Biaryl phosphane ligands in palladium-catalyzed amination

Synthesis of Azacarbolines via PhIO2-Promoted Intramolecular Oxidative Cyclization of α-Indolylhydrazones

An unprecedented synthesis of polysubstituted indole-fused pyridazines (azacarbolines) from α-indolylhydrazones under oxidative conditions using a combination of iodylbenzene (PhIO₂) and trifluoroacetic acid (TFA) has been developed. This transformation is conducted without the need for transition metals, harsh conditions, or an inert atmosphere.

Formation of the Tertiary Sulfonamide C(sp3)-N Bond Using Alkyl Boronic Ester via Intramolecular and Intermolecular Copper-Catalyzed Oxidative Cross-Coupling

A synthetic strategy for the formation of C(sp³)-N bonds, particularly through a copper-catalyzed oxidative cross-coupling, is rare. Herein, we report a novel synthetic approach for the preparation of tertiary sulfonamides via copper-catalyzed intra- and intermolecular oxidative C(sp³)-N cross-coupling reactions. This method allows the utilization of the readily available C(sp³)-based pinacol boronate as a substrate and the tolerance of a wide range of functional groups under mild reaction conditions. The success of this strategy relies on the unprecedented additive effects of silanol and NaIO₄.

Electrophilic Aminating Agents in Total Synthesis

Classical amination methods involve the reaction of a nitrogen nucleophile with an electrophilic carbon center; however, in recent years, umpoled strategies have gained traction where the nitrogen source acts as an electrophile. A wide range of electrophilic aminating agents are now available, and these underpin a range of powerful C-N bond-forming processes. In this Review, we highlight the strategic use of electrophilic aminating agents in total synthesis.

Transition metal complexes with functionalized indenyl phosphine ligands: structures and catalytic properties

Transition-metal indenyl complexes usually exhibit different reactivities compared with their cyclopentadienyl analogues. Up to now, at least 10 metal-indenyl bonding modes have been reported. Because of the "indenyl effect", transition-metal indenyl complexes usually show enhanced reactivity in substitution and related reactions. This review provides an overview on the use and impact of indenyl phosphines in organometallic chemistry and transition-metal-catalysed reactions in the recent two decades. Some cationic and zwitterionic metal complexes supported by P,N-substituted indene or indenide ligands are described. They have been reported to induce the cleavage of E-H (E = H, Si and B) bonds and can be used as catalysts for addition of E-H bonds to unsaturated substrates. 2-Aryl indenyl phosphine ligands L3-L11 have been proven to be a class of versatile ligands for palladium-catalysed C-C and C-N cross-coupling reactions. Moreover, optically active tethered indenyl phosphine ligands can have better stereoselective control over the chirality arising at the metal center in the oxidative addition of their rhodium complexes with alkyl halides.

Dehydrogenative Azolation of Arenes in a Microflow Electrochemical Reactor

The electrochemical synthesis of aryl azoles was performed for the first time in a microflow reactor. The reaction relies on the anodic oxidation of the arene partners making these substrates susceptible for C–H functionalization with azoles, thus requiring no homogeneous transition-metal-based catalysts. The synthetic protocol benefits from the implementation of a microflow setup, leading to shorter residence times (10 min), compared to previously reported batch systems. Various azolated compounds (22 examples) are obtained in good to excellent yields.

Electrochemical C-H phosphorylation of arenes in continuous flow suitable for late-stage functionalization

The development of efficient and sustainable methods for carbon-phosphorus bond formation is of great importance due to the wide application of organophosphorus compounds in chemistry, material sciences and biology. Previous C-H phosphorylation reactions under nonelectrochemical or electrochemical conditions require directing groups, transition metal catalysts, or chemical oxidants and suffer from limited scope. Herein we disclose a catalyst- and external oxidant-free, electrochemical C-H phosphorylation reaction of arenes in continuous flow for the synthesis of aryl phosphorus compounds. The C-P bond is formed through the reaction of arenes with anodically generated P-radical cations, a class of reactive intermediates remained unexplored for synthesis despite intensive studies of P-radicals. The high reactivity of the P-radical cations coupled with the mild conditions of the electrosynthesis ensures not only efficient reactions of arenes of diverse electronic properties but also selective late-stage functionalization of complex natural products and bioactive compounds. The synthetic utility of the electrochemical method is further demonstrated by the continuous production of 55.0 grams of one of the phosphonate products.

