C3 Selective Hydroxylation of Pyridines via Photochemical Valence Isomerization of Pyridine N-Oxides

The C-H hydroxylation of the pyridine C3 position is a highly desirable transformation but remains a great challenge due to the inherent electronic properties of this heterocycle core which bring difficulties in chemical reactivity and regioselectivity. Herein we present an efficient method for formal C3 selective hydroxylation of pyridines via photochemical valence isomerization of pyridine N-oxides. This metal-free transformation features operational simplicity and compatibility with a diverse array of functional groups, and the resulting hydroxylated products are amenable to further elaboration to synthetically useful building blocks. The synthetic utility of this strategy is further demonstrated in the effective late-stage functionalization of pyridine-containing medicinally relevant molecules and versatile derivatizations of 3-pyridinols.

Synthetic Strategies toward Ortho-3-propanoate Substituted Aryl Phosphonates by Three-Component Coupling Reactions of Arynes, Phosphites, and Acrylates

Mild, metal-free, and operationally simple three-component coupling reactions involving arynes, phosphites, and acrylates have been achieved. The reaction proceeded well with α- or β-substituted acrylates. Additionally, various functional groups were tolerated under these reaction conditions, resulting in diverse ortho-3-propanoate-substituted aryl phosphonates. Moreover, the reaction can be used to synthesize a range of organophosphorus compounds present in natural products, materials, and biologically active compounds.

Bromothiolation of Arynes for the Synthesis of 2-Bromobenzenethiol Equivalents

A new method to synthesize o-bromobenzenethiol equivalents through aryne intermediates is disclosed. Various o-bromobenzenethiol equivalents are prepared by the bromothiolation of aryne intermediates with potassium xanthates. Aryl xanthates serve in the synthesis of diverse organosulfurs involving phenothiazines and thianthrenes by further transformations.

The Synthesis and Reactivity of Naphthoquinonynes

The first systematic exploration of the synthesis and reactivity of naphthoquinonynes is described. Routes to two regioisomeric Kobayashi-type naphthoquinonyne precursors have been developed, and the reactivity of the ensuing 6,7- and 5,6-aryne intermediates has been investigated. Remarkably, these studies have revealed that a broad range of cycloadditions, nucleophile additions and difunctionalizations can be achieved while maintaining the integrity of the highly sensitive quinone unit. The methodologies offer a powerful diversity oriented approach to C6 and C7 functionalized naphthoquinones, which are typically challenging to access. From a reactivity viewpoint, the study is significant because it demonstrates that aryne-based functionalizations can be utilized strategically in the presence of highly reactive and directly competing functionality.

Asymmetric Cycloaddition Reactions of Aryne Intermediates with a Chiral Carbon-Carbon Axis: Syntheses of Axially Chiral Biaryl Compounds

An asymmetric synthesis via an axially chiral arylaryne intermediate was developed. A cycloaddition reaction with various arynophiles was used to obtain chiral biaryl compounds while preserving the enantiomeric excess (ee) of a precursor even though the reaction proceeds through an arylaryne intermediate, whose chirality decreases on a time-dependent basis. High chiral transfer from a precursor to a product was observed not only at low temperature (-78 °C) but also at room temperature.

The Lateral Metalation of Isoxazolo[3,4-d]pyridazinones towards Hit-to-Lead Development of Selective Positive Modulators of Metabotropic Glutamate Receptors

Isoxazolo[3,4-d] pyridazinones ([3,4-d]s) were previously shown to have selective positive modulation at the metabotropic glutamate receptor (mGluR) Subtypes 2 and 4, with no functional cross-reactivity at mGluR1a, mGluR5, or mGluR8. Additional analogs were prepared to access more of the allosteric pocket and achieve higher binding affinity, as suggested by homology modeling. Two different sets of analogs were generated. One uses the fully formed [3,4-d] with an N6-aryl with and without halogens. These underwent successful selective lateral metalation and electrophilic quenching (LM&EQ) at the C3 of the isoxazole. In a second set of analogs, a phenyl group was introduced at the C4 position of the [3,4-d] ring via a condensation of 4-phenylacetyl-3-ethoxcarbonyl-5-methyl isoxazole with the corresponding hydrazine to generate the 3,4-ds 2b and 2j to 2n.

