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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.

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...

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.

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.

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.

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 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.

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.

A simple α-C-H amination of cyclic ether with indole/carbazole derivatives has been accomplished by employing copper(II) chloride/bipy as the catalyst system. In the presence of the di-tert-butyl peroxide oxidant, cyclic ethers such as tetrahydrofuran, 1,4-dioxane, and tetrahydropyran successfully undergo C-H/N-H cross dehydrogenative coupling (CDC) with various carbazole or indole derivatives in good-to-excellent yields.

The first palladium-catalyzed allylic alkynylation reaction of allylic acetates with terminal alkynes has been realized. By empolying AgOTf as a cooperative catalyst, 1,4-enynes were synthesized in up to 98 % yield under mild conditions. Moreover, the possible asymmetric version of this allylic alkynylation reaction was demonstrated.

The first general examples of direct coupling of heteroaryl chlorides, especially substituted 2-pyridyl chlorides which were previously found to be problematic, with electron-deficient polyfluoroarenes are reported. Pd(OAc)2 associated with 3-(dicyclohexylphosphino)-2-phenylindole L1 serves as the effective catalyst which allows the challenging direct coupling of heteroaryl chlorides and polyfluoroarenes. In addition to heterocycles, a wide range of non-activated and activated aryl chlorides and alkenyl chlorides were also applicable under this catalyst system. A catalyst loading down to 1 mol % Pd can be achieved.

A versatile π-extension reaction was developed based on the three-component cross-coupling of aryl halides, 2-haloarylcarboxylic acids, and norbornadiene. The transformation is driven by the direction and subsequent decarboxylation of the carboxyl group, while norbornadiene serves as an ortho-C-H activator and ethylene synthon via a retro-Diels-Alder reaction. Comprehensive DFT calculations were performed to account for the catalytic intermediates.

A simple route for facile access of aryl(2-aminoaryl) sulfide was reported. With the aid of iron(III) chloride catalyst and diamine ligand, benzothiazole was efficiently S-arylated with various aryl iodides (19 examples) in water under air atmosphere. This operationally simple protocol provides aryl(2-aminoaryl) sulfides in moderate to good yields.

Direct intermolecular C-H arylation employing aryl bromide as the arene source has been developed. This process proceeds via a simple transition-metal-free pathway. With the aid of inexpensive and commercially available 2-pyridyl carbinol and potassium tert-butoxide, various unactivated arene C-H bonds can be directly arylated by aryl bromides through homolytic aromatic substitution.

A transition-metal-free oxidative coupling of allylic C–H and heterocyclic/aromatic N–H bonds was performed under mild conditions. Promoted by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), up to 99% yield could be achieved.

A palladium-catalyzed C((sp2))-H bond oxygenation reaction is described. This protocol represents the first example of a C-H bond cleavage/C-O bond formation sequence, by employing a ketone moiety as the directing group. With this new catalytic method, a variety of ortho-acylphenols can be easily accessed from arylketones.

General direct C2-alkenylation of oxazoles is reported using alkenyl tosylates at parts per million levels of palladium catalyst. From a series of ligands screened, PhMezole-Phos emerged as the promising ligand candidate to facilitate this reaction. Significantly, the method is scalable and exhibits excellent substrate tolerance. Highly sterically hindered substrates and small vinyl tosylate can be coupled successfully. Moreover, our method enables a rapid diversification of oxazole-based C^N ligands which can be readily derived into new group 9 organometallic compounds.

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 C-H arylation with aryl chloride is made viable through a transition-metal-free approach. In the presence of a simple diol associating with KOt-Bu, various phenanthridine derivatives can be conveniently accessed. In particular, only 10 mol % of simple and inexpensive ethylene glycol is required for this protocol. These results represent the first general examples of aryl chloride/C-H coupling under transition-metal-free conditions.

This study describes a direct oxidative C-2 arylation of benzoxazoles using arylsulfonyl hydrazides as the aryl sources. A simple catalyst system [Pd(OAc)2 and Ph3P] allows the reactions to proceed smoothly under oxidative reaction conditions. Other ­heteroarenes such as caffeine and benzothiazole are also applicable substrates. Notably, this catalytic system tolerates halogen substituents which provides a useful complement to the current cross-­coupling reactions which use aryl halides.

This study describes the efficacy of P,N-type benzimidazolyl phosphine ligands, which can be easily synthesized from commercially available and inexpensive starting materials. The application of this ligand array in palladium-catalyzed Suzuki–Miyaura coupling reaction of aryl chlorides with potassium aryltrifluoroborates is described. The air stable benzimidazolyl phosphines in combination with a palladium metal precursor provides highly effective catalysts for the Suzuki–Miyaura coupling of unactivated aryl chlorides and can achieve a catalyst loading of only 0.05 mol %.

This study describes an efficient class of hemilabile benzimidazolyl–phosphane ligands that can be easily accessed from commercially available and inexpensive starting materials. The application of this ligand array in the palladium-catalyzed Suzuki–Miyaura coupling reaction of aryl chlorides with arylboronic acids is described. The palladium catalyst generated from this hemilabile phosphane is highly effective in the Suzuki–Miyaura coupling of unactivated aryl chlorides, and catalyst loadings as low as 1 ppm can be achieved.