Buchwald-Hartwig Amination of Coordinating Heterocycles Enabled by Large-but-Flexible Pd-BIAN-NHC Catalysts*

A new class of large-but-flexible Pd-BIAN-NHC catalysts (BIAN=acenaphthoimidazolylidene, NHC=N-heterocyclic carbene) has been rationally designed to enable the challenging Buchwald-Hartwig amination of coordinating heterocycles. This robust class of BIAN-NHC catalysts permits cross-coupling under practical aerobic conditions of a variety of heterocycles with aryl, alkyl, and heteroarylamines, including historically challenging oxazoles and thiazoles as well as electron-deficient heterocycles containing multiple heteroatoms with BIAN-INon (N,N'-bis(2,6-di(4-heptyl)phenyl)-7H-acenaphtho[1,2-d]imidazol-8-ylidene) as the most effective ligand. Studies on the ligand structure and electronic properties of the carbene center are reported. The study should facilitate the discovery of even more active catalyst systems based on the unique BIAN-NHC scaffold.

Visible-Light- and PPh3-Mediated Direct C-N Coupling of Nitroarenes and Boronic Acids at Ambient Temperature

We present here a metal-free, visible-light- and triphenylphosphine-mediated intermolecular, reductive amination between nitroarenes and boronic acids at ambient temperature without any photocatalyst. Mechanistically, a slow reduction of nitroarenes to a nitroso and, finally, a nitrene intermediate occurs that leads to the amination product with concomitant 1,2-aryl/-alkyl migration from a boronate complex. A wide range of nitroarenes underwent C-N coupling with aryl-/alkylboronic acids providing high yields.

Cleavage via Selective Catalytic Oxidation of Lignin or Lignin Model Compounds into Functional Chemicals

Lignin, a complex aromatic polymer with different types of methoxylated phenylpropanoid connections, enables the sustainable supply of value-added chemicals and biofuels through its use as a feedstock. Despite the development of numerous methodologies that upgrade lignin to high-value chemicals such as drugs and organic synthesis intermediates, the variety of valuable products obtained from lignin is still very limited, mainly delivering hydrocarbons and oxygenates. Using selective oxidation and activation cleavage of lignin, we can obtain value-added aromatics, including phenols, aldehydes, ketones, and carboxylic acid. However, biorefineries will demand a broad spectrum of fine chemicals in the future, not just simple chemicals like aldehydes and ketones containing simple C = O groups. In particular, most n-containing aromatics, which have found important applications in materials science, agro-chemistry, and medicinal chemistry, such as amide, aniline, and nitrogen heterocyclic compounds, are obtained through n-containing reagents mediating the oxidation cleavage in lignin. This tutorial review provides updates on recent advances in different classes of chemicals from the catalytic oxidation system in lignin depolymerization, which also introduces those functionalized products through a conventional synthesis method. A comparison with traditional synthetic strategies reveals the feasibility of the lignin model and real lignin utilization. Promising applications of functionalized compounds in synthetic transformation, drugs, dyes, and textiles are also discussed.

Ligand-Controlled Regiodivergence for Catalytic Stereoselective Semireduction of Allenamides

Ligand-controlled regiodivergence has been developed for catalytic semireduction of allenamides with excellent chemo- and stereocontrol. This system also provides an example of catalytic regiodivergent semireduction of allenes for the first time. The divergence of the semireduction is enabled by ligand switch with the same palladium pre-catalyst under operationally simple and mild conditions. Monodentate ligand XPhos exclusively promotes selective 1,2-semireduction to afford allylic amides, while bidentate ligand BINAP completely switched the regioselectivity to 2,3-semireduction, producing (E)-enamide derivatives.

