Search

The highly substituted naphthalenes 1,2,3,4,5,6,7‐heptaphenylnaphthalene (13), 2,3,4,5,6,7,8‐heptaphenyl‐1‐naphthol (12), 1‐bromo‐2,3,4,5,6,7,8‐heptaphenylnaphthalene (4), and 1‐(phenylethynyl)‐2,3,4,5,6,7,8‐heptaphenylnaphthalene (5) were prepared by a variety of methods, and all but 5 were crystallographically characterized. The attempted Ullmann coupling of 4 to give tetradecaphenyl‐1,1′‐binaphthyl (3), at both 270 °C and 350 °C, yielded instead 1,2,3,4,5,6‐hexaphenylfluoranthene (17) via an intramolecular cyclization reaction. When the alkyne 5 was heated with tetracyclone (6) at 350 °C, 1‐(pentaphenylphenyl)‐2,3,4,5,6,7,8‐heptaphenylnaphthalene (7) was formed in 3 % yield. However, greater amounts of 5,6,7,8,9,14‐hexaphenyldibenzo[a,e]pyrene (20, 11 %) and 1,2,3,4,5,6,7‐heptaphenylfluoranthene (21, 11 %) were produced, the former by intramolecular cyclization and dehydrogenation of 5 and the latter by an intramolecular Diels‐Alder reaction of 5 followed by extrusion of acetylene. The X‐ray structure of 7 shows it to be an exceptionally crowded biaryl, and the X‐ray structure of 20 shows it to be a saddle shaped polycyclic aromatic hydrocarbon. [ABSTRACT FROM AUTHOR]

We report the construction of unsymmetrical dimeric carbazoles and π‐extended bis carbazoles (having an aryl ring spacer) via the C−H functionalization route. Generally, oxidative coupling and traditional cross‐coupling reactions have been used to construct bis‐ and π‐extended carbazoles. Natural bis carbazole alkaloids and synthetic dimeric carbazoles are important molecules in medicinal, materials chemistry research. There is scope for developing new synthetic transformations leading to structurally appealing bis carbazoles. The synthesis of symmetrical bis carbazoles via cross‐coupling and C−H functionalization is well known in the literature and it is noted that there exist limited reports on the construction of unsymmetrical bis carbazoles via the C−H functionalization route. Accordingly, this paper reveals the Pd(II)‐catalyzed bidentate directing group‐assisted C−H functionalization as a progressive route for the synthesis of a library of unsymmetrical dimeric carbazoles and π‐extended bis carbazoles (connected through an aryl ring spacer). [ABSTRACT FROM AUTHOR]

The increasing interest in axially chiral biaryl moieties, which are prevalent in chiral ligands, organocatalysts, and bioactive molecules, has raised the need for developing novel efficient synthetic methods for these types of molecules. In addition to the currently available methods, such as kinetic resolution, desymmetrization and enantio‐ and diastereo‐selective biaryl coupling, we herein report a lipase‐catalyzed dynamic kinetic resolution (DKR) of racemic 2‐hydroxybiaryls through enantioselective O‐acylation. This method features the production of enantiomerically enriched atropisomers (89 %–98 % ee) in 91 %–99 % yields from eleven racemates. Notably, the DKR proceeds without any racemization catalyst since in situ‐racemization was achieved by easy rotation about the biaryl axis of the substrates. The enzymatic O‐acylation then furnished conformationally stable biaryl‐containing esters, in which the increased steric bulkiness of the O‐acyl moiety suppresses the rotation, i. e., racemization, under the reaction conditions of 35–50 °C. This experimental study was accompanied by a computational determination of the rotational barrier of substrates and products. The choice of suitable substrates with a significant difference in their rotational barrier compared to that of their products turned out to be the key to an efficient implementation of this method. [ABSTRACT FROM AUTHOR]

Diverse libraries of biaryls/heterobiaryls were synthesized by aryl/hetero‐aryl tosylates as coupling partners in the ligand‐free, Ni‐catalyzed Suzuki coupling reaction, and Pd‐catalyzed Hiyama cross‐coupling reaction in ionic liquids (ILs) as green solvent. In this method easily available and economically viable tosylates were coupled with readily available boronic acids and phenyltriethoxysilanes in Suzuki and Hiyama cross‐coupling respectively to yield the corresponding biaryls/heterobiaryls. Mild reaction condition(s), easy workup, moderate to excellent yield of the isolated pure products, wide substrate scope, and recycling/reuse of the ILs are the advantages of this method over the other reported methods. [ABSTRACT FROM AUTHOR]

A room temperature Ni‐catalyzed Mn‐mediated homocoupling of (hetero)aryl and vinyl chlorides using Mn powders pre‐activated by trimethylsilylchloride (TMSCl) in DMA is reported. Large steric effects were observed while electronic influences from aryl chlorides proved to be rather small. High regioselectivity could be achieved between ortho‐Cl and para‐Cl/Br of aryl halides benefiting from the large steric effects. A double‐face role of TMSCl, i. e. activation of Mn powders but deactivation of nickel catalyst, was observed although TMSCl‐activated Mn powders appeared to be the privileged metallic reductant. Applications of the protocol have been demonstrated in a multigram synthesis of Daclatasvir. [ABSTRACT FROM AUTHOR]

Axially chiral biaryl compounds are ubiquitous scaffolds in natural products, bioactive molecules, chiral ligands and catalysts, but biocatalytic methods for their asymmetric synthesis are limited. Herein, we report a highly efficient biocatalytic route for the atroposelective synthesis of biaryls by dynamic kinetic resolution (DKR). This DKR approach features a transient six‐membered aza‐acetal‐bridge‐promoted racemization followed by an imine reductase (IRED)‐catalyzed stereoselective reduction to construct the axial chirality under ambient conditions. Directed evolution of an IRED from Streptomyces sp. GF3546 provided a variant (S‐IRED‐Ss‐M11) capable of catalyzing the DKR process to access a variety of biaryl aminoalcohols in high yields and excellent enantioselectivities (up to 98 % yield and >99 : 1 enantiomeric ratio). Molecular dynamics simulation studies on the S‐IRED‐Ss‐M11 variant revealed the origin of its improved activity and atroposelectivity. By exploiting the substrate promiscuity of IREDs and the power of directed evolution, our work further extends the biocatalysts' toolbox to construct challenging axially chiral molecules. [ABSTRACT FROM AUTHOR]

