Copper(ii)-catalyzed synthesis of multisubstituted indoles through sequential Chan–Lam and cross-dehydrogenative coupling reactions

Starting from arylboronic acids and ester (Z)-3-aminoacrylates, one-pot syntheses of diverse indole-3-carboxylic esters have been described through copper(ii)-catalyzed sequential Chan–Lam N-arylation and cross-dehydrogenative coupling (CDC) reactions. The initial Chan–Lam arylation can proceed in DMF at 100 °C for 24 h to give ester (Z)-3-(arylamino)acrylate intermediates in the presence of Cu(OAc)₂/tri-tert-butylphosphine tetrafluoroborate, a catalytic amount of myristic acid as the additive, KMnO₄ and KHCO₃. Sequentially, these in situ arylated intermediates can undergo an intramolecular oxidative cross-dehydrogenative coupling process in mixed solvents (DMF/DMSO = 2 : 1) at 130 °C to give C3-functionalized multi-substituted indole derivatives.

One-pot syntheses of diverse indole-3-carboxylic esters have been described through copper(ii)-catalyzed sequential oxidative Chan–Lam N-arylation and cross-dehydrogenative coupling (CDC) reaction.     

Modified graphene supported Ag–Cu NPs with enhanced bimetallic synergistic effect in oxidation and Chan–Lam coupling reactions

Herein, well dispersed Ag–Cu NPs supported on modified graphene have been synthesized via a facile and rapid approach using sodium borohydride as a reducing agent under ambient conditions. Dicyandiamide is selected as an effective nitrogen source with TiO₂ as an inorganic material to form two kinds of supports, labelled as TiO₂–NGO and NTiO₂–GO. Initially, the surface area analysis of these two support materials was carried out which indicated that N-doping of GO followed by anchoring with TiO₂ has produced support material of larger surface area. Using both types of supports, ten nano-metal catalysts based on Ag and Cu were synthesized. Benefiting from the bimetallic synergistic effect and larger specific surface area of TiO₂–NGO, Cu@Ag–TiO₂–NGO is found to be a highly active and reusable catalyst out of other synthesized catalysts. It exhibits excellent catalytic activity for oxidation of alcohols and hydrocarbons as well as Chan–Lam coupling reactions. The nanocatalyst is intensively characterized by BET, SEM, HR-TEM, ICP-AES, EDX, CHN, FT-IR, TGA, XRD and XPS.

Cu@Ag–TiO₂–NGO prepared from modified graphene by simple methodology exhibits enhanced catalytic activity towards oxidation and Chan–Lam coupling due to the synergistic effect between Ag and Cu NPs.     

Silver-catalyzed three-component reaction of uracils,arylboronic acids,and selenium: synthesis of 5-arylselanyluracils

Herein, we describe a simple and general multi-component synthesis of 5-arylselanyluracils by the regioselective C–H selenation of uracils. Reactions of uracils with arylboronic acid and Se powder in the presence of AgNO₃ (10 mol%) at 120 °C under aerobic conditions afforded various 5-arylselanyluracils. The source of the introduced selanyl group was prepared from a commercially available arylboronic acid and Se powder in the reaction system, thereby ensuring a simple and efficient protocol. This reaction represents the first example of the synthesis of a 5-arylselanyluracil in a multi-component system.

A simple and general multicomponent synthesis of 5-arylselanyluracils by regioselective C–H selenation of uracils is described.     

Iron catalyzed C–C dehydrogenative coupling reaction: synthesis of arylquinones from quinones/hydroquinones

An atom-economical approach for the synthesis of arylquinones was achieved successfully via direct oxidative C–C dehydrogenative coupling reaction of quinones/hydroquinones with electron-rich arenes using an inexpensive Fe–I₂–(NH₄)₂S₂O₈ system. The efficiency of this catalytic approach was established with a broad scope of substrates involving quinones and hydroquinones to give high yields (60–89%) of several arylated quinones. The present protocol is simple, practical, and shows good functional group tolerance.