Highly Efficient Production of Heteroarene Phosphonates by Dichromatic Photoredox Catalysis

A new strategy to achieve efficient aerobic phosphorylation of five-membered heteraroenes with excellent yields using dichromatic photoredox catalysis in a gel-based nanoreactor is described here. The procedure involves visible aerobic irradiation (cold white LEDs) of a mixture containing the heteroarene halide, trisubstituted phospite, N,N-diisopropylethylamine (DIPEA) as sacrificial agent, and catalytic amounts of 9,10-dicyanoanthracene (DCA) in the presence of an adequate gelator, which permits a faster process than at the homogeneous phase. The methodology, which operates by a consecutive photoinduced electron transfer (ConPET) mechanism, has been successfully applied to the straightforward and clean synthesis of a number of different heteroarene (furan, thiophene, selenophene, pyrrole, oxazole, or thioxazole) phosphonates, extending to the late-stage phosphonylation of the anticoagulant rivaroxaban. Strategically, employment of cold white light is critical since it provides both selective wavelengths for exciting first DCA (blue region) and subsequently its corresponding radical anion DCA^•- (green region). The resultant strongly reducing excited agent DCA^•-* is capable of even activate five-membered heteroarene halides (Br, Cl) with high reduction potentials (∼-2.7 V) to effect the C(sp²)-P bond formation. Spectroscopic and thermodynamic studies have supported the proposed reaction mechanism. Interestingly, the rate of product formation has been clearly enhanced in gel media because reactants can be presumably localized not only in the solvent pools but also through to the fibers of the viscoelastic gel network. This has been confirmed by field-emission scanning electron microscopy images where a marked densification of the network has been observed, modifying its fibrillary morphology. Finally, rheological measurements have shown the resistance of the gel network to the incorporation of the reactants and the formation of the desired products.

Transient Directing Groups in Metal-Organic Cooperative Catalysis

The direct functionalization of C-H bonds is among the most fundamental chemical transformations in organic synthesis. However, when the innate reactivity of the substrate cannot be utilized for the functionalization of a given single C-H bond, this selective C-H bond functionalization mostly relies on the use of directing groups that allow bringing the catalyst in close proximity to the C-H bond to be activated and these directing groups need to be installed before and cleaved after the transformation, which involves two additional undesired synthetic operations. These additional steps dramatically reduce the overall impact and the attractiveness of C-H bond functionalization techniques since classical approaches based on substrate pre-functionalization are sometimes still more straightforward and appealing. During the past decade, a different approach involving both the in situ installation and removal of the directing group, which can then often be used in a catalytic manner, has emerged: the transient directing group strategy. In addition to its innovative character, this strategy has brought C-H bond functionalization to an unprecedented level of usefulness and has enabled the development of remarkably efficient processes for the direct and selective introduction of functional groups onto both aromatic and aliphatic substrates. The processes unlocked by the development of these transient directing groups will be comprehensively overviewed in this review article.

Site-Selective Molecular Transformation: Acylation of Hydroxy Groups and C-H Amination

Control of site selectivity is an exciting direction for synthetic organic chemistry owing to the possibility of selective modification of multifunctionalized molecules, ultimately including biomacromolecules. In this review, our recent research related to site selectivity in two types of transformation, namely, the acylation of hydroxy groups and C-H amination, is summarized. Regarding the acylation of hydroxy groups, catalyst-controlled site selectivity enables unconventional retrosynthetic analysis, leading to efficient syntheses of sugar-related natural and unnatural products. Regarding C-H amination, the discovery of unprecedented reaction sites in intermolecular amination mediated by dirhodium nitrenes is described. The findings of this research demonstrate the power of site-selective transformation in the synthesis of a particular class of compounds.

