Phosphine-Catalyzed Asymmetric Organic Reactions

N-Heterocyclic Carbene Enabled Copper Catalyzed Asymmetric Synthesis of Pyrimidinyl Phosphine with both Axial and P-Stereogenicity

P-stereogenic phosphines, renowned for their utility as ligands and catalysts, have been instrumental in the field of asymmetric catalysis. However, the catalytic asymmetric synthesis of chiral ligands possessing both axial and phosphine chirality remains a significant challenge. Here, we present the successful demonstration of a Cu-catalyzed asymmetric C-P construction using in situ generated secondary phosphine and heteroaryl chloride. By introducing a chiral NHC ligand and an achiral diphosphine auxiliary ligand, we effectively alleviated the poisoning effect caused by phosphine(III) compounds and suppressed the nonenantioselective background reaction. The reaction exhibited excellent enantioselectivity, with up to 96 % ee, and good diastereoselectivity, with up to 14 : 1 dr, when employing less sterically hindered secondary phosphines. This particular substrate poses a significant challenge due to its strong poisoning effect in copper catalysis.

Interrupted Michael Reaction: Sulfophosphinoylation of α,β-Unsaturated Ketones Catalyzed by Phosphine

An efficient method for phosphine-catalyzed sulfophosphinoylation of α,β-unsaturated ketones for synthesis allylic organophosphorus compounds has been reported, in which α,β-unsaturated compounds acting as zwitterions react with electrophiles and nucleophiles to form a C-P bond and a C-O bond and obtain allylic organophosphorus with high regio- and stereoselectivity in moderate to excellent yields.

Phosphine-Catalyzed [4 + 1] Annulation of β'-Acetoxy Allenoate with α-Alkylidene Succinimides: Access to Functionalized Spirosuccinimide Derivatives

A phosphine-catalyzed [4 + 1] annulation of β'-acetoxy allenoate with α-alkylidene succinimides is described. This method demonstrates the nucleophilic dialkylation and cyclization of α-alkylidene succinimides, resulting in the formation of functionalized spirosuccinimide derivatives. The reaction exhibits a wide substrate scope and yields ranging from moderate to excellent under the optimized conditions. In addition, the biological evaluation indicates that the cycloadduct 3u presents satisfied inhibitory activities for three human cancer cell lines (HCT116, A549, and HepG2).

Phosphine-Catalyzed [3 + 4] Annulations of Salicylaldehyde Schiff Bases with α-Substituted Allenes: Construction of Functionalized Benzoxepine Fused Succinimide Derivatives

Herein we reported a novel strategy for constructing benzoxepine fused succinimide derivatives via a phosphine-catalyzed [3 + 4] cyclization of α-substituted allenes and salicylaldehyde Schiff bases. This methodology serves as a conduit for the construction of benzoxepine derivatives in good yields under mild conditions by an unprecedented mode involving the β'-carbon of allenes. Density functional theory calculations were conducted to study the possible mechanism. Moreover, this class of compounds exhibited the potential ability of cytotoxicity toward cancer cells.

DMAP Catalyzed Ring-Opening/Cycloaddition of Vinyl Oxiranes with Activated Ketone Compounds to Construct the 1,3-Dioxolane Skeletons

The present work develops a DMAP-catalyzed [3 + 2] cycloaddition of vinyl oxiranes with activated ketone compounds, affording dioxolane derivatives with moderate to excellent yields. This approach represents the first Lewis base (LB)-catalyzed ring-opening reaction of vinyl epoxides, simultaneously providing a rare oxygen-containing active intermediate in this field. The gram-scale preparation and facile derivatization of the cycloadduct highlight the significant synthetic potential of this strategy.

Advancing Heterogeneous Organic Synthesis With Coordination Chemistry-Empowered Single-Atom Catalysts

For traditional metal complexes, intricate chemistry is required to acquire appropriate ligands for controlling the electron and steric hindrance of metal active centers. Comparatively, the preparation of single-atom catalysts is much easier with more straightforward and effective accesses for the arrangement and control of metal active centers. The presence of coordination atoms or neighboring functional atoms on the supports' surface ensures the stability of metal single-atoms and their interactions with individual metal atoms substantially regulate the performance of metal active centers. Therefore, the collaborative interaction between metal and the surrounding coordination environment enhances the initiation of reaction substrates and the formation and transformation of crucial intermediate compounds, which imparts single-atom catalysts with significant catalytic efficacy, rendering them a valuable framework for investigating the correlation between structure and activity, as well as the reaction mechanism of catalysts in organic reactions. Herein, comprehensive overviews of the coordination interaction for both homogeneous metal complexes and single-atom catalysts in organic reactions are provided. Additionally, reflective conjectures about the advancement of single-atom catalysts in organic synthesis are also proposed to present as a reference for later development.

