Employing Arynes in Diels-Alder Reactions and Transition-Metal-Free Multicomponent Coupling and Arylation Reactions

One-pot formal [3 + 2] annulation of 2-pyridinyl-substituted p-quinone methides and arynes for the synthesis of 3-aryl pyrido[1,2-a]indoles

An efficient and metal-free method for the synthesis of 3-aryl pyrido[1,2-a]indoles from aryne intermediates and 2-pyridinyl-substituted p-QMs was successfully developed under ambient conditions. The reaction offered a novel and practical protocol to access some diverse functional molecules in good to excellent yields. The proposed mechanism indicated that the reaction proceeded via a formal [3 + 2] cycloaddition step.

Practical Access to Fused Carbazoles via Oxidative Benzannulation and their Photophysical Properties

An aryne annulation strategy for the synthesis of fused carbazoles is developed using indolyl β-ketonitrile in a cascade manner. The reaction sequence involves aryne-mediated [2 + 2] cycloaddition cleavage and intramolecular Michael addition, followed by oxidation under transition-metal-free reaction conditions. Subsequently, conversion of benzo[b]carbazole-6-carbonitrile to carbazole quinone is observed upon prolongation of the reaction time. Furthermore, these materials exhibit high quantum efficiency, which promotes the light-emitting diode applications.

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.

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Light-Induced Generation and Cycloaddition Reactions of Benzyne: Synthesis of Naphthoxindoles E and Annulated Indolizines

By virtue of their high electrophilic nature, benzynes serve as reactive dienophiles in numerous cycloaddition reactions. However, in situ generation of benzyne involves either base-mediated thermal reactions, low-temperature conditions, or metal-catalyzed reactions of substituted arenes. This limits the applicability of benzynes as suitable dipolarophiles in cycloaddition reactions. Herein, we have reported a UVA (365 nM)-induced in situ generation of benzynes (from triazenyl benzoic acid) and subsequently their [4 + 2] Diels-Alder and [3 + 2] cycloaddition reactions with appropriate reaction partners such as N-protected alkylidene oxindole carboxylates and pyridinium ylides to afford naphthoxindoles E and pyrido[2,1-a]isoindole, respectively, in moderate to excellent yield. The reactions occurred at room temperature and under reagent-free reaction conditions. Each of these building blocks is pharmaceutically relevant; hence, this highlights an interesting strategy to access these classes of compounds.

Generation of sulfones utilizing β-sulfinyl esters as masked aryl sulfinates under redox-neutral conditions

A method for generation of SVI sulfones from β-sulfinyl esters (SIV) under transition-metal-free non-oxidative mild conditions is presented. Various sulfones have been achieved with moderate to excellent yields. The advantage of using β-sulfinyl esters as masked aryl sulfinates has also been exemplified using brominated substrates. Oxygen isotope-labeling experiments indicated that the oxygen atoms incorporated into the sulfone product come from the sulfoxide of the β-sulfinyl ester. Successive β-elimination/O-addition/sulfinate esterification/β-elimination processes are proposed for the mechanism of generating SVI from SIV.

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.

Arylazo sulfones: multifaceted photochemical reagents and beyond

The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. The inherent dyedauxiliary group (-N2SO2R) embedded in the reagent is responsible for the absorption of visible light even in the absence of a photocatalyst, additive or oxidant, leading to the generation of three different radicals, viz. aryl (carbon-centred), sulfonyl (sulphur-centred) and diazenyl (nitrogen-centred) radicals, under different reaction conditions. Encountering a reagent with such a versatile behaviour is quite rare, which makes arylazo sulfones a highly interesting class of compounds. The mild reaction conditions under which these reagents can operate are an added advantage. Recently, they are also being used as non-ionic photoacid generators (PAGs), electron acceptors, and hydrogen atom transfer (HAT) and imination reagents in a number of synthetic transformations. They have displayed substantial damaging effect on the structure of DNA in the presence of light which can lead to their use as phototoxic pharmaceuticals for cancer treatment. Moreover, their photochemistry is also being exploited in polymerization reactions (as photoinitiators) and in materials chemistry (surface modification).

Synthesis of Three-Dimensional Ring Fused Heterocycles by a Selective [4 + 2] Cycloaddition Between Bicyclic Thiazolo 2-Pyridones and Arynes

A selective [4 + 2] cycloaddition reaction of thiazolo-2-pyridones with arynes has been demonstrated. The developed protocol allows rapid access to highly functionalized, structurally complex thiazolo-fused bridged isoquinolones in high yields, which are susceptible to further late-stage functionalization.