C-Boron Enolates Enable Palladium Catalyzed Carboboration of Internal 1,3-Enynes

A new family of carbon-bound boron enolates, generated by a kinetically controlled halogen exchange between chlorocatecholborane and silylketene acetals, is described. These C-boron enolates are demonstrated to activate 1,3-enyne substrates in the presence of a Pd⁰ /Senphos ligand complex, resulting in the first examples of a carboboration reaction of an alkyne with enolate-equivalent nucleophiles. Highly substituted dienyl boron building blocks are produced in excellent site-, regio-, and diastereoselectivity by the described catalytic cis-carboboration reaction.

Electrochemical phenothiazination of naphthylamines and its application in photocatalysis

N-Phenylphenothiazine as an inexpensive, highly reductive and oxygen tolerant organophotocatalyst has exhibited potential in various challenging photochemical transformations. Here we report a general and straightforward method to access structurally diverse N-phenylphenothiazine derivatives by means of a novel electrochemical tool. The introduction of a 2-naphthylamine moiety with an extended π-system and an amine group led to the variation of spectral characterization. Photochemical verification experiments demonstrated that the formed N-arylation products with good efficacy and chemo/site-control displayed competitive catalytic activity in challenging transformations.

Construction of Bulky Ligand Libraries by Ru(II)-Catalyzed P(III)-Assisted ortho-C-H Secondary Alkylation

Modification of commercially available biaryl monophosphine ligands via ruthenium^(II)-catalyzed P^(III)-directed-catalyzed ortho C-H secondary alkylation is described. The use of highly ring-strained norbornene as a secondary alkylating reagent is the key to this transformation. A series of highly bulky ligands with a norbornyl group were obtained in excellent yields. The modified ligands with secondary alkyl group outperformed common substituted phosphines in the Suzuki-Miyaura cross-coupling reaction at a ppm mole level of Pd catalyst.

Structural trends in a series of bulky dialkylbiarylphosphane complexes of CuI

Cu^I complexes containing the bulky dialkylbiarylphosphane 2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl (^tBuXPhos, L) and an ancillary ligand (Cl^-, Br^-, I^-, MeCN, ClO₄^- or SCN^-) have been structurally characterized, namely, chlorido[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I), [CuCl(C₂₉H₄₅P)], 1, bromido[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I), [CuBr(C₂₉H₄₅P)], 2, [2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]iodidocopper(I), [CuI(C₂₉H₄₅P)], 3, (acetonitrile-κN)[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I) hexafluoridophosphate, [Cu(CH₃CN)(C₂₉H₄₅P)]PF₆, 4, [2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP](perchlorato-κO)copper(I), [Cu(ClO₄)(C₂₉H₄₅P)], 5, and di-μ-thiocyanato-κ²S:N;κ²N:S-bis{[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I)}, [Cu₂(NCS)₂(C₂₉H₄₅P)₂], 6. Iodide complex 3 shows significant Cu^I-arene interactions, in contrast to its chloride 1 and bromide 2 counterparts, which is attributed to the weaker interaction between the iodide ion and the Cu^I centre. When replacing iodide with an acetonitrile (in 4) or perchlorate (in 5) ligand, the reduced interaction between the Cu^I atom and the ancillary ligand results in stronger Cu^I-arene interactions. No Cu^I-arene interactions are observed in dimer 6, due to the tricoordinated Cu^I centre having sufficient electron density from the coordinated ligands.

Synthesis of Indoles via Intermolecular and Intramolecular Cyclization by Using Palladium-Based Catalysts

As part of natural products or biologically active compounds, the synthesis of nitrogen-containing heterocycles is becoming incredibly valuable. Palladium is a transition metal that is widely utilized as a catalyst to facilitate carbon-carbon and carbon-heteroatom coupling; it is used in the synthesis of various heterocycles. This review includes the twelve years of successful indole synthesis using various palladium catalysts to establish carbon-carbon or carbon-nitrogen coupling, as well as the conditions that have been optimized.