The enzymatic atroposelective synthesis of biaryl compounds is relatively rare, despite considerable attention received by biocatalysis in the academic and industrial sectors. Imine reductases (IREDs) are an important class of enzymes that have been applied in the asymmetric synthesis of chiral amine building blocks. In this study, two IREDs (IR140 and IR189) were identified to catalyze the efficient desymmetrization of biaryls utilizing various amine donors. Further protein engineering enabled the identification of variants (IR189 M8–M9 and IR189 M13–M14) that are able to catalyze the formation of both (R) and (S) atropisomers in excellent yields and atroposelectivities (24 examples, up to 99 % ee and yield). The absolute configuration and rotational barriers were confirmed, and the reactions were readily scaled up to allow isolation of the atropisomeric product in 99 % ee and 82 % yield. The optically pure biaryl amines were further derivatized into various synthetically useful atropisomers. To shed light on the molecular recognition mechanisms, molecular dynamics (MD) simulations were performed, offering plausible explanations for the improved atroposelectivity and enzymatic activity. The current strategy expands the scope of the IRED‐catalyzed synthesis of axially chiral biaryl amines, contributing significantly to the field of atroposelective biocatalysis. [ABSTRACT FROM AUTHOR]

Axially chiral biaryl scaffolds are important in pharmaceuticals, natural products, and asymmetric synthesis. Atroposelective ring‐opening of configurationally labile biaryl reagents via dynamic kinetic asymmetric transformation provides a valuable approach to access axially chiral biaryl atropisomers. This review summarizes seminal contributions and recent advancements on this topic based on the use of different types of configurationally labile biaryl reagents. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Functionalized free radical addition/cyclization reactions represent an efficient way for introducing new functionality or coupling fragments to molecules. Ynones are good regional selectivity radical acceptors in organic synthesis, and many of bio‐relevant cyclic compounds could be easily obtained by direct radical cyclization reaction. Here, we report a photocatalytic cascade radical addition of biaryl ynones, for the divergent synthesis of privileged carbon cycles. Additionally, further transformation of the multi‐functional group product into a variety of other derivatives demonstrates the synthetic value of this developed method. [ABSTRACT FROM AUTHOR]

14,14′‐Bidibenzo[a,j]anthracenes (BDBAs) were prepared by iridium‐catalyzed annulation of 5,5′‐biterphenylene with alkynes. The molecular geometries of overcrowded BDBAs were verified by X‐ray crystallography. The two dibenzo[a,j]anthryl moieties are connected through the sterically hindered 14 positions, resulting in highly distorted molecular halves. The conformation with a small twist angle between two molecular halves can minimize steric conflicts between the substituents at 1 and 13 positions and the carbon atoms of the central axis, as well as steric clashes between those substituents. One such example is octafluoro‐substituted BDBA, where the interplanar angle between two anthryl moieties is approximately 31° (currently the lowest reported value, cf. 81° in 9,9′‐bianthracene). The intramolecular interactions and electronic couplings between two molecular halves resulted in upfield 1H NMR signals, redshifted absorption and emission bands, and a reduced HOMO–LUMO gap. Photodynamic investigations on BDBAs indicated that the formation of the conventional symmetry‐breaking charge transfer (SBCT) state was suspended by restricted rocking around the central C−C bond. Such a mechanism associated with this highly constrained conformation was examined for the first time. [ABSTRACT FROM AUTHOR]

In this research, a novel core-shell nanocatalyst with silica bi-shell around Fe3O4 and nickel active center, i.e. Fe3O4@xSiO2@ySiO2@BisPyP-Ni was synthesized and its characteristics were comprehensively discussed. This nanocatalyst was successfully used to synthesize biaryls (18 examples, 15–30 min, 92–98%) and diaryl sulfides (10 examples, 20–140 min, 79–98%) at 80 °C. Excellent performance in speeding up the reaction time, magnetic nature, high porosity, and immobilization of two layers around Fe3O4 are four prominent characteristics of this catalyst. Coating the magnetic core with silica layers led to saving the consumption of the catalyst because this trick leads to the bonding of more organic groups to the substrate, as a result, more nickel enters the mesoporous cavities, and the reaction with a smaller amount of catalyst is finished (in a shorter time). Other advantages of both our production lines are: the ability to recover and reuse the catalyst for up to 8 runs (without a noticeable decrease in its catalytic performance), extensive substrate scope, the employ of commercially accessible materials, simple workup, environmental safety and the heterogeneous nature of the catalyst (by confirming the reusability and hot filtration test results). [ABSTRACT FROM AUTHOR]

D2‐symmetric (R)‐binaphthyl‐bridged pyrenophanes containing thioether bonds were synthesized. The pyrenophanes exhibited the temperature‐induced sign inversion of circularly polarized luminescence (CPL) while maintaining the emission wavelength and reversibility. The Δglum value reached 0.02, and the FL quenching by heat was negligible. The sign inversion of CPL originates from the inversion of intramolecular excimer chirality associated with excitation dynamics. The two pyrenes form a kinetically trapped left‐handed twist excimer at low temperatures, while they form a thermodynamically favored right‐handed twist excimer at high temperatures. The thioether linkers can impart flexibility suitable for the inversion of chirality of the excimers. [ABSTRACT FROM AUTHOR]

