturated Lactams via an Aza-Heck Reaction

Abstract: The preparation of unsaturated secondary lactams via the palladium-catalyzed cyclization of O-phenyl hydroxamates onto a pendent alkene is reported. This method provides rapid access to a broad range of lactams that are widely useful building blocks in alkaloid synthesis. Mechanistic studies support an aza-Heck-type pathway.

Enantioselective oxidative boron Heck reactions

Abstract: This review highlights the use of the oxidative boron Heck reaction in enantioselective Heck-type couplings. The enantioselective oxidative boron Heck reaction overcomes several limitations of the traditional Pd(0)-catalysed Heck coupling and has subsequently allowed for intermolecular couplings of challenging systems such as cyclic enones, acyclic alkenes, and even site selectively on remote alkenes.

RhIII-Catalyzed C−H Olefination of Benzoic Acids under Mild Conditions using Oxygen as the Sole Oxidant

Abstract: Phthalide skeletons have been synthesized for the first time through a Rh(III) -catalyzed C-H olefination of benzoic acids under mild conditions using oxygen as the sole oxidant. Aromatic acids bearing a variety of functional groups could react with diverse alkenes to afford the desired cyclized lactones or uncyclized alkenylarenes in moderate-to-excellent yields.

Branched Arylalkenes from Cinnamates: Selectivity Inversion in Heck Reactions by Carboxylates as Deciduous Directing Groups.

Abstract: A decarboxylative Mizoroki-Heck coupling of aryl halides with cinnamic acids has been developed in which the carboxylate group directs the arylation into its β-position before being tracelessly removed through protodecarboxylation. In the presence of a copper/palladium catalyst, both electron-rich and electron-deficient aryl bromides and chlorides bearing numerous functionalities were successfully coupled with broadly available cinnamates, with selective formation of 1,1-disubstituted alkenes. This reaction concept, in which the carboxylate acts as a deciduous directing group, ideally complements traditional 1,2-selective Heck reactions of styrenes.

Construction of Quaternary Stereocenters by Nickel-Catalyzed Heck Cyclization Reactions.

Abstract: A nickel-catalyzed Heck cyclization for the construction of quaternary stereocenters is reported. This transformation is demonstrated in the synthesis of 3,3-disubstituted oxindoles, which are prevalent motifs seen in numerous biologically active molecules. The method shows broad scope, proceeds in synthetically useful yields, and provides a rare means to construct stereochemically complex frameworks by nonprecious-metal catalysis.

Palladium–S‐propyl‐2‐aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)

Abstract: A moisture- and air-stable heterogenized palladium catalyst was synthesized by coordination of palladium with S-propyl-2-aminothiobenzamide supported on Fe3O4 magnetic nanoparticles. The prepared nanocatalyst was characterized using Fourier transform infrared, energy-dispersive X-ray and inductively coupled plasma atomic emission spectroscopies, X-ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, dynamic laser scattering and thermogravimetric analysis. This catalyst could be dispersed homogeneously in water or poly(ethylene glycol) and further applied as an excellent nano-organometal catalyst for Suzuki and Heck reactions. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst was examined using hot filtration and inductively coupled plasma atomic emission spectroscopy. Also, the effects of various reaction parameters on the Suzuki and Heck reactions are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Fluorescence-Tuned Polyhedral Oligomeric Silsesquioxane-Based Porous Polymers