Site-Selective Cross-Coupling of Polyhalogenated Arenes and Heteroarenes with Identical Halogen Groups

Methods to functionalize arenes and heteroarenes in a site-selective manner are highly sought after for rapidly constructing value-added molecules of medicinal, agrochemical, and materials interest. One effective approach is the site-selective cross-coupling of polyhalogenated arenes bearing multiple, but identical, halogen groups. Such cross-coupling reactions have proven to be incredibly effective for site-selective functionalization. However, they also present formidable challenges due to the inherent similarities in the reactivities of the halogen substituents. In this Review, we discuss strategies for site-selective cross-couplings of polyhalogenated arenes and heteroarenes bearing identical halogens, beginning first with an overview of the reaction types that are more traditional in nature, such as electronically, sterically, and directing-group-controlled processes. Following these examples is a description of emerging strategies, which includes ligand- and additive/solvent-controlled reactions as well as photochemically initiated processes.

Synthesis of 3-aryl-1-phosphinoimidazo[1,5-a]pyridine ligands for use in Suzuki-Miyaura cross-coupling reactions

3-Aryl-1-phosphinoimidazo[1,5-a]pyridine ligands were synthesized from 2-aminomethylpyridine as the initial substrate via two complementary routes. The first synthetic pathway underwent the coupling of 2-aminomethylpyridine with substituted benzoyl chlorides, followed by cyclization, iodination and palladium-catalyzed cross-coupling phosphination reactions sequence to give our phosphorus ligands. In the second route, 2-aminomethylpyridine was cyclized with aryl aldehydes, followed by the iodination and palladium-catalyzed cross-coupling phosphination reactions to yield our phosphorus ligands. The 3-aryl-1-phosphinoimidazo[1,5-a]pyridine ligands were evaluated in palladium-catalyzed sterically-hindered biaryl and heterobiaryl Suzuki-Miyaura cross-coupling reactions.

Cycloaddition Cascades of Strained Alkynes and Oxadiazinones

We report a computational and experimental study of the reaction of oxadiazinones and strained alkynes to give polycyclic aromatic hydrocarbons (PAHs). The reaction proceeds by way of a pericyclic reaction cascade and leads to the formation of four new carbon-carbon bonds. Using M06-2X DFT calculations, we interrogate several mechanistic aspects of the reaction, such as why the use of non-aromatic strained alkynes can be used to access unsymmetrical PAHs, whereas the use of arynes in the methodology leads to symmetrical PAHs. In addition, experimental studies enable the rapid synthesis of new PAHs, including tetracene and pentacene scaffolds. These studies not only provide fundamental insight regarding the aforementioned cycloaddition cascades and synthetic access to PAH scaffolds, but are also expected to enable the synthesis of new materials.

Ligand-Controlled Regiodivergent Thiocarbonylation of Alkynes toward Linear and Branched α,β-Unsaturated Thioesters

Thiocarbonylation of alkynes offers an ideal procedure for the synthesis of unsaturated thioesters. A robust ligand-controlled regioselective thiocarbonylation of alkynes is developed. Utilizing boronic acid and 5-chlorosalicylic acid as the acid additive to in situ form 5-chloroborosalicylic acid (5-Cl-BSA), and bis(2-diphenylphosphinophenyl)ether (DPEphos) as the ligand, linear α,β-unsaturated thioesters were produced in a straightforward manner. Switching the ligand to tri(2-furyl)phosphine can turn the reaction selectivity to give branched products. Remarkably, this approach also represents the first example on thiocarbonylation of internal alkynes.