Simultaneous Determination of the Position and Cis-Trans Configuration of Lipid C═C Bonds via Asymmetric Derivatization and Ion Mobility-Mass Spectrometry

The position and cis-trans configuration of C═C bonds in unsaturated lipids significantly affect their biological activities. Simultaneous identification of the position and cis-trans configuration of C═C bonds in unsaturated lipids is important; nonetheless, it still remains a challenging task. Herein, a stereoselective asymmetric reaction was used to recognize cis-trans isomers of the C═C bonds, and the derivatized precursor ions and product ions were subjected to tandem ion mobility-mass spectrometry (IM-MS) analysis. The theoretical calculation revealed that the formation of intramolecular hydrogen bonds after the cyclization reaction amplified the structural difference between diastereomers and increased the separation efficiency in IM. Consequently, a simple, sensitive, and highly selective platform for simultaneous determination of the position and cis-trans configuration of various C═C bonds in unsaturated lipids was established. It was then successfully applied to pinpoint the cis-trans geometry conversion of the located C═C bonds in lipids of the bacterial membrane under environmental stress and track the heterogeneous distribution of unsaturated lipids in rats after spinal cord injury. The present study also offers new insights into the application of IM-MS technology in resolving molecular structures and demonstrates the potential as a platform for a broad range of applications.

Spirophosphine-Catalyzed Enantioselective [3 + 2] Cycloaddition of Allenoates and Unsaturated α-Ketimine Esters

A novel chiral spiro-monophosphine, OUC-Phos, was synthesized and utilized for the first time in the asymmetric Lu's [3 + 2] cycloaddition reaction of β,γ-unsaturated α-ketimine ester with allenoate. OUC-Phos, featuring a 3,3'-diphenyl-modified spirobiindane skeleton, demonstrated exceptional catalytic efficiency in the [3 + 2] cycloaddition to achieve high yields, enantioselectivities, and diastereoselectivities for the targeted products. The broad substrate scope encompassing diverse functional groups demonstrated the versatility of this methodology. Furthermore, the reaction was successfully scaled up, and the products were easily converted into their corresponding functionalized derivatives.

Phosphine-Promoted Synthesis of Naphthoquinones Fused with Cyclopentadienyl Moiety Via Ring Expansion: Synthesis, Reactivity, and Ring Contraction Via [1,5] Sigmatropic Rearrangement

Phosphine-promoted unprecedented [3 + 2] annulation reactions via ring expansion by using 2-benzylidene-indane-1,3-diones and diynoates for the synthesis of biologically interesting novel naphthoquinones fused with a five-membered ring bearing a phosphorus ylide up to 78% yield are described. Further ring contraction through [1,5] sigmatropic rearrangement to the spiro indan-1,3-diones by mCPBA oxidation was revealed and inferred through oxidation, followed by protonation. The relevant structures were confirmed by single-crystal X-ray diffraction. Electrochemical studies show that the naphthoquinones and lactones with phosphorus ylides could be applied to redox colorimetric materials.

Reactivities of tertiary phosphines towards allenic, acetylenic, and vinylic Michael acceptors

The addition of phosphines (PR3) to Michael acceptors is a key step in many Lewis-base catalysed reactions. The kinetics of the reactions of ten phosphines with ethyl acrylate, ethyl allenoate, ethyl propiolate, ethenesulfonyl fluoride, and ethyl 2-butynoate in dichloromethane at 20 °C was followed by photometric and NMR spectroscopic methods. The experimentally determined second-order rate constants k 2 show that electronic effects in sterically unencumbered phosphines affect their nucleophilicity towards different classes of Michael acceptors in the same ordering. Michael acceptors with sp-hybridised electrophilic centres, however, are less susceptible to changes in the PR3 nucleophilicity than those with sp2-hybridised reactive sites. Linear correlations of lg k 2 from this work with published rate constants for SN2 and SN1 reactions as well as with Brønsted basicities and fugalities for PR3 demonstrate the generality of the detected reactivity trends. Computed reaction barriers (ΔG ‡ calc) as well as reaction energies (ΔG add) for Michael adduct formations show excellent correlations with experimentally obtained reaction barriers (ΔG ‡ exp) corroborating the interpretation of the kinetic data and revealing the philicity/fugality features of the reactants in phospha-Michael additions.

Selective Synthesis of Mono- and Bis-Phosphorylated (Dihydro)pyrans via TMSCl-Mediated Cascade Phosphorylation Cycloisomerization of Enynones

A chlorotrimethylsilane (TMSCl)-mediated cascade phosphorylation and cycloisomerization of enynones with diphenylphosphine oxides is presented. This methodology enables the highly selective synthesis of monophosphorylated 2H-pyrans and bisphosphorylated dihydropyrans through precise solvent-reagent stoichiometry control. The strategy demonstrated excellent functional group compatibility and high yields (up to 96%), providing facile access to structurally diverse phosphorylated heterocycles with potential applications in medicinal chemistry and materials science.

Copper-Catalyzed Enantioselective Hydrophosphorylation of Unactivated Alkynes

P-stereogenic phosphorus compounds are essential across various fields, yet their synthesis via enantioselective P-C bond formation remains both challenging and underdeveloped. We report the first copper-catalyzed enantioselective hydrophosphorylation of alkynes, facilitated by a newly designed chiral 1,2-diamine ligand. Unlike previous methods that rely on kinetic resolution with less than 50 % conversion, our approach employs a distinct dynamic kinetic asymmetric transformation mechanism, achieving complete conversion of racemic starting materials. This reaction is compatible with a broad range of aromatic and aliphatic terminal alkynes, producing products with high yields (up to 95 %), exclusive cis selectivity, and exceptional regio- and enantioselectivity (>20 : 1 r.r. and up to 96 % ee). The resulting products were further transformed into a diverse array of enantioenriched P-stereogenic scaffolds. Preliminary mechanistic studies were conducted to elucidate the reaction details.

