Kinetic resolution of 1,1'-binaphthyl-2,2'-diamine derivatives by chiral calcium phosphate-catalyzed acylation

1,1'-Binaphthyl-2,2'-diamine (BINAM) is a useful axially chiral compound. The kinetic resolution of BINAM is one of the most crucial methods for synthesizing chiral BINAM. We have developed a chiral calcium phosphate-catalyzed kinetic resolution of BINAM by utilizing an acylation reaction to produce a mono-amide. The kinetic resolution of BINAM derivatives was achieved by using isobutyric anhydride in the presence of chiral calcium phosphate and 4-morpholinopyridine with up to s = 127. 6,6'-Substituted BINAM derivatives were also applicable for this reaction. The resulting mono-acylated BINAM could be transformed into BINAM by hydrolysis under acidic conditions.

2,2'-Tethered Binaphthyl-Embedded One-Handed Helical Ladder Polymers: Impact of the Tether Length on Helical Geometry and Chiroptical Property

Synthetic breakthroughs diversify the molecules and polymers available to chemists. We now report the first successful synthesis of a series of optically-pure 2,2'-tethered binaphthyl-embedded helical ladder polymers based on quantitative and chemoselective ladderization by the modified alkyne benzannulations using the 4-alkoxy-2,6-dimethylphenylethynyl group as the alkyne source, inaccessible by the conventional approach lacking the 2,6-dimethyl substituents. Due to the defect-free helix formation, the circular dichroism signal increased by more than 6 times the previously reported value. The resulting helical secondary structure can be fine-tuned by controlling the binaphthyl dihedral angle in the repeating unit with variations in the 2,2'-alkylenedioxy tethering groups by one carbon atom at a time. The optimization of the helical ladder structures led to a strong circularly polarized luminescence with a high fluorescence quantum yield (28 %) and luminescence dissymmetry factor (2.6×10-3 ).

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.

Atroposelective Synthesis of Axially Chiral Naphthylpyrroles by a Catalytic Asymmetric 1,3-Dipolar Cycloaddition/Aromatization Sequence

A straightforward methodology for the enantioselective preparation of axially chiral 2-naphthylpyrroles has been developed. This protocol is based on a CuI/Fesulphos-catalyzed highly enantioselective 1,3-dipolar cycloaddition of an azomethine ylide followed by pyrrolidine alkylation and pyrrolidine to pyrrole oxidation. The mild conditions employed in the DDQ/blue light-mediated aromatization process facilitate an effective central-to-axial chirality transfer affording the corresponding pyrroles with high atroposelectivity.

Eight-Membered Palladacycle Intermediate Enabled Synthesis of Cyclic Biarylphosphonates

Transition-metal-catalyzed coupling reactions that involve the direct functionalization of insert C-H bond represent one of the most efficient strategies for forming carbon-carbon bonds. Herein, a palladium-catalyzed intramolecular C-H bond arylation of triaryl phosphates is reported to access seven-membered cyclic biarylphosphonate targets. The reaction is achieved via a unique eight-membered palladacyclic intermediate and shows good functional group compatibility. Meanwhile, the product can be readily converted into other valuable phosphate compounds.

Efficient construction of a β-naphthol library under continuous flow conditions

A β-naphthol library has been efficiently constructed utilizing a mild continuous flow procedure, relying on a tandem Friedel-Crafts reaction and starting from readily available arylacetyl chloride and alkynes. Multiple functionalized β-naphthols can be acquired within 160 s in generally high yields (up to 83%). Using an electron-rich phenylacetyl chloride derivative (4-OH- or 4-MeO-) provides spirofused triene dione as the primary product. A scale-up preparation affords a throughput of 4.70 g h-1, indicating potential large-scale application. Herein, we present a rapid, reliable, and scalable method to obtain various β-naphthols in the compound library.

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.

Ligand-Free Ultrasmall Recyclable Iridium(0) Nanoparticles for Regioselective Aromatic Hydrogenation of Phosphine Oxide Scaffolds: An Easy Access to New Phosphine Ligands

Herein, we developed the recyclable ligand-free iridium (Ir)-hydride based Ir0 nanoparticles (NPs) for the first regioselective partial hydrogenation of PV -substituted naphthalenes. Both the isolated and in situ generated NPs are catalytically active. A control nuclear magnetic resonance (NMR) study revealed the presence of metal-surface-bound hydrides, most likely formed from Ir0 species. A control NMR study confirmed that hexafluoroisopropanol as a solvent was accountable for substrate activation via hydrogen bonding. High-resolution transmission electron microscopy of the catalyst supports the formation of ultrasmall NPs, and X-ray photoelectron spectroscopy confirmed the dominance of Ir0 in the NPs. The catalytic activity of NPs is broad as showcased by highly regioselective aromatic ring reduction in various phosphine oxides or phosphonates. The study also showcased a novel pathway toward preparing bis(diphenylphosphino)-5,5',6,6',7,7',8,8'-octahydro-1,1'-binaphthyl (H8 -BINAP) and its derivatives without losing enantioselectivity during catalytic events.