Ruthenium-catalyzed C-H amination of aroylsilanes

Acylsilane represents a valuable synthon in synthetic chemistry. We report on ruthenium(ii)-catalyzed ortho-C-H amination of aroylsilanes to provide facile access to synthetically useful imidobenzoylsilanes and tosyl-amidobenzoylsilanes. The protocols, with broad substrate scope and excellent functional group tolerance, are enabled with the weak chelation-assistance of acylsilane via C-H cyclometallation.

Cross-Coupling Reactions of Nitroarenes

Cross-coupling reactions are powerful synthetic tools to construct diverse chemical bonds often found in, for example, advanced materials and pharmaceuticals. Since their discovery, haloarenes have habitually been used as electrophilic coupling partners both in academic and industrial contexts. However, concerning the efficiency and the often-negative environmental impact of haloarene-based cross-coupling processes, more readily available, inexpensive, and environmentally friendly electrophiles have been explored.Nitroarenes, for example, are obtained from the facile nitration of aromatic compounds and, thus, represent one of the most easy-to-access feedstock electrophiles. Furthermore, their electron-deficient arene core can be functionalized easily and site-selectively through a wide variety of reactions. Yet, despite these advantages and even though the direct transformation of the NO₂ group would be an attractive option in cross-coupling chemistry, it has so far remained difficult to convert nitroarenes via a cleavage of the Ar-NO₂ bond given the inherent reactivity (or the lack thereof) of the nitro group. Such denitrative conversion has been performed by a conventional sequence of reduction, diazotization, and Sandmeyer reactions, which severely lacks efficiency and generality.This Account summarizes our recent research progress on cross-coupling reactions that employ nitroarenes as electrophiles. First, we developed the Suzuki-Miyaura coupling of nitroarenes using a palladium/BrettPhos catalyst. This reaction proceeds via an (at the time) unprecedented oxidative addition of the Ar-NO₂ bond, which was supported by experimental results and theoretical calculations. A widely accepted catalytic cycle for Pd-catalyzed cross-couplings has since been extended to include nitroarenes as electrophiles, which significantly increases substrate generality. Second, this denitrative coupling protocol was applied to various bond-forming reactions, namely, Buchwald-Hartwig amination, etherification, and hydrogenation reactions. Such diversification has enhanced the utility of nitroarenes as cross-coupling partners. To develop each reaction, it was necessary to modify the reaction conditions as required to overcome the obstacles deriving from nitro functionality including transmetalation and side reactions, as well as oxidative addition. Third, we designed a new Pd/NHC catalyst that exhibits higher activity than Pd/BrettPhos. The improved performance of Pd/NHC system was supported by its strong electron-donicity and structural robustness, and it allows the reduction of the catalyst loading significantly, thus increasing the efficacy and practicality of this method.The field of nitroarene-based cross-coupling has just started to flourish. In addition to our original work, several research groups have already adopted Pd/BrettPhos or Pd/NHC catalysts to develop new denitrative functionalizations. The utility of nitroarenes in the context of organic synthesis should be now revisited.

Copper-Catalyzed Enaminone C(sp2)-N Bond Phosphonation for Stereoselective Synthesis of Alkenylphosphonates

A direct enaminone C-N bond coupling functionalization that generates a new C-P bond using dialkyl phosphonate for the efficient and stereoselective synthesis of (E)-alkenylphosphonates is reported. The reactions toward target products proceed well with a broad scope, disclosing a valuable new synthetic application of enaminones by the interesting C(sp²)-N bond elaboration.

Visible-light-mediated phosphonylation reaction: formation of phosphonates from alkyl/arylhydrazines and trialkylphosphites using zinc phthalocyanine

In this work, we developed a ligand- and base-free visible-light-mediated protocol for the photoredox syntheses of arylphosphonates and, for the first time, alkyl phosphonates. Zinc phthalocyanine-photocatalyzed Csp2-P and Csp3-P bond formations were efficiently achieved by reacting aryl/alkylhydrazines with trialkylphosphites in the presence of air serving as an abundant oxidant. The reaction conditions tolerated a wide variety of functional groups.