The synthesis of arylquinones was achieved via direct oxidative C–H/C–H cross-coupling of quinones/hydroquinones with electron-rich arenes using Fe–I₂–(NH₄)₂S₂O₈ system involving quinones/hydroquinones to give high yields (60–89%) of arylquinones.     

Iron-catalyzed tandem reaction of C–Se bond coupling/selenosulfonation of indols with benzeneselenols

An iron-catalyzed tandem reaction of C–Se bond coupling/selenosulfonation was developed. Starting from sample indols and benzeneselenols versatile biologically active 2-benzeneselenonyl-1H-indoles derivatives were efficiently synthesized. The reaction mechanism was studied by the deuterium isotope study and in situ ESI-MS experiments. This protocol features mild reaction conditions, wider substrate scope and provides an economical approach toward C(sp²)–Se bond formation.

Iron-catalyzed tandem reaction of C–Se bond coupling/selenosulfonation.

Due to the important applications in the preparation of synthetic materials,¹ pharmaceutical agents,² fluorescent probes,³ and functional organic materials,⁴ organoselenium compounds synthesis has attracted extensive attention from synthetic chemists. It is known that transition-metal catalyzed cross coupling reaction is the mostly used methodology for the incorporation of a Se atom into aromatic frameworks.⁵ However, prefunctionalization of the substrate is generally requested. Similar methods of C(sp²)–Se bonds formation have been scarcely described.^6–8Comparative to the C(sp)–H, the C(sp²)–H bond activation need more harsh conditions and activated reaction systems.⁹ Considering the significance of diversifying synthetic strategies, our group focuses on tradition-metal catalyzed C–H bond functionalizations.¹⁰ Herein, we report a novel iron-catalyzed direct C(sp²)–H bond activation/C–Se cross coupling reaction of indols with benzeneselenols. Versatile biologically active compounds 2-benzeneselenonyl-1H-indoles were efficiently synthesized in good to high yields. In this reaction, the inactive C(sp²)–H bonds were smoothly direct selenosulfonation under a moderate condition. At last, the reaction mechanism was studied by the deuterium isotope study and the in situ ESI-MS experiments.At first, as shown in

Palladium/phosphorus-functionalized porous organic polymer with tunable surface wettability for water-mediated Suzuki–Miyaura coupling reaction

A series of phosphorus-functionalized porous organic polymers supported palladium catalysts with tunable surface wettability were successfully prepared using an easy copolymerization and successive immobilization method. The obtained polymers were carefully characterized by many physicochemical methods. Characterization results suggested that the prepared materials featured hierarchically porous structures, high pore volumes, tunable surface wettability and strong electron-donating ability towards palladium species. We demonstrated the use of these solid catalysts for water-mediated Suzuki–Miyaura coupling reactions. It was found that the surface wettability of the prepared catalysts has an important influence on their catalytic activities. The optimal catalyst, which has excellent amphipathicity and relatively high phosphorus concentration, displayed superior catalytic activity compared to the other catalysts. Under ambient conditions, a variety of aryl chlorides can be efficiently transformed to biaryls in high yields. Moreover, the catalyst could be easily recovered and reused at least six times.

A palladium/phosphorus-functionalized porous organic polymer with tunable surface wettability was successfully prepared. The catalyst displayed high catalytic activity for the water-mediated Suzuki–Miyaura coupling reaction of aryl chlorides.     

Palladium catalyst imbedded in polymers of intrinsic microporosity for the Suzuki–Miyaura coupling reaction

Polymers of intrinsic microporosity (PIMs) are porous polymers with rigid ladder-type chain structures. Synthesizing these polymers usually involves the step polymerization of two types of monomer, namely, active fluorine-substituted aromatic ring monomers and phenolic monomers. Herein, we report a new PIMs preparation method using self-synthesized fluorinated monomers and common monomer 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl spirobisindane. The fluorinated monomers were synthesized through the imidization of tetrafluorophthalic anhydride and aromatic diamines. The resulting PIMs served as a support for palladium, with the formed catalyst showing potential for application in the Suzuki–Miyaura coupling reaction.

