Arylation Of Thiophenes Research Articles

Double Direct C-H Bond Arylation of Thiophenes with Aryl Chlorides Catalyzed by the N-Heterocyclic Carbene-PdCl2-1-methylimidazole Complex.

With the combination of the N-heterocyclic carbene-PdCl2-1-methylimidazole complex and Cu2O, we succeeded in the first example of double direct C-H bond arylation reactions between thiophenes and aryl chlorides, giving the desired 2,5-diarylated thiophenes in moderate to high yields under suitable conditions, consistent with the density functional theory calculations.

Direct Arylation of Thiophenes in Continuous Flow

AbstractSynthetic methodologies involving direct C−H functionalization are promising to improve sustainability in organic synthesis. However, these newly developed strategies may have a scarce appeal for larger scale applications due to the high catalyst loading, harsh conditions or their typically long reaction times that affect severely the process productivity. Flow chemistry technology is a recognized tool to improve both the efficiency and scalability in organic synthesis that can overcome these issues. In the present paper we studied an “in flow” method for the direct arylation of thiophene derivatives with aromatic bromides to promptly afford heteroaromatic biaryls, which are recurrent motifs both in biologically active molecules and in functional materials. By using a packed‐bed reactor containing potassium carbonate as the solid base and an automated system, we could develop a reliable methodology for thiophene arylation in flow with yields up to 90 % within a residence time of 30–60 minutes. This strategy is suitable for a wide variety of substrates and allowed the reaction to be carried out at gram‐scale reaching a productivity value of 1.1 g h−1.

Palladium hetero‐di(N‐heterocyclic carbene) complexes and their catalytic activities in direct C–H arylation of heteroarenes

A library of neutral and cationic palladium complexes of cis‐chelating hetero‐dicarbene ligands have been prepared. These ligands contain two different NHC donors allowing for a wider degree of variation, and the impact of the distinct NHC units has been compared using various spectroscopic means. In addition, the catalytic activities of these complexes in the direct C‐H arylation of thiophenes with aryl halides were studied leading to the finding that the neutral dibromido complexes of the type [PdBr2(diNHC)] generally outperformed their cationic [Pd (NCMe)2(diNHC)](OTf)2 counterparts. More importantly, complexes containing more distinct NHC units give rise to superior catalysts due to an amplified “stereoelectronic asymmetry” within the complex. A preliminary photophysical study of some selected thiophene reaction products has been conducted as well. The ability to individually change each NHC donor in such dicarbene ligands allows for a better fine‐tuning of complex properties in search for superior catalysts.

Bis(imino)acenaphthene (BIAN)-Supported N-Heterocyclic Carbene Palladium Complexes with Ancillary Ligands: Readily Activated Precatalysts for Direct C–H Arylation of Thiophenes

Bis(imino)acenaphthene (BIAN)-Supported <i>N</i>-Heterocyclic Carbene Palladium Complexes with Ancillary Ligands: Readily Activated Precatalysts for Direct C–H Arylation of Thiophenes

Regioselective C–H Arylation of Thiophenes on a Ni-Coordinated Porous Phenanthroline-Derived Polymer

Regioselective C–H Arylation of Thiophenes on a Ni-Coordinated Porous Phenanthroline-Derived Polymer

Microwave-Assisted Protocol for Green Functionalization of Thiophenes With a Pd/β-Cyclodextrin Cross-Linked Nanocatalyst.

Microwaves (MW) are often the most efficient, in terms of heat exchange and conversion rate, of all the energy sources used to promote chemical reactions thanks to fast volumetric dielectric heating, and metal-catalyzed synthetic reactions under heterogeneous conditions are an eloquent example. We herein report a MW-assisted green protocol for the C-H arylation of thiophenes with substituted aryl halides. This sustainable protocol carried out in γ-valerolactone (GVL) is catalyzed by Pd nanoparticles embedded in cross-linked β-cyclodextrin. In view of the excellent results achieved with activated substrates, the one-pot synthesis of a 4(3H)-quinazolinone derivative has been accomplished. A pressure-resistant MW reactor, equipped with multiple gas inlets, was used for sequential (i) C-H arylation, (ii) reduction, and (iii) carbonylation in the presence of the same catalyst, but under different gas atmospheres. The robust heterogeneous Pd catalyst showed limited metal leaching in GVL, making this an efficient MW-assisted process with high atom economy.