A highly efficient Suzuki coupling of N‐tosyl aryltriazenes with diarylborinic acids or potassium diaryldifluoroborinates is reported under weak basic conditions in aqueous DME or dioxane, respectively. The shelf‐stable and easy‐to‐stoichiometry diaryldifluoroborinates displayed reactivities comparable to the corresponding diarylborinic acids. Scope and limitations of the protocol have been investigated, showing large electronic and steric effects from aryltriazenes. Utility of potassium diaryldifluoroborinates in the Suzuki coupling with activated aryltriazenes provides a cost‐effective and operationally practical access to biaryls from anilines. [ABSTRACT FROM AUTHOR]

2‐(2‐methoxyphenyl)benzoxazole (MBO) displays similar photophysical properties to 2‐(2‐hydroxyphenyl)benzoxazole (HBO), but it lacks the large Stokes shifts necessary for fluorescence microscopy applications. In this paper, we report the 5‐substitution of MBO with aryl groups to produce 2‐(4‐methoxy‐[1,1'‐biphenyl]‐3‐yl)benzoxazoles (MBBOs) with large Stokes shifts. The synthesis of MBBOs 6–15 was accomplished in moderate to good yields by microwave‐assisted Sonogashira cross couplings. Crystal structures for compounds 6–9 and 15 are provided. MBBOs 6–10, 12, and 14 displayed considerably blue‐shifted absorption maxima and slight bathochromic shifts of their fluorescence maxima relative to the unsubstituted MBO. [ABSTRACT FROM AUTHOR]

β‐Cyclodextrin has drawn significant attention as a special class of cyclic oligomers over the past few decades. They have been employed in many organic conversions as green alternative catalysts to perform satisfactorily in catalytic activity and modify the efficiency of organic reactions. Its availability, nontoxicity, low cost, renewability, and high performance in organic transformations are several benefits of cyclodextrins that have captured the interest of many research groups worldwide. In recent decades, great progress has been made in developing metal‐catalyzed coupling reactions to create carbon–carbon bonds. For the transition‐metal‐catalyzed cross‐coupling, using modified β‐cyclodextrin derivatives as catalysts is much more pleasant due to the obvious advantages such as valuable catalytic properties and the capability to create an inclusion complex with different metals. The particular purpose of this review is to summarize the application of β‐cyclodextrin‐based catalyst systems in Suzuki coupling reaction for the synthesis of biaryl compounds covering the years 2019–2023. [ABSTRACT FROM AUTHOR]

Immobilized Pd‐catalyzed Suzuki‐Miyaura coupling under continuous‐flow conditions using a packed‐bed reactor, representing an efficient, automated, practical, and safe technology compared to conventional batch‐type reactions. The core objective of this study is the development of an active and durable catalyst. In contrast to supported Pd nanoparticles, the attachment of Pd complexes onto solid supports through well‐defined coordination sites is considered a favorable approach for preparing highly dispersed and stabilized Pd species. These species can be directly employed in various flow reactions without the need for pre‐treatment. This concept paper explores recent achievements involving the application of immobilized Pd complexes as precatalysts for continuous‐flow Suzuki‐Miyaura coupling. Our focus is to elucidate the significance of the designed catalyst structures in relation to their catalytic performance under flow conditions. Additionally, we highlight various reaction systems and catalyst packing methods, emphasizing their crucial roles in establishing a practical synthesis process. [ABSTRACT FROM AUTHOR]

Dimeric naphthopyranones are known to be biologically active, however, for the corresponding monomeric naphthopyranones this information is still elusive. Here the first enantioselective total synthesis of semi‐viriditoxic acid as well as the synthesis of semi–viriditoxin and derivatives is reported. The key intermediate in the synthesis of naphthopyranones is an α,β‐unsaturated δ‐lactone, which we synthesized in two different ways (Ghosez–cyclization and Grubbs ring–closing metathesis), while the domino–Michael–Dieckmann reaction of the α,β‐unsaturated δ‐lactone with an orsellinic acid derivative is the key reaction. A structure‐activity relationship study was performed measuring the cytotoxicity in Burkitt B lymphoma cells (Ramos). The dimeric structure was found to be crucial for biological activity: Only the dimeric naphthopyranones showed cytotoxic and apoptotic activity, whereas the monomers did not display any activity at all. [ABSTRACT FROM AUTHOR]

4,4′‐Biazulene is a potentially attractive key component of an axially chiral biaryl compound, however, its structure and properties have not been clarified owing to the lack of its efficient synthesis. We report a breakthrough in the reliable synthesis of 4,4′‐biazulene, which is achieved by the access to azulen‐4‐ylboronic acid pinacol ester and 4‐iodoazulene as novel key synthetic intermediates for the Suzuki‐Miyaura cross‐coupling reaction. The X‐ray crystallographic analysis of 4,4′‐biazulene confirmed its axial chirality. The enantiomers of 4,4′‐biazulene were successfully resolved by HPLC on the chiral stationary phase column. The kinetic experiments and DFT calculations indicate that the racemization energy barrier of 4,4′‐biazulene is comparable to that of 1,1′‐binaphthyl. [ABSTRACT FROM AUTHOR]

Hydroquinones bearing an electron‐withdrawing group at the C2‐position can effectively underwent oxidative coupling with (hetero)arenes (e. g. indoles, electron‐rich benzene derivatives) in the presence of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) and FeCl3 to produce the corresponding biaryl products. In the present reactions, the DDQ‐mediated oxidation of hydroquinone derivatives produce benzoquinone intermediate, which subsequently underwent FeCl3‐catalyzed nucleophilic addition of (hetero)arenes to the α,β‐unsaturated carbonyl moiety to give the biaryl product in a one‐pot manner. Especially, the indole‐based biaryl products were further converted into tetracyclic aromatics through DDQ‐mediated oxidation followed by FeCl3‐catalyzed intramolecular cyclization. Thiophene derivatives were also applicable to give the tetracyclic aromatics. Moreover, the photophysical properties of the indole‐ and thiophene‐based tetracyclic aromatics in the solution and the solid states were investigated. [ABSTRACT FROM AUTHOR]