Catalytic Enantioselective Nucleophilic Addition to Arynes by a New Quaternary Guanidinium Salt-Based Phase-Transfer Catalyst

Owing to the mild generation methods, arynes have been widely used in synthetic chemistry. However, achieving asymmetric organocatalytic reactions with arynes remains a formidable and infrequent challenge, primarily because these neutral and transient species tend to spontaneously quench. To address this issue, a solid-liquid phase-transfer strategy is devised in which the generation speed of arynes could be controlled by the in situ generated fluoride-based chiral phase-transfer catalyst. In this study, we present a catalytic enantioselective nucleophilic addition reaction involving arynes, utilizing an amino amide-based guanidinium salt QG•X. Furthermore, we demonstrate the broad compatibility of this reaction with various arynes and cyclic/acyclic β-keto amides, leading to the creation of diverse α-aryl quaternary stereocenters with good stereoselectivity. Mechanistic investigations have uncovered the potential involvement of a chiral intramolecular cationic-anionic pair and HF during the ion exchange between QG•X and CsF for nucleophile activation and aryne generation. Additionally, DFT calculations suggested that the observed high levels of enantioselectivity can be attributed to steric repulsion and the cumulative noncovalent interactions between the catalysts and substrates.

Easy Access to Phenanthridinones via Metal-Free Cascade Benzannulation and C-N Bond Formation

A concise route for the synthesis of dihydrobenzo[j]phenanthridinones has been disclosed through an aryne annulation strategy under metal-free reaction conditions. The reaction involves multiple C-C and C-N bond cleavages/formations via Diels-Alder reaction, aromatization-driven C-N bond cleavage, and amide formation.

Substrate-Controlled Diversity-Oriented Synthesis of Novel Polycyclic Frameworks via [4 + 2] and [3 + 2] Annulations of Ninhydrin-Derived MBH Adducts with 3,4-Dihydroisoquinolines

Substrate-controlled diversity-oriented synthesis of polycyclic frameworks via [4 + 2] and [3 + 2] annulations between ninhydrin-derived Morita-Baylis-Hillman (MBH) adducts and 3,4-dihydroisoquinolines under similar reaction conditions have been developed. The reaction provides diversity-oriented synthesis of a series of novel and structurally complex spiro multi heterocyclic skeletons in good yields (up to 87% and 90%, respectively) with excellent diastereoselectivities (up to >25:1 dr). In particular, the switchable [4 + 2] and [3 + 2] annulation reactions are controlled by tuning the hydroxyl protecting group on the ninhydrin-derived MBH adduct to deliver structural diverse spiro[indene-2,2'-[1,3]oxazino[2,3-a]isoquinoline] and spiro[indene-2,1'-pyrrolo[2,1-a]isoquinoline], respectively. Furthermore, the relative configuration and chemical structure of two kinds of cycloadducts were confirmed through X-ray diffraction analysis.

K2CO3-Catalyzed Dual C-C-Coupled Cyclization to 3-Amino-4-benzoylbiphenyls and In Situ I2-Catalyzed C-N Bond Forming Annulation: A Metal-Free Synthesis of Arylacridones

Unprecedented metal-free cyclization catalysis reactions are developed in a highly regioselective fashion to synthesize 3-amino-4-benzoyl biphenyls and arylacridones with high atom economy. Catalytic K2CO3 is utilized as the only reagent for the unusual rapid dual C-C-coupled cyclization between β-keto enamines and cinnamaldehydes to furnish the functionalized biphenyls. Its C(sp2)-H functionalized C-N bond-forming cyclization was performed in situ using molecular I2 as a catalyst to furnish valuable arylacridones. Plausible mechanisms for the new cyclization reactions are predicted by conducting various control experiments and ESI-MS analyses.

Synthesis of Phosphachromones by Cyclized Coupling of Ethyl Hydrogen (Phenylethynyl)phosphonate with Arynes

A straightforward and efficient strategy for the synthesis of phosphachromones has been reported via the insertion of arynes into P-O bonds. This operationally simple reaction is compatible with different functional groups, affording various phosphachromones by the simultaneous formation of C-P and C-O bonds in one step with moderate to good yields, and the Fries rearrangement involving phosphorus atoms is a key step in the reaction.

