Asymmetric C–H Activation for the Synthesis of P- and Axially Chiral Biaryl Phosphine Oxides by an Achiral Cp*Ir Catalyst with Chiral Carboxylic Amide

Enantioselective Synthesis of Axially and Centrally Chiral Styrenes via Nickel-Catalyzed Desymmetric Hydrocyanation of Biaryl Dienes

Herein, a highly regio-, enantio-, and diastereoselective nickel-catalyzed desymmetric hydrocyanation of biaryl dienes for the simultaneous construction of axial and central chiralities is presented, which offers a convenient approach to a variety of tirenes containing the union of an axially chiral biaryl and a centrally α-chiral nitrile under mild conditions using a commercially available catalyst. The synthetic utility is highlighted by the development of a novel axially chiral phosphine ligand and biphenyl-based chiral diene ligand and their potential applications in the field of asymmetric catalytic reactions.

Second Generation Catalytic Enantioselective Nucleophilic Desymmetrization at Phosphorus (V): Improved Generality, Efficiency and Modularity

A broadly improved second generation catalytic two-phase strategy for the enantioselective synthesis of stereogenic at phosphorus (V) compounds is described. This protocol, consisting of a bifunctional iminophosphorane (BIMP) catalyzed nucleophilic desymmetrization of prochiral, bench stable P(V) precursors and subsequent enantiospecific substitution allows for divergent access to a wide range of C-, N-, O- and S- substituted P(V) containing compounds from a handful of enantioenriched intermediates. A new ureidopeptide BIMP catalyst/thiaziolidinone leaving group combination allowed for a far wider substrate scope and increased reaction efficiency and practicality over previously established protocols. The resulting enantioenriched intermediates could then be transformed into an even greater range of distinct classes of P(V) compounds by displacement of the remaining leaving group as well as allowing for even further diversification downstream. Density functional theory (DFT) calculations were performed to pinpoint the origin of enantioselectivity for the BIMP-catalyzed desymmetrization, to rationalize how a superior catalyst/leaving group combination leads to increased generality in our second-generation catalytic system, as well as shed light onto observed stereochemical retention and inversion pathways when performing late-stage enantiospecific SN2@P reactions with Grignard reagents.

Enantioselective Rhodium-Catalyzed C-H Arylation Enables Direct Synthesis of Atropisomeric Phosphines

Atropisomeric phosphines hold considerable significance in asymmetric catalysis, yet their synthesis presents a formidable challenge owing to intricate multistep procedures. In this context, a groundbreaking methodology has been presented for their preparation. This innovative approach entails an atroposelective rhodium-catalyzed C-H activation employing aryl and heteroaryl halides, chelated by a P(III) center. The essence of this strategy lies in its ability to directly construct chiral phosphine ligands in a single step, thereby exhibiting exceptional efficiency in terms of atom and redox economy. Illustrative examples serve to demonstrate the immense potential of in situ-formed ligands in asymmetric catalysis. Mechanistic experiments have further provided invaluable insights into this transformation.

Pd(II)-Catalyzed enantioselective C-H olefination toward the synthesis of P-stereogenic phosphinamides

P-Stereogenic phosphorus compounds are important structural elements in chiral ligands or organocatalysts. Herein, we report a Pd(II)-catalyzed enantioselective C-H olefination toward the synthesis of P-stereogenic phosphinamides using cheap commercially available L-pGlu-OH as a chiral ligand. A broad range of P-stereogenic phosphinamides were gained in good yields with high enantioselectivities (33 examples, up to 77% yield, 99% ee) via desymmetrization and kinetic resolution.

Catalytic Asymmetric Synthesis of Atropisomers Bearing Multiple Chiral Elements: An Emerging Field

With the rapid development of asymmetric catalysis, the demand for the enantioselective synthesis of complex and diverse molecules with different chiral elements is increasing. Owing to the unique features of atropisomerism, the catalytic asymmetric synthesis of atropisomers has attracted a considerable interest from the chemical science community. In particular, introducing additional chiral elements, such as carbon centered chirality, heteroatomic chirality, planar chirality, and helical chirality, into atropisomers provides an opportunity to incorporate new properties into axially chiral compounds, thus expanding the potential applications of atropisomers. Thus, it is important to perform catalytic asymmetric transformations to synthesize atropisomers bearing multiple chiral elements. In spite of challenges in such transformations, in recent years, chemists have devised powerful strategies under asymmetric organocatalysis or metal catalysis, synthesizing a wide range of enantioenriched atropisomers bearing multiple chiral elements. Therefore, the catalytic asymmetric synthesis of atropisomers bearing multiple chiral elements has become an emerging field. This review summarizes the rapid progress in this field and indicates challenges, thereby promoting this field to a new horizon.