C-F Transformations of Benzotrifluorides by the Activation of Ortho-Hydrosilyl Group

Single C-F transformations of aromatic trifluoromethyl compounds are challenging issues due to the strong C-F bond. We have recently developed selective methods for single C-F transformations such as allylation of o-hydrosilyl-substituted benzotrifluorides through the hydride abstraction with trityl cations. Single C-F thiolation and azidation of o-(hydrosilyl)benzotrifluorides were achieved using trityl sulfides and trityl azide catalyzed by Yb(OTf)3 . Treatment of o-(hydrosilyl)benzotrifluorides with trityl chloride resulted in single C-F chlorination. The resulting fluorosilyl group served in further transformations including protonation, halogenation, and Hiyama cross-coupling with C-Si cleavage. We also synthesized benzyl fluorides by LiAlH4 -reduction of the resulting fluorosilanes and further C-F transformations. These methods enabled us to prepare a broad range of organofluorines from simple benzotrifluorides through C-F and C-Si transformations.

Total Synthesis of Phenanthroindolizidines Using Strained Azacyclic Alkynes

We report a concise approach to phenanthroindolizidine alkaloids, wherein strained azacyclic alkynes are intercepted in Pd-catalyzed annulations. Two types of strained intermediates were evaluated: a functionalized piperidyne and a new strained intermediate, an indolizidyne. We show that each can be employed, ultimately allowing access to three natural products: tylophorine, tylocrebine, and isotylocrebine. These efforts demonstrate the successful merger of strained azacyclic alkyne chemistry with transition-metal catalysis for the construction of complex heterocycles.

Sodium Trifluoroacetate mediated Copper-Catalyzed aza-Michael addition of α,β-unsaturated olefins with aromatic amines

We present a sodium trifluoroacetate (CF3CO2Na) mediated copper-catalyzed aza-Michael addition of aromatic amines with activated olefins under mild, aqueous reaction conditions. This simplistic protocol employs a copper catalyst (10 mol%) and water as solvent. This transformation occurs precisely with aromatic substituted amines containing both electron-donating (EDG) and electron-withdrawing (EWG) groups. A broad range of substrates were tested under the optimized conditions, which are producing good to moderate yields.

Strain-promoted reactions of 1,2,3-cyclohexatriene and its derivatives

Since 18251, compounds with the molecular formula C6H6-most notably benzene-have been the subject of rigorous scientific investigation2-7. Of these compounds, 1,2,3-cyclohexatriene has been largely overlooked. This strained isomer is substantially (approximately 100 kcal mol-1) higher in energy compared with benzene and, similar to its relatives benzyne and 1,2-cyclohexadiene, should undergo strain-promoted reactions. However, few experimental studies of 1,2,3-cyclohexatriene are known8-12. Here we demonstrate that 1,2,3-cyclohexatriene and its derivatives participate in a host of reaction modes, including diverse cycloadditions, nucleophilic additions and σ-bond insertions. Experimental and computational studies of an unsymmetrical derivative of 1,2,3-cyclohexatriene demonstrate the potential for highly selective reactions of strained trienes despite their high reactivity and short lifetimes. Finally, the integration of 1,2,3-cyclohexatrienes into multistep syntheses demonstrates their use in rapidly assembling topologically and stereochemically complex molecules. Collectively, these efforts should enable further investigation of the strained C6H6 isomer 1,2,3-cyclohexatriene and its derivatives, as well as their application in the synthesis of important compounds.

