Aryne 1,2,3,5-Tetrasubstitution Enabled by 3-Silylaryne and Allyl Sulfoxide via an Aromatic 1,3-Silyl Migration

Base-Promoted Sulfur Arylation of Sulfenamides to Oxonium Aryne Precursors: Chemoselective Synthesis of Sulfilimines and o-Sulfanylanilines

In this study, a metal-free and efficient method for the synthesis of sulfilimines and o-sulfanylanilines in high yields with excellent chemoselectivities from oxonium aryne precursors with sulfenamides has been developed. This method features mild reaction conditions, simple operations, a general substrate scope, and good tolerance of functional groups. In addition, scale-up synthesis, related applications, and preliminary mechanistic explorations were also investigated.

Triptycene-Based Tripodal Molecular Platforms

Molecular platforms are essential components of various surface-mounted molecular devices. Here, we document the synthesis of two universal triptycene-based tripodal pedestals featuring terminal alkynes in the axial position. We showcase their versatility by incorporating them into the structures of diverse functional molecules such as unidirectional light-driven molecular motors, photoswitches, and Brownian molecular rotors using standard cross-coupling reactions. We also present their fundamental physical properties, including acidity constants, data from differential scanning calorimetry, and crystallographic analysis of two parent and five derived structures. Finally, and importantly, we demonstrate that the photochemical properties of selected photoswitch representatives remain uncompromised when fused with tripods.

Arynes Promoted Dehydrosulfurization of Thioamides: Access to Nitriles and Diaryl Sulfides

An aryne-promoted dehydrosulfurization reaction of thioamides to give nitriles and diaryl sulfides in a one-pot manner is presented. Aromatic, heteroaromatic, and aliphatic natural products and drug-derived nitriles and diaryl sulfides were obtained in good to excellent yields. Especially, selenoamide was also a suitable substrate and produced diaryl selenide and nitrile in high yields. The D-labeled experiments indicated that the protons of thioamides transfer to diaryl sulfides.

Cascade Aryne Aminoarylation for Biaryl Phenol Synthesis

We describe a transition metal-free approach to hindered 3-amino-2-aryl phenols through a cascade nucleophilic addition / Smiles-Truce rearrangement of a functionalized Kobayashi aryne precursor. Under anionic conditions, secondary alkyl amines add to the aryne intermediate to set up an aryl transfer from a neighboring sulfonate group. The use of a sulfonate, rather than the more typical sulfonamide, enables access to phenolic biaryl products that are important motifs in natural products and pharmaceuticals.

Access to N-Aryl (Iso)quinolones via Aryne-Induced Three-Component Coupling Reaction

N-Aryl (iso)quinolones are of increasing interest in material and medicinal chemistry, although general routes for their provision remain underexplored, especially when compared with its N-alkyl counterparts. Herein, we report a modular and transition-metal-free, aryne-induced three-component coupling protocol that allows the facile synthesis of structurally diverse N-aryl (iso)quinolones from readily accessible halo-(iso)quinolines in the presence of water. Preliminary results highlight the applicability of our method through scale-up synthesis, downstream derivatization, and flexible synthesis involving other types of aryne precursors.

Sulfonium-based precise alkyl transposition reactions

S-adenosyl-L-methionine (SAM), a sulfonium-based cofactor, plays an important role in numerous biological processes as methyl donor. Inspired by the function of sulfonium motif in this nature's synthetic toolkit, we here present an aryne-activation strategy that the sulfonium intermediates in situ generated from thioethers display unique reactivity toward alkyl group transposition. Experimental and theoretical studies indicate that the reaction occurs in an intermolecular fashion where the TfO--incorporated [K(18-crown-6)] complex acts as a key promoter for this thermodynamically favored process. Next, a series of robust, easy-to-prepare sulfonium salts are designed and developed as electrophilic alkylation reagents accordingly. Both systems feature for broad scope, excellent selectivity, and simple operation. Moreover, we highlight the synthetic value through molecular editing and late-stage modification of complex scaffolds or even active pharmaceutical ingredients.

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.

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.

Two Cascade Processes Initiated by the Insertion of Benzyne into the Se═O Bond

Two sets of cascade processes have been realized, both of which were initiated with a benzyne insertion into the Se═O bond. The key factors to differentiate these processes are based on the structures of diaryl selenium oxides and reaction conditions. When diaryl selenium oxides containing an ortho weak σ-electron-withdrawing group were used, triarylselenonium salts were obtained at room temperature, while ortho-(aryloxy)phenyl phenyl selanes could be produced from diaryl selenium oxides at 100 °C.

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.

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.

