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ConspectusThis Account presents an overview of a promising collection of phosphine ligands simply made from the modular Fischer indolization process and their applications in modern arylation processes. Using one easily accessible 2-arylindole scaffold, three major phosphino-moiety-positioned ligand series can be readily generated. We have attempted to explore challenging electrophilic and nucleophilic partners for the coupling reaction using the modular ligand tool. For the electrophilic partner study

An operationally simple protocol is described for the facile, modular and regioselective access of all-pyrano-moiety-substituted iminochromenes, particularly under undried acetonitrile and air atmosphere.

A general protocol for N-difluoromethylation of aniline derivatives is developed.

A comprehensive review overviewing the advances in Rh-catalyzed cross-dehydrogenative-coupling in the period of 2016–2021 is presented.

A [2+2+1]-NO-segment-incorporating heteroannulative cascade is described. This versatile method, particularly using modular cyanoarylated ketimine substrates, allows efficient access to structurally diversified quinolines embedded with an oxadiazole core. This metal-free protocol proceeds smoothly at 30 °C, offers easy manipulation of substituents on the quinoline moiety, and tolerates a spectrum of functional groups. Density functional theory calculation revealed that the cyano moiety is crucial to facilitate the early cyclization step in this heteroannulation process and is different from the previously established late cyclization mechanistic interpretation.

A DBU-mediated cascade strategy of propargylamines with dimethyl 3-oxoglutarate for constructing a functionalized benzo[c]chromen-6-one core has been achieved. This cascade process presumably involves a sequence of 1,4-conjugate addition, followed by lactonization, alkyne-allene isomerization, enol-keto tautomerization, 6π-electrocyclization, and aromatization. This protocol features mild reaction conditions, simple operation, rich structural diversity, and good functional group tolerance. A photophysical survey reveals that the benzo[c]chromen-6-one products exhibit fluorescence properties and show potential for exploring fluorescent material applications.

A redox-neutral benzylic C-O cyclization under beneficial transition-metal-free conditions is reported. Key to the success of this process is the utilization of the Tf anion as the leaving group for achieving the redox-neutral transformation. This protocol delivers a series of captivating helical compounds having various functionality in good-to-excellent yields. It is particularly noteworthy that sterically hindered helical compounds are conformationally stable. In addition to simple helical chromenes, the bihelical multiple-ring systems which are potentially useful in material chemistry are also easily attained by employing this method. DFT calculation revealed that quinone intermediate is the key species, among four possible mechanisms, for accomplishing the desired cyclization via an oxa-6π-electrocyclization pathway.

A new series of hemilabile benzimidazolyl phosphines is reported. Entities in this ligand family can be easily assembled and prepared on a large scale via a simple one-pot procedure. X-ray crystall...

With a tandem DMAP-catalyzed reaction between o-AQM, in which it is generated in situ from propargylic amine, and acyl carbene surrogate (from pyridinium ylide), a variety of polyarylated chromenes are assembled in good yields. This process does not require transition-metal catalyst and exhibits easy manipulation of the arene group and good functional group compatibility, particularly the -Br group which can be further transformed to other functionalities by cross-coupling reactions. The modular feature of o-AQM substrates and the simple operation procedures add further advantages to this synthetic method.

A palladium-catalyzed C-N bond coupling reaction between arylhydrazines and aryl tosylates for facile synthesis of unsymmetrical N,N-diarylhydrazines has been developed. Employing the catalyst system of Pd(TFA)2 associated with newly developed phosphine ligand L1, the monoarylation of arylhydrazine proceeds smoothly to afford desired products in good-to-excellent yields (up to 95%) with good functional group compatibility. This method provides an alternative synthetic pathway for accessing structurally diversified N,N-diarylhydrazines from simple and easily accessible coupling components.

A DMAP-catalyzed cascade approach allowing facile assembly of alkynyl coumarins is reported. By virtue of reactive o-AQM (in situ generated from modular propargylamine) and a new synthetic equivale...

A DBU-catalyzed one-pot cascade reaction of propargylamines and water for the synthesis of flavanones has been developed. This process proceeds via a sequence of 1,4-conjugate addition of water to alkynyl o-quinone methide (o-AQM), followed by the alkyne-allene isomerization and subsequent intramolecular oxa-Michael addition. This strategy provides a convenient method for accessing a broad range of flavanones in good to excellent yields with good functional-group tolerance, in particular, the reactive halo functional groups.