This study describes the efficacy of benzimidazolyl phosphine ligands, which are easily synthesized from inexpensive and commercially available o-phenylenediamine, 2-bormobenzoic acid, and chlorophosphines, in the Buchwald-Hartwig amination of aryl chlorides. Primary and secondary aromatic/aliphatic amines are effective substrates in this catalytic system. Functional groups such as keto and esters are also compatible. The catalyst loading can be reduced to 0.1 mol% Pd.

This study describes a general palladium-catalyzed cyanation of aryl bromides using K 4 [Fe(CN) 6 ] as the cyanide surrogate. The reactions can be successfully conducted under mild reaction conditions (at 50 °C) in mixed solvents (water/MeCN = 1:1) without any surfactant additives, and afford the desired aryl nitriles in good-to-excellent yields. Particularly noteworthy is that this system allows the mildest reaction temperature reported so far for palladium-catalyzed cyanation of aryl bromides with K 4 [Fe(CN) 6 ] source in general. Common functional groups, including keto, aldehyde, free amine, and heterocyclic substrates are compatible under this system. Interestingly, the phosphine ligands bearing –PCy 2 moiety, which usually show excellent activity in aryl halide couplings, are found less effective than the corresponding ligands with –PPh 2 group.

A series of chiral secondary alcohols were easily prepared by means of asymmetric hydrogenation of prochiral aromatic ketones using a new ((Rax)-BuP)/(R,R)-DPEN–Ru(II) complex catalyst system. The hydrogenation of 2-methylacetophenone in n-butanol (t-BuOK/Ru = 45.6/1, S/C = 500, 20 atm. of H2, 20 °C, 48 h) afforded (S)-1-(2′-methylphenyl)ethanol in 92% ee and >99% conversion.

The first general examples of palladium-catalyzed Suzuki-type cross-coupling of aryl and heteroaryl mesylates with potassium aryl and heteroaryltrifluoroborates are presented. In addition to biaryl couplings, the cross-coupling reactions of aryl mesylates with alkyl and vinyltrifluoroborate salts have also been successfully accomplished.

The first Suzuki-type cross-coupling between arylboronic acids and vinyl acetate is disclosed. i ne acetoxy moiety as the leaving group is realized in the coupling process. Rhodium complexes were found to be highly effective for promoting this transformation. In contrast, the present well-known nickel and palladium complexes were inferior for this catalysis when vinyl acetate was used as the electrophilic partner.

Commercially available FeCl 3 ·6H 2 O with conformationally rigid diamine ligand is a highly effective catalyst for N-arylation of pyrazoles using aryl and heteroaryl iodides. It is notable to show that this complex is tolerable under aqueous medium and particularly the whole reaction utilizes water as the sole solvent without any additional organic co-solvents and surfactants. Attempted study using other nitrogen nucleophiles is described. This newly developed system provides an alternative protocol to Cu- and Pd-catalyzed N-arylation reactions.

A highly efficient chiral-bridged biphenyl diphosphine ligand [(R ax )-BuP] modified cationic palladium(II) catalyst system for the synthesis of optically active polyketone by stereoselective alternating copolymerization ofpropene and carbon monoxide is reported for the first time. The results show that [Pd(MeCN) 4 ][OTf] 2 is an excellent catalyst precursor in a mixed solvent of MeNO 2 -MeOH. The highest catalytic activity was found to be 221 g polymer/(g Pd·h). A chiral polyketone with molecular weight M n = 2.9 × 10 4 , polydispersity = 1.4, and molar optical rotation = +37° was afforded under optimized reaction conditions.

A family of indolyl phosphine ligands was applied to Suzuki-Miyaura cross-coupling of aryl tosylates. Catalyst loading can be reduced to 0.2 mol % for coupling of nonactivated aryl tosylate. A challenging example for room temperature coupling is realized. The scope of this highly active Pd/L2 system can be extended to other boron nucleophiles, including trifluoroborate salts and boronate esters. The ligand structural comparisons toward the reactivity in tosylate couplings are also described.

This review describes the concepts of and recent developments on monophosphine P,O-type ligands. The attractive synthetic pathways to these ligands are highlighted, and the applications of the ligands in cross-coupling reactions are fully illustrated. The hemilabile properties of P,O-type ligands on complexation with transition metals are also discussed. 1 Introduction 2 Different P,O-Type Ligands 2.1 P,O-Type Ligands with an Acetal Moiety 2.2 P,O-Type Ligands with a Sulfonyl Group 2.3 P,O-Type Ligands with an Amido Group 3 Chirality of P,O-Type Ligands 4 Achiral P,O-Type Ligands with a Ferrocenyl Scaffold 5 Conclusion

This review article illustrates the concept and approach for designing new C 2 -symmetric chelating atropisomeric chiral phosphines containing heterocyclic scaffolds. The versatility in structural modification is highlighted, and that it offers an effective avenue to access chiral ligands of diverse electronic and steric properties for optimization in various catalytic asymmetric transformations. In this article, the uses of atropisomeric chiral phosphines in some asymmetric transformations such as hydrogenation and alkyl-/arylation reactions will be discussed with reference to updated literature findings as well as the author's original research.