Polymers of intrinsic microporosity (PIMs) are porous polymers with rigid ladder-type chain structures.     

Step-saving synthesis of star-shaped hole-transporting materials with carbazole or phenothiazine cores via optimized C–H/C–Br coupling reactions

In most research papers, synthesis of organic hole-transporting materials relies on a key-reaction: Stille cross-couplings. This requires tedious prefunctionalizations including the preparation and treatment of unstable organolithium and toxicity-concern organotin reagents. In contrast to traditional multistep synthesis, this work describes that a series of star-shaped small molecules with a carbazole or phenothiazine core can be efficiently synthesized through a shortcut using optimized direct C–H/C–Br cross-couplings as the key step, thus avoiding dealing with the highly reactive organolithium or the toxic organotin species. Device fabrication of perovskite solar cells employing these molecules (6–13) as hole-transporting layers exhibit promising power conversion efficiencies of up to 17.57%.

Carbazole or phenothiazine core-based hole-transport materials are facilely accessed by an optimized synthesis-shortcut. Perovskite solar cell devices with 6–13 demonstrate PCEs of up to 17.57%.     

Iridium-catalyzed ortho-selective carbon–hydrogen amidation of benzamides with sulfonyl azides in ionic liquid

An efficient and convenient iridium(iii) catalyzed ortho-C–H bond amidation of weakly coordinating benzamides treated with readily available sulfonyl azides as the amino source has been described. In this transformation, ionic liquids represents an ideal reaction medium, giving rise to a broad range of amidation products under mild conditions in the open air. This protocol offers moderate to excellent chemical yields, exclusive regioselectivities, and good functional group tolerance.

Ir-catalyzed ortho-C–H amidation of benzamides with sulfonyl azides has been conducted effectively in ionic liquid reaction medium.     

Iridium-catalyzed regioselective C–H sulfonamidation of 1,2,4-thiadiazoles with sulfonyl azides in water

We have developed a regioselective C–N cross-coupling of 1,2,4-thiadiazoles with sulfonyl azides through iridium catalysis in water. This method tactically linked the 1,2,4-thiadiazoles and sulfonamides together, and the novel molecules increased the diversity of 1,2,4-thiadiazoles which may have potential applications.

We have developed a regioselective C–N cross-coupling of 1,2,4-thiadiazoles with sulfonyl azides through iridium catalysis in water.     

Computational elucidation of the reaction mechanism for synthesis of pyrrolidinedione derivatives via Nef-type rearrangement – cyclization reaction

This paper reports a quantum chemical study of all stages of a one-pot synthesis of pyrrolidinedione derivatives from nitromethane and coumarin, which includes Michael addition, migration of an oxygen atom (Nef-type rearrangement), and cyclization to a pyrrolidine ring. The energy barrier of deprotonated nitromethane addition to coumarin is 21.7 kJ mol⁻¹, while the barrier of proton transfer from the methylene to the nitro group in the nitromethyl group is notably higher, 197.8 kJ mol⁻¹. The second stage of the reaction, migration of an oxygen atom within the nitromethyl group, occurs with lowest energy barrier, 142.4 kJ mol⁻¹, when it is assisted by an additional water molecule. The last stage – cyclization, passes with a very low energy barrier of 11.9 kJ mol⁻¹ but the tautomerization of the nitrosohydroxymethyl group to the hydroxy-N-hydroxyiminomethyl, necessary for the process, has an energy barrier of 178.4 kJ mol⁻¹. Analogous calculations for the same process with the ethyl ester of 3-coumarin-carboxylic acid as substrate show that the relative energies of the intermediates and transition states are by at most 10–16 kJ mol⁻¹ more stable than the corresponding structures with coumarin.

A quantum chemical study of all stages of pyrrolidinedione derivative synthesis from nitromethane and coumarin, which includes Michael addition, migration of an oxygen atom (Nef-type rearrangement), and cyclization to a pyrrolidine ring is reported.     

