The Asymmetric Buchwald-Hartwig Amination Reaction

Catalytic asymmetric C-N cross-coupling towards boron-stereogenic 3-amino-BODIPYs

3-Amino boron dipyrromethenes (BODIPYs) are a versatile class of fluorophores widely utilized in live cell imaging, photodynamic therapy, and fluorescent materials science. Despite the growing demand for optically active BODIPYs, the synthesis of chiral 3-amino-BODIPYs, particularly the catalytic asymmetric version, remains a challenge. Herein, we report the synthesis of boron-stereogenic 3-amino-BODIPYs via a palladium-catalyzed desymmetric C-N cross-coupling of prochiral 3,5-dihalogen-BODIPYs. This approach features a broad substrate scope, excellent functional group tolerance, high efficiency, and remarkable enantioselectivities, under mild reaction conditions. Further stereospecific formation of chiral 3,5-diamino-BODIPYs, along with an investigation into the photophysical properties of the resulting optical BODIPYs are also explored. This asymmetric protocol not only enriches the chemical space of chiroptical BODIPY dyes but also contributes to the realm of chiral boron chemistry.

Synthesis of Quinoline-Indole Hybrids through Cu(II)-Catalyzed Amination and Annulation between N-Oxides and o-Alkynylanilines

The synthesis of (iso)quinoline-indole hybrids by reacting (iso)quinoline N-oxides with o-alkynylanilines in the presence of a combination of copper(II) catalyst and a bidentate 2,2'-bipyridine ligand is described. The utility of this method was demonstrated through site-selective functionalization of the synthesized products. A plausible reaction pathway for site-selective amination followed by annulative indole formation was elucidated by a series of mechanistic investigations.

Chiral Biaryl N-Heterocyclic Carbene-Palladium Catalysts with Anagostic C-H···Pd Interaction for Enantioselective Desymmetric C-N Cross-Coupling

Novel chiral biaryl imidazo[1,5-a]pyridine carbene-palladium complexes (ImPy-Pd) featuring an anagostic C-H···Pd interaction and a C5-aryl substituent have been developed and successfully applied to the Pd-catalyzed enantioselective desymmetric C-N cross-coupling of malonamide derivatives, providing chiral 3,4-dihydroquinoline-2-ones with quaternary stereocenters in high yields (≤99%) and enantioselectivities (≤97:3 er). The chiral catalyst exerts stereocontrol by restricting the rotation of substituents around the metal center through anagostic interactions with sterically bulky substituents.

Transition-metal-catalyzed enantioselective C-N cross-coupling

Chiral amine scaffolds are among the most important building blocks in natural products, drug molecules, and functional materials, which have prompted chemists to focus more on their synthesis. Among the accomplishments in chiral amine synthesis, transition-metal-catalyzed enantioselective C-N cross-coupling is considered one of the most efficient protocols. This approach combines traditional C(sp2)-N cross-coupling methods (such as the Buchwald-Hartwig reaction Ullmann-type reaction, and Chan-Evans-Lam reaction), aryliodonium salt chemistry and radical chemistry, providing an attractive pathway to a wide range of structurally diverse chiral amines with high enantioselectivity. This review summarizes the established protocols and offers a comprehensive outlook on the promising enantioselective C-N cross-coupling reaction.

Simultaneous construction of inherent and axial chirality by cobalt-catalyzed enantioselective C-H activation of calix[4]arenes

The simultaneous construction of multiple stereogenic elements in a single step is highly appealing and desirable in the field of asymmetric synthesis. Furthermore, the catalytic enantioselective synthesis of inherently chiral calix[n]arenes with high enantiopurity has long been a challenging endeavor. Herein, we report an enantioselective cobalt-catalyzed C-H activation/annulation for the efficient construction of inherently chiral calix[4]arenes bearing multiple C-N axially chiral element. By employing the benzamide tethered calix[4]arene as the substrate, the C-H annulation with alkynes can be successfully accomplished, leading to the generation of multiple stereogenic elements. A wide range of calix[4]arenes and alkynes are found to be well compatible, and exhibit good yields, high enantioselectivity and excellent diastereoselectivity. Notably, the gram-scale reaction, catalytic application, synthetic transformations, and chiral recognition further showcase the potential applications of this protocol.