Synthesis of Sulfilimines via Multicomponent Reaction of Arynes, Sulfamides, and Thiosulfonates

In this work, a facile and efficient method for the synthesis of sulfilimines through multicomponent reaction of arynes, sulfamides, and thiosulfonates was developed. A variety of structurally diverse substrates and functional groups were very compatible in the reaction, giving the corresponding sulfilimines in good to high yields. This protocol could be conducted on a gram scale, and the product was easily converted to sulfide and sulfoximine. Mechanism studies revealed that sulfenamide generated in situ is the key intermediate for the reaction.

Synthesis of Sulfilimines via Aryne and Cyclohexyne Intermediates

An efficient and metal-free approach for the synthesis of sulfilimines from sulfenamides with aryne and cyclohexyne precursors has been developed. The reaction proceeds through unusual S-C bond formation, which offers a novel and practical entry to access a wide range of sulfilimines in moderate to good yields with excellent chemoselectivity. Moreover, this protocol is amenable to gram-scale synthesis and is applicable to the transformation of the products into useful sulfoximines.

Empowering boronic acids as hydroxyl synthons for aryne induced three-component coupling reactions

Boronic acids have become one of the most prevalent classes of reagents in modern organic synthesis, displaying various reactivity profiles via C-B bond cleavage. Herein, we describe the utilization of a readily available boronic acid as an efficient surrogate of hydroxide upon activation via fluoride complexation. The hitherto unknown aryne induced ring-opening reaction of cyclic sulfides and three-component coupling of fluoro-azaarenes are developed to exemplify the application value. Different from metal hydroxides or water, this novel hydroxy source displays mild activation conditions, great functionality tolerance and structural tunability, which shall engender a new synthetic paradigm and in a broad context offer new blueprints for organoboron chemistry. Detailed computational studies also recognize the fluoride activation mode, provide in-depth insights into the unprecedented mechanistic pathway and elucidate the reactivity difference of ArB(OH) x F y complexes, which fully support the experimental data.

3-sulfonyloxyaryl(mesityl)iodonium triflates as 1,2-benzdiyne precursors with activation via ortho-deprotonative elimination strategy

Benzyne has long captivated the attention of chemists and has gained numerous synthetic achievements. Among typical benzyne generation methods, removal of two vicinal substituents from 1,2-difunctionalized benzenes, i.e., Kobayashi's protocol, are prevailing, while ortho-deprotonative elimination from mono-substituted benzene lags far behind. Despite the advantages of atom economy and ready achievability of precursors, a bottle neck for ortho-deprotonative elimination strategy resides in the weak acidity of the ortho-hydrogen, which normally demands strong bases as the activating reagents. Here, an efficient aryne generation protocol is developed, where ortho-deprotonative elimination on 3-sulfonyloxyaryl(mesityl)iodonium triflates occurs under mild conditions and the generated 3-sulfonyloxyarynes can serve as efficient 1,2-benzdiyne synthons. This array of 1,2-benzdiyne precursors can be conveniently prepared with high functional group tolerance, and densely substituted scaffolds can be accessed as well. Carbonate and fluoride salts are found to serve as efficient activating reagents, which are the weakest bases used in ortho-deprotonative elimination strategies. Particularly, this scaffold has predictable chemoselective generation of the designated aryne intermediates. The success of this ortho-deprotonative elimination protocol sets up a unique platform with a broad spectrum of synthetic applications.

Asymmetric reactions involving aryne intermediates

Although arynes are usually considered fleeting intermediates, they are highly valuable synthons because they enable the introduction of aromatic rings and the simultaneous formation of new bonds at two sites. Although catalytic reactions using transition metals are excellent method for constructing complex polycyclic aromatic molecules in a single step, the use of asymmetric catalysis for the capture of arynes remains a crucial goal for the progress of aryne chemistry. Catalytic asymmetric reactions of arenes are challenging, requiring sufficient interactions between the neutral and highly reactive short-lived aryne intermediates in a stereo-controlled fashion. In addition, spontaneous decomposition, as well as side reactions, has hindered their development and, until recently, highly enantioselective reactions using arynes had remained elusive. This Review highlights asymmetric reactions using arynes, featuring diastereoselective, enantioselective and catalytic enantioselective reactions.

Base-Controlled Synthesis of Fluorescent Acridone Derivatives via Formal (4 + 2) Cycloaddition

A transition-metal-free formal (4 + 2) cycloaddition for the direct assembly of acridone derivatives has been developed from simple and easily accessible o-aminobenzamides and 2-(trimethylsilyl)aryl triflates. The base played an important role in the selective controlled synthesis of N-H and N-aryl acridones. A preliminary study on the fluorescence properties of N-aryl acridones demonstrated that they could be used as fluorescent materials with a broad emission range.