Asymmetric Conjugate Addition of Phosphine Sulfides to α-Substituted β-Nitroacrylates Using Cinchona Alkaloid Amide Catalysts

Chiral phosphine-containing amino acids are useful motifs in pharmaceutical compounds. In this study, we developed the asymmetric conjugate addition of phosphine sulfides with α-substituted β-nitroacrylates to synthesize phosphine-containing amino acid precursors with chiral tetrasubstituted carbon centers. This method showed a wide substrate scope, and the obtained products were converted into various chiral compounds. The origin of the enantioselectivity was clarified by computational analysis.

Highly regio- and stereoselective (3 + 2) annulation reaction of allenoates with 3-methyleneindolin-2-ones catalyzed by a planar chiral [2.2]paracyclophane-based bifunctional phosphine-phenol catalyst

A planar chiral [2.2]paracyclophane-based phosphine-phenol catalyst catalyzed the (3 + 2) annulation reaction of ethyl 2,3-butadienoate with 3-methyleneindolin-2-ones to produce 2,5-disubstituted cyclopentene-fused C3-spirooxindoles in high yields with high regio-, diastereo-, and enantioselectivities. This catalyst was suitable for reactions of not only benzylideneindolinones but also alkylideneindolinones, the chiral phosphine-catalyzed reactions of which have not yet been reported. Density functional theory calculations suggested that the formation of hydrogen bonds between the phenolic OH group of the catalyst and the allenoate carbonyl group, rather than between the OH group and the carbonyl group of indolinone, contributed to the formation of an efficient reaction space at the enantiodetermining step.

Mechanochemistry for Organic and Inorganic Synthesis

In recent years, mechanochemistry has become an innovative and sustainable alternative to traditional solvent-based synthesis. Mechanochemistry rapidly expanded across a wide range of chemistry fields, including diverse organic compounds and active pharmaceutical ingredients, coordination compounds, organometallic complexes, main group frameworks, and technologically relevant materials. This Review aims to highlight recent advancements and accomplishments in mechanochemistry, underscoring its potential as a viable and eco-friendly alternative to conventional solution-based methods in the field of synthetic chemistry.

Spirocyclopropanes and Substituted Furans by Controlling Reactivity of 1,3-Enynoates: γ- and δ-Addition of Phosphines to Conjugate Acceptors

In the Morita-Baylis-Hillman (MBH) reaction, a nucleophile undergoes β-addition to activated alkenes or alkynes, forming reactive intermediates for subsequent carbon-carbon or carbon-hetero bond formation. By using a π-conjugated acceptor, however, an unprecedented reactivity of 1,3-enynoates and indane-1,3-diones was uncovered in the presence of phosphines. When indan-1,3-diones were used, γ-addition of phosphines to 1,3-enynoates was observed for the first time; moderate to good yields were obtained for 14 substances containing the prominent spirocyclopropane scaffold with 100 % retention of (Z)-alkene. When 2-methyl-indan-1,3-diones were used, di(tri)-substituted furans were produced through the δ-addition pathway, with 20 substances and a yield of up to 88 % being achieved. Control experiments and density functional theory calculations were conducted to obtain insights into the unconventional γ-addition reaction pathway.

Phosphine-catalyzed enantioselective and diastereodivergent [3+2] cyclization for the construction of oxetane dispirooxindole skeletons

We have developed a phosphine catalyzed asymmetric [3+2] cyclization of 3-oxetanone derived MBH carbonates with activated methyleneoxindole, to construct oxetane dispirooxindole skeletons. Diastereodivergent synthesis was realized via the control of the phosphine catalyst. The (-)-DIOP provides the syn diastereoisomers, while the spiro phosphine (R)-SITCP achieves the anti-epimers.

Enantioselective Synthesis of Cyclopentanes by Phosphine-Catalyzed β,γ-Annulation of Allenoates

Herein, we report the enantioselective phosphine-catalyzed β,γ-annulation of electron-poor allenes with bifunctional malonates. The reaction exploits a 2C phosphonium synthon that when accessed using (R)-SITCP gives 23 cyclopentanes with high stereoselectivity (most >95:5 er and >9:1 dr) and yield. In addition to the (3+2) annulation, a one-pot three-component variant to give the same cyclopentanes and a (3+2) annulation/Dieckmann cyclization cascade, along with mechanistic studies, are reported.

Pyridine-Catalyzed Chemoselective Four-Component Cascade Reaction of Aromatic Aldehydes, Malononitrile/Cyanoacetates, MBH Carbonates, and Alcohols

An efficient pyridine-catalyzed chemoselective four-component cascade reaction of aromatic aldehydes, malononitrile/cyanoacetates, Morita-Baylis-Hillman (MBH) carbonates, and alcohols has been established. This one-pot reaction progressed in an unusual reaction with solvent participation via a Knoevenagel condensation/oxa-Michael addition/SN2' substitution sequence. This method allowed for facile access to an array of functionalized chain alkylbenzenes and dihydroquinolinones bearing one all-carbon quaternary center in moderate to excellent yields. It is worth noting that the configuration of the all-carbon quaternary center could be modulated by changing only the electron-withdrawing groups via a tandem reduction/cyclization reaction.