Catalyst-Controlled Annulations of Strained Cyclic Allenes with π-Allylpalladium Complexes

Strained cyclic allenes are a class of in situ-generated fleeting intermediates that, despite being discovered more than 50 years ago, has received significantly less attention from the synthetic community compared to related strained intermediates. Examples of trapping strained cyclic allenes that involve transition metal catalysis are especially rare. We report the first annulations of highly reactive cyclic allenes with in situ-generated π-allylpalladium species. By varying the ligand employed, either of two isomeric polycyclic scaffolds can be obtained with high selectivity. The products are heterocyclic and sp3-rich and bear two or three new stereocenters. This study should encourage the further development of fragment couplings that rely on transition metal catalysis and strained cyclic allenes for the rapid assembly of complex scaffolds.

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.

Expedient Synthesis and Ring-Opening Metathesis Polymerization of Pyridinonorbornenes

Pyridine-containing polymers are promising materials for a variety of applications from the capture of contaminants to the self-assembly of block copolymers. However, the innate Lewis basicity of the pyridine motif often hampers living polymerization catalyzed by transition-metal complexes. Herein, we report the expedient synthesis of pyridinonorbornene monomers via a [4+2] cycloaddition between 2,3-pyridynes and cyclopentadiene. Well-controlled ring-opening metathesis polymerization was enabled by careful structural design of the monomer. Polypyridinonorbornenes exhibited high Tg and Td, a promising feature for high-temperature applications. Investigation of the polymerization kinetics and of the reactivity of the chain ends shed light on the influence of nitrogen coordination on the chain-growth mechanism.

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.

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.

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.

pi-Extension of Heterocycles via a Pd-Catalyzed Heterocyclic Aryne Annulation: pi-Extended Donors for TADF Emitters

We report the annulation of heterocyclic building blocks to access pi-extended polycyclic aromatic hydrocarbons (PAHs). The method involves the trapping of short-lived hetarynes with catalytically-generated biaryl palladium intermediates and allows...

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...

2-(Chlorodiisopropylsilyl)-6-(trimethylsilyl)phenyl triflate: a modified platform for intramolecular benzyne cycloadditions

2-(Chlorodiisopropylsilyl)-6-(trimethylsilyl)phenyl triflate serves as an efficient aryne precursor for intramolecular benzyne [4 + 2] or (2 + 2 + 2) cycloadditions. Key features of this precursor are (1) rapid connection of various arynophiles to the precursor via a Si-O bond and (2) generation of aryne under mild conditions using a combination of Cs₂CO₃ and 18-crown-6.

Phosphine-Catalyzed Aryne Oligomerization: Direct Access to α,ω-Bisfunctionalized Oligo(ortho-arylenes)

A phosphine-catalyzed oligomerization of arynes using selenocyanates was developed. The use of JohnPhos as a bulky phosphine is the key to accessing α,ω-bisfunctionalized oligo(ortho-arylenes) with RSe as the substituent at one terminus and CN as the substituent at the other. The in situ formation of R₃PSeR' cations, serving as sterically encumbered electrophiles, hinders the immediate reaction that affords the 1,2-bisfunctionalization product and instead opens a competitive pathway leading to oligomerization. Various optimized conditions for the predominant formation of dimers, but also for higher oligomers such as trimers and tetramers, were developed. Depending on the electronic properties of the electrophilic reaction partner, even compounds up to octamers were isolated. Optimization experiments revealed that a properly tuned phosphine as catalyst is of crucial importance. Mechanistic studies demonstrated that the cascade starts with the attack of cyanide; aryne insertion into n-mers leading to (n+1)-mers was ruled out.

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.

Toward 2-Thiophyne: Ketocarbene versus Hetaryne Intermediates from 2-(Trimethylsilyl)thiophen-3-yl Triflate

The reaction of 2-(trimethylsilyl)thiophen-3-yl triflate with CsF in the presence of 2,3,4,5-tetraphenylcyclopentadienone affords 4,5,6,7-tetraphenylbenzo[b]thiophene, as it would be expected from the hypothesized generation and trapping of 2-thiophyne. However, a detailed experimental and computational study discards the intermediacy of this elusive 5-membered hetaryne. Instead, a complex mechanism involving the generation of an intermediate ketocarbene, which adds to the cyclopentadienone to give an isolable tricyclic intermediate, followed by thermal rearrangements, is proposed.