The first palladium-catalyzed cross-coupling reaction of aryl/heteroaryl and alkenyl mesylates and tosylates with aryl titanium as the multi-functional reagent is reported. Using the catalyst system of Pd(OAc)2 associated with the new NMe2-CM-Phos (L14), a broad range of electron-rich, electron-neutral, electron-deficient, and sterically hindered aryl/heteroaryl and alkenyl mesylates and tosylates are well coupled with aryl titanium reagents to give the corresponding products in good to excellent yields. The catalyst loading down to 0.2 mol% Pd and the reaction time shortening to 10 min can be achieved. The reaction can be easily scaled up to the gram scale without diminishing the product yield.

We herein report a denitrogenative palladium-catalyzed cascade for the modular and regioselective synthesis of polysubstituted fluorenes. Hydrazone facilitates the Pd(ii) to Pd(iv) oxidative addition in a Catellani pathway and is also the methylene synthon in the proposed reaction. Aryl iodides and 2-bromoarylaldehyde hydrazones undergo a norbornene-controlled tandem reaction sequence to give a broad scope of fluorenes in the presence of a palladium catalyst. The method described is scalable and adaptable to a three-component reaction with in situ generation of the hydrazone group. Preliminary mechanistic investigations have been conducted., Hydrazone assists Pd(ii)/(iv) oxidative addition and is the methylene synthon in a palladium-catalyzed, norbornene-mediated regioselective synthesis of fluorenes.

Phosphine ligands embodying a carbazolyl motif have been found to be successful in many palladium-catalyzed biaryl syntheses and direct C–H bond arylation processes. Here, a practical scaled-up syn...

A family of 2-(9H-carbazol-9-yl)phenyl-based phosphine ligands were synthesized and their efficacy in promoting the steric hindered Buchwald–Hartwig amination was evaluated. In the presence of Pd(OAc)2 (0.03–1.0 mol%) associated with the newly developed a carbazolyl-derived phosphine ligand, the synthesis of tetra-ortho-substituted diarylamines proceeded smoothly with excellent product yields (up to 99%). A remarkable result was obtained even for the coupling of highly sterically congested 2,6-diisopropylaniline and hindered 2-chloro-1,3,5-triisopropylbenzene (96% isolated yield). A possible decomposition pathway for the anthracenyl C–N coupling product is also reported.

Tosyloxy- and mesyloxyflavones derived from abundant and biologically important hydroxyflavones were used to synthesize a series of functionalized flavones through versatile palladium-catalyzed cross-coupling reactions. A Pd(OAc)2/2-[2-(dicyclohexylphosphino)phenyl]-1-methyl-1H-indole system effectively catalyzed the reactions of a broad range of tosyloxy- and mesyloxyflavones as electrophilic coupling partners with various nucleophiles to give the corresponding products in good to excellent yields. Catalyst loadings of as little as 0.1 mol% Pd were successfully used. Importantly, we demonstrated that this protocol provided a significantly improved efficiency in the synthesis of a potential chromen-4-one-based analogue of a potent inhibitor of DNA-dependent protein kinase.

A DBU-catalyzed one-pot cascade reaction of propargylamines and water for the synthesis of flavanones has been developed. This process proceeds via a sequence of 1,4-conjugate addition of water to alkynyl

The scope and limitations of the monoselective N-arylation of various amines by using aryl and hetaryl tosylates are presented. The air-stable and easily accessible Pd(OAc)2 /CM-phos {CM-phos=2-[2-(dicyclohexylphosphino)phenyl]-1-methyl-1H-indole}catalyst system was able to deal with a wide range of aryl tosylate substrates as well as amine nucleophiles, including primary and secondary cyclic/acyclic aliphatic amines and anilines. NH-Bearing heterocycles such as indole, carbazole, pyrrole, 10-phenothiazine, and 10-phenoxazine were shown to be feasible coupling partners under this catalytic system. The described reaction conditions tolerate a wide range of functional groups and allow an array of aromatic amines as well as unsymmetrical amine products to be easily accessed from the various phenolic derivatives. Interestingly, this catalyst system even offers the opportunity to perform the reaction in water medium. We also report the intermolecular coupling of optically active α-central chiral amines with aryl tosylates without erosion of the enantiomeric purity.

The first general examples of direct C–H arylation of electron-deficient polyfluoroarenes with challenging di-ortho-substituted aryl(heteroaryl) chlorides for tetra-ortho-substituted biaryl synthesis are reported. Key to success is the use of Buchwald-type biaryl phosphine ligand, notably with inexpensive −PPh2 moiety (instead of −PCy2 group). Pd(OAc)2 associated with ligand L9 exhibits even higher efficiency than the corresponding SPhos toward this reaction. A wide range of sterically hindered di-ortho-substituted chloroarenes bearing electron-donating or -withdrawing groups are found applicable. Excellent product yields are obtained under mild reaction conditions, and the catalyst loading down to 0.25 mol % of Pd can also be achieved.