Rapid Construction of Cycloheptatriene through Organocatalyzed [4 + 3] Annulation of Coumalates

A protocol for the construction of cycloheptatrienes has been developed. 4-(Dimethylamino)pyridine (DMAP) was found to be an efficient catalyst to promote the [4 + 3] annulation between coumalates and γ-alkyl-substituted allenoate or γ-aryl-3-butynoates to deliver a variety of cycloheptatrienes in moderate to good yield with excellent chemoselectivity. The asymmetric version of this annulation was also realized by using bifunctional phosphine catalyst to provide the chiral products with 32-97% ee and 29-64% yield.

Diastereoselective and Enantioselective Hydrophosphinylations of Conjugated Enynes, Allenes and Dienes via Synergistic Pd/Co Catalysis

Different from the reported work focusing on the construction of single P- or C-stereocenter via hydrophosphinylation of unsaturated carbon bonds, the highly diastereo- and enantioselective hydrophosphinylation reaction of allenes, conjugated enynes and 1,3-dienes is achieved via a designed Pd/Co dual catalysis and newly modified masked phosphinylating reagent. A series of allyl motifs bearing both a tertiary C- and P-stereocenter are prepared in generally good yields, >20 : 1 dr, >20 : 1 rr and 99 % ee. The unprecedented diastereo- and enantioselective hydrophosphinylation of 1,3-enynes is established to generate skeletons containing both a P-stereocenter and a nonadjacent chiral axis. The first stereodivergent hydrophosphinylation reaction is also developed to achieve all four P-containing stereoisomers. The present protocol features the use of only 3-minutes reaction time and 0.1 % catalyst, and with the observation of up to 730 TON. A set of mechanistic studies reveal the necessity and roles of two metal catalysts and corroborate the designed synergistic process.

Atroposelective Arene-Forming Wittig Reaction by Phosphorus PIII/PV=O Redox Catalysis

The Wittig reaction is renowned as exceptionally versatile method for converting a diversity of aldehydes and ketones into alkenes. Recently, strategies for chiral phosphine catalysis under PIII/PV=O redox cycling emerged to render this venerable transformation stereoselective. Herein, we describe that phosphine redox catalysis enables the enantioselective synthesis of pertinent biaryl atropisomers by means of a stereocontrolled arene-forming Wittig reaction. Key to the process is the release of an endogenous base from readily accessible tert-butyloxycarbonylated Morita-Baylis-Hillman adducts triggered by catalyst intramolecularization, permitting mild phosphine redox catalysis for atroposelective Wittig reactions. By this strategy, a broad diversity of biaryl atropisomers is obtained with up to 94 : 6 enantioselectivity.

Radical-Based Enantioconvergent Reductive Couplings of Racemic Allenes and Aldehydes

Transition metal-catalyzed radical-based enantioconvergent reactions have become a powerful strategy to synthesize enantiopure compounds from racemic starting materials. However, existing methods primarily address precursors with central chirality, neglecting those with axial chirality. Herein, we describe the enantioconvergent reductive coupling of racemic allenes with aldehydes, facilitated by a photoredox, chromium, and cobalt triple catalysis system. This method selectively affords one product from sixteen possible regio- and stereoisomers. The protocol leverages CoIII-H mediated hydrogen atom transfer (MHAT) and Cr-catalyzed radical-polar crossover for efficient stereoablation of axial chirality and asymmetric addition, respectively. Supported by mechanistic insights from control experiments, deuterium labeling, and DFT calculations, our approach offers synthetic chemists a valuable tool for creating enantioenriched chiral homoallylic alcohols, promising to advance radical-based strategies for synthesizing complex chiral molecules.

Copper-Catalysed Synthesis of (E)-Allylic Organophosphorus Derivatives: A Low Toxic, Mild, Economical, and Ligand-Free Method

Organophosphorus compounds are fundamental for the chemical industry due to their broad applications across multiple sectors, including pharmaceuticals, agrochemicals, and materials science. Despite their high importance, the sustainable and cost-effective synthesis of organophoshoryl derivatives remains very challenging. Here, we report the first successful regio- and stereoselective hydrophosphorylation of terminal allenamides using an affordable copper catalyst system. This reaction offers an efficient protocol for the synthesis of (E)-allylic organophosphorus derivatives from various types of P-nucleophiles, such as H-phosphonates, H-phosphinates, and secondary phosphine oxides. Key advantages of this ligand-free and atom-economic strategy include low toxicity of the Cu-based catalyst, cost effectiveness, mild reaction conditions, and experimental simplicity, making it competitive with methods that use toxic and expensive Pd-based catalysts. In an effort to comprehend this process, we conducted extensive DFT calculations on this system to uncover the mechanistic insights of this process.

Enantioselective Synthesis of Cyclopentenes by (3+2) Annulation via a 2-Carbon Phosphonium

Herein we report a catalytic enantioselective (3+2) annulation, in which a vinyl phosphonium intermediate serves as the 2-carbon component. The reaction involves an α-umpolung β-umpolung coupling sequence, enabled by β-haloacrylates and chiral enantioenriched phosphepine catalysts. The reaction shows good generality, providing access to an array of cyclopentenes, with mechanistic studies supporting stereospecific formation of the vinyl phosphonium intermediate which, then undergoes annulation with turn over limiting catalyst elimination. Beyond defining a new approach to cyclopentenes, these studies demonstrate that β-haloacrylates can replace ynoates in reaction designs that require exclusive umpolung coupling at the α- and β-positions.