Benzyne-Mediated Esterification Reaction

A benzyne-mediated esterification of carboxylic acids and alcohols under mild conditions has been realized, which is made possible via a selective nucleophilic addition of carboxylic acid to benzyne in the presence of alcohol. After a subsequent transesterification with alcohol, the corresponding esters can be produced efficiently. This benzyne-mediated protocol can be used on the modification of Ibuprofen, cholesterol, estradiol, and synthesis of nandrolone phenylpropionate. In addition, benzyne can also be used to promote lactonization and amidation reaction.

Study on the Gas-Phase Reactivity of Charged Pyridynes

The reactivities of three isomeric, charged ortho-pyridynes, the 1,2-, 2,3-, and 3,4-didehydropyridinium cations, were examined in the gas phase using Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry. The structures of selected product ions were probed using collision-activated dissociation (CAD) experiments in a linear quadrupole ion trap (LQIT) mass spectrometer. Mechanisms based on quantum chemical calculations are proposed for the formation of all major products. The products of the reactions of the charged ortho-pyridynes in the gas phase were found to closely resemble those formed upon reactions of neutral ortho-arynes in solution, but the mechanisms of these reactions exhibit striking differences. Additionally, no radical reactions were observed for any of the charged ortho-pyridynes examined, in contrast to previous proposals that ortho-benzyne can occasionally react via radical mechanisms. Finally, the relative reactivities of those charged gaseous ortho-pyridynes that yielded similar product distributions were found to be affected mainly by the (calculated) vertical electron affinities of the dehydrocarbon sites, which suggests that the reactivity of these species is controlled by polar effects.

Carbon Atom Insertion into Pyrroles and Indoles Promoted by Chlorodiazirines

Herein, we report a reaction that selectively generates 3-arylpyridine and quinoline motifs by inserting aryl carbynyl cation equivalents into pyrrole and indole cores, respectively. By employing α-chlorodiazirines as thermal precursors to the corresponding chlorocarbenes, the traditional haloform-based protocol central to the parent Ciamician-Dennstedt rearrangement can be modified to directly afford 3-(hetero)arylpyridines and quinolines. Chlorodiazirines are conveniently prepared in a single step by oxidation of commercially available amidinium salts. Selectivity as a function of pyrrole substitution pattern was examined, and a predictive model based on steric effects is put forward, with DFT calculations supporting a selectivity-determining cyclopropanation step. Computations surprisingly indicate that the stereochemistry of cyclopropanation is of little consequence to the subsequent electrocyclic ring opening that forges the pyridine core, due to a compensatory homoaromatic stabilization that counterbalances orbital-controlled torquoselectivity effects. The utility of this skeletal transform is further demonstrated through the preparation of quinolinophanes and the skeletal editing of pharmaceutically relevant pyrroles.

Leveraging Fleeting Strained Intermediates to Access Complex Scaffolds

Arynes, strained cyclic alkynes, and strained cyclic allenes were validated as plausible intermediates in the 1950s and 1960s. Despite initially being considered mere scientific curiosities, these transient and highly reactive species have now become valuable synthetic building blocks. This Perspective highlights recent advances in the field that have allowed access to structural and stereochemical complexity, including recent breakthroughs in asymmetric catalysis.

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.

Benzyne 1,2,4-Trisubstitution and Dearomative 1,2,4-Trifunctionalization

Both 1,2,4-trisubstitution and dearomative 1,2,4-trifunctionalization of benzyne have been accomplished from sulfoxides bearing a penta-2,4-dien-1-yl moiety. These cascade transformations proceed through a benzyne insertion into the S═O bond and an uncommon regiospecific anionic [4,5]-sigmatropic rearrangement, furnishing a C-O, C-S, and C-C bond on the C1-, C2-, and C4-position of a benzene ring, respectively. This study showcases new cascade benzyne reaction modes involving both distal C-H bond functionalization and dearomatization.