Palladium(0)-catalyzed aryne annulation: a powerful strategy for the synthesis of thio-bridged compounds

A method for the construction of various thio-bridged compounds is developed using readily available o-(trimethylsilyl)aryl triflates as a source of aryne precursor, catalyzed by simple Pd(dba)₂/dppe complex. This operationally simple and modular protocol allows thio-bridged compound via C(sp²)-C(sp²) and C(sp²)-C(sp³) bond formation in promising yields with a broad substrate scope. The key part is in situ generation of an aryne from o-(trimethylsilyl)aryl triflates and their subsequent intermolecular annulation.

Synergism of Fe/Ti Enabled Regioselective Arene Difunctionalization

Regioselective difunctionalization of arenes remains a long-standing challenge in organic chemistry. We report a novel and general Fe/Ti synergistic methodology for regioselective synthesis of various polysubstituted arenes through either E/E' or Nu/E ortho difunctionalizations of arenes. Preliminary results showed that an unprecedented 1,2-Fe/Ti heterobimetallic arylene intermediate bearing two distinct C-M bonds is essential to the regioselective difunctionalization.

Arynes as synthetic linchpins towards the construction of diversely functionalized natural product skeletons

Arynes are a privileged class of reactive intermediates in synthetic organic chemistry, and their unusual reactivities have been the subject of engrossing research interest. Recently, there are many reports on novel aryne-based synthetic innovations as a linchpin approach to accomplish the total synthesis of structurally diverse natural products or their derivatives in a racemic and enantiopure fashion. This review provides an overview of the literature on synthetic strategies, employing arynes as crucial intermediates to construct architecturally intriguing bioactive natural products/derivatives in a period of 2019 to 2022. This study highlights the need to investigate the effective synthesis and search for new biological uses of highly functionalized natural product skeletons.

Gold-catalyzed multicomponent reactions

Multicomponent reactions (MCRs) have emerged as an important branch in organic synthesis for the creation of complex molecular structures. This review is focused on gold-catalyzed MCRs with a special emphasis on the recent developments.

Atroposelective Synthesis of Triaryl α-Pyranones with 1,2-Diaxes by N-Heterocyclic Carbene Organocatalysis

Atropisomers bearing multiple stereogenic axes are of increasing importance to the field of material science, pharmaceuticals, and catalysis. However, the atroposelective construction of multi-axis atropisomers remains rare and challenging, due to the intrinsical difficulties in the stereo-control of the multiple stereogenic axes. Herein, we demonstrate a single-step construction of a new class of 1,2-diaxially chiral triaryl α-pyranones by an N-heterocyclic carbene organocatalytic asymmetric [3+3] annulation of well-designed alkynyl acylazolium precursors and enolizable sterically hindered 2-aryl ketones. The protocol features broad substrate scope (>50 examples), excellent stereo-control (most cases >20 : 1 dr, up to 99.5 : 0.5 er), and potentially useful synthetic applications. The success of this reaction relies on the rational design of structurally matched reaction partners and the careful selection of the asymmetric catalytic system. DFT calculations have also been performed to discover and rationalize the origin of the high stereoselectivity of this reaction.

Arylation and Aryne Insertion into C-Acylimines: A Simple, Flexible, and Divergent Synthesis of C2-Aryl Indoles

We reveal a direct strategy for the flexible synthesis of C2-aryl/heteroaryl indoles without transition metal catalysts. The synthesis involves a one-pot, four-component reaction of readily available starting materials to offer diversity around the indole moiety with a broad substrate scope and high yields. The reaction proceeds via the Friedel-Crafts C-arylation of C-acylimine formed in situ, followed by N-arylation with aryne, a formal [3+2] cycloaddition, and a subsequent aromatization cascade.

Synthesis of 3-(2-oxopropyl)-2-arylisoindolinone derivatives via a three-component reaction of diaryliodonium salts with 2-formylbenzonitriles and phenylacetylenes

A copper-catalyzed multicomponent cascade cyclization using readily available substrates, including 2-formylbenzonitriles, phenylacetylenes, and diaryliodonium salts, is achieved. A broad reaction scope is presented with good functional group compatibility, giving rise to a range of 3-(2-oxopropyl)-2-arylisoindolinones in moderate to good yields.

