P-Stereogenic Amino-Phosphines as Chiral Ligands: From Privileged Intermediates to Asymmetric Catalysis

Highly Enantioselective Synthesis of 3,3-Diarylpropyl Amines and 4-Aryl Tetrahydroquinolines via Ir-Catalyzed Asymmetric Hydrogenation

Chiral nitrogen-containing compounds are crucial for the chemical, pharmaceutical, and agrochemical industries. Nevertheless, the synthesis of certain valuable scaffolds remains underdeveloped due to the vast chemical space available. In this work, we present a diastereoselective methodology for synthesizing 3,3-diarylallyl phthalimides, which, following iridium-catalyzed asymmetric hydrogenation using Ir-UbaPHOX, yield 3,3-diarylpropyl amines with high enantioselectivity (98-99% ee). The importance of alkene purity to achieve high enantioselectivity is discussed. The synthetic utility of the chiral propylamines obtained is demonstrated through the preparation of medicinally useful bioactive compounds like the drugs tolterodine and tolpropamine and 4-aryl tetrahydroquinolines. This strategy enables the synthesis of these compounds with the highest enantioselectivity reported to date.

Synthesis of P-Stereogenic Phosphinamides via Nickel-Catalyzed Kinetic Resolution of H-Phosphinamides by Alkenylation and Arylation

A nickel-catalyzed enantioselective cross-coupling for the synthesis of P-stereogenic phosphinamides has been developed. The asymmetric alkenylation and arylation of racemic H-phosphinamides using alkenyl and aryl bromides resulted in the formation of P-stereogenic N-phosphinyl compounds with good yields and high enantioselectivities. This method tolerates a variety of functional groups, and its applications are explored through scale-up reactions and product transformations.

Synergistically activating nucleophile strategy enabled organocatalytic asymmetric P-addition of cyclic imines

Herein, we present an attractive organocatalytic asymmetric addition of P-nucleophiles to five-membered cyclic N-sulfonyl imines facilitated by phosphonium salt catalysis, enabling the highly enantioselective synthesis of tri- and tetra-substituted cyclic phosphorus-containing benzosultams. With this protocol, various cyclic α-aminophosphonates were efficiently synthesized with high yields and exceptional enantioselectivities (up to >99% ee) under mild reaction conditions. The utility and practicality of this method were demonstrated through gram-scale reactions and straightforward elaborations. Notably, the success of this approach relies on the deliberate selection of a synergistic organocatalytic system, which helps circumvent foreseeable side effects while handling secondary phosphine oxides (SPOs). Systematic mechanistic studies, incorporating experiments and DFT calculations, have revealed the critical importance of judiciously selecting bifunctional phosphonium salt catalysts for effectively activating P-nucleophiles while stereoselectively controlling the P-attack process.

P-Stereogenic Phosphorus Ligands in Asymmetric Catalysis

Chiral phosphorus ligands play a crucial role in asymmetric catalysis for the efficient synthesis of useful optically active compounds. They are largely categorized into two classes: backbone chirality ligands and P-stereogenic phosphorus ligands. Most of the reported ligands belong to the former class. Privileged ones such as BINAP and DuPhos are frequently employed in a wide range of catalytic asymmetric transformations. In contrast, the latter class of P-stereogenic phosphorus ligands has remained a small family for many years mainly because of their synthetic difficulty. The late 1990s saw the emergence of novel P-stereogenic phosphorus ligands with their superior enantioinduction ability in Rh-catalyzed asymmetric hydrogenation reactions. Since then, numerous P-stereogenic phosphorus ligands have been synthesized and used in catalytic asymmetric reactions. This Review summarizes P-stereogenic phosphorus ligands reported thus far, including their stereochemical and electronic properties that afford high to excellent enantioselectivities. Examples of reactions that use this class of ligands are described together with their applications in the construction of key intermediates for the synthesis of optically active natural products and therapeutic agents. The literature covered dates back to 1968 up until December 2023, centering on studies published in the late 1990s and later years.

Carbene-Catalyzed and Pnictogen Bond-Assisted Access to PIII-Stereogenic Compounds

Intermolecular pnictogen bonding (PnB) catalysis has received increased interest in non-covalent organocatalysis. It has been demonstrated that organic electron-deficient pnictogen atoms can act as prospective Lewis acids. Here, we present a catalytic approach for the asymmetric synthesis of chiral PIII compounds by combining intramolecular PnB interactions and carbene catalysis. Our design features a pre-chiral phosphorus molecule bearing two electron-withdrawing benzoyl groups, resulting in the formation of a σ-hole at the P atom. X-ray and non-covalent interaction (NCI) analysis indicate that the model substrates exhibit intrinsic PnB interaction between the oxygen atom of the formyl group and the phosphorus atom. This induces a conformational locking effect, leading to the crystallization of the phosphorus substrate in a preferred conformation (P212121 chiral group). Under the catalysis of N-heterocyclic carbene, the aldehyde moiety activated by the pnictogen bond selectively reacts with an alcohol to yield the corresponding chiral monoester/phosphorus product with excellent enantioselectivity. This Lewis acidic phosphorus center, aroused by the non-polarized intramolecular pnictogen bond interaction, assists in conformational and selective regulations, providing unique opportunities for catalysis and beyond.

