Substrate-Controlled Selectivity Switch in the Three-Component Coupling Involving Arynes, Aromatic Tertiary Amines, and CO2

Aryne Polymerization Enabled by Pyrazole-Induced Nucleophilic Aromatic Substitution

Despite the widespread use of arynes in organic synthesis, their polymerization remains a significant challenge due to the intrinsic instability and short lifetime of aryne intermediates. Here, we report a method for aryne polymerization using a simple organonucleophile, N-arylpyrazole, as an initiator. This polymerization proceeds via a unique pyrazole-induced nucleophilic aromatic substitution mechanism, facilitating the formation of poly(ortho-arylene)s with narrow polydispersity and well-defined structures. The high chemical stability of N-arylpyrazole allows for a broader scope of applications, including aryne polymerization at the side chain of preformed polymers (graft polymerization) and the synthesis of star-shaped poly(ortho-arylene)s.

Recent Progress on Multi-Component Reactions Involving Nucleophile, Arynes and CO2

Carbon dioxide (CO2) is a non-toxic, abundant and recoverable source of carbon monoxide. Despite its thermodynamically stable and kinetically inert nature, research on CO2 utilisation is ongoing. CO2-based aryne reactions, crucial for synthesising ortho-substituted benzoic acids and their cyclisation products, have garnered significant attention, and multi-component reactions (MCRs) involving CO2, aryne and nucleophilic reagents have been extensively studied. This review highlights recent advancements in CO2 capture reactions utilising phenylalkyne reactive intermediates. Mechanistic insights into these reactions are provided together with prospects for further development in this field.

Easy access to polyhalogenated biaryls: regioselective (di)halogenation of hypervalent bromines and chlorines

Polyhalogenated biaryls are unique motifs offering untapped potential as versatile building blocks for the expedient synthesis of complex biaryl compounds. Overcoming the limitations of conventional syntheses, we introduce a novel, metal-free, operationally simple and one-pot approach to regioselectively (di)halogenate biaryl compounds under mild conditions using cyclic biaryl hypervalent bromine and chlorine substrates as masked arynes. Through chemoselective post-functionalizations, these valuable products can expand the toolbox for synthesizing biaryl-containing scaffolds, addressing a critical gap in the field.

Copper-Assisted (Pseudo-)Halochalcogenation of Arynes

In this report, we describe the multicomponent coupling reaction between arynes, (pseudo)halides, and an electrophilic chalcogen species. Addition of a copper salt enabled smooth conversion by suppressing side reactions. A variety of different aryne precursors as well as seleno- and thiosulfonates were employed, yielding a broad spectrum of ortho-(pseudo)halogenated chalcogenides. This motif was subjected to different cross-coupling approaches, demonstrating the applicability of these compounds as building blocks for more complex structures.

Base-mediated carboxylation of C-nucleophiles with CO2

Carbon dioxide (CO2) is an available, abundant, and renewable C1 resource, which could be converted into value-added chemicals. Due to its inherent thermodynamic stability and kinetic inertness, it is difficult to realize its efficient utilization. Nevertheless, many elegant strategies for the utilization of CO2 have been developed using Lewis bases, frustrated Lewis pairs, hydroxyl-containing compounds, amino-group-containing compounds or transition metal catalysis. Among them, base-mediated carboxylation of C-nucleophiles is an environmentally friendly strategy for CO2 conversion, which is operationally simple, using low-toxicity bases and economical available promoters, without the use of complex ligands or cocatalysts. This review summarizes related work on the base-mediated carboxylation of C-nucleophiles with CO2, based on the effects of nucleophiles, promoters, additives, and solvents. The types of pronucleophile are categorized as follows: hydrocarbon with C(sp3)-H, C(sp2)-H or C(sp)-H bonds, organosilanes, organotin, organoboron, and N-tosylhydrazones. Typical mechanisms and applications of these carboxylation reactions are also depicted. Moreover, mechanistic comprehension of CO2 activation and conversion at a molecular level aims to further expand the repertoire of carboxylation transformations mediated by bases.

Aryne and CO2-based formal [2 + 2 + 2] annulation to access tetrahydroisoquinoline-fused benzoxazinones

Tetrahydroisoquinoline and its fused polyheterocycles are prevalent structural motifs found in numerous natural products. In this study, we report a highly efficient and convergent synthetic approach for the construction of tetrahydroisoquinoline-fused polyheterocycles through a three-component formal [2 + 2 + 2] annulation process by combining 3,4-dihydroisoquinolines, CO2, and benzynes. Notably, electron-rich 3,4-dihydroisoquinolines and electron-deficient benzynes exhibit greater reactivity in this annulation. Moreover, this method benefits from the convergent synthesis and the utilization of carbon dioxide, providing a valuable strategy for the facile synthesis of tetrahydroisoquinoline-fused polyheterocycles, with potential applications in the discovery and development of novel organic molecules.