Diverse Synthesis of Triarylselenonium Salts and o-(Alkoxy)aryl Aryl Selanes via Insertion of Benzyne into the Se═O Bond

An insertion of benzyne into the Se═O bond has been realized. In this reaction, two types of compounds containing selenium could be synthesized from different substrates. When diaryl selenium oxides were used, triarylselenonium salts were furnished, while o-(alkoxy)phenyl phenyl selanes could be produced from aryl alkyl selenium oxides.

Mechanism and the Origins of Periselectivity in Cycloaddition Reactions of Benzyne with Dienes

Density functional theory calculations have been used to explore the reaction mechanism of (4 + 2) and (2 + 2) cycloadditions of benzyne with classical dienes. The results indicate the following: (1) (4 + 2) products arise via concerted pathways, (2) (2 + 2) products arise via stepwise pathways with diradical intermediates, and (3) these diradical intermediates are formed via isomerization of carbene intermediates. The origins of periselectivity in these reactions are analyzed using distortion/interaction analysis for the key steps, and they indicate that the tiny distortion in the very early [4 + 2] transition structure, coupled with an entropic favorability, controls selective (4 + 2) cycloaddition.

Merging Metals and Strained Intermediates

Strained intermediates such as cyclic alkynes and allenes are most commonly utilized in nucleophilic additions and cycloadditions, but have seen increased use in a third area of reactivity: metal-mediated transformations. The merger of strained intermediates and metal catalysis has enabled rapid access to complex, polycyclic systems. Following a discussion of relevant landmark studies involving metals and strained intermediates, this article highlights recent advances in transition metal-mediated transformations from our laboratory. Specifically, this includes the use of arynes in the synthesis of decorated organometallic complexes, and the utilization of cyclic allenes to access enantioenriched heterocycles. Moreover, the broad applicability of such transformations, and exciting future areas of research are discussed.

CF3SO2Na-Mediated Five-Component Carbonylation of Triarylboroxines with TMSCF3 and THF/LiOH/NaI to Give Aroyloxyalkyl Iodides

Herein, we developed an efficient and transition-metal-free multicomponent coupling reaction for the synthesis of aroyloxyl alkyl iodides. In the reaction among 2,4,6-triarylboroxines, THF, TMSCF₃, LiOH, and NaI, five-component reactions could be precisely controlled by modulating CF₃SO₂Na, supplying one type of aroyloxyl alkyl iodides in moderate to high yields. The reaction exhibits good functional group tolerance and a wide substrate scope and can be easily transformed into other useful compounds. The mechanism is proposed on the basis of the control experiments.

Synthesis of Trisubstituted Oxazoles via Aryne Induced [2,3] Sigmatropic Rearrangement-Annulation Cascade

A transition-metal-free, [2,3] sigmatropic rearrangement-annulation cascade of 2-substituted thio/amino acetonitriles with arynes allowing the synthesis of 2,4,5-trisubstituted oxazoles under mild conditions has been demonstrated. The key sulfur/nitrogen ylides were generated by the initial S/N arylation followed by proton transfer, which was followed by the selective [2,3] sigmatropic rearrangement involving the -CN moiety and a subsequent annulation to afford the desired products in reasonable yields.

Synthesis of Tritylones via Cascade Reaction of Arynes with 5-Ethoxyoxazoles

A cascade reaction involving arynes and 5-ethoxyoxazoles has been developed toward the synthesis of 9-alkyl/aryl tritylones. 5-Ethoxyoxazoles undergo a [4 + 2] cycloaddition reaction with arynes followed by retro-[4 + 2] cycloaddition, a second intermolecular [4 + 2] cycloaddition reaction, and hydrolytic ring cleavage to generate substituted tritylones in good yields. The conversion of tritylone products to a series of spirocyclic anthrone derivatives has been demonstrated. The reaction is expeditious, exhibits wide scope, and employs readily available starting materials.

A Method to Access Highly Functionalized Dibenzobicyclo[3.2.1]octadienones: Application to the Construction of the 6/6/5/6/6 Carbon Skeleton of Rubialatin A

The dibenzobicyclo[3.2.1]octadienone scaffold, which has been found in naphthocyclinones, engelharquinones, rubialatin A, etc., has been synthesized under mild transition metal-free conditions by aryne insertion reaction with 2-keto-1,3-indandiones. The application of this methodology has been demonstrated for the synthesis of the 6/6/5/6/6 scaffold of rubialatin A. ¹H NMR experimental studies confirm that the reaction proceeds through the formation of benzocyclobutane followed by a 7-member carbocycle ring.