Tf2O-Mediated P(O)-N Bond Formation of Either P(O)-OH or P(O)-H Reagents with Multitype Amines

We have developed a Tf2O-mediated approach for the direct amination of either P(O)-OH or P(O)-H reagents with a variety of aliphatic or aromatic amines. Without the requirement of precious metals and toxic reagents, this protocol provides an alternative route to various phosphinamides and phosphoramides. The reaction proceeds under simple and mild conditions and can be effectively scaled up with similar efficiency.

Chemoselective Staudinger Reactivity of Bis(azido)phosphines Supported with a π-Donating Imidazolin-2-iminato Ligand

Synthesis and characterization of new P(III) and P(V) bis(azido)phosphines/phosphoranes supported by an N,N'-bis(2,6-diisopropylphenyl) imidazolin-2-iminato (IPrN) ligand and their reactivity with various secondary and tertiary phosphines result in the formation of chiral and/or asymmetric mono(phosphinimino)azidophosphines via the Staudinger reaction. The reaction of IPrNP(N3)2 (2) or IPrNP(S)(N3)2 (4S) with an excess of tertiary phosphine resulted in the chemoselective formation of IPrNP(N3)(NPMe3) (7) or IPrNP(S)N3(NPR3) (5R), respectively. The chemoselective Staudinger reactivity was also observed in reactions using a secondary phosphine (HPCy2) to produce IPrNP(S)N3[NP(H)Cy2] (6a), which exists in equilibrium with a tautomeric IPrNP(S)N3[N(H)PCy2] form (6b), as confirmed by 31P-31P nuclear Overhauser effect spectroscopy (NOESY). Density functional theory (DFT) calculations point to a combination of energetically unfavorable lowest unoccupied molecular orbitals (LUMOs) and the accumulation of increasing negative charge at the terminal azido-nitrogen upon a single azide-to-phosphinimine conversion that gave rise to the observed chemoselectivity.

Sadphos as Adaptive Ligands in Asymmetric Palladium Catalysis

ConspectusPalladium catalysis, as one of the most important strategies in asymmetric synthesis, has continuously attracted the attention of organic chemists. With the development of chiral ligands, increasingly challenging reactions and substantial progress in asymmetric catalysis are being realized.Since 2014, we have focused on exploiting a series of sulfinamide phosphine ligands called "Sadphos," including Ming-Phos, Xu-Phos, Xiao-Phos, Xiang-Phos, TY-Phos, PC-Phos, GF-Phos, and WJ-Phos. These ligands can be easily prepared in two to four steps using commercial materials. These new types of ligands have shown remarkable performance in transition-metal-catalyzed reactions, especially in Pd-catalyzed transformations. X-ray diffraction analysis, mechanistic studies, and density functional theory calculations have revealed that Sadphos ligands can coordinate with the Pd0 and PdII species in the Pd0/P, Pd0/P,S, or PdII/P,O modes.This Account summarizes our recent efforts toward palladium-catalyzed enantioselective reactions using Sadphos ligands. These ligands were found to be privileged and very crucial to promote the reactions by increasing the reactivity and enantioselectivity. Ming-Phos is an effective ligand in Pd-catalyzed asymmetric coupling and intramolecular Heck reactions, providing highly enantioselective trisubstituted allenes, axially chiral anilides, gem-diarylmethine silanes, and disubstituted dihydroisoquinolinones. Incorporation of an electron-rich cyclohexyl group in the phosphine moiety afforded Xu-Phos, which showed a unique effect in a series of asymmetric transformations, including reductive Heck, dearomative Mizoroki-Heck, tandem Heck/Suzuki coupling, carboiodination, carboamination, and cross-coupling reactions. Using a similar strategy, our group synthesized more electron-rich TY-Phos and Xiang-Phos ligands bearing t-butyl and 1-adamantyl group at P atoms, respectively. Regarding stereoelectronic features, these two characteristic ligands were the best choice to satisfy the requirements of the palladium-catalyzed fluoroarylation of gem-difluoroalkenes, intermolecular α-arylation of aldehydes, carboetherification of alkenyl oximes, and carboheterofunctionalization of 2,3-dihydrofurans. Compared with the aforementioned Sadphos ligands, the attractive features of Xiao-Phos, including high nucleophilicity originating from the CH2PPh2 group and the ortho-substituent effect at the side of the aryl ring, are presumably responsible for its efficiency. The Pd/Xiao-Phos catalyst system shows good performance in a series of cross-coupling reactions of secondary phosphine oxides, affording P-stereogenic products bearing multiple types of molecular skeletons. The modification of the basic Sadphos backbone by introducing a xanthene skeleton motivated us to design and synthesize monophosphines, named PC-Phos and GF-Phos. PC-Phos is effective in various reactions, including arylation of sulfenate anions, denitrogenative cyclization of benzotriazoles, and dearomatization of indoles. The practicability of GF-Phos was validated in the Pd-catalyzed asymmetric three-component coupling of N-tosylhydrazones, aryl halides, and terminal alkynes, as well as in the cross-coupling of N-tosylhydrazones and vinyl iodides with pendent amines. In addition, ferrocene-derived WJ-Phos was employed in the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction, affording axially chiral biaryl monophosphine oxides in excellent enantiomeric excesses.