Benzylaminate C,N-palladacycles exhibit high catalytic activity in the Suzuki—Miyaura cross–coupling of p-bromoanisole with phenylboronic acid under mild conditions. The influence of the α-substituent and the environment of the nitrogen atom in azapalladacycles on their efficiency as catalysts was assessed. [ABSTRACT FROM AUTHOR]

A new series of biaryls, bi‐linear‐terphenylenes (BLTPs), were prepared using the tert‐butyllithium‐mediated cyclization as the key synthetic step. The three‐dimensional structures of the studied compounds were verified using X‐ray crystallography and DFT calculations. Tetraaryl(ethynyl)‐substituted BLTPs are highly crowded molecules, and the internal rotation around the central C−C bond is restricted due to a high barrier (>50 kcal/mol). These structures contain several aryl/terphenylenyl/aryl sandwiches, where the through‐space π‐π (TSPP) interactions are strongly reflected in the shielding of 1H NMR chemical shifts, reduction of oxidation potentials, increasing aromaticity of the central six‐membered ring and decreasing antiaromaticity of the four‐membered rings in a terphenylenyl moiety based on NICS(0) and iso‐chemical shielding surfaces. Despite the restricted C−C bond associated intramolecular TSPP interactions for BLTPs in the ground state, to our surprise, the electronic coupling between two linear terphenylenes (LTPs) in BLTPs in the excited state is weak, so that the excited‐state behavior is dominated by the corresponding monomeric LTPs. In other words, all BLTPs undergo ultrafast relaxation dynamics via strong exciton‐vibration coupling, acting as a blue‐light absorber with essentially no emission. [ABSTRACT FROM AUTHOR]

Routes to the framework of perylenequinone‐derived mycotoxins of the biphenyl type are described. 1,2,11,12‐Tetrahydroperylenequinone is most suitably prepared in seven steps starting with 3‐hydroxyacetophenone. Key steps are an Ullmann coupling, pinacol‐type cyclization, bromination, enolate reaction, and intramolecular Friedel‐Crafts cyclization. A second approach starting with 1,5‐dihydroxynaphthalene yields the respective decarbonylated core. Key steps of this 5‐step sequence are again an Ullmann coupling and a McMurry olefination. The cleavage of the preferentially utilized hexyl protecting group could be achieved with boron bromide. [ABSTRACT FROM AUTHOR]

A wide range of polyaryl compounds (π‐extended biaryls) including terphenyls, tetraphenyls, pentaphenyls, and hexaphenyls were assembled in a single operation of Pd(II)‐catalyzed C−H coupling of biaryl carboxamides and iodobiaryls. Traditionally, cross‐coupling protocols involving organometallic reagents were employed to assemble the core structure of π‐extended biaryls (polyphenylenes or polyaryls). The pre‐assembling of organometallic reagents is a limitation in investigations pertaining to the aryl‐aryl cross‐coupling reactions affording polyaryls (polyphenylenes). We report the application of Pd(II)‐catalyzed bidentate directing group (DG)‐aided C−H arylation method for constructing polyaryl motifs (π‐extended biaryls) using biaryl‐based carboxamides and iodobiaryls as the coupling partners in a single operation. The current investigation on the bidentate DG‐aided C−H arylation of biaryl carboxamides with iodobiaryls is expected to serve as a useful route to enrich the library of π‐extended biaryls (polyphenylenes or polyaryls). [ABSTRACT FROM AUTHOR]

This article discusses the development of Pd(II)-catalyzed, directing-group (DG)-mediated, site-selective functionalization of C-H bonds in small organic molecules. The focus is on the functionalization of remote C-H bonds, specifically β-C-H bonds in carboxylic acid substrates and γ-C-H bonds in amine substrates. The article provides detailed information on the reaction conditions and yields of the functionalization reactions. The text describes a study on the synthesis of arylated derivatives of phenylalaninol using a Pd(II)-catalyzed δ-C–H arylation reaction. The researchers tested different reaction conditions and directing groups to optimize the yield of the desired products. The study also explored the substrate scope by using racemic and enantiopure phenylalaninol substrates. The text describes a series of chemical reactions involving the treatment of various substrates with different aryl iodides in the presence of specific catalysts and additives. These reactions result in the formation of bis δ-C–H (ortho) arylated products, specifically phenylalaninol-based terphenyl derivatives. The reactions are performed under specific conditions and yield varying percentages of the desired products. The text also explores the extension of these reactions to enantiopure substrates and the synthesis of enantiopure bis δ-C–H (ortho) arylated products. Additionally, the text discusses attempts to perform alkylation, [Extracted from the article]

The tandem intramolecular hydroarylation of alkynes accompanied by a 1,2‐aryl shift is described. Harnessing the unique electron‐rich character of 1,4‐dihydropyrrolo[3,2‐b]pyrrole scaffold, we demonstrate that the hydroarylation of alkynes proceeds at the already occupied positions 2 and 5 leading to a 1,2‐aryl shift. Remarkably, the reaction proceeds only in the presence of cationic gold catalyst, and it leads to heretofore unknown π‐expanded, centrosymmetric pyrrolo[3,2‐b]pyrroles. The utility is verified in the preparation of 13 products that bear six conjugated rings. The observed compatibility with various functional groups allows for increased tunability with regard to the photophysical properties as well as providing sites for further functionalization. Computational studies of the reaction mechanism revealed that the formation of the six‐membered rings accompanied with a 1,2‐aryl shift is both kinetically and thermodynamically favourable over plausible formation of products containing 7‐membered rings. Steady‐state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S‐shaped N‐doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. Their optical properties are rationalized through time‐dependent density functional theory calculations. We anticipate that this chemistry will empower the creation of new materials with various functionalities. [ABSTRACT FROM AUTHOR]