Abstract: Two series of new polyhedral oligomeric silsesquioxane (POSS)-based fluorescent hybrid porous polymers, HPP-1 and HPP-2, have been prepared by the Heck reaction of octavinylsilsesquioxane with 2,2',7,7'-tetrabromo-9,9'-spirobifluorene and 1,3,6,8-tetrabromopyrene, respectively. Three sets of reaction conditions were employed to assess their effect on fluorescence. These materials exhibit tunable fluorescence from nearly no fluorescence to bright fluorescence both in the solid state and dispersed in ethanol under UV light irradiation by simply altering the reaction conditions. We speculated that the difference may be attributable to the fluorescence quenching induced by Et3 N, P(o-CH3 Ph)3 , and their hydrogen bromide salts employed in the reactions. This finding could give valuable suggestions for the construction of porous polymers with tunable/controllable fluorescence, especially those prepared by Heck and Sonogashira reactions in which these quenchers are used as organic bases or co-catalysts. In addition, the porosities can also be tuned, but different trends in porosity have been found in these two series of polymers, which suggests that various factors should be carefully considered in the preparation of porous polymers with tunable/controllable porosity. Furthermore, HPP-1 c showed moderate CO2 uptake and fluorescence that was efficiently quenched by nitroaromatic explosives, thereby indicating that these materials could be utilized as solid absorbents for the capture and storage of CO2 and as sensing agents for the detection of explosives.

Palladium(II)@Zirconium-Based Mixed-Linker Metal–Organic Frameworks as Highly Efficient and Recyclable Catalysts for Suzuki and Heck Cross-Coupling Reactions

Abstract: Two series of amine-functionalized Zr-based mixed-linker metal–organic frameworks (MOFs; UiO-66-Mix and UiO-67-Mix) have been synthesized with different ratios of 1,4-benzenedicarboxylate/2-amino-1,4-benzenedicarboxylate and 4,4′-biphenyldicarboxylic acid/2-amino-biphenyl-4,4′-dicarboxylic acid incorporated into their structures. The pendant amino groups were postmodified by the condensation reaction with pyridine-2-carboxaldehyde, and Pd metal centers were anchored onto the MOFs by coordination to the pyridylimine moieties. The two series of heterogeneous Pd catalysts (UiO-66-Mix-PI-Pd and UiO-67-Mix-PI-Pd) were utilized for the Suzuki and Heck cross-coupling reactions in ethanol/water under mild reaction conditions and they showed a remarkably high catalytic activity. The porosity of the MOFs and the density of the metal binding sites of the Pd catalysts had great influence on the Suzuki and Heck cross-coupling reactions. The best results were achieved with a very low Pd loading (0.054 mol %), and the use of UiO-67-3-PI-Pd catalyst led to the complete conversion of reaction substrates. Moreover, the catalysts were readily recovered and recycled in at least 10 cycles without significant leaching or loss of catalytic activity. The catalysts were generally applicable for different reaction substrates with various substituents in both Suzuki and Heck reactions.

Graphene anchored palladium complex as efficient and recyclable catalyst in the Heck cross-coupling reaction

Abstract: The immobilization of organometallic molecular catalysts on carbon nanomaterials requires an appropriate synthesis and functionalization methodology to yield active heterogeneous systems. In this work, molecular palladium complexes were synthesized on the aromatic network of a graphenic material employing diazonium chemistry and additional simple modifications to generate a bidentate coordination site for the palladium atoms. The presence of 0.2–0.25 nm palladium(II) species on the surface of the graphenic layers was confirmed by XPS and HRTEM. The modified palladium-graphene hybrid was found to be active as catalyst in the cross-coupling Heck reaction between styrene or n -butyl acrylate with a wide range of aryl bromides substituted with different electron-acceptor and electron-withdrawing groups. The coupled products were obtained in good to excellent yields, at initial TOFs as high as 1.1 s −1 . In addition, the catalyst showed excellent cyclability and air stability, and was reused over 8 cycles without any loss of activity.

Palladium-Schiff Base Complex Immobilized Covalently on Magnetic Nanoparticles as an Efficient and Recyclable Catalyst for Heck and Suzuki Cross-Coupling Reactions

Abstract: A new palladium-Schiff base complex immobilized covalently on magnetic nanoparticles (Pd-imino-Py-γ-Fe2O3) was synthesized via the reaction of chloro-functionalized γ-Fe2O3 with iminopyridine followed by the reaction with palladium acetate. Characterization of Pd-imino-Py-γ-Fe2O3 was carried out by various techniques such as XRD, SEM, TEM, FT-IR, TGA, ICP, XPS, VSM and elemental analysis. Pd-imino-Py-γ-Fe2O3 was successfully applied as a magnetically recyclable heterogeneous catalyst in Heck and Suzuki cross-coupling reactions of various aryl halides (iodide, bromides and chlorides as challenging substrates) with olefins and phenylboronic acid, respectively. The synthesized catalyst was separated easily by using an external magnet and recycled eight runs without appreciable loss of its catalytic activity and leaching of the significant quantity of Pd.