Transition from Kwon [4+2]- to [3+2]-cycloaddition enabled by AgF-assisted phosphine catalysis

Phosphine catalysis generally relies on the potential of carbanion-phosphonium zwitterions that are generated via nucleophilic addition of phosphine catalyst to electrophilic reactants. Consequently, structural modification of zwitterions using distinct electrophilic reactants has emerged as a prominent strategy to enhance catalysis diversity. Herein, we present an alternative strategy that utilizes AgF additive to expand phosphine catalysis. We find that AgF can readily transform the canonical carbanion-phosphonium zwitterion into silver enolate-fluorophosphorane intermediate, eventually furnishing a P(III)/P(V) catalytic cycle. This strategy has been successfully applied to the phosphine-catalyzed reaction of 2-substituted allenoate and imine, resulting in the transition from Kwon [4 + 2] cycloaddition to [3 + 2] cycloaddition. This [3 + 2] cycloaddition features remarkable diastereoselectivity, high yield, and broad substrate scope. Experimental and computational studies have validated the proposed mechanism. Given the prevalence of carbanion-phosphonium zwitterions in phosphine catalysis, this AgF-assisted strategy is believed to hold significant potential for advancing P(III)/P(V) catalysis.

PPh3-Promoted Direct Deoxygenation of Epoxides to Alkenes

Deoxygenation of epoxides into alkenes is one of the most important strategies in organic synthesis, biomass conversions, and medicinal chemistry. Although metal-catalyzed direct deoxygenation provides one of the most commonly encountered protocols for the conversion of epoxides to alkenes, the requirement of expensive catalysts and extra reductants has largely limited their universal applicability. Herein, we report an efficient PPh3-promoted metal-free strategy for deoxygenation of epoxides to generate alkene derivatives. The success of deoxyalkenylation of epoxides bearing a wide range of functional groups to give terminal, 1,1-disubstituted, and 1,2-disubstituted alkenes manifests the powerfulness and versatility of this strategy. Moreover, gram-scale synthesis with excellent yield and modification of biologically active molecules exemplifies its generality and practicability.

Phosphine vs DBU-Catalyzed Annulation Reactions of β'-Acetoxy Allenoates with Acyl-Tethered Benzothiazole Bisnucleophiles: (4 + 3) or (4 + 1) vs (3 + 3) Annulation

Dearomative annulation reaction of acyl-tethered benzothiazole bisnucleophiles with β'-acetoxy allenoates by switching the Lewis base is developed. The DBU-catalyzed reaction gives benzothiazole-fused 1,4-dihydropyridine carboxylates by (3 + 3) annulation chemoselectively. By contrast, the PR3-catalyzed reaction gives benzothiazole-fused azepines by (4 + 3) annulation and cyclopentene carboxylates by (4 + 1) annulation; the ratio of the latter two products depends on the solvent. A possible rationale for the difference in the reactivity, based on the 1,4/1,5-addition of the 2-acyl-tethered benzothiazole to the key phosphonium intermediate, is provided.

Catalytic (4+2) Annulation via Regio- and Enantioselective Interception of in-situ Generated Alkylgold Intermediate

A regio- and stereoselective stepwise (4+2) annulation of N-propargylamides and α,β-unsaturated imines/ketones has been accomplished with synergetic catalysis by a combination of a gold-complex and a chiral quinine-derived squaramide (QN-SQA), leading to highly functionalized chiral tetrahydropyridines/dihydropyrans in good to high yields with generally excellent enantioselectivity. Mechanistic studies and DFT calculations indicate that the in situ formed alkylgold species is the key intermediate in this transformation, and the amide group served as a traceless directing group in this highly selective transformation. This method complements the enantioselective (4+2) annulation of allene reagents, providing the formal internal C-C π-bond cycloaddition products, which is challenging and remains elusive.

Enantioselective phosphine-catalyzed [6 + 1] annulations of α-allyl allenoates with 1,1-bisnucleophiles

Organocatalytic annulations between allenes and bisnucleophiles represent one of the most convenient routes to various carbocycles and heterocycles. However, most examples are limited to the formation of five- and six-membered rings, probably owing to relatively easy handling of short-chained biselectrophiles. Here we report long-chained α-allyl allenoate-derived 1,6-biselectrophiles for the first time, enabling a phosphine catalyzed [6 + 1] annulation with readily available 1,1-bisnucleophilic reagents. The reaction proceeds via a tandem γ-umpolung addition and δ'-addition process, smoothly constructing both seven-membered N-heterocycles and carbocycles with a broad scope of substrates, high atom economy and excellent enantioselectivity (up to 99% yield and up to 96% ee). Mechanistic experiments revealed a conversion of the 1,6-dipole into a 1,6-biselectrophilic intermediate through proton abstraction.