Versatile cross-linked fatty acid-based polycarbonate networks obtained by thiol–ene coupling reaction

Bio-sourced polycarbonate networks have been synthesized from an alkene-functional fatty-acid based polycarbonate precursor. Cross-linked networks were created using the radical thiol–ene coupling reaction. The resulting polycarbonate materials exhibited versatile properties either influenced by the structure of the cross-linker or the cross-linker/olefin unit ratio. Indeed, the storage modulus above the glass transition temperature could be modulated from 0.9 to 8.9 MPa only by changing the type of cross-linker, i.e. 1,9-nonanedithiol vs. 1,4-benzenedimethanethiol. The cross-linker/olefin unit ratio was also shown to largely impact the polycarbonate networks properties. An elongation at break of nearly 200% was reached when a low cross-linker/olefin ratio was applied. Moreover, functional polycarbonate networks bearing pendant thiol groups were obtained when an excess of dithiol was used with respect to olefin groups.

Bio-sourced polycarbonate networks have been synthesized from an alkene-functional fatty-acid based polycarbonate precursor.     

Efficient in situ N-heterocyclic carbene palladium(ii) generated from Pd(OAc)2 catalysts for carbonylative Suzuki coupling reactions of arylboronic acids with 2-bromopyridine under inert conditions leading to unsymmetrical arylpyridine ketones: synthesis,characterization and cytotoxic activities

N,N-Substituted benzimidazole salts were successfully synthesized and characterized by ¹H-NMR, ¹³C {¹H} NMR and IR techniques, which support the proposed structures. Catalysts generated in situ were efficiently used for the carbonylative cross-coupling reaction of 2 bromopyridine with various boronic acids. The reaction was carried out in THF at 110 °C in the presence of K₂CO₃ under inert conditions and yields unsymmetrical arylpyridine ketones. All N,N-substituted benzimidazole salts 2a–i and 4a–i studied in this work were screened for their cytotoxic activities against human cancer cell lines such us MDA-MB-231, MCF-7 and T47D. The N,N-substituted benzimidazoles 2e and 2f exhibited the most cytotoxic effect with promising cytotoxic activity with IC₅₀ values of 4.45 μg mL⁻¹ against MDA-MB-231 and 4.85 μg mL⁻¹ against MCF7 respectively.

The in situ prepared four component system Pd(OAc)₂, 1,3-dialkylbenzimidazolium halides 2a–i and 4a–i, K₂CO₃ under CO atmosphere catalyses carbonylative cross-coupling reaction of 2-bromopyridine with various boronic acids to yield unsymmetrical arylpyridine ketones.     

Application of Pauson–Khand reaction in the total synthesis of terpenes

The Pauson–Khand reaction (PKR) is a formal [2 + 2 + 1] cycloaddition involving an alkyne, an alkene and carbon monoxide mediated by a hexacarbonyldicobaltalkyne complex to yield cyclopentenones in a single step. This versatile reaction has become a method of choice for the synthesis of cyclopentenone and its derivatives since its discovery in the early seventies. The aim of this review is to point out the applications of PKR in the total synthesis of terpenes.

The Pauson–Khand reaction (PKR) is a formal [2 + 2 + 1] cycloaddition involving an alkyne, an alkene and carbon monoxide mediated by a hexacarbonyldicobaltalkyne complex to yield cyclopentenones in a single step.     