Double C-H Amination of Naphthylamine Derivatives by the Cross-Dehydrogenation Coupling Reaction

A high-efficiency tandem process has been developed for the formation of two C-N bonds through a cross-dehydrogenative coupling (CDC) amination of spiro[acridine-9,9'-fluorene]s (SAFs) with amines. This method offers a strategically innovative and atom-economical approach to obtaining diamine-substituted SAFs. Notably, the approach eliminates the need for metal catalysts and other additives, relying solely on O2 as the oxidant. A self-activation mechanism has been proposed to elucidate the effective double amination in the CDC process.

Organocatalytic Csp2-O Amination of Quinolin-4(1H)-ones with 3-Alkynyl-3-hydroxyisoindolinones

The Brønsted acid catalytic Csp2-O amination of quinolin-4(1H)-ones with 3-alkynyl-3-hydroxyisoindolinones as animation reagents has been developed. The cascade dehydration/conjugate addition/intramolecular annulation/ring-opening reaction proceeded smoothly to afford a broad scope of aminated products with high efficiency. Furthermore, the enantioselective construction of Csp2-N atropisomers was also investigated in the presence of chiral phosphoric acid. Importantly, this work not only realized the organocatalytic Csp2-O amination of quinolin-4(1H)-ones but also laid the foundation for directly asymmetric synthesis of Csp2-N atropisomers.

Synthesis of C-N Axially Chiral N-Arylbenzo[g]indoles via a Central-to-Axial Chirality Conversion Strategy

Gold-catalyzed cascade cyclization of diynes for the synthesis of previously unexplored C-N axially chiral N-arylbenzo[g]indoles was described. The transformation was achieved via a central-to-axial chirality conversion strategy. The chiral conversion exhibited high efficiency. Besides single C-N chiral axis, N-arylbenzo[g]indoles bearing both C-N and C-C chiral axes were also afforded. The title compound derived monophosphine ligand was prepared and was evaluated in Pd-catalyzed asymmetric allylic substitutions, showing excellent chiral induction ability.

Scalable Transition-Metal-Free Synthesis of Aryl Amines from Aryl Chlorides through X@RONa-Catalyzed Benzyne Formation

Aryl amines are highly useful organic chemicals, but large-scale, transition-metal-free syntheses of aryl amines are surprisingly underdeveloped. A mild and scalable (up to 500 mmol) aryl amine synthesis from benzyne chemistry was invented using easily accessible aryl chlorides as precursors, NaH as a stoichiometric base, and a new type of sodium alkoxide cluster, X@RONa, as a catalyst. The cluster catalyst X@RONa featured an externally hydrophobic dodecameric sodium alkoxide shell housing an encapsulated center anion. The cluster made from methoxy-tert-butanol was found to be the most effective. The intramolecular version of this reaction allowed the synthesis of indolines and indoles. Experimental and computational mechanistic studies revealed that the rate-determining step was likely the transport of solid NaH into the X@RONa cluster in the organic phase.

Atroposelective Chan-Evans-Lam Amination

The synthetic control of atropoisomerism along C-N bonds is a major challenge, and methods that allow C-N atroposelective bond formation are rare. This is a problem because each atropoisomer can feature starkly differentiated biological properties. Yet, among the three most practical and applicable classical amination methods available: 1) the Cu-catalyzed Ullmann-Goldberg reaction, 2) the Pd-catalyzed Buchwald-Hartwig reaction, and 3) the Cu-catalyzed Chan-Evans-Lam reaction, none has truly been rendered atroposelective at the newly formed C-N bond. The first ever Chan-Evans-Lam atroposelective amination is herein described with a simple copper catalyst and newly designed PyrOx chiral ligand. This method should find important applications in asymmetric synthesis, in particular for medicinal chemistry.