Well-defined palladium(0) complexes bearing N-heterocyclic carbene and phosphine moieties: efficient catalytic applications in the Mizoroki-Heck reaction and direct C-H functionalization.

Abstract: Two series of well-defined palladium(0) complexes with phosphine-functionalized N-heterocyclic carbene ligands were prepared. These complexes featured six- and seven-membered chelate rings in the two series. Among the seven-membered chelate complexes, those featuring the PCy2 moiety exhibited observable fluxional behavior on the NMR time scale, corresponding to the interchange between two sets of conformations. Most of these novel complexes were successfully structurally characterized by single-crystal X-ray diffraction studies. These two series of palladium(0) complexes were tested for their potential catalytic applications in two mechanistically distinct reactions, namely, Mizoroki–Heck coupling and direct C–H functionalization reactions. One of the six-membered chelate complexes was found to be an efficient pre-catalyst for mediating the coupling reactions between aryl chlorides and alkenes. The palladium(0) complex could also be effectively applied in the direct C–H functionalization reactions of aryl bromides with 1,2-dimethylimidazole.

Continuous Consecutive Reactions with Inter‐Reaction Solvent Exchange by Membrane Separation

Abstract: Pharmaceutical production typically involves multiple reaction steps with separations between successive reactions. Two processes which complicate the transition from batch to continuous operation in multistep synthesis are solvent exchange (especially high-boiling- to low-boiling-point solvent), and catalyst separation. Demonstrated here is membrane separation as an enabling platform for undertaking these processes during continuous operation. Two consecutive reactions are performed in different solvents, with catalyst separation and inter-reaction solvent exchange achieved by continuous flow membrane units. A Heck coupling reaction is performed in N,N-dimethylformamide (DMF) in a continuous membrane reactor which retains the catalyst. The Heck reaction product undergoes solvent exchange in a counter-current membrane system where DMF is continuously replaced by ethanol. After exchange the product dissolved in ethanol passes through a column packed with an iron catalyst, and undergoes reduction (>99 % yield).

Noncovalent Substrate-Directed Enantioselective Heck Reactions: Synthesis of S- and P-Stereogenic Heterocycles

Abstract: S- and P-Stereogenic heterocycles were synthesized by a remarkably simple enantioselective Heck desymmetrization reaction based on the unprecedented noncovalent directing effect of S=O and P=O functionalities. Selected prochiral symmetric substrates were efficiently arylated using the recently disclosed chiral PyraBOx ligand under mild and open-flask reaction conditions. Several five-membered aryl- sulfones, sulfoxides, and phosphine oxides were synthesized in good to excellent yields, in good to high diastereoselectivity, and enantiomeric ratios up to 98:2. Theoretical calculations also support the noncovalent directing effect of the S=O and P=O functionalities during the arylation process.

Application of Pd-2A3HP-MCM-41 to the Suzuki, Heck and Stille coupling reactions and synthesis of 5-substituted 1H-tetrazoles

Abstract: An ecofriendly heterogeneous catalyst has been synthesized by anchoring palladium onto the surface of organically modified mesoporous silica. The prepared catalyst was characterized using X-ray diffraction, Fourier transform infrared and energy-dispersive X-ray spectroscopies, transmission and scanning electron microscopies, inductively coupled plasma and thermogravimetric techniques. The catalyst shows high activity in the Suzuki, Heck and Stille cross-coupling reactions and the synthesis of 5-substituted 1H-tetrazoles from sodium azide (NaN3). These methods have the advantages of high yields, green reaction conditions, simple methodology and easy separation and workup. Copyright © 2016 John Wiley & Sons, Ltd.