Phthalocyanine-based organic semiconductors catalyzed C&amp;minus;H activation for heteroarenes functional materials in the sunlight

Organic conjugated materials have attracted much attention in organic optoelectronics due to their excellent optical and electrical properties. In effort of continuous work, material system is continuously enriched, and the performance is rapidly improved. Currently, devices based on organic conjugate functional materials have achieved remarkable development, such as OLED, OFET, OPV, OLET, OFEW. Meanwhile, developing simple, efficient and green organic synthesis methods for these materials is a significant topic. And the most efficient synthesis method is the direct arylation of heteroarenes by C−H bond activation. Synthetic methods based on transition metal, for example, Ru and Ir complexes, catalyzed C−H activation are widely used to construct organic conjugated functional materials. Compared with the transition metal catalyzed reaction, photocatalytic reaction conditions are mild, low temperature and more environmentally friendly. Recently, the direct C−H activation using semiconductor photo-catalysts, owing to good light absorption, is found to be a simple and effective method for organic functional materials. Lots of works based on inorganic semiconductors, such as CdS, ZnO, TiO2, have been developed. Few works based on organic semiconductors, such as Eosin Y, porphyrin have also been reported. But, it is still not systematic enough, and necessary to further expand the kinds of organic semiconductor photocatalysis and develop a photocatalytic system with high efficiency and stability. In this paper, a green method for synthesizing heteroarenes functional materials via direct C−H activation has been developed. Phthalocyanine-based semiconductors are used as photocatalysts, and sunlight, the most common clean energy, is used as a light source at room temperature. Firstly, the reaction conditions were optimized for the direct arylation of thiophene ( 2a ) with diazonium salt ( 1a ), 2 h sunlight irradiation, and 1 mol% phthalocyanine catalyst at room temperature. It’s found that the desired product was obtained in all cases and titanium-phthalocyanine (TiOPc) semiconductor material exhibites the highest catalytic efficiency. The energy band structure of a photocatalytic material plays a key role in determining the performances of photocatalyst. According to the reported works, energy gaps of Pc, CuPc, TiOPc are respectively 1.40, 1.60−1.70, 1.10−1.20 eV. Narrower gaps response to better and wider light absorb. Having optimized the reaction conditions, we examined the scope of the reaction of thiophene with different aryl diazonium salts. Among the aryl diazonium salts used for direct arylation of thiophene, electron-acceptor (−NO2) diazonium salt is found to be more efficient for product formation than electron donor substituted ones (−OCH3, Br, Cl). Notably, halogen-substituted aryl diazonium salts successfully underwent C−H bond arylation leaving the C−halogen bond intact, which is useful for further synthetic elaboration. The C−H arylation of heteroarenes with aryl diazonium salts using TiOPc was expected to proceed through a radical mechanism. A mechanism for the photocatalytic, kinds of direct C–H arylation of heteroarenes with aryl diazonium salts catalyzed by TiO2, TiCl3, eosin Y, porphyrin were proposed. The crucial step involves generation of an aryl radical through single-electron transfer from the excited state of listed photocatalysts, to the aryl diazonium salt and its subsequent addition to a heteroarene to furnish an aryl radical intermediate. We reason that in our case a similar mechanism should operate. Under light irradiation, exited TiOPc proved to be efficient electron donors and acceptors. Furthermore, semiconductor functional material with common anthracene-based structure is synthesized with TiOPc direct catalyzing C−H activation. For further optimized the catalytic efficiency, applying an external electric field or fabricating a semiconductor heterojunction should be considered. In summary, this green method could be further extended to the synthesis of other organic semiconductor functional materials, which is of great significance in organic optoelectronics.

Pd‐Catalyzed β‐Selective C−H Arylation of Thiophenes with Triarylantimony Difluorides

AbstractRegioselective C−H arylation using pentavalent organoantimony compounds as a new class of arylating reagents is described. The reaction of thiophenes with triarylantimony difluorides in the presence of 5 mol% of and 2 equiv. CuCl2 at 80 °C under aerobic conditions afforded the β‐arylated thiophene derivatives in moderate‐to‐high yields. The reaction is sensitive to the electronic nature of the triarylantimony difluorides – those bearing an electron‐donating group on the phenyl ring showed higher reactivity than those have an electron‐withdrawing group.