Kinetically Controlled Stereoselective Synthesis of 2-Oxo-2-aryl-1,3,2-dioxaphosphorinane Derivatives via a Palladium-Catalyzed Reaction

Chiral phosphonate esters have been widely applied in the fields of organic chemistry, medicine, and photoelectric materials. However, it requires the challenging enantioselective synthesis of cyclic phosphonate esters with the desired chiral configuration. The two epimers of 2-oxo-2H-1,3,2-dioxaphosphorinane derivatives should have different reactivities in Pd-catalyzed coupling reactions, which could lead to an effective methodology for the asymmetric synthesis of 2-oxo-2-aryl-1,3,2-dioxaphosphorinane derivatives. A thorough investigation of the coupling reactions both computationally and experimentally led to the stereoselective synthesis of chiral cyclic phosphonate esters. The axial isomer of products can be obtained with both high diastereoselectivity and good chemical yields from the mixture of 2-oxo-2H-1,3,2-dioxaphosphorinane derivatives under kinetically controlled conditions.

Pd-Catalyzed Asymmetric Larock Indole Synthesis to Access Axially Chiral N-Arylindoles

Larock indole synthesis is one of the most straightforward and efficient methods for the synthesis of indoles; however, there has been no asymmetric version yet for the construction of indole-based axially chiral N-arylindoles since its initial report in 1991. Herein we report the first example of an asymmetric Larock indole synthesis by employing a chiral sulfinamide phosphine (SadPhos) ligand (Ming-Phos) with palladium. It allows rapid construction of a wide range of axially chiral N-arylindole compounds in good yields up to 98:2 er. The application of this unique chiral scaffold as an organocatalyst is promising. Furthermore, a kinetic study has revealed that the alkyne migratory insertion is the rate-determining step, which has been proven by the density functional theory (DFT) calculations. Additionally, DFT studies also suggest that the N-C dihedral difference caused by the steric hindrance of the ligand contributes to enantioselectivity control.

Visible-Light-Driven Iron-Catalyzed Intermolecular Benzylic C(sp3)-H Amination with 1,2,3,4-Tetrazoles

A visible-light-driven iron-catalyzed C(sp3)-H amination of diphenylmethane derivatives with 1,2,3,4-tetrazoles under mild conditions has been developed. The reaction proceeds with photosensitizer-free conditions and features satisfactory to good yields. Mechanistic studies revealed that the reaction proceeded via an iron-nitrene intermediate, and H atom abstraction was the rate-determining step. Computational studies showed that the denitrogenation of 1,2,3,4-tetrazole depends on the conversion of the sextet ground state of 1,2,3,4-tetrazole-bounding iron species to the quartet spin state under visible-light irradiation.

Recent advances in Pd-catalyzed asymmetric cyclization reactions

Over the past few decades, there have been major developments in transition metal-catalyzed asymmetric cyclization reactions, enabling the convenient access to a wide spectrum of structurally diverse chiral carbo- and hetero-cycles, common skeletons found in fine chemicals, natural products, pharmaceuticals, agrochemicals, and materials. In particular, a plethora of enantioselective cyclization reactions have been promoted by chiral palladium catalysts owing to their outstanding features. This review aims to collect the latest advancements in enantioselective palladium-catalyzed cyclization reactions over the past eleven years, and it is organized into thirteen sections depending on the different types of transformations involved.

Catalytic Asymmetric Synthesis of N-N Biaryl Atropisomers

Atropisomers have emerged as important structural scaffolds in natural products, drug design, and asymmetric synthesis. Recently, N-N biaryl atropisomers have drawn increasing interest due to their unique structure and relatively stable axes. However, its asymmetric synthesis remains scarce compared to its well-developed C-C biaryl analogs. In this concept, we summarize the asymmetric synthesis of N-N biaryl atropisomers including N-N pyrrole-pyrrole, N-N pyrrole-indole, N-N indole-indole, and N-N indole-carbazole, during which a series synthetic strategies are highlighted. Also, a synthetic evolution is briefly reviewed and an outlook of N-N biaryl atropisomers synthesis is offered.