Benzophenone assisted UV-activated synthesis of unique Pd-nanodendrite embedded reduced graphene oxide nanocomposite: a catalyst for C–C coupling reaction and fuel cell

In this work we report the use of benzophenone (BP) for the synthesis of a palladium (Pd) embedded on reduced graphene oxide (rGO) nanocomposite (Pd/rGO) using a simple aqueous solution and UV irradiation. The simple and facile evolution of thermodynamically unstable branched Pd(0) nanodendrites was achieved by BP photoactivation, circumventing the growth of more stable nanomorphologies. The synthesis of Pd(0)-embedded rGO nanosheets (PRGO-nd) was made possible by the simultaneous reduction of both the GO scaffold and PdCl₂ by introducing BP into the photoactivation reaction. The nanocomposites obtained in the absence of BP were common triangular and twinned Pd(0) structures which were also implanted on the rGO scaffold (PRGO-nt). The disparity in morphologies presumably occurs due to the difference in the kinetics of the reduction of Pd²⁺ to Pd⁰ in the presence and absence of the BP photoinitiator. It was observed that the PRGO-nd was composed of dense arrays of multiple Pd branches around nucleation site which exhibited (111) facet, whereas PRGO-nt showed a mixture of (100) and (111) facets. On comparing the catalytic efficiencies of the as-synthesized nanocatalysts, we observed a superiority in efficiency of the thermodynamically unstable PRGO-nd nanocomposite. This is due to the evolved active facets of the dendritic Pd(0) morphology with its higher surface area, as testified by Brunauer–Emmett–Teller (BET) analysis. Since both PRGO-nd and PRGO-nt contain particles of similar size, the dents and grooves in the structure are the cause of the increase in the effective surface area in the case of nanodendrites. The unique dendritic morphology of the PRGO-nd nanostructures makes them a promising material for superior catalysis, due to their high surface area, and the high density of surface atoms at their edges, corners, and stepped regions. We investigated the efficiency of the as-prepared PRGO-nd catalyst in the Suzuki–Miyaura coupling reaction and showed its proficiency in a 2 h reaction at 60 °C using 2 mol% catalyst containing 0.06 mol% active Pd. Moreover, the electrochemical efficiency for the catalytic hydrogen evolution reaction (HER) was demonstrated, in which PRGO-nd provided a decreased overpotential of 68 mV for a current density of 10 mA cm⁻², a small Tafel slope of 57 mV dec⁻¹ and commendable stability during chronoamperometric testing for 5 h.

Benzophenone photoinitiator aided synthesis of Pd-nanodendrite embedded rGO nanocatalyst possessing superior potential in C–C coupling reaction and fuel cell application.     

The sustainable synthesis of peptidomimetics via chemoenzymatic tandem oxidation–Ugi reaction

A simply and green synthetic protocol based on the selective laccase-oxidation of alcohol to a corresponding aldehyde and a following Ugi reaction in a micellar system made of SDS was developed and is reported herein. Special emphasis was placed on the metal-free chemoenzymatic tandem reaction based on alcohol oxidation strategies using molecular oxygen from air, followed by an Ugi reaction. The reaction was carried out without the use of a transition metal or organic solvents as a reaction medium. The presented protocol offers an efficient and environmentally friendly procedure.

A simply and green synthetic protocol based on the selective laccase-oxidation of alcohol to a corresponding aldehyde and a following Ugi reaction in a micellar system made of SDS was developed and is reported herein.     

Highly efficient synthesis of 3,4-diarylbutadiene sulfones using Heck–Matsuda reaction

For the first time we describe a general method for the synthesis of previously not synthesized unsymmetrical 3,4-diarylbutadiene sulfones which can be stable convenient precursors for 2,3-diaryl-1,3-butadienes. Our method for arylation of butadiene sulfones via Heck–Matsuda reaction allows to obtain unsymmetrical 3,4-diarylbutadiene sulfones with a variety of alkyl, alkoxy, nitro, ethoxycarbonyl, perfluoroalkyl and halogen substituents (30 examples) in very good yields using readily available reagents and catalysts.

An efficient and facile Pd-catalyzed synthesis of 3,4-diarylbutadiene sulfones with high regioselectivity from aryldiazonium salts and butadiene sulfone was developed.     