Palladium-catalyzed C-H dimethylamination of 1-chloromethyl naphthalenes with N,N-dimethylformamide as the dimethyl amino source

Palladium-catalyzed remote C-H dimethylamination of 1-chloromethylnaphthalenes using N,N-dimethylformamide as the dimethylamino source is described for the first time. The dimethylamination took place exclusively at the 4-position of 1-chloromethylnaphthalenes in 2-methyltetrahydrofuran under mild conditions to afford 1-(N,N-dimethylamino)-4-alkylnaphthalenes in good to high yields. The halogen atom remained intact during the dimethylamination of 1-chloromethylnaphthalenes. A P,N bidentate ligand was conveniently synthesized and successfully utilized as the ligand in the Kumada-Corriu reaction.

N-2-(Phenylamino) Benzamide Derivatives as Dual Inhibitors of COX-2 and Topo I Deter Gastrointestinal Cancers via Targeting Inflammation and Tumor Progression

Given the close association between inflammation and cancer, combining anti-inflammation therapy is prominent to improve the anticancer effect. Based on I-1, a series of agents targeting COX-2 and Topo I were designed by combining fenamates and phenols. The optimal compound 1H-30 displayed an enhanced inhibitory effect on COX-2 compared to tolfenamic acid and I-1 and showed better inhibition of Topo I than I-1. Importantly, 1H-30 showed potential anticancer effects and suppressed the activation of the NF-κB pathway in cancer cells. 1H-30 inhibited the nuclear translocation of NF-κB and suppressed the production of NO, COX-2, and IL-1β in RAW264.7. In vivo, 1H-30 showed acceptable pharmacokinetic parameters, decreased the tumor growth without affecting the body weight, down-regulated COX-2 and MMP-9, and induced apoptosis in the CT26.WT tumor-bearing mice. Accordingly, 1H-30 as a potential Topo I/COX-2 inhibitor which possessed anti-inflammatory and anticancer effects, with inhibition of the NF-κB pathway, is promising for gastrointestinal cancer therapy.

Substrate-Controlled Regioselectivity Switchable [3 + 2] Annulations To Access Spirooxindole Skeletons

The additive-free [3 + 2] annulation from isatins, amino acids with 2-styrylbenzoxazoles, was described, providing a series of functional and structurally complex 3,3'-pyrrolidinyl-spirooxindole derivatives containing four contiguous and two quaternary stereogenic centers in high yields (up to 95%) and excellent diastereoselectivities (up to >25:1 dr). Interestingly, the reaction exhibits switchable regioselectivity depending on the substrate of amino acids. With proline or thioproline as the substrate, the reaction afforded α-regioselective spirooxindole skeletons. In contrast, when piperidine acid is the substrate, the reaction provided γ-regioselective spirooxindole skeletons.

One-pot synthesis of 3-substituted-3-hydroxyindolin-2-ones: three component coupling of N-protected isatin, aryne precursor and 1,3-cyclodione under metal-free conditions

A transition-metal free synthetic strategy for the direct synthesis of 3-substituted-3-hydroxy-indolin-2-ones via three component coupling of N-protected isatin, aryne precursor, and 1,3-cyclodione.

Access to acridones by tandem copper(I)-catalyzed electrophilic amination/Ag(I)-mediated oxidative annulation of anthranils with arylboronic acids

An efficient and practical approach for the synthesis of medicinally important acridones was developed from anthranils and commercially available arylboronic acids by a tandem copper(I)-catalyzed electrophilic amination/Ag(I)-mediated oxidative annulation strategy. This new and straightforward protocol displayed a broad substrate scope (25 examples) and high functional group tolerance. What's more, a possible mechanistic proposal was also presented.

Three-Component, Diastereoselective [6 + 3] Annulation of Tropone, Imino Esters, and Arynes

A transition-metal-free, three-component, and diastereoselective [6 + 3] annulation reaction employing tropone, imino esters, and arynes allowing the synthesis of bridged azabicyclo[4.3.1]decadienes is demonstrated. The key nitrogen ylides for the [6 + 3] annulation were generated by the addition of imino esters to the arynes followed by a proton transfer. The nitrogen ylides undergo a regioselective addition to tropone to furnish the desired products in moderate to good yields with good functional group tolerance under mild conditions.