A Powerful P-N Connection: Preparative Approaches, Reactivity, and Applications of P-Stereogenic Aminophosphines

For more than five decades, P-stereogenic aminophosphine chalcogenides and boranes have attracted scientific attention and are still in the focus of ongoing research. In the last years, novel transition metal-based synthesis methods have been discovered, in addition to the long-known use of chiral auxiliaries. Enantiomerically pure compounds with N-P+ -X- (X=O, S, BH3 ) motifs served as valuable reactive building blocks to provide new classes of organophosphorus derivatives, thereby preserving the stereochemical information at the phosphorus atom. Over the years, intriguing applications in organocatalysis and transition metal catalysis have been reported for some representatives. Asymmetric reductions of C=C, C=N, and C=O double bonds were feasible with selected P-stereogenic aminophosphine oxides in the presence of hydrogen transfer reagents. P-stereogenic aminophosphine boranes could be easily deprotected and used as ligands for various transition metals to enable catalytic asymmetric hydrogenations of olefins and imines. This review traces the emergence of a synthetically and catalytically powerful functional compound class with phosphorus-centered chirality in its main lines, starting from classical approaches to modern synthesis methods to current applications.

Nickel-Catalyzed Asymmetric Synthesis of P-Stereogenic Phosphanyl Hydrazine Building Blocks

Catalytic asymmetric methods for the synthesis of synthetically versatile P-stereogenic building blocks offer an efficient and practical approach for the diversity-oriented preparation of P-chiral phosphorus compounds. Herein, we report the first nickel-catalyzed synthesis of P-stereogenic secondary aminophosphine-boranes by the asymmetric addition of primary phosphines to azo compounds. We further demonstrate that the P-H and P-N bonds on these phosphanyl hydrazine building blocks can be reacted sequentially and stereospecifically to access various P-stereogenic compounds with structural diversity.

Sequential In Situ-Formed Kukhtin-Ramirez Adduct and P(NMe2)3-Catalyzed O-Phosphination of α-Dicarbonyls with P(O)-H

O-Phosphination of α-dicarbonyls via sequential in situ formation of a Kukhtin-Ramirez adduct and a P(NMe2)3-catalyzed process has been exploited for the synthesis of α-phosphoryloxy carbonyls. A range of P(O)-H derivatives, including diarylphosphine oxides, arylphosphinates, and phosphinates, are competent candidates to be introduced into the α-dicarbonyls in this transformation, and various α-phosphoryloxy carbonyls are obtained. This approach possesses advantages of mild conditions, simple operations, atom economy, high efficiency, and gram-scale synthesis, which make it promising in the synthesis toolbox.

Modular Synthesis of Phosphino Hydrazones and Their Use as Ligands in a Palladium-Catalysed Cu-Free Sonogashira Cross-Coupling Reaction

Phosphino hydrazones represent a versatile class of nitrogen-containing phosphine ligands. Herein, we report a modular synthesis of phosphino hydrazone ligands by hydrazone condensation reaction of three different aryl hydrazines with 3-(diphenylphosphino)propanal (PCHO). Complexation reactions of these phosphino hydrazone ligands with palladium(II) and platinum(II) were investigated and the catalytic activity of the palladium(II) complexes was explored in a Cu-free Sonogashira cross-coupling reaction achieving yields up to 96 %. Additionally it was shown that the catalytically active species is homogeneous.

Asymmetric construction of phosphono dihydropyranones from α-ketophosphonates enabled by Pd/chiral isothiourea relay catalysis

A highly enantio- and diastereoselective approach has been developed for the synthesis of chiral phosphono dihydropyranones. This approach is enabled by Pd/chiral isothiourea relay catalysis under mild reaction conditions, starting from readily available benzyl bromides, CO, and α-ketophosphonates. The cascade reaction involves the generation of a ketene intermediate from Pd-catalyzed carbonylation of benzyl bromide and subsequent chiral Lewis base catalyzed formal [4 + 2] reaction. Phosphono lactone products can also be transformed to chiral 1,5-diester products in good yield and high stereoselectivity.

Access to Enantiomerically Pure P-Chiral 1-Phosphanorbornane Silyl Ethers

Sulfur-protected enantiopure P-chiral 1-phosphanorbornane silyl ethers 5a,b are obtained in high yields via the reaction of the hydroxy group of P-chiral 1-phosphanorbornane alcohol 4 with tert-butyldimethylsilyl chloride (TBDMSCl) and triphenylsilyl chloride (TPSCl). The corresponding optically pure silyl ethers 5a,b are purified via crystallization and fully structurally characterized. Desulfurization with excess Raney nickel gives access to bulky monodentate enantiopure phosphorus(III) 1-phosphanorbornane silyl ethers 6a,b which are subsequently applied as ligands in iridium-catalyzed asymmetric hydrogenation of a prochiral ketone and enamide. Better activity and selectivity were observed in the latter case.