Recent Advancement in H8-BINOL Catalyzed Asymmetric Methodologies

H₈-BINOL, a partially reduced form of BINOL, is widely employed in a broad array of organocatalyzed asymmetric methodologies. Over the last 25 years, asymmetric organocatalysis has witnessed an incredible improvement, and an advancement still continues to get a single enantio-enriched product. The broad-spectrum applications of H₈-BINOL organocatalyst in C-C bond formation, C-heteroatom bond construction, name reactions, pericyclic reactions, and one pot and multicomponent reaction are attracting the attention of researchers. A diversified unique H₈-BINOL-based catalyst has been synthesized and screened for catalytic activity. In this Review we frame out the H₈-BINOL catalyzed novel discoveries from the last two decades.

Synthesis of tetracyclic 4H-benzo[5,6]chromeno[3,4-d]oxazoles via palladium-catalyzed intramolecular direct heteroarylation

We report a palladium-catalyzed intramolecular direct heteroarylation of oxazole tethered β-naphthols to access corresponding tetracyclic 4H-benzo[5,6]chromeno[3,4-d]oxazoles. Various functional groups are well tolerated and furnished the desired products in good to excellent yields under the present reaction conditions. The scale-up reaction and synthetic utility of the resulting molecules have been demonstrated. Moreover, UV/vis absorption and fluorescence emission properties have been evaluated for these polyheterocyclic compounds.

Synthesis and Characterizations of 5,5'-Bibenzo[rst]pentaphene with Axial Chirality and Symmetry-Breaking Charge Transfer

Exploration of novel biaryls consisting of two polycyclic aromatic hydrocarbon (PAH) units can be an important strategy toward further developments of organic materials with unique properties. In this study, 5,5'-bibenzo[rst]pentaphene (BBPP) with two benzo[rst]pentaphene (BPP) units is synthesized in an efficient and versatile approach, and its structure is unambiguously elucidated by X-ray crystallography. BBPP exhibits axial chirality, and the (M)- and (P)-enantiomers are resolved by chiral high-performance liquid chromatography and studied by circular dichroism spectroscopy. These enantiomers have a relatively high isomerization barrier of 43.6 kcal mol^-1 calculated by density functional theory. The monomer BPP and dimer BBPP are characterized by UV-vis absorption and fluorescence spectroscopy, cyclic voltammetry, and femtosecond transient absorption spectroscopy. The results indicate that both BPP and BBPP fluoresce from a formally dark S₁ electronic state that is enabled by Herzberg-Teller intensity borrowing from a neighboring bright S₂ state. While BPP exhibits a relatively low photoluminescence quantum yield (PLQY), BBPP exhibits a significantly enhanced PLQY due to a greater S₂ intensity borrowing. Moreover, symmetry-breaking charge transfer in BBPP is demonstrated by spectroscopic investigations in solvents of different polarity. This suggests high potential for singlet fission in such π-extended biaryls through appropriate molecular design.

Deracemization of Binaphthyl by Suzuki Diarylation: The Role of Electronic and Steric Effects

We report a Suzuki 2,2'-diarylation of the racemic 2,2'-diiodo-1,1'-binaphthyl which proceeds with deracemization via a pallada(IV)cyclic intermediate, induced by a simple chiral ligand─BINAP [2,2'-bis(diphenylphosphino)-1,1',-binaphthyl]. A systematic study of the reaction scope, using 45 arylboronic acids, reveals that the diarylated product is formed when meta- and/or para-substituted phenylboronic acids are functionalized with a substituent with the Hammett constant from -0.5 to +0.4. Multiparametric analysis accounting for the effect of geometry on the reactivity using Boltzmann-weighted Sterimol parameters and electronic effects described by Hammett descriptors shows that the enantioselectivity depends on steric effects only, with enhanced enantioselectivity observed for substituents with a larger length, wL, and reduced for substituents with a larger maximum width, wB₅. We show that careful tuning of these parameters, with the aid of the presented mathematical model, can lead to excellent enantioselectivity. Additional factors that are investigated and found to affect the stereoselective course of the reaction include the reaction temperature, palladium source, palladium to ligand ratio, and the type of boronic acid derivative. During the chromatographic separation of diarylated products on an achiral silica gel, we observed a rare phenomenon: the diarylated products undergo self-disproportionation of enantiomers, with the major enantiomer being eluted first.

