Sulfonium Ylides by (3+2) Cycloaddition of Arynes with Vinyl Sulfides: Stereoselective Synthesis of Highly Substituted Alkenes

Hydrothiolation of Triisopropylsilyl Acetylene Sulfur Pentafluoride - Charting the Chemical Space of β-SF5 Vinyl Sulfides

Recently, we suggested liquid and high-boiling TIPS-CC-SF5 (TASP) as a versatile reagent to access so far elusive SF5-containing building blocks by less specialized laboratories under bench-top conditions. The synthesis of non-aromatic SF5 building blocks generally requires on-site fluorination or pentafluorosulfanylation steps employing toxic and/or gaseous reagents. Herein, we underline the versatility of this reagent by reporting a benign bench-top protocol for the synthesis of Z-configured β-pentafluorosulfanylated vinyl sulfides in good to excellent yields (up to 99 %) with exclusive (Z)-diasteroselectivity and broad functional group tolerance. This method exploits an in-situ protodesilylation-hydrothiolation sequence. This so far uncharted class of compounds was characterized by means of NMR-spectroscopy as well as SC-XRD. Furthermore, we suggest the reaction to proceed via a kinetically controlled closed-shell reaction pathway, corroborated by in-silico experiments.

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.

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.

Advances in the synthesis of nitrogen-containing heterocyclic compounds by in situ benzyne cycloaddition

Nitrogen-containing heterocyclic compounds are prevalent in various natural products, medicines, agrochemicals, and organic functional materials. Among strategies to prepare nitrogen-containing heterocyclic compounds, pathways involving benzyne intermediates are attractive given that they can readily assemble highly diverse heterocyclic compounds in a step-economical manner under transition-metal-free conditions. The synthesis of nitrogen-containing heterocyclic compounds from benzyne intermediates offers an alternative strategy to the conventional metal-catalyzed activation approaches. In the past years, chemists have witnessed the revival of benzyne chemistry, mainly attributed to the wide application of various novel benzyne precursors. The cycloaddition of benzynes is a powerful tool for the synthesis of nitrogen-containing heterocyclic compounds, which can be constructed by [n + 2] cyclization of benzyne intermediates in situ generated from benzyne precursors under mild reaction conditions. This review focuses on the application of cycloaddition reactions involving in situ benzynes in the construction of various nitrogen-containing heterocyclic compounds.

Synthese von α-Arylacrylamiden via Lewis Base vermitteltem Aryl/Wasserstoff-Austausch

Hierin stellen wir eine neue Methode für die Synthese von α‐Arylacrylamiden vor. Die Reaktion basiert auf der Nutzung polarer S‐zu‐C Arylwanderungen, induziert durch einen Lewis‐basischen Organokatalysator. Im Unterschied zu zuvor publizierten radikalischen Arylwanderungen von Sulfonylacrylamiden, ermöglicht dieser polare Prozess eine darauffolgende Eliminierung, wodurch in Summe ein formaler Aryl/Wasserstoff‐Austausch unter Ausscheidung von SO2 stattfindet. Die vorgestellte Reaktion ist selektiv für elektronenarme aromatische Gruppen, während eine Vielfalt von Substituenten am Stickstoff und an der β‐Position toleriert werden, und erzeugt nützliche Bausteine für Folgereaktionen wie Zykloadditionen und Zyklisierungen. Der Reaktionsmechanismus wurde mithilfe quantenchemischer Berechnungen erforscht, die die unerwartete Rolle der Lewis Base in mehreren Schlüsselschritten darlegten.

Synthesis of α-Aryl Acrylamides via Lewis-Base-Mediated Aryl/Hydrogen Exchange

Herein we report a method for the synthesis of α-aryl acrylamides leveraging polar S-to-C aryl migrations induced by a Lewis basic organocatalyst. In contrast to previously reported radical aryl migrations of sulfonyl acrylimides, this polar process enables subsequent elimination, ultimately leading to a formal aryl/hydrogen exchange including SO₂ extrusion. This reaction is selective for electron-deficient aromatic groups, while tolerating a variety of substituents on nitrogen and in the β-position, and it delivers useful building blocks for further transformations, including cycloaddition and cyclisation reactions. The mechanism was investigated in detail using quantum chemical calculations, which unexpectedly revealed the Lewis base to be involved in several decisive steps.

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.

Access to diverse organosulfur compounds via arynes: a comprehensive review on Kobayashi's aryne precursor

Arynes are highly reactive transient intermediates having enormous applications in organic synthesis. In the last three decades aryne chemistry has shown incredible developments in carbon-carbon and carbon-heteroatom bond formation reactions. After the discovery of Kobayashi's protocol for the generation of aryne intermediates in a mild way, this field of chemistry witnessed rapid growth in synthetic organic chemistry. One aspect of development in this field involves C-S bond formation under mild conditions which has a tremendous scope for the synthesis of various important organosulfur building blocks.

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.

Redox-Neutral Rhodium(III)-Catalyzed Chemospecific and Regiospecific [4+1] Annulation between Indoles and Alkenes for the Synthesis of Functionalized Imidazo[1,5-a]indoles

Exploiting internal alkenes embedded with an oxidizing function/leaving group as a rare and unconventional one-carbon unit, a redox-neutral rhodium(III)-catalyzed chemo- and regiospecific [4+1] annulation between indoles and alkenes for the synthesis of functionalized imidazo[1,5-a]indoles has been achieved. Internal alkenes employed here can fulfill an unusual [4+1] annulation rather than normal [4+2] annulation/C-H alkenylation. This method is characterized by excellent chemo- and regioselectivity, broad substrate scope, good functional group tolerance, good to high yields, and redox-neutral conditions.