Aryne-mediated [2,3]-sigmatropic rearrangement of tertiary 2,3-allenylamines bearing an electron-withdrawing group at the α-position

An unprecedented [2,3]-sigmatropic rearrangement reaction of quaternary 2,3-allenylammonium ylides, generated in situ from tertiary 2,3-allenylamines and arynes, has been established. With 2-(trimethylsilyl)aryl triflates as aryne precursors, a range of tertiary 2,3-allenylamines bearing an electron-withdrawing group at the α-position smoothly participated in the aryne-mediated [2,3]-sigmatropic rearrangement at room temperature, delivering structurally diverse 2-vinylallyamines or 1-amino-1,3-dienes in moderate to excellent yields. The reaction proceeds in the absence of strong bases and transition metals, is compatible with moisture and air, and tolerates a wide variety of functional groups.

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.

o-Quinone Methides and o-Quinone Sulfides via Arynes: Synthesis of Ortho-Disubstituted Arenes and Heterocycles

In recent decades, o-quinone methides and o-quinone sulfides have been extensively highlighted as reactive intermediates for the synthesis of diversely functionalized ortho-disubstituted arenes and heterocycles. Additionally, ortho-disubstituted arenes offer a constructive path for the synthesis of fused carbocycles, heterocycles, natural products, and drug candidates. In the lieu of that, this Synopsis highlights a comprehensive overview on the potential applications of in situ generated o-quinone methides and o-quinone sulfides for one-pot synthesis of ortho-disubstituted arenes and heterocycles via arynes.

Gold-Catalyzed Formal Hexadehydro-Diels-Alder/Carboalkoxylation Reaction Cascades

A dual gold-catalyzed hexadehydro-Diels-Alder/carboalkoxylation cascade reaction is reported. In this transformation, the gold catalyst participated in the hexadehydro-Diels-Alder step, switching the mechanism from a radical type to a cationic one, and then the catalyst activated the resulting aryne to form an ortho-Au phenyl cation species, which underwent a carboalkoxylation rearrangement rather than the expected aryne-ene reaction.

Acylalkylation of Arynes Generated from o-Iodoaryl Triflates with Hydrosilanes and Cesium Fluoride

An efficient method to generate aryne intermediates from o-iodoaryl triflates triggered by triethylsilane and cesium fluoride is disclosed. This method realized the acylalkylation of arynes using easily available o-iodoaryl triflate-type precursors, which was difficult when using conventional nucleophilic activators. A wide range of (hetero)arenes including various fused benzothiazoles were successfully synthesized from o-iodoaryl triflates by virtue of their good accessibility and divergent transformations of aryne intermediates.

Modular and Divergent Syntheses of Protoberberine and Protonitidine Alkaloids

A modularly convergent and divergent strategy was established for the family synthesis of both protoberberine and protonitidine alkaloids. The robust, scalable, and flexible synthetic route featured a collective preparation of protoberberine and protonitidine alkaloids from a common isoquinoline assembled from pyridyne as the key synthon, which was based on the selective N-C or C-C cyclization via distinct processes. Through the strategy, 20 protoberberine alkaloids, 5 protonitidine alkaloids, and 11 analogues with diverse substituents were comprehensively aquired.

Rh(I)-Catalyzed Carbene Migration/Carbonylation/Cyclization: Straightforward Construction of Fully Substituted Aryne Precursors

The Rh(I)-catalyzed cascade formation of carbenoid followed by a carbonylative cyclization of silyl diynes has been established to achieve diverse ortho silyl-substituted phenolics, enabling access to fully substituted aryne precursors via a one-step fluorosulfurylation. The silyl mask on the termini of alkynes is demonstrated not only to suppress the undesired oxidation but also to control the selectivity of CO insertion. Straightforward access to fully substituted arynes was comprehensively established and applied for the efficient construction of polycyclic aromatic molecules.

Silica gel-induced aryne generation from o-triazenylarylboronic acids as stable solid precursors

We developed o-triazenylarylboronic acids as stable solid aryne precursors, which generate arynes under mild conditions using silica gel as the sole reagent and undergo reactions with a range of arynophiles both in solution and in the solid-state.