Rhodium-catalyzed selective direct arylation of phosphines with aryl bromides

The widespread use of phosphine ligand libraries is frequently hampered by the challenges associated with their modular preparation. Here, we report a protocol that appends arenes to arylphosphines to access a series of biaryl monophosphines via rhodium-catalyzed P(III)-directed ortho C-H activation, enabling unprecedented one-fold, two-fold, and three-fold direct arylation. Our experimental and theoretical findings reveal a mechanism involving oxidative addition of aryl bromides to the Rh catalyst, further ortho C-H metalation via a four-membered cyclometalated ring. Given the ready availability of substrates, our approach opens the door to developing more general methods for the construction of phosphine ligands.

Asymmetric Azide-Alkyne Cycloaddition with Ir(I)/Squaramide Cooperative Catalysis: Atroposelective Synthesis of Axially Chiral Aryltriazoles

An Ir(I)/squaramide cooperative catalytic strategy for atroposelective synthesis of axially chiral aryltriazoles has been developed for the first time. Diverse structurally novel aryltriazole skeletons that cannot be accessed by traditional click reactions were synthesized in good yields with excellent enantioselectivity. Both enantiomers were easily obtained from a pair of diastereoisomeric natural quinidine- and quinine-derived squaramides. A significant Ir(I)/squaramide coordination activation, but no self-quenching phenomenon was observed in this metal/organo cooperative catalytic system.

Stereoisomeric Tris-BINOL-Menthol Bulky Monophosphites: Synthesis, Characterisation and Application in Rhodium-Catalysed Hydroformylation

Four stereoisomeric monoether derivatives, based on axially chiral (R)- or (S)-BINOL bearing a chiral (+)- or (−)-neomenthyloxy group were synthesised and fully characterised by NMR spectroscopy and X-ray crystallography. The respective tris-monophosphites were thereof prepared and fully characterised. The coordination ability of the new bulky phosphites with Rh(CO)₂(acac), was attested by ³¹P NMR, which presented a doublet in the range of δ = 120 ppm, with a ¹J(¹⁰³Rh-³¹P) coupling constant of 290 Hz. The new tris-binaphthyl phosphite ligands were further characterised by DFT computational methods, which allowed us to calculate an electronic (CEP) parameter of 2083.2 cm⁻¹ and an extremely large cone angle of 345°, decreasing to 265° upon coordination with a metal atom. Furthermore, the monophosphites were applied as ligands in rhodium-catalysed hydroformylation of styrene, leading to complete conversions in 4 h, 100% chemoselectivity for aldehydes and up to 98% iso-regioselectivity. The Rh(I)/phosphite catalytic system was also highly active and selective in the hydroformylation of disubstituted olefins, including (E)-prop-1-en-1-ylbenzene and prop-1-en-2-ylbenzene.

Bimetallic ruthenium–rhodium particles supported on carbon nanotubes for the hydrophosphinylation of alkenes and alkynes

RuRh bimetallic particles supported on carbon nanotubes were applied to the hydrophosphinylation of alkenes and alkynes. This recyclable system operates under sustainable conditions: low catalyst loading, room temperature and atmospheric pressure.

Synthesis of 2-Hydroxy-2'-aroyl-1,1'-biaryls via Oxidative Ring-Opening of 9H-Fluoren-9-ols

An Oxone-mediated oxidative ring-opening reaction of 4,5-disubstituted 9H-fluoren-9-ols by cleavage of a carbon-carbon bond is reported. 2-Hydroxy-2'-aroyl-1,1'-biaryls can be efficiently prepared by simply heating the mixture of fluoren-9-ols, Oxone, and 1,1,1,3,3,3-hexafluoroisopropanol at 60 °C for 4 h. The persulfate-involved ring-expansion processes were proposed and supported by the DFT calculations.

Nickel Complexes in C‒P Bond Formation

This review is a comprehensive account of reactions with the participation of nickel complexes that result in the formation of carbon-phosphorus (C‒P) bonds. The catalytic and non-catalytic reactions with the participation of nickel complexes as the catalysts and the reagents are described. The various classes of starting compounds and the products formed are discussed individually. The several putative mechanisms of the nickel catalysed reactions are also included, thereby providing insights into both the synthetic and the mechanistic aspects of this phosphorus chemistry.

Atropo-Enantioselective Oxidation-Enabled Iridium(III)-Catalyzed C-H Arylations with Aryl Boronic Esters

Atropo-enantioselective biaryl coupling through C-H bond functionalization is an emerging technology allowing direct construction of axially chiral molecules. This approach is largely limited to electrophilic coupling partners. We report a highly atropo-enantioselective C-H arylation of tetralone derivatives paired with aryl boronic esters as nucleophilic components. The transformation is catalyzed by chiral cyclopentadienyl (Cpx ) iridium(III) complexes and enabled by oxidatively enhanced reductive elimination from high-valent cyclometalated Ir-species.