Palladium-Catalyzed Asymmetric Desymmetrization for the Simultaneous Construction of Chiral Phosphorus and Quaternary Carbon Stereocenters

A palladium-catalyzed asymmetric tandem Heck and carbonylation of bisallyl-phosphine oxides has been developed. This desymmetrization process provided an efficient route to the simultaneous synthesis of a chiral P-stereogenic center and a chiral quaternary carbon stereocenter in good yields with good diastereo- and enantioselectivities.

Phosphine-Catalyzed Ring-Opening Regioselective Addition of Cyclopropenones with Amides

A series of amides, including α-bromo hydroxamates, N-alkoxyamides, and N-aryloxyamides, were subjected to phosphine-catalyzed ring-opening O-selective addition with cyclopropenones, producing various special α,β-unsaturated esters containing oxime ether motif, in moderate to excellent yields, with high regioselectivity, and exclusive O-selectivity. The methodology is highly atom-economical, with simple operation procedures, and compatible with a wide substrate scope (more than 44 examples).

Phosphine-promoted intramolecular Rauhut-Currier/Wittig reaction cascade to access (hetero)arene-fused diquinanes

We describe the first phosphine-promoted intramolecular Rauhut-Currier reaction that triggers an intramolecular Wittig process assembling new classes of diquinanes. The one-pot strategy provides ready access to simple diquinanes and various (hetero)arene-fused diquinanes incorporated with up to two contiguous all-carbon quaternary centers under metal-free and neutral conditions. We showcased the generality of the method on a broad range of substrates and demonstrated its synthetic utility in accessing various advanced intermediates relevant to natural product synthesis and material science.

Dual Nickel- and Photoredox-Catalyzed Asymmetric Reductive Cross-Couplings: Just a Change of the Reduction System?

ConspectusIn recent years, nickel-catalyzed asymmetric coupling reactions have emerged as efficient methods for constructing chiral C(sp3) carbon centers. Numerous novel approaches have been reported to rapidly construct chiral carbon-carbon bonds through nickel-catalyzed asymmetric couplings between electrophiles and nucleophiles or asymmetric reductive cross-couplings of two different electrophiles. Building upon these advances, our group has been devoted to interrogating dual nickel- and photoredox-catalyzed asymmetric reductive cross-coupling reactions.In our endeavors over the past few years, we have successfully developed several dual Ni-/photoredox-catalyzed asymmetric reductive cross-coupling reactions involving organohalides. While some probably think that this system is just a change of the reduction system from traditional metal reductants to a photocatalysis system, a question that we also pondered at the beginning of our studies, both the achievable reaction types and mechanisms suggest a different conclusion: that this dual catalysis system has its own advantages in the chiral carbon-carbon bond formation. Even in certain asymmetric reactions where the photocatalysis regime functions only as a reducing system, the robust reducing capability of photocatalysts can effectively accelerate the regeneration of low-valent nickel species, thus expanding the selectable scope of chiral ligands. More importantly, in many transformations, besides reducing nickel catalysts, the photocatalysis system can also undertake the responsibility of alkyl radical formation, thereby establishing two coordinated, yet independent catalytic cycles. This catalytic mode has been proven to play a crucial role in achieving diverse asymmetric coupling reactions with great challenges.In this Account, we elucidate our understanding of this system based on our experience and findings. In the Introduction, we provide an overview of the main distinctions between this system and traditional Ni-catalyzed asymmetric reductive cross-couplings with metal reductants and the potential opportunities arising from these differences. Subsequently, we outline various chiral carbon-carbon bond-forming types obtained by this dual Ni/photoredox catalysis system and their mechanisms. In terms of chiral C(sp3)-C(sp2) bond formation, extensive discussion focuses on the asymmetric arylations of α-chloroboronates, α-trifluoromethyl alkyl bromides, α-bromophosphonates, and so on. In the realm of chiral C(sp3)-C(sp) bond formation, asymmetric alkynylations of α-bromophosphonates and α-trifluoromethyl alkyl bromides have been presented herein. Regarding C(sp3)-C(sp3) bond formation, we take the asymmetric alkylation of α-chloroboronates as a compelling example to illustrate the great efficiency of this dual catalysis system. This summary would enable a better grasp of the advantages of this dual catalysis system and clarify how the photocatalysis regime facilitates enantioselective transformations. We anticipate that this Account will offer valuable insights and contribute to the development of new methodologies in this field.

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.

Phosphine-catalyzed (3+3) annulation of cinnamaldehyde-derived Morita-Baylis-Hillman carbonates with dinucleophiles

The phosphine-catalyzed (3+3) annulation reaction of cinnamaldehyde-derived Morita-Baylis-Hillman (MBH) carbonates with 1,3-dicarbonyl compounds as dinucleophiles has been developed, giving hexahydrochromenone derivatives in high yields with moderate to good diastereoselectivities. The reaction worked through double conjugate addition of 1,3-dicarbonyl compounds to the phosphonium intermediates generated from the cinnamaldehyde-derived MBH carbonates.

Phosphine-catalyzed dearomative [3+2] cycloaddition of 4-nitroisoxazoles with allenoates or Morita-Baylis-Hillman carbonates

An efficient phosphine-catalyzed dearomative [3+2] annulation of 4-nitroisoxazoles with allenoates or Morita-Baylis-Hillman carbonates has been established for the convenient synthesis of bicyclic isoxazoline derivatives. This reaction approach showed a broad substrate scope, high functional group compatibility, and excellent regioselectivity and diastereoselectivity. Furthermore, the success at the gram-scale and synthetic applications of the obtained compound 3a demonstrate the great potential of this methodology for practical applications in organic synthesis.