The Stannum-Ene Reactions of Benzyne and Cyclohexyne with Superb Chemoselectivity for Cyclohexyne

The stannum-ene reactions of both benzyne and cyclohexyne were realized, which is particularly suitable for cyclohexyne with a broad substrate scope and excellent chemoselectivity. Our DFT calculations via distortion/interaction analysis revealed that both stannum- and hydrogen-ene reactions with cyclohexyne have later transition states due to their higher distortion energies in the transition states than those in benzyne reactions, which lead to enhanced Pauli repulsion as the decisive factor in the interaction energy accompanied with enlarged energy gap between two types of ene reactions. Therefore, excellent chemoselectivity was disclosed in the cyclohexyne-ene reaction.

Solution Phase Reactivity of Dibenzo[c,e][1,2]azaborinine: Activation and Insertion into Si-E Single Bonds (E=H, OSi(CH3 )3 , F, Cl) by a BN-Aryne

The boron-nitrogen analogue of ortho-benzyne, 1,2-azaborinine, is a reactive intermediate that features a formal boron-nitrogen triple bond. We here show by combining experimental and computational techniques that the Lewis acidity of the boron center of dibenzo[c,e][1,2]azaborinine allows interaction with the silicon containing single bonds Si-E through the silicon bonding partner E (E=F, Cl, OR, H). The binding to boron activates the Si-E bonds for subsequent insertion reaction. This shows that the BN-aryne is a ferocious species that even can activate and insert into the very strong Si-F bond.

The Aryne Phosphate Reaction

Condensed phosphates are a critically important class of molecules in biochemistry. Non-natural analogues are important for various applications, such as single-molecule real-time DNA sequencing. Often, such analogues contain more than three phosphate units in their oligophosphate chain. Consequently, investigations into phosphate reactivity enabling new ways of phosphate functionalization and oligophosphorylation are essential. Here, we scrutinize the potential of phosphates to act as arynophiles, paving the way for follow-up oligophosphorylation reactions. The aryne phosphate reaction is a powerful tool to-depending on the perspective-(oligo)phosphorylate arenes or arylate (oligo-cyclo)phosphates. Based on Kobayashi-type o-silylaryltriflates, the aryne phosphate reaction enables rapid entry into a broad spectrum of arylated products, like monophosphates, diphosphates, phosphodiesters and polyphosphates. The synthetic potential of these new transformations is demonstrated by efficient syntheses of nucleotide analogues and an unprecedented one-flask octaphosphorylation.

Transition-Metal-Free Synthesis of 4-Amino Isoquinolin-1(2H)-ones via Tandem Reaction of Arynes and Oxazoles

A facile and transition-metal-free method for the synthesis of 4-amino isoquinolin-1(2H)-ones has been developed. Arynes react with 4, 5-disubstituted oxazoles through a tandem Diels-Alder reaction/dehydrogenation-aromatization/tautamerization process to produce 4-amino isoquinolin-1(2H)-ones...

(3 + 2)-Annulation of 1,3-N,Si-tetraorganosilane reagents TsHNCH2SiBnR1R2 with arynes for efficient synthesis of 3-silaindolines

1,3-N,Si-Tetraorganosilane reagents TsHNCH2SiBnR1R2 were developed as robust synthons to prepare 3-silaindolines via a Cs2CO3-promoted (3 + 2)-annulation reaction with arynes.

MnSO4-Promoted S-O Bond Cleavage to Synthesize Functionalized Sulfonium Ylides from Activated Alkynes and Sulfoxides

A variety of functionalized sulfonium ylides were prepared in good yields through MnSO4-promoted S-O bond cleavage from activated alkynes and sulfoxides. Experimental results showed that MnSO4-catalyst played important roles to...

Reactivity of Vinyl Epoxides/Oxetanes/Cyclopropanes toward Arynes: Access to Functionalized Phenanthrenes

The reactivity of vinyl epoxides/oxetanes/cyclopropanes toward arynes has been demonstrated under mild conditions to give the corresponding phenanthrenes in moderate to good yields. This transition-metal-free cascade process involves a series of Diels-Alder reaction, ring-opening aromatization, and ene reaction. Various functionalized phenanthrenes could be synthesized utilizing the versatile hydroxy group. Interestingly, vinyl epoxides/oxiranes experience preferentially the Diels-Alder reaction toward arynes over nucleophilic attack of epoxides/oxiranes.