Phosphorus-Based Catalysis

Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.

Synthesis of Axially Chiral 2,2'-Bisphosphobiarenes via a Nickel-Catalyzed Asymmetric Ullmann Coupling: General Access to Privileged Chiral Ligands without Optical Resolution

We report an asymmetric homocoupling of ortho-(iodo)arylphosphine oxides and ortho-(iodo)arylphosphonates resulting in highly enantioenriched axially chiral bisphosphine oxides and bisphosphonates. These products are readily converted to enantioenriched biaryl bisphosphines without need for chiral auxiliaries or optical resolution. This provides a practical route for the development of previously uninvestigated atroposelective biaryl bisphosphine ligands. The conditions have also proven effective for asymmetric dimerization of other, non-phosphorus-containing aryl halides.

Metal-Free Intramolecular Aminophosphination of Allenes

A metal-free intramolecular aminophosphination of sulfonamidoallenes with diarylphosphine oxides and Tf₂O was developed. This method offers a general and practical procedure to construct valuable alkenylphosphine-substituted N-heterocycles via the bifunctionalization reaction of allenes in good yields under mild conditions.

[2,2′-Bis(diphenylphosphanyl)-1,1′-binaphthyl-κ2 P,P′]dichloridoplatinum(II) acetonitrile trisolvate

The crystal structure of racemic di­chloro­[2,2′-bis­(di­phenyl­phosphino)-1,1′-binaphth­yl]platinum(II) has been determined at 150 K. The asymmetric unit consists of a single mol­ecule of the title compound co-crystallized with three aceto­nitrile solvent mol­ecules.

The crystal structure (150 K) of the racemic title compound, [PtCl₂(C₄₄H₃₂P₂)]·3CH₃CN, has been determined. The asymmetric unit comprises a single mol­ecule of the title compound co-crystallized with three aceto­nitrile solvent mol­ecules. Four mol­ecules are observed in the unit cell, with R and S enanti­omers present in a 2:2 ratio. Evidence of intra­molecular π-stacking is observed with no discernable inter­molecular inter­actions.

Catalytic Asymmetric [4 + 2] Cycloaddition of ortho-Alkenyl Naphthols/Phenols with ortho-Quinone Methides: Highly Stereoselective Synthesis of Chiral 2,3,4-Trisubstituted Chromans

Chiral phosphoric acid-catalyzed biomimetic asymmetric [4 + 2] cycloaddition of ortho-alkenyl naphthols/phenols and ortho-quinone methides (o-QMs) has been demonstrated to afford various important 2,3,4-trisubstituted chromans in high yields with excellent enantio- and diastereoselectivities (up to 99% yield, 99% ee, >20:1 dr). Notably, this methodology not only enabled access to the trans-cis chiral trisubstituted chromans from 1-alkenyl 2-naphthols but also is compatible with 2-alkenyl 1-naphthols and phenols to deliver trans-trans chiral trisubstituted chromans.

Enantioselective Cross-Coupling for Axially Chiral Tetra-ortho-Substituted Biaryls and Asymmetric Synthesis of Gossypol

The axially chiral tetra-ortho-substituted biaryl skeleton exists in numerous biologically important natural products, pharmaceutical molecules, chiral catalysts, and ligands. The efficient synthesis of chiral tetra-ortho-substituted biaryl structures remains a challenging but unsolved problem. Among various asymmetric synthetic protocols, enantioselective Suzuki-Miyaura cross-coupling represents one of the most straightforward and versatile approaches. Herein we describe a powerful Suzuki-Miyaura coupling enabled by a P-chiral monophosphorus ligand BaryPhos, providing a broad range of synthetically challenging chiral tetra-ortho-substituted biaryls in excellent enantioselectivities and yields. In addition to the enhanced reactivity for sterically hindered cross-coupling, the rational design of BaryPhos also enabled a new catalysis mode of asymmetric cross-coupling involving noncovalent interactions between the ligand and two coupling partners to effect efficient stereoinduction. This protocol is robust and practical, allowing for a concise enantioselective synthesis of therapeutically valuable male contraceptive and antitumor agent gossypol.

Catalyst Repurposing Sequential Catalysis by Harnessing Regenerated Prolinamide Organocatalysts as Transfer Hydrogenation Ligands

A catalyst repurposing strategy based on a sequential aldol addition and transfer hydrogenation giving access to enantiomerically enriched α-hydroxy-γ-butyrolactones is described. The combination of a stereoselective, organocatalytic step, followed by an efficient catalytic aldehyde reduction induces an ensuing lactonization to provide enantioenriched butyrolactones from readily available starting materials. By capitalizing from the capacity of prolineamides to act as both an organocatalyst and a transfer hydrogenation ligand, catalyst repurposing allowed the development of an operationally simple, economic, and efficient sequential catalysis approach.