Facile synthesis of 2-vinylindolines via a phosphine-mediated α-umpolung/Wittig olefination/cyclization cascade process

A novel phosphine-mediated α-umpolung/Wittig olefination/cyclization cascade process between o-aminobenzaldehydes and Morita-Baylis-Hillman (MBH) carbonates has been ingeniously developed. This protocol serves as a practical tool for the facile synthesis of a broad range of 2-vinylindolines in moderate to good yields under mild reaction conditions. The applicability of this method was demonstrated with gram-scale reaction and various transformations of the corresponding product.

Synthesis of 3,4-Disubstituted Maleimide Derivatives via Phosphine-Catalyzed Isomerization of α-Succinimide-Substituted Allenoates Cascade γ'-Addition with Aryl Imines

3,4-disubstituted maleimides find wide applications in various pharmacologically active compounds. This study presents a highly effective approach for synthesizing derivatives of 3,4-disubstituted maleimides through the direct isomerization of α-succinimide-substituted allenoates, followed by a cascade γ'-addition and aryl imines using PR3 as a catalyst. The resulting series of 3,4-disubstituted maleimides exhibited excellent stereoselectivities, achieving yields of up to 86%. To our knowledge, the phosphine-mediated γ'-addition reaction of allenoates is seldom reported.

Phosphine-Catalyzed Stereospecific and Enantioselective Desymmetrizative [3+2] Cycloaddition of MBH Carbonates and N-(2-tert-Butylphenyl)maleimides

Herein, we report an l-valine-derived amide phosphine-catalyzed [3+2] cyclization of MBH carbonates and N-(2-tert-butylphenyl)maleimides via asymmetric desymmetrization. Bicyclic N-aryl succinimide derivatives bearing three continuous chiral centers with a remote C-N atropisomeric chirality were constructed stereospecifically and enantioselectively. A wide variety of MBH carbonates could be employed in this process to deliver highly optically pure succinimide derivatives in moderate to excellent yields.

Photoredox-catalyzed C(sp3)─H radical functionalization to enable asymmetric synthesis of α-chiral alkyl phosphine

α-Chiral alkyl phosphines are privileged structural motifs with a wide application in organic and medical synthesis. It is highly desirable to develop stereoselective methods to prepare these enantioenriched molecules. The incorporation of C(sp3)─H functionalization and chiral phosphine chemistry is much less explored, probably because of the weak reactivity of C(sp3)─H bonds and/or the challenging site- and stereoselectivity issues. Herein, we disclose a synergistic catalysis system to enable an enantioselective radical addition process of α-substituted vinylphosphine oxides. An array of diverse α-chiral alkyl phosphors compounds is smoothly accessed by using the readily available chemicals as the inert C(sp3)─H bond reagent, such as sulfides, amines, alkenes, and toluene derivatives, exerting remarkable chemo-, site-, and enantioselectivity. On the basis of the mechanistic studies, both the C(sp3)─H bond activation and the stereochemistry-determining step are proposed to involve a single-electron transfer/proton transfer process.

Phosphine-Catalyzed γ'-Carbon 1,6-Conjugate Addition of α-Succinimide Substituted Allenoates with Para-Quinone Methides: Synthesis of 4-Diarylmethylated 3,4-Disubstituted Maleimides

In this paper, an interesting γ'-carbon 1,6-conjugate addition for phosphine-catalyzed α-succinimide substituted allenoates has been disclosed. A wide array of substrates was found to participate in the reaction, resulting in the production of diverse 4-diarylmethylated 3,4-disubstituted maleimides with satisfactory to outstanding yields. Furthermore, a plausible mechanism for the reaction was proposed by the investigators.

Visible-Light-Induced Regioselective Radical-Polar Crossover 1,4-Hydrophosphinylation of 1,3-Enynes: Access to Trisubstituted Allenes Bearing a Phosphine Oxide Group

The radical 1,4-functionalizations of 1,3-enynes have emerged as a powerful strategy for the synthesis of multisubstituted allenes. However, the phosphorus-centered radical-initiated transformations remain largely elusive. Herein, visible-light photoredox catalytic regioselective radical hydrophosphinylation of 1,3-enynes with diaryl phosphine oxides as phosphinoyl radical precursors has been realized. This protocol features mild conditions, a wide substrate scope, and good functional group tolerance, producing a diverse range of phosphinoyl-substituted allenes in moderate to good yields with high atom economy. Detailed mechanistic experiments revealed a radical-polar crossover process in the reaction.

Metal-Free Enantioselective 1,4-Addition of Diarylphosphine Oxides to α,β-Unsaturated Carboxylic Esters

The catalytic asymmetric conjugate addition of phosphorus nucleophiles to unsaturated compounds, catalyzed by metallic or nonmetallic catalysts, has been extensively developed. However, the enantioselective transformations involving α,β-unsaturated carboxylic esters for constructing chiral c-p bonds have been rarely reported, particularly in metal-free processes. In this study, we present a novel metal-free methodology for enantioselective 1,4-addition of diarylphosphine oxides to α,β-unsaturated carboxylic esters using classical chiral oxazaborolidine catalysts. Remarkably high yields and enantioselectivities were obtained for most of the products. Furthermore, these valuable chiral phosphorus esters serve as crucial intermediates that can be transformed into various derivatives including amides, acids, and alcohols in a single step.