The dimeric β‐diketiminato calcium hydride, [(DippBDI)CaH]2 (DippBDI = HC{(Me)CN‐2,6‐i‐Pr2C6H3}2), reacts with ortho‐, meta‐ or para‐tolyl mercuric compounds to afford hydridoarylcalcium compounds, [(DippBDI)2Ca2(μ‐H)(μ‐o‐,m‐,p‐tolyl)], in which dimer propagation occurs either via μ2‐η1‐η1 or μ2‐η1‐η6 bridging between the calcium centers. In each case, the orientation and hapticity of the aryl units is dependent upon the position of the methyl substituent. While wholly organometallic meta‐ and para‐tolyl dimers, [(DippBDI)Ca(m‐tolyl)]2 and [(DippBDI)Ca(p‐tolyl)]2, can be prepared and are stable, the ortho‐tolyl isomer is prone to isomerization to a calcium benzyl analog. Computational analysis of this latter process with density functional theory (DFT) highlights an unusual mechanism invoking the generation of an intermediate dicalcium species in which the group 2 centers are bridged by a toluene dianion formed by the formal attachment of the original hydride anion to the initially generated ortho‐tolyl substituent. Use of a more sterically encumbered aryl substituent, {3,5‐t‐Bu2C6H3}, facilitates the selective formation of [(DippBDI)Ca(μ‐H)(μ‐3,5‐t‐Bu2C6H3)Ca(DippBDI)], which can be converted into the unsymmetrically‐substituted σ‐aryl calcium complexes, [(DippBDI)Ca(μ‐Ph)(μ‐3,5‐t‐Bu2C6H3)Ca(DippBDI)] and [(DippBDI)Ca(μ‐p‐tolyl)(μ‐3,5‐t‐Bu2C6H3)Ca(DippBDI)] by reaction with the appropriate mercuric diaryl. Conversion of [(DippBDI)Ca(H)(Ph)Ca(DippBDI)] to afford [{{(DippBDI)Ca}2(μ2‐Cl)}2(C6H5‐C6H5)], comprising a biphenyl dianion, is also reported. Although this latter transformation is serendipitous, AIM analysis highlights that, in a related manner to the ortho‐tolyl to benzyl isomerization, the requisite C–C coupling may be facilitated in an "across dimer" fashion by the experimentally‐observed polyhapto engagement of the aryl substituents with each calcium. [ABSTRACT FROM AUTHOR]

Abstract The dimeric β‐diketiminato calcium hydride, [(DippBDI)CaH]2 (DippBDI = HC{(Me)CN‐2,6‐i‐Pr2C6H3}2), reacts with ortho‐, meta‐ or para‐tolyl mercuric compounds to afford hydridoarylcalcium compounds, [(DippBDI)2Ca2(μ‐H)(μ‐o‐,m‐,p‐tolyl)], in which dimer propagation occurs either via μ2‐η1‐η1 or μ2‐η1‐η6 bridging between the calcium centers. In each case, the orientation and hapticity of the aryl units is dependent upon the position of the methyl substituent. While wholly organometallic meta‐ and para‐tolyl dimers, [(DippBDI)Ca(m‐tolyl)]2 and [(DippBDI)Ca(p‐tolyl)]2, can be prepared and are stable, the ortho‐tolyl isomer is prone to isomerization to a calcium benzyl analog. Computational analysis of this latter process with density functional theory (DFT) highlights an unusual mechanism invoking the generation of an intermediate dicalcium species in which the group 2 centers are bridged by a toluene dianion formed by the formal attachment of the original hydride anion to the initially generated ortho‐tolyl substituent. Use of a more sterically encumbered aryl substituent, {3,5‐t‐Bu2C6H3}, facilitates the selective formation of [(DippBDI)Ca(μ‐H)(μ‐3,5‐t‐Bu2C6H3)Ca(DippBDI)], which can be converted into the unsymmetrically‐substituted σ‐aryl calcium complexes, [(DippBDI)Ca(μ‐Ph)(μ‐3,5‐t‐Bu2C6H3)Ca(DippBDI)] and [(DippBDI)Ca(μ‐p‐tolyl)(μ‐3,5‐t‐Bu2C6H3)Ca(DippBDI)] by reaction with the appropriate mercuric diaryl. Conversion of [(DippBDI)Ca(H)(Ph)Ca(DippBDI)] to afford [{{(DippBDI)Ca}2(μ2‐Cl)}2(C6H5‐C6H5)], comprising a biphenyl dianion, is also reported. Although this latter transformation is serendipitous, AIM analysis highlights that, in a related manner to the ortho‐tolyl to benzyl isomerization, the requisite C–C coupling may be facilitated in an “across dimer” fashion by the experimentally‐observed polyhapto engagement of the aryl substituents with each calcium.

A heterogeneous nanocatalyst comprising palladium (Pd/PdO) and iron-(III) oxide (Fe2O3) in the dimension of 1–4 nm was synthesized using sodium-exchanged zeolite-Y or zeolite-NaY [a type of faujasite (FAU) zeolite having an aluminosilicate framework with a general formula of (Na2)3.5[Al7Si17O48]·32H2O] as a support matrix. The catalyst was investigated as a true heterogeneous catalyst for activation of the robust C–Cl bond of aryl chlorides in the Suzuki–Miyaura cross-coupling (SMCC) reaction. The catalyst with very low Pd loading (0.0037 mol %) exhibited high reactivity in the SMCC reaction with various derivatives of aryl chlorides (Ar–Cl). Biaryl products were obtained with up to a 92% yield, high selectivity, and a good turnover number with this Pd/PdO–Fe2O3-Y catalyst. The catalyst exhibited good thermal stability and was highly recyclable. The reaction was found to be reliant on various parameters such as solvent system, temperature, time, and catalyst amount. A small aliquot of water (H2O) mixed with methanol (CH3OH) dramatically brought a substantial improvement in the product yield of the desired biaryl product. The role of zeolite-NaY was also investigated by comparing the results with various other synthesized catalysts. Different experimental studies indicated that the surface hydroxyl (−OH) groups of zeolite-NaY, modification of basic sites, and the ability to influence the reduction temperature of iron (Fe) and palladium (Pd) influenced the catalytic performance of the synthesized catalyst. The impact of Fe on the electronic structure and reactivity of Pd was analyzed through a density functional theory calculation. This study provided strong evidence for creation of a negative (−ve) charge on Pd with an increasing amount of Fe content and thereby favored the in situ transformation of Pd-(II) to Pd(0) as required in the activation of the C–Cl bond. [ABSTRACT FROM AUTHOR]