In situ templating synthesis of mesoporous Ni–Fe electrocatalyst for oxygen evolution reaction

Low-cost and efficient electrocatalysts with high dispersion of active sites and high conductivity are of high importance for oxygen evolution reaction (OER). Herein, we use amorphous mesoporous fumed silica (MFS) as a skeleton material to disperse Ni²⁺ and Fe³⁺ through a simple impregnation strategy. The MFS is in situ etched away during the OER process in 1 M KOH to prepare a stable mesoporous Ni–Fe electrocatalyst. The high specific surface area and abundant surface silanol groups in the mesoporous fumed silica afford rich anchor sites for fixing metal atoms via strong chemical metal–oxygen interactions. Raman and XPS investigations reveal that Ni²⁺ formed covalent bonds with surface Si–OH groups, and Fe³⁺ inserted into the framework of fumed silica forming Fe–O–Si bonds. The mesoporous Ni–Fe catalysts offer high charge transfer abilities in the OER process. When loaded on nickel foam, the optimal 2Ni1Fe-MFS catalyst exhibits an overpotential of 270 mV at 10 mA cm⁻² and a Tafel slope of 41 mV dec⁻¹. Notably, 2Ni1Fe-MFS shows a turnover frequency value of 0.155 s⁻¹ at an overpotential of 300 mV, which is 80 and 190 times higher than that of the state-of-the-art IrO₂ and RuO₂ catalysts. Furthermore, 2Ni1Fe-MFS exhibits 100% faradaic efficiency, large electrochemically active surface area, and good long-term durability, confirming its outstanding OER performance. Such high OER efficiency can be ascribed to the synergistic effect of high surface area, dense metal active sites and interfacial conductive path. This work provides a promising strategy to develop simple, cost-effective, and highly efficient porous Ni–Fe based catalysts for OER.

A stable mesoporous Ni–Fe–O electrocatalyst with high OER efficiency is constructed using mesoporous fumed silica as a template.     

Core–shell Pd–P@Pt–Ni nanoparticles with enhanced activity and durability as anode electrocatalyst for methanol oxidation reaction

Pd–P@Pt–Ni core–shell nanoparticles, which consisted of a Pd–P alloy as a core and Pt–Ni thin layer as a shell, were explored as electrocatalysts for methanol oxidation reaction. The crystallographic information and the electronic properties were fully investigated by X-ray diffraction and X-ray photoelectron spectroscopy. In the methanol electrooxidation reaction, the particles showed high catalytic activity and strong resistance to the poisoning carbonaceous species in comparison with those of commercial Pt/C and the as-prepared Pt/C catalysts. The excellent durability was demonstrated by electrochemically active surface area loss and chronoamperometric measurements. These results would be due to the enhanced catalytic properties of Pt by the double synergistic effects from the core part and the nickel species in the shell part.

The Pd–P@Pt–Ni core–shell nanoparticles consist of an amorphous core and a low-crystalline shell. They exhibit the excellent catalytic properties in MOR owing to the double synergistic effects from the core and the nickel species in the shell.     

A palladium complex confined in a thiadiazole-functionalized porous conjugated polymer for the Suzuki–Miyaura coupling reaction

Porous organic polymers (POPs) with well-distributed and tunable functional groups acting as ligands for specific reactions are promising supports for confining useful novel metals such as Pd, Au, and Pd. Herein, a thiadiazole-containing POP has been successfully synthesized and used for immobilizing Pd species. Pd immobilized inside the micropores (2.3 nm) of the POP material is easily prepared owing to a large amount of the strong anchoring group, thiadiazole, which is intrinsically distributed in the as-prepared POP. The rigid thiadiazole-containing polymer can stabilize the central metal rather than poisoning it. The as-prepared catalyst shows excellent catalytic activity in Suzuki–Miyaura coupling reactions under mild reaction conditions and low catalyst loading. Importantly, the intrinsically distributed thiadiazole ligands can stabilize the Pd moiety, preventing aggregation and leaching, and afford excellent catalytic lifetimes. Consequently, the catalyst can be reused 10 times without a significant loss of its catalytic activity.

A novel Pd moiety confined thiadiazole-containing conjugated porous polymer was synthesized, and its catalytic performance was examined by coupling of aryl bromides with phenylboronic acids under mild conditions.