New Optically Active tert-Butylarylthiophosphinic Acids and Their Selenium Analogues as the Potential Synthons of Supramolecular Organometallic Complexes: Syntheses and Crystallographic Structure Determination

The aim of the research described in this publication is two-fold. The first is a detailed description of the synthesis of a series of compounds containing a stereogenic heteroatom, namely the optically active P-stereogenic derivatives of tert-butylarylphoshinic acids bearing sulfur or selenium. The second is a detailed discussion dedicated to the determination of their structures by an X-ray analysis. Such a determination is needed when considering optically active hetero-oxophosphoric acids as new chiral solvating agents, precursors of new chiral ionic liquids, or ligands in complexes serving as novel organometallic catalysts.

P-Stereogenic Ir-MaxPHOX: A Step toward Privileged Catalysts for Asymmetric Hydrogenation of Nonchelating Olefins

The Ir-MaxPHOX-type catalysts demonstrated high catalytic performance in the hydrogenation of a wide range of nonchelating olefins with different geometries, substitution patterns, and degrees of functionalization. These air-stable and readily available catalysts have been successfully applied in the asymmetric hydrogenation of di-, tri-, and tetrasubstituted olefins (ee's up to 99%). The combination of theoretical calculations and deuterium labeling experiments led to the uncovering of the factors responsible for the enantioselectivity observed in the reaction, allowing the rationalization of the most suitable substrates for these Ir-catalysts.

Rhodium and ruthenium complexes of methylene-bridged, P-stereogenic, unsymmetrical diphosphanes

Enantiopure P-stereogenic methylphosphane-boranes (S_P)-P(BH₃)PhArMe (ArMe; Ar = 1-naphthyl (NpMe), and 2-biphenylyl (BiphMe)) have been used to prepare diphosphanes of the type ArPhPCH₂PR₂ (R = Ph, iPr or tBu; ArR). The ligands have been reacted with [Rh(COD)₂]BF₄ to furnish the corresponding six monochelated [Rh(COD)(ArR)]BF₄ organometallic compounds (RhArR) or, depending on the reaction conditions, the bis(chelated) coordination compound [Rh(BiphiPr)₂]BF₄ as a mixture of cis and trans isomers. The crystal structure of cis-[Rh(BiphiPr)₂]BF₄ was obtained. The coordination of the BiphR with [RuCl(μ-Cl)(η⁶-p-cymene)₂]₂ under different conditions produced cationic chelated complexes of the type [RuCl(η⁶-p-cymene)(κ²-BiphR)]PF₆ (RuBiphR) and the neutral monocoordinated complex [RuCl₂(η⁶-p-cymene)(κ¹-BiphPh)] (RuBiphPh') with the uncoordinated P-stereogenic moiety. The Rh(I) complexes were used in the catalytic hydrogenation of functionalized olefins and the Ru(II) complexes were tested in the transfer hydrogenation of acetophenone. Both precursors displayed good activities with moderate enantioselectivities.

Investigation of the Asymmetric Addition Reactions Induced by Pentacoordinated Hydrospirophosphorane Substrate

Pentacoordinated bisaminoacyl hydrospirophosphoranes were first found to induce the asymmetric addition reactions as a novel chiral organic framework. Asymmetric addition reactions of bisaminoacyl hydrospirophosphoranes with aromatic aldehyde and in situ generated imine were investigated, and the corresponding α-hydroxyspirophosphonates and α-amino spirophosphonates were obtained. The addition reaction of hydrospirophosphoranes with Δ_P configuration showed better stereoselectivity than that with Λ_P configuration, not only for the addition reaction to aromatic aldehyde but also to in situ generated imine. Furthermore, the stereochemical mechanisms of asymmetric addition reactions induced by pentacoordinated hydrospirophosphorane were proposed by ³¹P NMR tracing experiment and X-ray diffraction analysis.

A Ni-catalyzed asymmetric C(sp)-P cross-coupling reaction for the synthesis of P-stereogenic alkynylphosphines

Due to the high reactivity of the triple bond, P-stereogenic alkynylphosphines could be easily derivatized, serving as universal building blocks for structurally diverse phosphine compounds. However, the synthesis of alkynylphosphines via direct P-C bond formation was unprecedented. Here, we report an efficient method for the synthesis of P-stereogenic alkynylphosphines with high enantioselectivity via a Ni-catalyzed asymmetric cross-coupling reaction. The reaction could tolerate a variety of functional groups, affording products that can be converted into useful phosphine derivatives.