Transition-Metal-Free C2-Functionalization of Pyridines through Aryne Three-Component Coupling

The direct C2-functionalization of pyridines through a transition-metal-free protocol by using aryne multicomponent coupling is demonstrated. The reaction allowed a broad-scope synthesis of C2-substituted pyridine derivatives bearing the -CF₃ group in good yields with α,α,α-trifluoroacetophenones as the third component. Activated keto esters could also be employed as the third component in this formal 1,2-di(hetero)arylation of ketones. Performing the reaction under dilute conditions inhibited the competing pyridine-aryne polymerization pathway. Nucleophilic attack by the initially generated pyridylidene intermediate on the carbonyl followed by an S_N Ar process resembling the Smiles rearrangement affords the desired products.

An Umpolung Oxa-[2,3] Sigmatropic Rearrangement Employing Arynes for the Synthesis of Functionalized Enol Ethers

An oxa-[2,3] sigmatropic rearrangement involving arynes is reported featuring the umpolung of ketones, where the C═O bond polarity is reversed. The in situ-generated sulfur ylides from β-keto thioethers and arynes undergo efficient rearrangement allowing the facile and robust synthesis of functionalized enol ethers in high yields and excellent functional group compatibility. Preliminary mechanistic studies rule out the possibility of Pummerer-type rearrangement operating in this case.

Rapid Synthesis of Zwitterionic Phosphonium Benzoates by a Three-Component Coupling Involving Phosphines, Arynes and CO2

A mild and easy to perform multicomponent coupling involving phosphines, arynes generated from 2-(trimethylsilyl)aryl triflates, and CO₂ allowing the transition-metal-free synthesis of zwitterionic phosphonium benzoates has been developed. The reaction proceeds via the generation of 1 : 1 zwitterionic intermediates from phosphines and arynes followed by the interception with CO₂ to deliver the carboxylates in moderate to good yields instead of the anticipated benzooxaphosphol-3(1H)-ones.

A visible light-mediated, decarboxylative, desulfonylative Smiles rearrangement for general arylethylamine syntheses

A decarboxylative, desulfonylative Smiles rearrangement is reported for the synthesis of a wide range of biologically relevant arylethylamines, including fluorinated phenylethylamines, heterocyclic amphetamines and an unnatural amino acid.

1,2-Aminohalogenation of arynes with amines and organohalides

An unprecedented use of inexpensive organohalides as halogen electrophiles to trap the zwitterion intermediates generated from amines and arynes has been developed to access structurally diverse tertiary 2-haloanilines. Effective organohalides include carbon tetrachloride, hexachloroethane, N-chlorosuccinimide, carbon tetrabromide, fluorotribromomethane, N-bromosuccinimide, carbon tetraiodide, and N-iodosuccinimide.

Transition-Metal-Free Thioamination of Arynes Using Sulfenamides

The insertion of arynes into the S-N σ-bond of sulfenamides allowing the synthesis of o-sulfanylaniline derivatives with reasonable functional group compatibility is presented. The aryne generated from 2-(trimethylsilyl)aryl triflates using CsF in DME was the key for the success of this transition-metal-free thioamination reaction, which involves new C-N and C-S bond formations in a single step under mild conditions. Moreover, the synthetic potential of this method was demonstrated by the synthesis of the antidepressant drug vortioxetine.

Aryne insertion into the PO bond: one-pot synthesis of quaternary phosphonium triflates

A novel transition-metal free synthetic strategy for the direct synthesis of quaternary phosphonium triflates via insertion of aryne into phosphine oxide.

The aryne Sommelet–Hauser rearrangement

An aryne induced transition-metal-free and mild Sommelet–Hauser rearrangement of tertiary benzylamines for the synthesis of α-aryl amino acid derivatives in moderate to good yields and with broad substrate scope is presented.

A cascade process for the synthesis of ortho-formyl allyl aryl ethers and 2H-chromen-2-ol derivatives from arynes via trapping of o-quinone methide with an activated alkene

A transition-metal free synthetic strategy for the direct synthesis of ortho-formyl substituted allyl aryl ethers and 2H-chromen-2-ol derivatives via a cascade three-component coupling of arynes, activated alkene and N,N-dimethylformamide.

Direct bromocarboxylation of arynes using allyl bromides and carbon dioxide

An unprecedented multicomponent reaction involving arynes, allyl bromides, and CO₂ has been developed to construct various allyl o-bromobenzoate scaffolds.