Transition-Metal-Catalyzed 1,2-Diaminations of Olefins: Synthetic Methodologies and Mechanistic Studies

1,2-Diamines are synthetically important motifs in organo-catalysis, natural products, and drug research. Continuous utilization of transition-metal based catalyst in direct 1,2-diamination of olefines, in contrast to metal-free transformations, with numerous impressive advances made in recent years (2015-2023). This review summarized contemporary research on the transition-metal catalyzed/mediated [e. g., Cu(II), Pd(II), Fe(II), Rh(III), Ir(III), and Co(II)] 1,2-diamination (asymmetric and non-asymmetric) especially emphasizing the recent synthetic methodologies and mechanistic understandings. Moreover, up-to-date discussion on (i) paramount role of oxidant and catalyst (ii) key achievements (iii) generality and uniqueness, (iv) synthetic limitations or future challenges, and (v) future opportunities are summarized related to this potential area.

Enantioselective Synthesis of N-N Amide-Pyrrole Atropisomers via Paal-Knorr Reaction

The catalytic asymmetric construction of monoheteroaryl N-N axially chiral compounds and chiral five-membered aryl-based scaffolds remains challenging. Herein, we present a highly efficient enantioselective synthesis of monoheteroaryl N-N atropisomers via an asymmetric Paal-Knorr reaction, affording a diverse array of N-N amide-pyrrole atropisomers with excellent enantioselectivities. Gram-scale synthesis and post-transformations of the product demonstrated the synthesis utility of this method. Racemization experiments confirmed the configurational stability of these N-N axially chiral products. This study not only provides the first de novo cyclization example for accessing an asymmetric monoheteroaryl N-N scaffold but also offers a new member of the N-N atropisomer family with potential synthetic and medicinal applications.

Aryl Chloride-Directed Enantioselective C(sp2)-H Borylation Enabled by Iridium Catalysis

We herein report the iridium-catalyzed enantioselective C-H borylation of aryl chlorides. A variety of prochiral biaryl compounds could be well-tolerated, affording a vast array of axially chiral biaryls with high enantioselectivities. The current method exhibits a high turnover number (TON) of 7000, which represents the highest in functional-group-directed asymmetric C-H activation. The high TON was attributed to a weak catalyst-substrate interaction that was caused by mismatched chirality between catalyst and substrate. We also demonstrated the synthetic application of the current method by C-B, ortho-C-H, and C-Cl bond functionalization, including programmed Suzuki-Miyaura coupling for the synthesis of axially chiral polyarenes.

Copper Complexes with N,N,N-Tridentate Quinolinyl Anilido-Imine Ligands: Synthesis and Their Catalytic Application in Chan-Lam Reactions

The treatment of 2-(ArNC(H))C6H4-HNC9H6N with n-BuLi and the subsequent addition of CuCl2 afforded the anilido-aldimine Cu(II) complexes 1-5 Cu[{2-[ArN=C(H)]C6H4}N(8-C9H6N)]Cl (Ar = 2,6-iPr2C6H3 (1), 2,4,6-(CH3)3C6H2 (2), 4-OCH3C6H4 (3), 4-BrC6H4 (4), 4-ClC6H4 (5)), respectively. All the copper complexes were fully characterized by IR, EPR and HR-MS spectra. The X-ray diffraction analysis reveals that 2 and 4 are mononuclear complexes, and the Cu atom is sitting in a slightly square-planar geometry. These Cu(II) complexes have exhibited excellent catalytic activity in the Chan-Lam coupling reactions of benzimidazole derivatives with arylboronic acids, achieving the highest yields of up to 96%.

Recent advances in metal directed C-H amidation/amination using sulfonyl azides and phosphoryl azides

Transition metal-catalyzed C-N bond formation reactions have gained popularity as a method for selectively transforming common C-H bonds into N-functionalized molecules. This approach is particularly useful for synthesizing aminated molecules, which require aminating reagents and amidated building blocks. Over the past two decades, significant advancements have been achieved in transition-metal-catalyzed C-H functionalization, with organic azides emerging as promising amino sources and internal oxidants. This review focuses on recent developments in utilizing sulfonyl and phosphoryl azides as building blocks for directed intra- and intermolecular C-H functionalization reactions. Specifically, it discusses methods for synthesizing sulfonamidates and phosphoramidates using sulfonyl and phosphoryl azides, respectively. The article highlights the potential of C-H functionalization reactions with organic azides for efficiently and sustainably synthesizing N-functionalized molecules, providing valuable insights into the latest advancements in this field.