Recent Progress in Cyclic Aryliodonium Chemistry: Syntheses and Applications

Hypervalent aryliodoumiums are intensively investigated as arylating agents. They are excellent surrogates to aryl halides, and moreover they exhibit better reactivity, which allows the corresponding arylation reactions to be performed under mild conditions. In the past decades, acyclic aryliodoniums are widely explored as arylation agents. However, the unmet need for acyclic aryliodoniums is the improvement of their notoriously low reaction economy because the coproduced aryl iodides during the arylation are often wasted. Cyclic aryliodoniums have their intrinsic advantage in terms of reaction economy, and they have started to receive considerable attention due to their valuable synthetic applications to initiate cascade reactions, which can enable the construction of complex structures, including polycycles with potential pharmaceutical and functional properties. Here, we are summarizing the recent advances made in the research field of cyclic aryliodoniums, including the nascent design of aryliodonium species and their synthetic applications. First, the general preparation of typical diphenyl iodoniums is described, followed by the construction of heterocyclic iodoniums and monoaryl iodoniums. Then, the initiated arylations coupled with subsequent domino reactions are summarized to construct polycycles. Meanwhile, the advances in cyclic aryliodoniums for building biaryls including axial atropisomers are discussed in a systematic manner. Finally, a very recent advance of cyclic aryliodoniums employed as halogen-bonding organocatalysts is described.

Access to Enantiomerically Pure P-Stereogenic Primary Aminophosphine Sulfides under Reductive Conditions

Stereochemically pure phosphines with phosphorus-heteroatom bonds and P-centered chirality are a promising class of functional building blocks for the design of chiral ligands and organocatalysts. A route to enantiomerically pure primary aminophosphine sulfides was opened through stereospecific reductive C-N bond cleavage of phosphorus(V) precursors by lithium in liquid ammonia. The chemoselectivity of the reaction as a function of reaction time, substrate pattern, and chiral auxiliary was investigated. In the presence of exclusively aliphatic groups bound to the phosphorus atom, all competing reductive side reactions are totally prevented. The absolute configurations of all P-stereogenic compounds were determined by single-crystal X-ray diffraction analysis. Their use as synthetic building blocks was demonstrated. The lithium salt of (R)-BINOL-dithiophosphoric acid proved to be a useful stereochemical probe to determine the enantiomeric purity. Insights into the coordination mode of the lithium-based chiral complex formed in solution was provided by NMR spectroscopy and DFT calculations.

Deamination of 1-Aminoalkylphosphonic Acids: Reaction Intermediates and Selectivity

Deamination of 1-aminoalkylphosphonic acids in the reaction with HNO₂ (generated "in situ" from NaNO₂) yields a mixture of substitution products (1-hydroxyalkylphosphonic acids), elimination products (vinylphosphonic acid derivatives), rearrangement and substitution products (2-hydroxylkylphosphonic acids) as well as H₃PO₄. The variety of formed reaction products suggests that 1-phosphonoalkylium ions may be intermediates in such deamination reactions.

Racemization Pathway for MoO2(acac)2 Favored over Ray-Dutt, Bailar, and Conte-Hippler Twists

Chiral cis-MoO2(acac)2 racemizes via four pathways that agree with and extend upon Muetterties' topological analysis for dynamic MX2(chel)2 complexes. Textbook Ray-Dutt and Bailar twists are the least favored with barriers of 27.5 and 28.7 kcal/mol, respectively. Rotating both acac ligands of the Bailar structure by 90° gives the lower Conte-Hippler twist (20.0 kcal/mol), which represents a valley-ridge inflection that invokes the trans isomer. The most favorable is a new twist that was found by 90° rotation of only one acac ligand of the Bailar structure. The gas-phase barrier of 17.4 kcal/mol for this Dhimba-Muller-Lammertsma twist further decreases upon inclusion of the effects of solvents to 16.3 kcal/mol (benzene), 16.2 kcal/mol (toluene), and 15.4 kcal/mol (chloroform), which are in excellent agreement with the reported experimental values.

Indane-Based Chiral Aryl Chalcogenide Catalysts: Development and Applications in Asymmetric Electrophilic Reactions

Asymmetric electrophilic reactions provide an ideal method for the construction of chiral molecules by incorporating one or more functional groups into the parent substrates under mild conditions. However, due to the issues of the reactivities of electrophilic species and the possible racemization of chiral intermediates as well as the restriction of the chiral scaffolds of chiral catalysts, many limitations remain in this field, such as the narrow scopes of substrates and electrophiles as well as the limited types of nucleophiles and reactions. To overcome the limitations in the synthesis of diversified chiral molecules, we developed a series of indane-based chiral amino aryl chalcogenide catalysts. These catalysts are easily prepared based on the privileged chiral indane scaffold. They can provide an appropriate H-bonding effect by varying the amino protecting groups as well as offer a proper Lewis basicity and steric hindrance by adjusting different substituents on the aryl chalcogenide motifs. These features allow for them to meet the requirements of reactivity and the chiral environment of the reactions. Notably, they have been successfully applied to various asymmetric electrophilic reactions of alkenes, alkynes, and arenes, expanding the field of electrophilic reactions.Using these catalysts, we realized the enantioselective CF₃S-lactonization of olefinic carboxylic acids, enantioselective CF₃S-aminocyclization of olefinic sulfonamides, desymmetrizing enantioselective CF₃S-carbocyclization of gem-diaryl-tethered alkenes, enantioselective CF₃S-oxycyclization of N-allylamides, enantioselective intermolecular trifluoromethylthiolating difunctionalization and allylic C-H trifluoromethylthiolation of trisubstituted alkenes, formally the intermolecular CF₃S-oxyfunctionalization of aliphatic internal alkenes, intermolecular azidothiolation, oxythiolation, thioarylation of N-allyl sulfonamides, desymmetrizing enantioselective chlorocarbocyclization of aryl-tethered diolefins, enantioselective Friedel-Crafts-type electrophilic chlorination of N-allyl anilides, and enantioselective chlorocarbocyclization and dearomatization of N-allyl 1-naphthanilides. Additionally, the enantioselective electrophilic carbothiolation of alkynes to construct enantiopure carbon chirality center-containing molecules and axially chiral amino sulfide vinyl arenes and the electrophilic aromatic halogenation to produce P-chirogenic compounds can be accomplished. In these reactions, a bifunctional binding mode is proposed in the catalytic cycles, in which an acid-derived anion-binding interaction might exist and account for the high enantioselectivities of the reactions.In this Account, we demonstrate our achievements in asymmetric electrophilic reactions and share our thoughts on catalyst design, our understanding of asymmetric electrophilic reactions, and our perspectives in the field of chiral chalcogenide-catalyzed asymmetric electrophilic reactions. We hope that the experience we share will promote the design and development of other novel organocatalysts and new challenging reactions.