A cobalt-catalyzed chelation-assisted tandem C-H activation/C-C cleavage/C-H cyclization of aromatic amides with alkylidenecyclopropanes is reported. This process allows the sequential formation of two C-C bonds, which is in sharp contrast to previous reports on using rhodium catalysts for the formation of C-N bonds. Here the inexpensive catalyst system exhibits good functional-group compatibility and relatively broad substrate scope. The desired products can be easily transformed into polycyclic lactones with m-CPBA. Mechanistic studies revealed that the tandem reaction proceeds through a C-H cobaltation, β-carbon elimination, and intramolecular C-H cobaltation sequence.

A regioselective aromatic π-extension reaction of internal alkynes is reported. The proposed method employs three easily available components, namely aryl halides, 2-haloarylcarboxylic acids, and disubstituted acetylenes. The transformation is driven by a controlled reaction sequence of C-H activation, decarboxylation, and annulation to give poly(hetero)aromatic compounds in a site-selective fashion. Unlike in previously reported palladium-catalyzed three-component annulations, alkyne carbopalladation is the last step of this tandem reaction.

Transition metal-catalysed C–H bond functionalisation is an attractive approach for assembling valuable complex intermediates for the synthesis of pharmaceuticals, natural products, agrochemicals and fine chemicals. Selective functionalisation of one specific C–H site within a complex molecule without the assistance of a directing group is one of the major challenges in organic synthesis. The non-directed functionalisation of C–H bonds is more attractive and straightforward than the directed approach. While several reviews have covered (hetero)aryl (pseudo)halides as coupling partners in non-directed C–H bond functionalisation, this review will complement these existing contributions by focusing on the recent developments involving the employment of organometallic reagents for palladium-catalysed non-directed C–H bond functionalisation of (hetero)arene C–H bonds. Additionally, C–H/C–H bond coupling and other coupling partners will also be fully described.

A palladium/norbornene cocatalyzed three-component reaction of aryl iodides, O-benzoylhydroxylamines, and acetone is reported. o'-Aminoaryl acetones or o,o'-diaminoaryl acetones are efficiently prepared via tandem ortho-C-H amination/ipso-C-I α-arylation sequence, and the regiospecificity has been confirmed by X-ray analysis. The proposed method addresses the condensation/amination of free-N-H-bearing substrates in acetone monoarylations and the synthesis of extremely congested 2,6-disubstituted aryl acetones.

We have developed a synthetic strategy to access axially chiral biaryls through a dynamic-kinetic resolution-semipinacol rearrangement process. The axial chirality together with a sp3 quaternary carbon can be introduced in a single chemical operation. The products can be further ring-expanded to yield biologically relevant seven-membered dibenzolactams with inverted axial chirality.

Facile access to π-extended heterobiaryl compounds via a non-cross-coupling strategy has been achieved. In the presence of an inexpensive ZnI2 catalyst and versatile propargylamine and β-naphthol (or β-naphthylamine and β-naphthyl mercaptan) starting materials, a variety of sterically hindered heterobiaryl frameworks can be easily obtained. The present catalytic system offers excellent selectivity, good-to-excellent product yields, and good functional group tolerance including, for instance, -CN, -COOH, -C(O)R, -Br and -Cl groups. This cyclization process is proposed to proceed via in situ generated alkynyl o-quinone methides (o-AQMs), following a cascade intermolecular 1,4-conjugate addition/5-exo-dig annulation/1,3-H shift pathway.

Functionalized aryl chlorides are more economically attractive but usually much more difficult as substrates in metal-mediated couplings than the corresponding bromides and iodides. A catalyst prepared from a bulky (biaryl)diphenyl phosphane and a common ruthenium source (1:1) mediates selective direct monoarylations of arenes bearing 2-pyridyl and related ortho-directing groups in good yields. Sequential arylations to heterodiarylated products also proceed in satisfactory yields.

We report a newly developed carbazoyl-derived P,N-type phosphine ligand (L1) for the monoarylation of acetone with aryl chlorides. The proposed Pd(dba)2/L1 catalyst exhibited remarkable catalytic reactivity toward highly electron rich and sterically congested aryl chlorides, with catalyst loading as low as 0.1 mol % of Pd along with excellent chemoselectivity. A reaction rate study of the system using electronically diverse aryl chlorides determined the mechanisms regarding the rate-limiting steps in this reaction. The oxidative addition adduct of Pd-PhenCar-Phos with p-chlorotoluene showed the participation of N–Pd coordination in the metal complex. The isolated palladium complex C1 could be utilized as a precatalyst in the transformation and achieved performance comparable to that of the in situ generated palladium species.