Transition‐Metal‐Free Approach for the Direct Arylation of Thiophene: Experimental and Theoretical Investigations towards the (Het)‐Aryne Route

This paper presents the results of our investigations on the arylation of thiophene using the transition‐metal‐free “aryne coupling” methodology. The reaction was studied by both experiment and computation (density functional theory) and comparison with phenyllithium was established. In parallel, the effects of the ligand and the salt on the coupling reaction were examined. The results underline the remarkable effect of such additives on the coupling reaction and the potency of the method to construct hetaryl–aryl backbones which open up promising access to a wide range of heterobiaryl structures using the novel “Het‐Aryne” route.

Exploring Green Solvents Associated to Pd/C as Heterogeneous Catalyst for Direct Arylation of Heteroaromatics with Aryl Bromides

AbstractMetal residues are certainly one of the major sources of contamination of products in metal‐catalyzed direct arylation reactions. We found that the use of only 1 mol% of the heterogeneous catalyst Pd/C promotes very efficiently the direct arylations of most heteroaromatics. In the presence of this catalyst and potassium acetate as the base, the direct arylation of thiophenes, furans, pyrroles, thiazoles, imidazoles or isoxazoles, using aryl bromides as coupling partners, proceeds highly regioselectively and in moderate to very high yields. With several heteroarenes both electron‐deficient and electron‐rich aryl bromides were tolerated; moreover, with the most reactive heteroarenes, the Pd/C catalyst tolerated green solvents such as diethyl carbonate, 3‐methylbutan‐1‐ol and pentan‐1‐ol, affording a synthetic scheme with low environmental impact.magnified image

Construction of 3,7-Dithienyl Phenothiazine-Based Organic Dyes via Multistep Direct C-H Arylation Reactions.

Herein, an effective and feasible approach to prepare 3,7-dithienyl phenothiazine-based organic dyes has been developed. In this synthetic procedure, the Pd-catalyzed multistep direct C-H arylation of thiophene derivatives with phenothiazine bromides was employed for the first time to construct the 3,7-dithienyl phenothiazine core scaffold, which greatly streamlines access to this class of organic dyes. 3-Thienyl phenothiazine-based dyes were also synthesized via the direct C-H arylation of thiophenes as references. Most of the 3,7-dithienyl phenothiazine-based dyes exhibit better photovoltaic performances than the 3-thienyl phenothiazine-based dyes. Among these organic dyes, the solar cell device based on 6d exhibits the highest conversion efficiency of 8.9%. Compared with 6d, organic dyes with longer π-conjugation, also including bithiophene as the π-spacer, show dramatically reduced conversion efficiencies of cell devices. The introduction of the more electron-rich 3,4-ethylenedioxythiophene to the C3- and/or C7-position of phenothiazine instead of thiophene does not significantly improve the photoelectric conversion performance. The highly efficient synthetic strategy herein developed and these primary results may be helpful to design and synthesize a variety of new 3,7-dithienyl phenothiazine-based organic dyes.

Palladium/Copper Dual Catalysis for the Cross‐Coupling of Aryl(trialkyl)silanes with Aryl Bromides

AbstractWhereas aryl(trialkyl)silanes are considered to be ideal organometallic reagents for cross‐coupling reactions owing to their stability, low toxicity, solubility, and easy accessibility, they are generally inert under typical cross‐coupling conditions. Disclosed herein is a palladium/copper catalytic system that enables the cross‐coupling of trimethyl, triethyl, tert‐butyldimethyl, and triisopropyl aryl silanes with aryl bromides. This process is applicable to the sequential C−H and C−Si bond arylation of thiophenes and the synthesis of poly(thiophene–fluorene)s.

Palladium/Copper Dual Catalysis for the Cross-Coupling of Aryl(trialkyl)silanes with Aryl Bromides.

Whereas aryl(trialkyl)silanes are considered to be ideal organometallic reagents for cross-coupling reactions owing to their stability, low toxicity, solubility, and easy accessibility, they are generally inert under typical cross-coupling conditions. Disclosed herein is a palladium/copper catalytic system that enables the cross-coupling of trimethyl, triethyl, tert-butyldimethyl, and triisopropyl aryl silanes with aryl bromides. This process is applicable to the sequential C-H and C-Si bond arylation of thiophenes and the synthesis of poly(thiophene-fluorene)s.