Iridium-Catalyzed Asymmetric Hydrogenation of 2,3-Diarylallyl Amines with a Threonine-Derived P-Stereogenic Ligand for the Synthesis of Tetrahydroquinolines and Tetrahydroisoquinolines

Chiral compounds containing nitrogen heteroatoms are fundamental substances for the chemical, pharmaceutical and agrochemical industries. However, the preparation of some of these interesting scaffolds is still underdeveloped. Herein we present the synthesis of a family of P-stereogenic phosphinooxazoline iridium catalysts from L-threonine methyl ester and their use in the asymmetric hydrogenation of N-Boc-2,3-diarylallyl amines, achieving very high enantioselectivity. Furthermore, the synthetic utility of the 2,3-diarylpropyl amines obtained is demonstrated by their transformation to 3-aryl-tetrahydroquinolines and 4-benzyl-tetrahydroisoquinolines, which have not yet been obtained in an enantioselective manner by direct reduction of the corresponding aromatic heterocycles. This strategy allows the preparation of these types of alkaloids with the highest enantioselectivity reported up to date.

Green and Effective Preparation of α-Hydroxyphosphonates by Ecocatalysis

A green and effective approach for the synthesis of structurally diversed α-hydroxyphosphonates via hydrophosphonylation of aldehydes under solventless conditions and promoted by biosourced catalysts, called ecocatalysts "Eco-MgZnOx" is presented. Ecocatalysts were prepared from Zn-hyperaccumulating plant species Arabidopsis halleri, with simple and benign thermal treatment of leaves rich in Zn, and without any further chemical treatment. The elemental composition and structure of Eco-MgZnOx were characterized by MP-AES, XRPD, HRTEM, and STEM-EDX techniques. These analyses revealed a natural richness in two unusual and valuable mixed zinc-magnesium and iron-magnesium oxides. The ecocatalysts were employed in this study to demonstrate their potential use in hydrophosphonylation of aldehydes, leading to various α-hydroxyphosphonate derivatives, which are critical building blocks in the modern chemical industry. Computational chemistry was performed to help discriminate the role of some of the constituents of the mixed oxide ecocatalysts. High conversions, broad substrate scope, mild reaction conditions, and easy purification of the final products together with simplicity of the preparation of the ecocatalysts are the major advantages of the presented protocol. Additionally, Eco-MgZnOx-P could be recovered and reused for up to five times.

Ni-catalyzed asymmetric hydrophosphinylation of conjugated enynes and mechanistic studies

The catalytic asymmetric synthesis of P-stereogenic phosphines is an efficient strategy to access structurally diverse chiral phosphines that could serve as organocatalysts and ligands to transition metals and motifs of antiviral drugs. Herein, we describe a Ni catalyzed highly regio and enantioselective hydrophosphinylation reaction of secondary phosphine oxides and enynes. This method afforded a plethora of alkenyl phosphine oxides which could serve as valuable precursors to bidentate ligands. A new type of mechanism was discovered by combined kinetic studies and density functional theory (DFT) calculations, which was opposed to the widely accepted Chalk-Harrod type mechanism. Notably, the alkene moiety which could serve as a directing group by coordinating with the Ni catalyst in the transition state, plays a vital role in determining the reactivity, regio and enantioselectivity.

Copper(I)-Catalyzed Asymmetric Synthesis of P-Chiral Aminophosphinites

Herein, a copper(I)-catalyzed reaction of diarylphosphines and O-benzoyl hydroxylamines is developed. In the cases of symmetrical diarylphosphines, a series of aminophosphinites is prepared in high yields. In the cases of unsymmetrical diarylphosphines, an array of P-chiral aminophosphinites is synthesized in high yields with high enantioselectivity by using a copper(I)-(R,R_P )-Ph-FOXAP complex as a chiral catalyst. Based on several control experiments and ³¹ P NMR studies, a two-electron redox mechanism involving the dynamic kinetic asymmetric transformation of unsymmetrical diarylphosphines is proposed for the copper(I)-catalyzed asymmetric reaction. Finally, one representative P-chiral phosphoric amide generated through the oxidation with H₂ O₂ is transformed to a chiral diarylphosphinate in high yield with retained enantioselectivity, which allows further transformations towards various P-chiral tertiary phosphines.