Atroposelective hydroarylation of biaryl phosphines directed by phosphorus centres

Prized for their ability to generate chemical complexity rapidly, catalytic carbon-hydrogen (C-H) activation and functionalization reactions have enabled a paradigm shift in the standard logic of synthetic chemistry. Directing group strategies have been used extensively in C-H activation reactions to control regio- and enantioselectivity with transition metal catalysts. However, current methods rely heavily on coordination with nitrogen and/or oxygen atoms in molecules and have therefore been found to exhibit limited generality in asymmetric syntheses. Here, we report enantioselective C-H activation with unsaturated hydrocarbons directed by phosphorus centres to rapidly construct libraries of axially chiral phosphines through dynamic kinetic resolution. High reactivity and enantioselectivity are derived from modular assembly of an iridium catalyst with an endogenous phosphorus atom and an exogenous chiral phosphorus ligand, as confirmed by detailed experimental and computational studies. This reaction mode significantly expands the pool of enantiomerically enriched functional phosphines, some of which have shown excellent efficiency for asymmetric catalysis.

Cu-mediated enantioselective C-H alkynylation of ferrocenes with chiral BINOL ligands

A wide range of Cu(II)-catalyzed C-H activation reactions have been realized since 2006, however, whether a C-H metalation mechanism similar to Pd(II)-catalyzed C-H activation reaction is operating remains an open question. To address this question and ultimately develop ligand accelerated Cu(II)-catalyzed C-H activation reactions, realizing the enantioselective version and investigating the mechanism is critically important. With a modified chiral BINOL ligand, we report the first example of Cu-mediated enantioselective C-H activation reaction for the construction of planar chiral ferrocenes with high yields and stereoinduction. The key to the success of this reaction is the discovery of a ligand acceleration effect with the BINOL-based diol ligand in the directed Cu-catalyzed C-H alkynylation of ferrocene derivatives bearing an oxazoline-aniline directing group. This transformation is compatible with terminal aryl and alkyl alkynes, which are incompatible with Pd-catalyzed C-H activation reactions. This finding provides an invaluable mechanistic information in determining whether Cu(II) cleaves C-H bonds via CMD pathway in analogous manner to Pd(II) catalysts.

Synthesis of P-Stereogenic Phosphinamides via Pd(II)-Catalyzed Enantioselective C-H Alkynylation

P-Stereogenic phosphinamides represent important structural elements in chiral organocatalysts and bioactive compounds. Herein, we report Pd(II)-catalyzed enantioselective C-H alkynylation using cheap commercially available l-pyroglutamic acid as a chiral ligand. A range of structurally diverse P-stereogenic phosphinamides was prepared in good yields with high enantioselectivities via desymmetrization and kinetic resolution. A tailor-made congested directing group, N-ethyl-N-(3-methylpyridin-2-yl)amino, was crucial for the reactivity.

Photoinduced Copper-Catalyzed C(sp3)-P Bond Formation by Coupling of Secondary Phosphines with N-(Acyloxy)phthalimides and N-Fluorocarboxamides

A photoinduced copper-catalyzed C(sp³)-P bond formation has been developed by using N-(acyloxy)phthalimides as radical precursors and secondary phosphine boranes as coupling partners. A variety of alkyl carboxylic acid derivatives can be readily transformed into the corresponding phosphines with high reaction efficiency and structural diversity. Besides, utilizing the 1,5-HAT of the N-centered radical process, the δ C(sp³)-H bond can be coupled with secondary phosphines, which provides a novel method for the regioselective formation of C(sp³)-P bonds.

Copper-Catalyzed Asymmetric Boroprotonation of Phosphinylallenes

Synthesis of chiral phosphorus compounds from readily available substrates by a facile method is an attractive strategy. In this study, an efficient route for copper-catalyzed asymmetric boroprotonation of phosphinylallenes with bis(pinacolato)diboron with high regioselectivity was developed, affording chiral allylphosphine oxides in high yields with high enantioselectivities of up to 98% ee. The synthetic utility was further demonstrated by the facile transformation of the chiral allylphosphine oxides to several stereospecific products.

(SCp)Rhodium-Catalyzed Asymmetric Satoh-Miura Reaction for Building-up Axial Chirality: Counteranion-Directed Switching of Reaction Pathways

Satoh-Miura reaction is an important method for extending π-systems by forging multi-substituted benzene rings via double aryl C-H activation and annulation with alkynes. However, the development of highly enantioselective Satoh-Miura reaction remains rather challenging. Herein, we report an asymmetric Satoh-Miura reaction between 1-aryl benzo[h]isoquinolines and internal alkynes enabled by a SCpRh-catalyst. Judiciously choosing the counteranion of the Rh-catalyst is crucial for the desired reactivity over the competitive formation of azoniahelicenes. Detailed mechanistic studies support the proposal of counteranion-directed switching of reaction pathways in Rh-catalyzed asymmetric C-H activation.