Pd-Catalyzed Thiophene-Aryl Coupling Reaction via C-H Bond Activation in Deep Eutectic Solvents.

Direct arylation of 5-octylthieno[3,4-c]pyrrole-4,6-dione with a series of functionalized aryl iodides via C-H bond activation is demonstrated in a deep eutectic solvent made of choline chloride and urea in non-anhydrous conditions and without exclusion of air. This is the first demonstration of a thiophene-aryl coupling via direct arylation in deep eutectic solvents.

Microwave-assisted, ligand-free, direct C–H arylation of thiophenes in biomass-derived γ-valerolactone

We report a ligand-free green synthesis of arylthiophenes and poly(3-hexyl)thiophene in GVL under microwave irradiation.

ChemInform Abstract: Carboxylic Acids as Traceless Directing Groups for the Rhodium(III)‐Catalyzed Decarboxylative C—H Arylation of Thiophenes.

AbstractThe method is first applied to the coupling of various functionalized thiophenes with acid (II).

Pd(OAc)2/AgOAc Catalytic System Based Bidentate Ligand Directed Regiocontrolled C–H Arylation and Alkylation of the C‐3 Position of Thiophene‐ and Furan‐2‐carboxamides

AbstractA contemporary method is reported for the Pd(OAc)2/AgOAc catalytic system based bidentate ligand directed, regioselective C–H activation and C–C bond formation at the C‐3 position of thiophene‐ and furan‐2‐carboxamides, which are derived from 8‐aminoquinoline or 2‐(methylthio)aniline. The Pd‐catalyzed C–H arylation of thiophene‐ and furan‐2‐carboxamides with a variety of aryl iodides and heteroaryl iodides was highly regioselective and afforded C‐3‐arylated thiophene‐2‐carboxamides and furan‐2‐carboxamides in good to very good yields. The bidentate ligand directed Pd(OAc)2/AgOAc based strategy was also successfully employed for benzylation and alkylation reactions of the thiophene‐2‐carboxamides. These reactions occurred with high regioselectivity to afford the C‐3‐benzylated and C‐3‐alkylated thiophene‐2‐carboxamides in good yields. The observed regioselectivity of these reactions was confirmed by X‐ray crystal structure analyses of compounds 3e, 5a, and 6a.

Carboxylic Acids as Traceless Directing Groups for the Rhodium(III)‐Catalyzed Decarboxylative CH Arylation of Thiophenes

AbstractA rhodium(III)‐catalyzed carboxylic acid directed decarboxylative CH/CH cross‐coupling of carboxylic acids with thiophenes has been developed. With a slight adjustment of the reaction conditions based on the nature of the substrates, aryl carboxylic acids with a variety of substituents could serve as suitable coupling partners, and a broad variety of functional groups were tolerated. This method provides straightforward access to biaryl scaffolds with diverse substitution patterns, many of which have conventionally been synthesized through lengthy synthetic sequences. An illustrative example is the one‐step gram‐scale synthesis of a biologically active 3,5‐substituted 2‐arylthiophene by way of the current method.

Carboxylic acids as traceless directing groups for the rhodium(III)-catalyzed decarboxylative C-H arylation of thiophenes.

A rhodium(III)-catalyzed carboxylic acid directed decarboxylative C-H/C-H cross-coupling of carboxylic acids with thiophenes has been developed. With a slight adjustment of the reaction conditions based on the nature of the substrates, aryl carboxylic acids with a variety of substituents could serve as suitable coupling partners, and a broad variety of functional groups were tolerated. This method provides straightforward access to biaryl scaffolds with diverse substitution patterns, many of which have conventionally been synthesized through lengthy synthetic sequences. An illustrative example is the one-step gram-scale synthesis of a biologically active 3,5-substituted 2-arylthiophene by way of the current method.

Synthesis of functionalized thiophene/phenyl co-oligomers by direct arylation of thiophenes

π-Conjugated rod-like molecules have proven to be powerful candidates for the generation of well-defined nanostructures with interesting optica l and optoelectrical properties. Their synthesis, however, turns out to be rather complex in some cases. Here, we have optimized the synthesis of oligomers consisting of thiophene and phenylene groups with three or four aromatic units using a direct arylation approach, which allo ws us to use cheap starting materials and to minimize the number of reaction steps considerably.