Recent Advances in the Enantioselective Synthesis of Chiral Amines via Transition Metal-Catalyzed Asymmetric Hydrogenation

Chiral amines are key structural motifs present in a wide variety of natural products, drugs, and other biologically active compounds. During the past decade, significant advances have been made with respect to the enantioselective synthesis of chiral amines, many of them based on catalytic asymmetric hydrogenation (AH). The present review covers the use of AH in the synthesis of chiral amines bearing a stereogenic center either in the α, β, or γ position with respect to the nitrogen atom, reported from 2010 to 2020. Therefore, we provide an overview of the recent advances in the AH of imines, enamides, enamines, allyl amines, and N-heteroaromatic compounds.

Betti base derived P-stereogenic phosphine-diamidophosphite ligands with a single atom spacer and their application in asymmetric catalysis

Small bite-angle P-chirogenic PNP ligands have been synthesized stereo-selectively and employed in Rh-catalyzed asymmetric hydrogenation and Pd-catalyzed asymmetric allylic substitution resulting in moderate to excellent enantioselectivities.

C 1-Symmetric diphosphorus ligands in metal-catalyzed asymmetric hydrogenation to prepare chiral compounds

Asymmetric hydrogenation has remained an important and challenging research area in industry as well as academia due to its high atom economy and ability to induce chirality. Among several types of ligands, chiral bidentate phosphine ligands have played a pivotal role in developing asymmetric hydrogenation. Although C₂-symmetric chiral bidentate phosphine ligands have dominated the field, it has been found that several C₁-symmetric ligands are equally effective and, in many cases, have outperformed their C₂-symmetric counterparts. This review evaluates the possibility of the use of C₁-symmetric diphosphorus ligands in asymmetric hydrogenation to produce chiral compounds. The recent strategies and advances in the application of C₁-symmetric diphosphorus ligands in the metal-catalyzed asymmetric hydrogenation of a variety of CC bonds have been summarized. The potential of diphosphorus ligands in asymmetric hydrogenation to produce pharmaceutical intermediates, bioactive molecules, drug molecules, agrochemicals, and fragrances is discussed. Although asymmetric hydrogenation appears to be a problem that has been resolved, a deep dive into the recent literature reveals that there are several challenges that are yet to be addressed. The current asymmetric hydrogenation methods mostly employ precious metals, which are depleting at a fast pace. Therefore, scientific interventions to perform asymmetric hydrogenation using base metals or earth-abundant metals that can compete with established precious metals hold significant potential.

BOM-Phosphinite as an Electrophilic P-Stereogenic Transfer Reagent for the Synthesis of Bulky Phosphines: Synthesis of tert-Butyl(3,5-di-tert-butylphenyl)BisP

BOM-tert-butylmethylphosphinite borane is an efficient electrophilic P-stereogenic transfer reagent for the synthesis of bulky tertiary phosphines. The novel methodology relies on a one-pot deprotection/substitution on the trivalent phosphinite that takes place with very high stereospecificity. The potential of this strategy is demonstrated with the synthesis of a wide scope of tertiary phosphines in excellent enantiomeric excess. The methodology was applied to the synthesis of a bulky P-stereogenic BisP* ligand analogue.

Asymmetric synthesis of organophosphorus compounds using H-P reagents derived from chiral alcohols

Chiral organophosphorus compounds, especially those containing C-stereogenic carbons in the proximity of the phosphorus atom, are known for their unique properties and have found wide applications that span from medicinal chemistry to enantioselective catalysis. However, the synthesis of such chiral molecules, especially with the precise control of stereochemistry at chiral carbon atoms, still remains a very challenging task. This review summarizes recent advances in the highly stereoselective formation of C- and, in some cases, also P-stereogenic organophosphorus compounds. The presented synthesis strategy is based on the use of H-P reagents bearing TADDOL, BINOL or a menthol moiety attached to the phosphorus atom and serving as a chiral auxiliary. Reactions of such chiral H-P species with different partners, e.g., alkenes, alkynes, imines, and carbonyl compounds, leading to structurally diverse chiral organophosphorus compounds with up to five chiral centers are comprehensively discussed. In each case, the stereochemical outcome of the reaction is influenced by the presence of the chiral alcohol used; therefore, the content of this review is compiled into sections with respect to the type of chiral alcohol attached to the phosphorus atom in the H-P species applied.