Dearomative di- and trifunctionalization of aryl sulfoxides via [5,5]-rearrangement

Aromatic [5,5]-rearrangement can in principle be an ideal protocol to access dearomative compounds. However, the lack of competent [5,5]-rearrangement impedes the advance of the protocol. In this Article, we showcase the power of [5,5]-rearrangement recently developed in our laboratory for constructing an intriguing dearomative sulfonium specie which features versatile and unique reactivities to perform nucleophilic 1,2- and 1,4-addition and cyclization, thus achieving dearomative di- and trifunctionalization of easily accessible aryl sulfoxides. Impressively, the dearomatization products can be readily converted to sulfur-removed cyclohexenones, naphthalenones, bicyclic cyclohexadienones, and multi-substituted benzenes. Mechanistic studies shed light on the key intermediates and the remarkable chemo-, regio- and stereoselectivities of the reactions.

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.

Serendipitous synthesis of 2-alkenyl- and 2-aryl-4-thiazolidinones using dithiodiglycolic anhydride

Dithiodiglycolic anhydride undergoes an efficient formal cycloaddition with imines to afford functionalized 4-thiazolidinones, without complications arising from the anhydride-imine reaction or the sulfa-Michael reaction (in the case of 1,3-azadienes).

Reactions of Sulfoxides with Benzynes

Sulfoxides are important organic synthons that have been used in a variety of transformations. In this account, we focus on advances in the reaction of sulfoxides with benzynes, which can be divided into two types: benzyne ortho-difunctionalization and benzyne multifunctionalization.

1 Introduction

2 Benzyne ortho-Difunctionalization

3 Benzyne Multifunctionalization

4 Conclusion

Selective synthesis of sulfoxides and sulfones via controllable oxidation of sulfides with N-fluorobenzenesulfonimide

A practical and mild method for the switchable synthesis of sulfoxides or sulfones via selective oxidation of sulfides using cheap N-fluorobenzenesulfonimide (NFSI) as the oxidant has been developed. These highly chemoselective transformations were simply achieved by varying the NFSI loading with H₂O as the green solvent and oxygen source without any additives. The good functional group tolerance makes the strategy valuable.

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.

1,3-Aza-Brook Rearrangement of Aniline Derivatives: In Situ Generation of 3-Aminoaryne via 1,3-C-(sp2)-to-N Silyl Migration

The design, synthesis, and validation of 3-aminobenzyne precursors induced by C-(sp²)-to-N 1,3-aza-Brook rearrangement have been achieved, allowing access to diverse aniline derivatives. Through crossover experiments, we demonstrated the intramolecular mechanism of 1,3-C-to-N silyl transfer. To gain insight into the regioselectivity observed in the reactions, we performed density functional theory calculations. Finally, the method was applied to the synthesis of xylanigripones A in five linear steps in an overall yield of 30%.

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.

Sulfurane [S(IV)]-Mediated Fusion of Benzynes Leads to Helical Dibenzofurans

Here we disclose a sulfurane-mediated method for the formation of dimeric dibenzofuran helicenes via the reaction between diaryl sulfoxides and hexadehydro-Diels-Alder (HDDA) derived benzynes. A variety of S-shaped and U-shaped helicenes were formed under thermal conditions. Both experimental and DFT studies support a sulfur(IV)-based coupling (aka ligand coupling) mechanism involving tetracarbo-ligated S(IV) intermediates undergoing reductive elimination to afford the helicene products. This process involves the de novo generation of five new rings in a single operation and constitutes a new method for the construction of topologically interesting, polycyclic aromatic compounds.

Ruthenium-Catalyzed Isomerization of ortho-Silylanilines to Their para Isomers

The catalytic ortho to para transposition of a silyl group in aniline derivatives is described. [RuCl₂(p-cymene)]₂/BINAP in conjunction with a Cu(OAc)₂ additive serves as a potent catalytic system. This method is also applicable to the isomerization of 2-silylpyrrole derivatives to the corresponding 3-silyl isomers.

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.

Construction of 6H-benzo[c]thiochromenes via a tandem reaction of arynes with thionoesters

A mild and transition-metal free method has been proposed for the synthesis of 6H-benzo[c]thiochromenes via the tandem reactions of arynes with thionoesters.

Metal-free dearomative [5+2]/[2+2] cycloaddition of 1H-indoles with ortho-(trimethylsilyl)aryl triflates

Herein, we report a mild dearomative [5+2]/[2+2] cycloaddition of 1H-indoles with ortho-(trimethylsilyl)aryl triflates. The unique [5+2] cycloaddition enables the synthesis of a series of dibenzo[b,e]azepine derivatives in moderate to good yields. Increasing the steric hindrance at the C2-position of 1H-indoles leads to the [2+2] cycloaddition. Mechanistic investigations support that the reaction of 1H-indoles with arynes undergoes a [2+2] cycloaddition step, followed by a ring expansion to the [5+2] cycloaddition product.