A simple and effective method for the synthesis of 9‐sulfenylphenanthrenes was developed via BF3 ⋅ OEt2‐mediated annulation of 2‐alkynyl biaryls with N‐arylthio succinimides at room temperature. Through this methodology, a series of 9‐sulfenylphenanthrenes could be efficiently and conveniently obtained in good to excellent yields under mild and metal‐free conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pd-loaded chitosan-based-polyurethane foam facilitates C-C coupling reactions. • Synthesis of a series of biaryl and benzimidazole derivatives is achieved. • This nano-Pd catalyst works at room temperature with exceptional stability, recyclability and reusability for at least 8 times. • The leaching of Pd from the catalytic material has been completely minimized. • The scope of products can be extended to the synthesis of biologically significant molecules. Though Pd-based catalysts have been the most efficient in catalytic C-C coupling reactions, but the leaching of Pd is one of the serious limitations. To shed more light on the Pd-based catalysts to overcome the existing disadvantages, four different new functionalized polyurethane foams, namely, PUCS-Pd, PUCS-CA-Pd, PUCS-TA-Pd and PUCS-GA-Pd (where PU = polyurethane; CS = chitosan, CA = citric acid, TA = tartaric acid and GA = gallic acid) were prepared. Further, these materials were employed as an effective catalytic system in C-C coupling reactions yielding a series of biaryl products (80–98%) and benzimidazole derivatives (80–98%) at room temperature. The structures and compositions of these catalysts were well characterized to understand the morphology and physicochemical properties. The BET surface area of all these chitosan-based PU foams can be altered and was achieved as high as 12.156 m2g−1. The TEM data demonstrate the presence of 3 to 10 nm sized nano-Pd species grafted on the surface of polymer support. The catalyst, PUCS-CA-Pd facilitated the cross-coupling reactions even at a low Pd-loading of 0.624 mg in methanol-water. Because of the pore structure toward the captured Pd species, PUCS-CA-Pd displayed exceptional stability, recyclability and reusability at least 8 times without loss of activity. [ABSTRACT FROM AUTHOR]

We demonstrated a straightforward photo-induced strategy for decarbonylative aryl C H arylation with the aldehydes. This transformation proceeds with operational simplicity and solvent-free conditions, does not need for 1,2-dinitrobenzene additive, and tolerates unsuccessful functionalities (e.g., 4-pyridine, NO 2 and SO 2 Me) in previously reported protocols. [Display omitted] • Developing a new photothermal-catalytic approach for divergent construction of biaryl skeletons avoiding the use of equivalent o -dinitrobenzene. • High functional-group tolerance such as previously unsuccessful 4-pyridine, -NO 2 and -SO 2 Me. • Offering a new strategy for aliphatic aldehydes for the first time. • The reaction proceeds through decarbonylation of aldehyde via photothermal excitation to generate an aromatic anion. Here, by using eosin Y as a preferable catalyst, we present a photothermally induced decarbonylative aryl C H arylation with the aldehydes. This transformation proceeds with operational simplicity and solvent-free conditions, does not need for 1,2-dinitrobenzene additive, and tolerates unsuccessful functionalities (e.g., 4-pyridine, NO 2 and SO 2 Me) in previously reported protocols. In addition to the aryl aldehydes, the alkyl ones are also compatible with this transformation. Mechanistic investigations reveal that the reaction undergoes aldehyde decarbonylation to afford aryl radicals in situ , its regioselective addition to the arenes followed by single electron oxidation and homolytic hydrogen abstraction gives rise to the desired cross-coupling products. Give the striking features, this work offers a useful platform to directly access various biaryls. [ABSTRACT FROM AUTHOR]

A tremendous research has been appeared on Pd-catalyzed Suzuki–Miyaura cross-coupling (SMC) during the last four decades due to its high prominence in constructing biaryl motifs of several complexes as well as simple organic compounds of high biological and commercial significance. The use of organic solid waste–derived materials for SMC in benign solvents like water/aqueous media is a very good achievement in these cases. We report in this article the usability of water extract of Tamarindus indica seeds ash (WETS) as a renewable base and reaction medium for Pd(OAc)2-catalyzed SMC reaction at room temperature (RT). The WETS has been characterized using powder XRD, EDAX, SEM, and FTIR analysis. Furthermore, this process is highly environmentally beneficial by the waste repurposing to prominent chemical transformation along with the advantages such as ambient condition and avoids non-renewable chemicals like volatile organic solvents, ligands, promoters, and bases. Based on these merits and the quick reactions with high yields of products, this method can attain the interest of the scientific community in exploring the waste-derived ashes to significant chemical transformations. Tamarindus indica seed ash extract for C–C coupling under added organics and volatile organic solvent-free conditions: a waste repurposing technique for Suzuki–Miyaura reaction [ABSTRACT FROM AUTHOR]