Catalytic Asymmetric Synthesis of Atropisomers Featuring an Aza Axis

ConspectusAtropisomers bearing a rotation-restricted axis are common structural units in natural products, chiral ligands, and drugs; thus, the prevalence of asymmetric synthesis has increased in recent decades. Research into atropisomers featuring an N-containing axis (N-X atropisomers) remains in its infancy compared with the well-developed C-C atropisomer analogue. Notably, N-X atropisomers could offer divergent scaffolds, which are extremely important in bioactive molecules. The asymmetric synthesis of N-X atropisomers is recognized as both appealing and challenging. Recently, we devoted our efforts to the catalytic asymmetric synthesis of N-X atropisomers, benzimidazole-aryl N-C atropisomers, indole-aryl N-C atropisomers, hydrogen-bond-assisted N-C atropisomers, pyrrole-pyrrole N-N atropisomers, pyrrole-indole N-N atropisomers, and indole-indole N-N atropisomers. To obtain the N-C atropisomers, an asymmetric Buchwald-Hartwig reaction of amidines or enamines was employed. Using a Pd(OAc)2/(S)-BINAP or Pd(OAc)2/(S)-Xyl-BINAP catalyst system, benzimidazole-aryl N-C atropisomers and indole-aryl N-C atropisomers were readily obtained. To address the issue of the reduced stability of the diarylamine axis, a six-membered intramolecular N-H-O hydrogen bond was introduced into the N-C atropisomer scaffold. A tandem N-arylation/oxidation process was used for the chiral phosphoric acid (CPA)-catalyzed asymmetric synthesis of N-aryl quinone atropisomers. For N-N atropisomers, a copper-mediated asymmetric Friedel-Crafts alkylation/arylation reaction was developed. The desymmetrization process was completed successfully via a Cu(OTf)2/chiral bisoxazoline or (CuOTf)·Tol/bis(phosphine) dioxide system, thereby achieving the first catalytic asymmetric synthesis of N/N bipyrrole atropisomers. Asymmetric Buchwald-Hartwig amination of enamines was utilized to provide N-N bisindole atropisomers with excellent stereogenic control. This was the first asymmetric synthesis of N-N atropisomers featuring a bisindole structural scaffold using the de novo indole construction strategy. The asymmetric N-N heterobiaryl atropisomer synthesis was substantially facilitated using palladium-catalyzed transient directing group (TDG)-mediated C-H functionalization. Atropisomeric alkenylation, allylation, or alkynylation was accomplished using the Pd(OAc)2/l-tert-leucine system. Herein, we summarize our work on the palladium-, copper-, and CPA-catalyzed asymmetric syntheses of N-C and N-N atropisomers. Furthermore, the application of our work in the synthesis of bioactive molecule analogues and axially chiral ligands is demonstrated. Subsequently, the stability of the chiral N-containing axis is briefly discussed in terms of single crystals and obtained rotational barriers. Finally, an outlook on the asymmetric N-X atropisomer synthesis is provided.

Cobalt-catalyzed atroposelective C-H activation/annulation to access N-N axially chiral frameworks

The N-N atropisomer, as an important and intriguing chiral system, was widely present in natural products, pharmaceutical lead compounds, and advanced material skeletons. The anisotropic structural characteristics caused by its special axial rotation have always been one of the challenges that chemists strive to overcome. Herein, we report an efficient method for the enantioselective synthesis of N-N axially chiral frameworks via a cobalt-catalyzed atroposelective C-H activation/annulation process. The reaction proceeds under mild conditions by using Co(OAc)2·4H2O as the catalyst with a chiral salicyl-oxazoline (Salox) ligand and O2 as an oxidant, affording a variety of N-N axially chiral products with high yields and enantioselectivities. This protocol provides an efficient approach for the facile construction of N-N atropisomers and further expands the range of of N-N axially chiral derivatives. Additionally, under the conditions of electrocatalysis, the desired N-N axially chiral products were also successfully achieved with good to excellent efficiencies and enantioselectivities.