Recent developments in decarboxylative C(aryl)-X bond formation from (hetero)aryl carboxylic acids

Decarboxylative coupling reactions using readily available (hetero)aryl carboxylic acids are a highly efficient approach for the formation of new C-C and C-X bonds. These decarboxylative coupling reactions eliminate CO2 as a by-product, resulting in a greener and environmentally more benign approach than conventional coupling reactions. In this review, we summarize the recent developments in ipso-decarboxylative C-X (X = O/N/halo/S/Se/P/CN) bond formations using (hetero)aryl carboxylic acids. Furthermore, we highlight the current limitations and future research opportunities of aryl-decarboxylative coupling reactions.

Metal-catalysed C-Het (F, O, S, N) and C-C bond arylation

The formation of C-aryl bonds has been the focus of intensive research over the last decades for the construction of complex molecules from simple, readily available feedstocks. Traditionally, these strategies involve the coupling of organohalides (I, Br, Cl) with organometallic reagents (Mg, Zn, B, Si, Sn,…) such as Kumada-Corriu, Negishi, Suzuki-Miyaura, Hiyama and Sonogashira cross-couplings. More recently, alternative methods have provided access to these products by reactions with less reactive C-Het (F, O, S, N) and C-C bonds. Compared to traditional methods, the direct cleavage and arylation of these chemical bonds, the essential link in accessible feedstocks, has become increasingly important from the viewpoint of step-economy and functional-group compatibility. This comprehensive review aims to outline the development and advances of this topic, which was organized into (1) C-F bond arylation, (2) C-O bond arylation, (3) C-S bond arylation, (4) C-N bond arylation, and (5) C-C bond arylation. Substantial attention has been paid to the strategies and mechanistic investigations. We hope that this review can trigger chemists to discover more efficient methodologies to access arylation products by cleavage of these C-Het and C-C bonds.

Bioorthogonal Reactions of Triarylphosphines and Related Analogues

Bioorthogonal phosphines were introduced in the context of the Staudinger ligation over 20 years ago. Since that time, phosphine probes have been used in myriad applications to tag azide-functionalized biomolecules. The Staudinger ligation also paved the way for the development of other phosphorus-based chemistries, many of which are widely employed in biological experiments. Several reviews have highlighted early achievements in the design and application of bioorthogonal phosphines. This review summarizes more recent advances in the field. We discuss innovations in classic Staudinger-like transformations that have enabled new biological pursuits. We also highlight relative newcomers to the bioorthogonal stage, including the cyclopropenone-phosphine ligation and the phospha-Michael reaction. The review concludes with chemoselective reactions involving phosphite and phosphonite ligations. For each transformation, we describe the overall mechanism and scope. We also showcase efforts to fine-tune the reagents for specific functions. We further describe recent applications of the chemistries in biological settings. Collectively, these examples underscore the versatility and breadth of bioorthogonal phosphine reagents.

A platform for on-the-complex annulation reactions with transient aryne intermediates

Organometallic complexes are ubiquitous in chemistry and biology. Whereas their preparation has historically relied on ligand synthesis followed by coordination to metal centers, the ability to efficiently diversify their structures remains a synthetic challenge. A promising yet underdeveloped strategy involves the direct manipulation of ligands that are already bound to a metal center, also known as chemistry-on-the-complex. Herein, we introduce a versatile platform for on-the-complex annulation reactions using transient aryne intermediates. In one variant, organometallic complexes undergo transition metal-catalyzed annulations with in situ generated arynes to form up to six new carbon-carbon bonds. In the other variant, an organometallic complex bearing a free aryne is generated and intercepted in cycloaddition reactions to access unique scaffolds. Our studies, centered around privileged polypyridyl metal complexes, provide an effective strategy to annulate organometallic complexes and access complex metal-ligand scaffolds, while furthering the synthetic utility of strained intermediates in chemical synthesis.