Rhodium-catalyzed enantioselective C-H alkynylation of sulfoxides in diverse patterns: desymmetrization, kinetic resolution, and parallel kinetic resolution

Rhodium-catalyzed enantioselective C-H alkynylation of achiral and racemic sulfoxides is disclosed with alkynyl bromide as the alkynylating reagent. A wide range of chiral sulfoxides have been constructed in good yield and excellent enantioselectivity (up to 99% ee, s-factor up to > 500) via desymmetrization, kinetic resolution, and parallel kinetic resolution under mild reaction conditions. The high enantioselectivity was rendered by the chiral cyclopentadienyl rhodium(iii) catalyst paired with a chiral carboxamide additive. The interactions between the chiral catalyst, the sulfoxide, and the chiral carboxylic amide during the C-H bond cleavage offer the asymmetric induction, which is validated by DFT calculations. The chiral carboxamide functions as a base to promote C-H activation and offers an additional chiral environment during the C-H cleavage.

Secondary Phosphine Sulfide-Enabled Iridium-Catalyzed Asymmetric Allylic Substitution

An iridium-catalyzed asymmetric synthesis of branched allylic phosphine compounds under mild conditions is reported. Products bearing various functional groups can be synthesized with excellent stereoselectivity (up to 99.9 % ee) and regioselectivity. The employment of phosphine sulfides with relatively low deactivation capacity against metal catalysts is crucial for the success of this reaction.

Cobalt(III)/Chiral Carboxylic Acid-Catalyzed Enantioselective Synthesis of Benzothiadiazine-1-oxides via C-H Activation

Among sulfoximine derivatives containing a chiral sulfur center, benzothiadiazine-1-oxides are important for applications in medicinal chemistry. Here, we report that the combination of an achiral cobalt(III) catalyst and a pseudo-C₂ -symmetric H₈ -binaphthyl chiral carboxylic acid enables the asymmetric synthesis of benzothiadiazine-1-oxides from sulfoximines and dioxazolones via enantioselective C-H bond cleavage. With the optimized protocol, benzothiadiazine-1-oxides with several functional groups can be accessed with high enantioselectivity.

Cobalt/Salox-Catalyzed Enantioselective C-H Functionalization of Arylphosphinamides

Previous methods on Co^III -catalyzed asymmetric C-H activation rely on the use of tailor-made cyclopentadienyl-ligated Co^III complexes, which require lengthy steps for the preparation. Herein, we report an unprecedented enantioselective C-H functionalization enabled by a simple cobalt/salicyloxazoline (Salox) catalysis. The chiral Salox ligands can be easily prepared in one step from salicylonitrile and chiral amino alcohols. A broad range of P-stereogenic compounds were synthesized in high yields with excellent enantioselectivities (45 examples, up to 99 % yield and >99 % ee). The isolation and characterization of several intermediates provided insights into the generation of active catalytic cobalt species, the action of Salox, and the mode of stereocontrol.

Synthesis of P- and S-Stereogenic Compounds via Enantioselective C–H Functionalization

Transition metal-catalyzed enantioselective C–H functionalization has emerged as an efficient and powerful strategy to access various chiral molecules. Recently, this strategy has also provided a complementary pathway to the construction of P- and S-stereogenic compounds. In this short review, we summarize the development and applications of various catalytic systems: Pd(II)/mono-N-protected amino acids (MPAA), Pd(0)/trivalent phosphorus chiral ligands, chiral cyclopentadienyl-ligated metal catalysts [CpxM(III)] (M = Rh, Ir), half-sandwich d6 Ir(III) and Ru(II) with a chiral carboxylic acid (CCA) ligand, Ir(I)/chiral bidentate boryl ligand, and Ir(I)/chiral cation, for accessing these chiral compounds via enantioselective C–H functionalization.

1 Introduction

2 Pd(II)/Mono-N-protected Amino Acids

3 Pd(0)/Trivalent Phosphorus Chiral Ligands

4 Chiral Cyclopentadienyl-Ligated Metal Catalysts [CpxM(III)] (M = Rh, Ir)

5 Half-sandwich d6 Ir(III) and Ru(II) with a Chiral Carboxylic Acid (CCA) Ligand

6 Ir(I)/Chiral Bidentate Boryl Ligand

7 Ir(I)/Chiral Cation

8 Conclusion and Outlook