The Pd‐catalyzed Suzuki‐Miyaura cross‐couplings (SMRs) are utilized as the most practical method to construct C−C bond, especial for biaryls. However, a major disadvantage of current protocols is the requirement of excess organoboron coupling partner (1.5–3.0 equiv.). Herein, a novel palladacyclic 1,3‐bis(2,6‐diisopropylphenyl)acenaphthoimidazol‐2‐ylidene (AnIPr) precatalyst possessing a chiral oxazoline was designed, which enabled a general protocol towards bulky tri‐ortho‐substituted biaryls, ternaphthalenes and diarylanthracenes via the Pd‐catalyzed SMR employing equimolar organoborons and aryl bromides. A remarkable scope of substrates with various functional groups and heterocycles were well compatible with an adaptability to synthesize useful ligands. [ABSTRACT FROM AUTHOR]

A denitrogenative palladium-catalyzed C(sp2)–C(sp2) cross-coupling of aryl-substituted diazenes capped with a trimethylsilyl group and functionalized aryl bromides is reported. A PEPPSI™ catalyst in the presence of NaO t -Bu enables the activation of the N -aryl- N ′-silyldiazene pronucleophile with concomitant loss of dinitrogen and subsequent coupling of the in-situ-formed aryl nucleophile. By this, biaryl compounds bearing a variety of substituents can be prepared. [ABSTRACT FROM AUTHOR]

In recent years, gold catalysis involving Au(I)/Au(III) redox cycle has gained significant attention. This account summarizes our contributions to the development of Au(I)/Au(III) catalysis, focusing on cross-coupling reactions and 1,2-difunctionalization reactions of C–C multiple bonds. A special emphasis has been given to understanding the mechanism of the reactions. 1 Introduction 2 Gold-Catalyzed Cross-Coupling Reactions 3 Gold-Catalyzed 1,2-Difunctionalization of C–C Multiple Bonds 4 Conclusion and Outlook [ABSTRACT FROM AUTHOR]

Dearomatization reactions involving radical cyclizations can facilitate the synthesis of complex polycyclic systems that find applications in medicinal chemistry and natural product synthesis. Here we employ redox‐neutral photocatalysis to affect a radical spirocyclization that transforms biaryls into spirocyclic cyclohexadienones under mild reaction conditions. In a departure from previously reported methods, our work demonstrates the polarity mismatched addition of a nucleophilic radical to an electron rich arene, and allows the regioselective synthesis of 2,4‐ or 2,5‐cyclohexadienones with broad functional group tolerance. By transforming biaryls into spirocycles, our methodology accesses underexplored three‐dimensional chemical space, and provides an efficient means of creating quaternary spirocenters that we apply to the first synthesis of the cytotoxic plant metabolite denobilone A. [ABSTRACT FROM AUTHOR]

The present study provides a practical and safe cross‐coupling strategy for the synthesis of biaryls via decarboxylation of aryl carboxylic acids. In this method, BF@Propyl/Tris/Pd was used as a new catalyst to synthesize biaryls. The structural and morphological characteristics of the catalyst were investigated by FT‐IR, EDX, XRD, TGA, and SEM analyses. This catalyst system has some advantages, such as good stability, excellent workup, and reusability. We used it as a recyclable heterogeneous catalyst by easily separating it from the medium of reaction. [ABSTRACT FROM AUTHOR]

A novel organonickel sigma-complex [NiBr(Tcpp)(bpy)], where Tcpp is 2,4,6-tricyclopentylphenyl, bpy is 2,2'-bipyridine has been generated in solution by electrochemical macroscale synthesis. The monitoring of the macroscale electrosynthesis and also the cyclic voltammetric measurements have shown that the organonickel sigma-complex is formed at the electrolysis but, in contrast to its analogues with ortho-substituted aromatic fragments, is unstable and decomposes to the homo-coupling product, namely, the earlier unknown sterically hindered biaryl derivative 2,2',4,4',6,6'-hexacyclopentyl-1,1'-biphenyl, the molecular and crystal structure of which are described by NMR spectroscopy and X-ray diffraction techniques. [ABSTRACT FROM AUTHOR]

The transition‐metal‐catalyzed C−P bond cleavage has emerged as a powerful tool for the formation of both C−C and C−P bond. However, the transition‐metal‐catalyzed stereoselective cleavage of C−P bond is still undeveloped. Herein, we report a palladium‐catalyzed stereoselective cleavage of C−P bond for the construction of P‐stereogenic phosphines and stereogenic axis. This protocol enables the quick synthesis of atropisomers bearing a P‐stereogenic center in high yields, diastereo‐ and enantioselectivities of up to 98 % ee, >25 : 1 dr. The product is able to serve as chiral catalyst in phosphine catalyzed [3+2] cycloaddition of allenoates to imines, showing the great potential of the present methodology. [ABSTRACT FROM AUTHOR]

A hierarchical titanium dioxide microspheres-supported palladium catalyst (Pd/TiO2-350) was prepared and characterized using BET, XRD, XPS, SEM, EDX, and TEM analyses. An ICP-OES analysis of Pd/TiO2-350 further confirmed the successful Pd immobilization on TiO2 with a palladium loading of 0.1 mmol g−1. Pd/TiO2-350 efficiently catalyzed the Suzuki-Miyaura reaction of aryl iodides with arylboronic acids to give the corresponding biaryl derivatives in good to excellent yields. After the reaction, the catalyst was recovered by centrifugation and reused three times without significant loss of its catalytic activity. Moreover, the loading of palladium species further decreased to 0.001 mol%, and the total turnover number and turnover frequency of the catalyst reached as high as 99 000 and 0.57 s−1, respectively.