Polycyclic aromatic systems are important in synthetic chemistry, material science, and pharmaceutical industry. Therefore, extensive efforts have been made by the aromatic extension for the efficient access to diverse polycyclic aromatic systems. This review focuses on recent developments of palladium-catalyzed regioselective synthetic strategies with pre- and in situ-formed biaryl fragments, which enable the aromatic extension of readily available precursors into extended (hetero)aromatic systems in a rapid and facile manner.

Alkenes and terminal alkynes are commonly available building blocks for a variety organic syntheses. The state-of-art transition metal-catalyzed Mizoroki-Heck and Sonogashira cross-couplings represent versatile and reliable protocols for further modification these molecules. In the past few decades, these reactions were found generally to proceed-well in the presence of homogenous palladium catalyst. Recent advancements showed that palladacycles become one of the most promising catalyst systems for these transformations. It should be attractive to note that the palladacyclic complexes are usually thermally stable and easily to be synthesized. This book chapter summarizes the recent developments on palladacycles for Mizoroki-Heck and Sonogashira cross-couplings. Some unique catalytic performances of the palladacycles in relevant transformations are also described.

Contemporary Science! Homogeneous catalysis plays a significant role in fundamental research and industry. After decades of development, it is still steadily growing: higher catalytic efficiency and selectivity, deeper mechanistic understanding, and more applications continue to emerge. The past few years have seen the rise of young chemists in this field from Asia. This special issue honors their contribution in the field of homogeneous catalysis.

Palladium-catalyzed C–N bond coupling reaction between NH-sulfoximines and aryl halides (e.g., −Br, −I, and −Cl and pseudohalides −OTf and −ONf) was successfully achieved. Nevertheless, aryl tosylates/mesylates left much to be achieved. In this report, a general N-arylation of sulfoximines with aryl sulfonates is described. Using Pd(OAc)2/MeO-CM-phos complex, the N-aryl sulfoximine products can be obtained in good-to-excellent yields (up to 99%) with good common functional group compatibility. In addition to arene moieties, alkenyl tosylates are shown to be successful coupling partners.

The first general examples of direct C-H arylation of electron-deficient polyfluoroarenes with challenging di- ortho-substituted aryl(heteroaryl) chlorides for tetra- ortho-substituted biaryl synthesis are reported. Key to success is the use of Buchwald-type biaryl phosphine ligand, notably with inexpensive -PPh

A ligand-enabled Pd-catalyzed Suzuki-Miyaura coupling of haloterthienyls for the synthesis of various thiophene-based π-conjugated oligomers including quinquethiophenes is demonstrated. An indolyl phosphine ligand plays an important role in this transformation. Thiopheneboronic acids were well applied, which might open up a window for the application of thiopheneboronic acids in the synthesis of thiophene-based π-conjugated oligomers in materials chemistry.

A palladium(II)-catalyzed oxidative Mizoroki–Heck reaction of arylsulfonyl hydrazides with alkenes was developed employing atmospheric air as the sole oxidant in an open-vessel manner. By using palladium(II) acetate associating with inexpensive, air-stable and moisture stable pyridine ligand L9 as the catalyst system, the efficiency of the reaction could be significantly enhanced. A wide range of arylsulfonyl hydrazides underwent the oxidative Mizoroki–Heck reaction with alkenes smoothly. Good-to-excellent product yields and excellent regio- and stereoselectivity were achieved. Functional groups such as halo, ester etc. were well-tolerated under these optimized reaction conditions.

Cross-dehydrogenative-coupling (CDC) between C–H/C–H bonds of indoles and cyclic ethers/cycloalkanes is made viable through a simple transition-metal-free pathway. With the aid of only di-tert-butyl peroxide, a number of inactive cyclic ethers and cycloalkanes can be directly coupled with indole derivatives in satisfactory yields.

A new benzo[c]carbazolyl-based phosphine ligand has been designed and synthesized. This newly developed ligand efficiently facilitates the Pd-catalyzed tetra-ortho-substituted biaryl syntheses via Suzuki–Miyaura cross-coupling. With 1 mol% of the Pd(OAc)2/L6 catalyst, sterically congested biaryls were afforded in good-to-excellent yields. In particular, the mild reaction conditions exhibited good compatibility of heterocycles and functional groups including esters and nitrile. L6 was structurally characterized by X-ray crystallographic analysis.