Synthesis of Arenesulfonyl Fluorides via Sulfuryl Fluoride Incorporation from Arynes

Transition-metal-free multicomponent reactions involving aryne precursors, secondary amines, and sulfuryl fluoride are reported herein. Zwitterionic intermediates formed from the reaction of arynes with amine nucleophiles can capture SO₂F₂ under mild conditions, offering a novel and practical protocol for the synthesis of 2-dialkyl-, 2-alkylaryl-, or 2-diarylamino-substituted arenesulfonyl fluoride derivatives in good to excellent yields.

Sequential σ-Bond Insertion/Benzannulation Involving Arynes: Selective Synthesis of Polysubstituted Naphthalenes

An interesting σ-bond insertion/benzannulation reaction for the synthesis of polysubstituted naphthalene derivatives has been developed from readily accessible ketones, arynes, and alkynoates. This practical and transition-metal-free method provides a novel route to diverse naphthalenes through a substrate-controlled rearrangement reaction with the cleavage of C-C bonds.

Mechanistic Insights into the Ni-Catalyzed Reductive Carboxylation of C-O Bonds in Aromatic Esters with CO2 : Understanding Remarkable Ligand and Traceless-Directing-Group Effects

The mechanism of the Ni⁰ -catalyzed reductive carboxylation reaction of C(sp² )-O and C(sp³ )-O bonds in aromatic esters with CO₂ to access valuable carboxylic acids was comprehensively studied by using DFT calculations. Computational results revealed that this transformation was composed of several key steps: C-O bond cleavage, reductive elimination, and/or CO₂ insertion. Of these steps, C-O bond cleavage was found to be rate-determining, and it occurred through either oxidative addition to form a Ni^II intermediate, or a radical pathway that involved a bimetallic species to generate two Ni^I species through homolytic dissociation of the C-O bond. DFT calculations revealed that the oxidative addition step was preferred in the reductive carboxylation reactions of C(sp² )-O and C(sp³ )-O bonds in substrates with extended π systems. In contrast, oxidative addition was highly disfavored when traceless directing groups were involved in the reductive coupling of substrates without extended π systems. In such cases, the presence of traceless directing groups allowed for docking of a second Ni⁰ catalyst, and the reactions proceed through a bimetallic radical pathway, rather than through concerted oxidative addition, to afford two Ni^I species both kinetically and thermodynamically. These theoretical mechanistic insights into the reductive carboxylation reactions of C-O bonds were also employed to investigate several experimentally observed phenomena, including ligand-dependent reactivity and site-selectivity.

Multiheterocyclic Motifs via Three-Component Reactions of Benzynes, Cyclic Amines, and Protic Nucleophiles

A broadly general, three-component reaction strategy for the construction of compounds containing multiple heterocycles is described. Thermal benzyne formation (by the hexadehydro-Diels-Alder (HDDA) reaction) in the presence of tertiary cyclic amines and a protic nucleophile (HNu) gives, via ring-opening of intermediate ammonium ion/Nu- ion pairs, heterocyclic products. Many reactions are efficient even when the stoichiometric loading of the three reactants approaches unity. Use of HOSO2CF3 as the HNu gives ammonium triflate intermediates, which can then be ring opened by an even wider variety of nucleophiles.

Synthesis of 3-aryl-3-benzazepines via aryne [1,2] Stevens rearrangement of 1,2,3,4-tetrahydroisoquinolines

An efficient method for the synthesis of 3-aryl-3-benzazepines via aryne induced [1,2] Stevens rearrangement of 1,2,3,4-tetrahydroisoquinolines is described.

Current advances in the catalytic conversion of carbon dioxide by molecular catalysts: an update

Recent advances (2015–) in the catalytic conversion of CO₂ by metal-based and metal-free systems are discussed.

Synthesis of 2-aminobenzophenones through acylation of anilines with α-oxocarboxylic acids assisted by tert-butyl nitrite

A highly facile all-in-one-pot synthesis of 2-aminobenzophenones directly from anilines, tert-butyl nitrite and α-oxocarboxylic acids under the catalysis of Pd(OAc)₂ is presented.

Nucleophilic addition of tertiary propargylic amines to arynes followed by a [2,3]-sigmatropic rearrangement

Treatment of tertiary propargylic amines with 2-(trimethylsilyl)aryl triflates under mild conditions provides convenient access to amino-substituted allenes or conjugated dienes.

Synthesis of fused benzimidazoles via successive nucleophilic additions of benzimidazole derivatives to arynes under transition metal-free conditions

An expedient and efficient strategy was developed for the synthesis of benzimidazole derivatives from aryne precursors under transition metal-free conditions.