Synthesis, crystal structures and magnetic properties of a P-stereogenic ortho-(4-amino-tempo)phosphinic amide radical and its CuII complex

The synthesis of phosphinic amides containing one 4-amino-TEMPO substituent at the ortho position has been achieved through copper(i) catalyzed cross-coupling reactions of ortho-iodophosphinic amides with 4-amino-TEMPO. The method has been extended to the preparation of the first example of a P-stereogenic ortho-(4-amino-tempo)phosphinic amide radical 10. The reaction of 10 with Cu(hfac)2 afforded the P-stereogenic CuII complex 19. The crystal structure of both chiral compounds is reported. The molecular structure of 10 consists of a supramolecular zig-zag chain formed by intermolecular hydrogen bonds between the NH group of the phosphinic amide moiety and the nitroxide oxygen atom. In complex 19, the ligand acts as a bridge between two CuII ions coordinated to the oxygen atoms of the P[double bond, length as m-dash]O and N-O· groups leading to the formation of a polymeric helicate chain in which the metal ions exist in a distorted octahedral geometry. The magnetic behavior of ligand 10 is characterized by very weak intermolecular antiferromagnetic interactions, whereas ferro- and anti-ferromagnetic interactions are present in complex 19.

The Discovery of Multifunctional Chiral P Ligands for the Catalytic Construction of Quaternary Carbon/Silicon and Multiple Stereogenic Centers

The development of highly effective chiral ligands is a key topic in enhancing the catalytic activity and selectivity in metal-catalyzed asymmetric synthesis. Traditionally, the difficulty of ligand synthesis, insufficient accuracy in controlling the stereoselectivity, and poor universality of the systems often become obstacles in this field. Using the concept of nonequivalent coordination to the metal, our group has designed and synthesized a series of new chiral catalysts to access various carbon/silicon and/or multiple stereogenic centers containing products with excellent chemo-, diastereo-, and enantioselectivity.In this Account, we summarize a series of new phosphine ligands with multiple stereogenic centers that have been developed in our laboratory. These ligands exhibited good to excellent performance in the transition-metal-catalyzed enantioselective construction of quaternary carbon/silicon and multiple stereogenic centers. In the first section, notable examples of the design and synthesis of new chiral ligands by non-covalent interaction-based multisite activation are described. The integrations of axial chirality, atom-centered chirality, and chiral anions and multifunctional groups into a single scaffold are individually highlighted, as represented by Ar-BINMOLs and their derivative ligands, HZNU-Phos, Fei-Phos, and Xing-Phos. In the second, third, and fourth sections, the enantioselective construction of quaternary carbon stereocenters, multiple stereogenic centers, and silicon stereogenic centers using our newly developed chiral ligands is summarized. These sections refer to detailed reaction information in the chiral-ligand-controlled asymmetric catalysis based on the concept of nonequivalent coordination with multisite activation. Accordingly, a wide array of transition metal and main-group metal catalysts has been applied to the enantioselective synthesis of chiral heterocycles, amino acid derivatives, cyclic ketones, alkenes, and organosilicon compounds bearing one to five stereocenters.This Account shows that this new model of multifunctional ligand-controlled catalysts exhibits excellent stereocontrol and catalytic efficiency, especially in a stereodivergent and atom-economical fashion. Furthermore, a brief mechanistic understanding of the origin of enantioselectivity from our newly developed chiral catalyst systems could inspire further development of new ligands and enhancement of enantioselective synthesis by asymmetric metal catalysis.

Synthesis and applications of high-performance P-chiral phosphine ligands

Metal-catalyzed asymmetric synthesis is one of the most important methods for the economical and environmentally benign production of useful optically active compounds. The success of the asymmetric transformations is significantly dependent on the structure and electronic properties of the chiral ligands coordinating to the center metals, and hence the development of highly efficient ligands, especially chiral phosphine ligands, has long been an important research subject in this field. This review article describes the synthesis and applications of P-chiral phosphine ligands possessing chiral centers at the phosphorus atoms. Rationally designed P-chiral phosphine ligands are synthesized by the use of phosphine-boranes as the intermediates. Conformationally rigid and electron-rich P-chiral phosphine ligands exhibit excellent enantioselectivity and high catalytic activity in various transition-metal-catalyzed asymmetric reactions. Recent mechanistic studies of rhodium-catalyzed asymmetric hydrogenation are also described.

Copper-catalyzed arylation of polycyclic aromatic hydrocarbons by the P[double bond, length as m-dash]O group

The first example of a directed and regioselective arylation of polycyclic aromatic hydrocarbons (PAHs) by using a P[double bond, length as m-dash]O directing group is reported herein. The protocol uses a cheap copper catalyst, and results in a breakthrough meta-selective C-H functionalization of arylphosphine oxide compounds. Substrates with potential fluorescence properties, for example, pyrene and fluoranthene, were successfully arylated under the system, thus achieving an efficient modification of fluorescent molecules containing the P[double bond, length as m-dash]O functional group.

1,1-Addition of α-C2-Bridged Biphospholes with Alkynes

An unusual chemoselective 1,1-addition of α-C₂-bridged biphospholes to terminal alkynes is reported. The developed protocol provides simple access to the unknown 1,3-diphosphepines, which has potential applications in the coordination and catalyst chemistry. Their Pd and Mo complexes were studied by single-crystal X-ray diffraction analysis. This method features excellent chemoselectivity, high step and atom economy, mild reaction conditions, and wide substrate scope.