Catalytic asymmetric dynamic kinetic resolution of configurationally labile bridged biaryls is emerging as a powerful strategy for atropisomer synthesis. However, the reported examples suffer from an inherent challenge as the reactivity is highly dependent on the torsional strain of the biaryl substrates, which significantly narrows down the scope and hampers the application. Herein, we report our discovery and development of a torsional strain‐independent reaction between biaryl thionolactones and activated isocyanides. By employing auto‐tandem silver catalysis, a universal synthesis of both tri‐ and tetra‐ortho‐substituted thiazole‐containing biaryls was realized in high yields with high enantioselectivities. In addition, these products could be facilely converted to a novel type of bridged biaryls bearing an eight‐membered lactone. Mechanistic studies were carried out to elucidate the cause of this unusual torsional strain‐independent reactivity. [ABSTRACT FROM AUTHOR]

A glycerol‐based Deep Eutectic Solvent (DES) enables the Pd‐catalyzed activation of (hetero)arylchlorides and promotes the formation of 2,2'‐bipiyridines and biaryls through an Ullmann‐type homocoupling in smooth experimental conditions (80 °C) with Ca(OH)2 as a green base and Pd/C as heterogeneous catalyst. Noteworthy, the coupling does not need the addition of external reducing agents, like metals, since the glycerol present in the DES acts as a safe and green organic reductant. The heterogeneous catalytic system (DES‐Pd/C) showed to be easily recyclable and has been applied to the sustainable synthesis of the Abametapir drug. [ABSTRACT FROM AUTHOR]

Suzuki–Miyaura cross-coupling is one of the most powerful strategies for constructing biaryl compounds. However, classic Suzuki–Miyaura coupling suffers from hour-scale reaction time and competitive protodeboronation. To address these problems, a mild nonaqueous potassium trimethylsilanolate (TMSOK)-assisted Suzuki–Miyaura coupling strategy was designed for the microsynthesis of biaryls in paper spray ionization (PSI). Due to the acceleration power facilitated by microdroplet chemistry in reactive PSI, the microsynthesis of biaryls by reactive PSI was accomplished within minutes with comparable yields to the bulk, showing good substrate applicability from 32 Suzuki–Miyaura reactions of aryl bromides and aryl boronic acid/borates bearing different substituents. Based on the above TMSOK-assisted Suzuki–Miyaura coupling strategy, we further developed a high-sensitivity and selective PSI mass spectrometry (MS) method for quantitative analysis of aryl bromides, a class of environmentally persistent organic pollutants that cannot be directly detected by ambient mass spectrometry due to their low ionization efficiency. In situ derivatization of aryl bromides was achieved with aryl borates bearing quaternary ammonium groups in PSI. The proposed PSI-MS method shows good linearity over the 0.01–10 μmol L–1 range with low detection limits of 1.8–4.8 nmol L–1 as well as good applicability to the rapid determination of six aryl bromides in three environmental water samples. The proposed PSI-MS method also shows good applicability to brominated flame retardants (polybrominated diphenyls/diphenyl esters). Overall, this study provides a simple, rapid, low-cost, high-sensitivity, and high-selectivity strategy for trace aryl bromides and other brominated pollutants in real samples with minimal/no sample pretreatment. [ABSTRACT FROM AUTHOR]

A mild and practical protocol for selectively time-dependent dehydrogenative C-C coupling, as well as tandem coupling-cyclization reaction between indoles or/and other heteroaromatics via electrochemically oxidative process has been demonstrated. The reaction runs under noble catalyst, external oxidant and inert gas free condition, allowing tunable access to a wide variety of synthetically useful symmetrical or nonsymmetrical heteroarene with aggregation-induced emission (AIE), and polycyclic 3-D indole derivatives with aggregation-caused quenching (ACQ) fluorescence properties. Finally, preliminary mechanistic study indicated that tunable generation of indole cation under various electrolysis potential via regulating N-protecting group was the key to achieve cross-coupling between indoles and other heteroaromatics. [ABSTRACT FROM AUTHOR]

In this paper, we report the Pd(II)-catalyzed, picolinamide DG-aided sp2 γ-C–H functionalization and expansion of the library of enantiopure α-methylbenzylamine and phenylglycinol scaffolds. We have shown the synthesis of a wide range of racemic and enantiopure ortho -C–H arylated, alkylated, brominated, and iodinated α-methylbenzylamine and phenylglycinol scaffolds. Various racemic and R and S (chiral) sp2 γ-C–H functionalized α-methylbenzylamine and phenylglycinol scaffolds were synthesized with good enantiopurities. Racemic and enantiopure α-methylbenzylamine and phenylglycinol derivatives are important building blocks in organic synthesis and medicinal chemistry. Accordingly, this work contributes to the expansion of the libraries of α-methylbenzylamine and phenylglycinol motifs and substrate scope development through the Pd(II)-catalyzed bidentate directing group picolinamide-aided site-selective C–H activation and functionalization method. [ABSTRACT FROM AUTHOR]

Many efforts have been done to develop new catalysts for organic reactions. In this study, preparation and characterization of palladium immobilized on modified magnetic Fe3O4 nanocatalyst (Fe3O4@SiO2@DPA-Pd) have been reported; dipicolylamine (DPA) groups are used as linkers to fix palladium nanoparticles on silica-coated Fe3O4 nanoparticles without agglomeration. The structure of the nanocatalyst was investigated using scanning electron microscopy, X-ray powder diffraction, Fourier-transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller (BET) and thermogravimetry analysis. The data showed that the nanoparticles have spherical morphology with an average size of about 40 nm and 49.16 m2/g BET surface area. The inductively coupled plasma analysis confirmed that the Pd2+ had been successfully loaded on the Fe3O4@SiO2@DPA support with a high amount of 1.03 mmol g−1. The synthesized nanocatalyst was considered for synthesis of biaryls by the Suzuki–Miyaura coupling reaction in water/ethanol as the solvent system and in the absence of toxic phosphine ligand. The reaction conditions were mild, and coupling reaction yields were excellent (68–95%). The synthesis is compatible with the environment. The nanocatalyst can be easily recycled from the reaction mixture using an external magnet and was used at least five times without significant loss of catalytic activity. [ABSTRACT FROM AUTHOR]