Chiral Bisphosphine-Catalyzed Asymmetric Staudinger/aza-Wittig Reaction: An Enantioselective Desymmetrizing Approach to Crinine-Type Amaryllidaceae Alkaloids

An unprecedented chiral bisphosphine-catalyzed asymmetric Staudinger/aza-Wittig reaction of 2,2-disubstituted cyclohexane-1,3-diones is reported, enabling the facile access of a broad range of cis-3a-arylhydroindoles in high yields with excellent enantioselectivities. The key to the success of this work relies on the first application of chiral bisphosphine DuanPhos to the asymmetric Staudinger/aza-Wittig reaction. An effective reductive system has been established to address the challenging PV═O/PIII redox cycle associated with the chiral bisphosphine catalyst. In addition, comprehensive experimental and computational investigations were carried out to elucidate the mechanism of the asymmetric reaction. Leveraging the newly developed chemistry, the enantioselective total syntheses of several crinine-type Amaryllidaceae alkaloids, including (+)-powelline, (+)-buphanamine, (+)-vittatine, and (+)-crinane, have been accomplished with remarkable conciseness and efficiency.

Combined Computational and Experimental Study Reveals Complex Mechanistic Landscape of Brønsted Acid-Catalyzed Silane-Dependent P═O Reduction

The reaction mechanism of Brønsted acid-catalyzed silane-dependent P═O reduction has been elucidated through combined computational and experimental methods. Due to its remarkable chemo- and stereoselective nature, the Brønsted acid/silane reduction system has been widely employed in organophosphine-catalyzed transformations involving P(V)/P(III) redox cycle. However, the full mechanistic profile of this type of P═O reduction has yet to be clearly established to date. Supported by both DFT and experimental studies, our research reveals that the reaction likely proceeds through mechanisms other than the widely accepted "dual activation mode by silyl ester" or "acid-mediated direct P═O activation" mechanism. We propose that although the reduction mechanisms may vary with the substitution patterns of silane species, Brønsted acid generally activates the silane rather than the P═O group in transition structures. The proposed activation mode differs significantly from that associated with traditional Brønsted acid-catalyzed C═O reduction. The uniqueness of P═O reduction originates from the dominant Si/O═P orbital interactions in transition structures rather than the P/H-Si interactions. The comprehensive mechanistic landscape provided by us will serve as a guidance for the rational design and development of more efficient P═O reduction systems as well as novel organophosphine-catalyzed reactions involving P(V)/P(III) redox cycle.

Phosphine-Catalyzed Domino Annulation of γ-Vinyl Allenoates: Synthesis of Tetrahydrofuro[3,2-c]quinoline Derivatives

A novel phosphine-catalyzed domino annulation reaction of γ-vinyl allenoates and o-aminotrifluoacetophenones for the construction of terahydrofuro[3,2-c]quinoline derivatives has been developed. In this domino reaction, two kinds of terahydrofuro[3,2-c]quinoline compounds containing CF3 groups were obtained with good yields under mild conditions, three new C-N, C-C, and C-O bonds can be built in one step, and the reaction selectivity is achieved by adjusting the reaction conditions. Furthermore, preliminary studies on an asymmetric variant of this reaction proceeded with moderate enantioselectivity.

Phosphine-Catalyzed (4 + 2) Annulation of Allenoates Bearing Acidic Hydrogen with 1,1-Dicyanoalkenes

α-succinimide-substituted allenoates were employed as phosphine acceptors in phosphine-catalyzed (4 + 2) annulation with 1,1-dicyanoalkenes. They served as C4 synthons in the annulation reaction under mild reaction conditions and produced hexahydroisoindole derivatives in moderate to high yields with good to excellent diastereoselectivities.

Enantioselective copper-catalyzed B-H bond insertion reaction of α-diazo phosphonates to access chiral α-boryl phosphonates

Chiral phosphorus-containing compounds find applications across various fields, including asymmetric catalysis, medicinal chemistry, and materials science. Despite the abundance of reported highly enantioselective methods for synthesizing various chiral phosphorus compounds, the enantioselective synthesis of α-boryl phosphorus compounds still remains an unknown territory. Here, we report a method for the construction of chiral α-boryl phosphates by asymmetric B-H insertion reaction using α-diazo phosphates as carbene precursors, cheap and readily available copper salt as the catalyst and chiral oxazoline as the ligand. This method can directly afford a series of stable α-boryl phosphates with a yield up to 97% and an enantioselectivity up to 98% ee. The operating procedure of this method is straightforward, offering a broad substrate applicability, remarkable tolerance towards various functional groups, and gentle reaction conditions.

Kinetic Resolution of P-Chiral Phosphindole Oxides through Rhodium-Catalyzed Asymmetric Arylation

Highly efficient kinetic resolution of P-chiral phosphindole oxides via rhodium-catalyzed asymmetric arylation under mild conditions is described. Selectivity factors of up to 569 were achieved by employing chiral diene* as a ligand. The transformation of the enantiopure benzophosphole derivative into a useful P-chiral bisphosphine ligand is also demonstrated.