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.

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.

Arynes as Radical Acceptors: TEMPO-Mediated Cascades Comprising Addition, Cyclization, and Trapping

The application of arynes as radical acceptors is described. The stable radical TEMPO (2,2,6,6-tetramethyl piperidine 1-oxyl) is shown to add to various ortho-substituted benzynes generating the corresponding aryl radicals which engage in 5-exo or 6-endo cyclizations. The cyclized radicals are eventually trapped by TEMPO. The introduced method provides ready access to various dihydrobenzofurans, oxindoles, and sultones by a conceptually novel approach.

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.

One-step synthesis of benzo[b]thiophenes by aryne reaction with alkynyl sulfides

An aryne reaction with alkynyl sulfides affording benzo[b]thiophenes is disclosed. A wide range of 3-substituted benzothiophenes were synthesized from easily available o-silylaryl triflates and alkynyl sulfides in a one-step intermolecular manner. The synthesis of diverse multisubstituted benzothiophene derivatives involving a pentacyclic compound was achieved by virtue of the good functional group tolerance and versatile C2 functionalizations.

Uncovering the Neglected Similarities of Arynes and Donor-Acceptor Cyclopropanes

Arynes and donor-acceptor (D-A) cyclopropanes are two classes of strained systems having the potential for numerous applications in organic synthesis. The last two decades have witnessed a renaissance of interest in the chemistry of these species primarily because of the mild and robust methods for their generation or activation. Commonly, arynes as easily polarizable systems result in 1,2-disubstitution, whereas D-A cyclopropanes as polarized systems lead to 1,3-bisfunctionalization thereby showing striking similarities. Transformations with 1,2- and 1,3-dipoles afford cyclic structures. With arynes, emerging four-membered rings as intermediates might react further, whereas the analogous five-membered rings obtained from D-A cyclopropanes are most often the final products. However, there are a few cases where these intermediates behave surprisingly differently. This Minireview highlights the parallels in reactivity between arynes and D-A cyclopropanes thereby shedding light on the neglected similarities of these two reactive species.

Reaction of Vinyl Aziridines with Arynes: Synthesis of Benzazepines and Branched Allyl Fluorides

We report the cycloaddition between vinyl aziridines and arynes. Depending on the reaction conditions and the choice of the aryne precursor, the aziridinium intermediate can be trapped through two distinct mechanistic pathways. The first one proceeds through a formal [5+2] cycloaddition to furnish valuable multi-substituted benzazepines. In the second pathway, the aziridinium is intercepted by a fluoride ion to afford allylic fluorides in good yields. Both reactions proceed stereospecifically and furnish enantiopure benzazepines and allylic fluorides.

Reaction of ketone hydrazones with TeCl4: isolation and reactions of novel divinyl telluride

The reaction of acetophenone hydrazones with TeCl₄ in the presence of DBU gave divinyl tellurides. The reaction of divinyl tellurides with bromine or benzyne afforded the corresponding tellurium dibromides or (E)-2-alkenyl tellurides.

Practical and regioselective halo-trifluoromethylthiolation of sulfur ylides

A H2O mediated practical and highly regioselective chloro- and bromo-trifluoromethylthiolation of sulfur ylides is reported using a difunctionalization strategy. In the reaction sequence, sulfur ylides presumably react with an electrophilic trifluoromethylthiolating reagent to generate an α-SCF3 substituted sulfonium salt intermediate, which then undergoes a substitution with nucleophilic halogens.

Synthesis of Densely Functionalized N-Alkenyl 2-Pyridones via Benzyne-Induced Ring Opening of Thiazolino-Fused 2-Pyridones

We report the synthesis of 6-arylthio-substituted-N-alkenyl 2-pyridones by ring opening of bicyclic thiazolino-2-pyridones with arynes. Varied functionalization was used to investigate scope and substituent influences on reactivity. Selected conditions favor thioether ring opening over [4 + 2] cycloaddition and an unusual aryne incorporating ring expansion. Deuterium labeling was used to clarify observed reactivity. Using the knowledge, we produced drug-like molecules with complex substitution patterns and show how thioether ring opening can be used on scaffolds with competing reactivities.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

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.

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.

One-pot mild and efficient synthesis of [1,3]thiazino[3,2-a]indol-4-ones and their anti-proliferative activity

One-pot synthesis of [1,3]thiazino[3,2-a]indol-4-one frameworks is developed in aqueous medium and the anti-proliferative activity of the synthesized compounds is evaluated against two triple negative breast cancer cell lines.

Sequential cycloaddition and ring expansion reaction of arynes and methylenebenzothiopheneones: synthesis of a benzo-fused eight-membered ring via sulfonium ylides

Efficient construction of benzo-fused eight-membered ring containing sulfur. New reaction profile with sulfonium ylides.

Direct methylation and carbonylation of in situ generated arynes via HDDA-Wittig coupling

A high-efficiency HDDA-Wittig coupling strategy for synthesis of fully functionalized benzenes is reported. Direct methylation and carbonylation of aryne intermediates reacted with phosphorus ylides to form the carbonylated 2,3-dihydro-1H-indenes.