Octalithium, Tetrasodium, and Decalithium Compounds Based on Pyrrolyl Ligands: Synthesis, Structures, and Activation of the C-H Bonds of Pyrrolyl Rings and C═N Bonds of a Series of Ligands by Organolithium Reagents

The organometallic compounds of lithium ions have garnered continuous interest as indispensable precursors for the syntheses of organometallic complexes of main-group metals, transition metals, lanthanide metals, and actinide metals. In this work, we present a strategy for the preparation of a series of polynuclear lithium complexes. This methodology features the utilization of organolithium reagents both as metal sources to coordinate with the ligands and as nucleophilic reagents to undergo nucleophilic addition to the C═N bonds of the ligands. Reaction of a ligand HL1 [HL1 = 2-(((1-(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methylene)amino)phenol] with n-BuLi produced complex [Li8(L1a)4]·1.5Tol (1·1.5Tol) [H2L1a = 2-((1-(1-(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)pentyl)amino)phenol]. One prominent feature regarding the formation of 1·1.5Tol is the occurrence of nucleophilic addition of n-BuLi to the C═N bond of HL1, leading to the generation of a new [L1a]2- ligand that contains both aminophenol and 1-(2-pyrrolyl)alkylamine scaffolds. The developed protocol can be adapted to a series of organolithium reagents. Compounds [Li8(L1b)4] (2) and [Li8(L1c)4] (3) were afforded by treatment of HL1 with sec-BuLi and LiCH2SiMe3, respectively. Reaction of an analogous ligand HL2 [HL2 = 2-(((1-(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methylene)amino)-4-methylphenol] with n-BuLi generated compound [Li8(L2a)4] (4). C═N bond activation was not observed in the reaction of HL1 with NaOtBu, and the complex [Na4(L1)4]·Tol (5·Tol) was obtained. A decanuclear complex [Li10(L3a)2(L3b)2] (6) was also prepared via the reaction of HL3 [HL3 = 2-(2-((((1H-pyrrol-2-yl)methylene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine] with t-BuLi. A remarkable feature in terms of the synthesis of 6 is the simultaneous occurrence of hydrogen atom abstraction from the C-H bond of the pyrrolyl ring and nucleophilic addition to the C═N bond of the HL3 ligand by t-BuLi. A series of amines containing biologically and physiologically important moieties were achieved by hydrolysis of the crude products from the reactions of the HL1-HL3 ligands and organolithium reagents. This work provides an efficient approach to high-nuclearity lithium compounds as well as a series of amines.

Amino Acid-Derived Ionic Chiral Catalysts Enable Desymmetrizing Cross-Coupling to Remote Acyclic Quaternary Stereocenters

Synthetic application of asymmetric catalysis relies on strategic alignment of bond construction to creation of chirality of a target molecule. Remote desymmetrization offers distinctive advantages of spatial decoupling of catalytic transformation and generation of a stereogenic element. However, such spatial separation presents substantial difficulties for the chiral catalyst to discriminate distant enantiotopic sites through a reaction three or more bonds away from a prochirality center. Here, we report a strategy that establishes acyclic quaternary carbon stereocenters through cross-coupling reactions at distal positions of aryl substituents. The new class of amino acid-derived ionic chiral catalysts enables desymmetrizing (enantiotopic-group-selective) Suzuki-Miyaura reaction, Sonogashira reaction, and Buchwald-Hartwig amination between diverse diarylmethane scaffolds and aryl, alkynyl, and amino coupling partners, providing rapid access to enantioenriched molecules that project substituents to widely spaced positions in the three-dimensional space. Experimental and computational investigations reveal electrostatic steering of substrates by the C-terminus of chiral ligands through ionic interactions. Cooperative ion-dipole interactions between the catalyst's amide group and potassium cation aid in the preorganization that transmits asymmetry to the product. This study demonstrates that it is practical to achieve precise long-range stereocontrol through engineering the spatial arrangements of the ionic catalysts' substrate-recognizing groups and metal centers.