3-Thioaryne Intermediates for the Synthesis of Diverse Thioarenes

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.

Electrophilic Activation of S-Si Reagents by Silylium Ions for Their Regio- and Diastereoselective Addition Across C-C Multiple Bonds

A regioselective silylium-ion-promoted thiosilylation of internal C-C triple bonds with control over the double bond geometry is described. Both a C(sp2)-S and a C(sp2)-Si bond are formed with a trans relationship in this two-component reaction of an alkyne and a thiosilane. The resulting orthogonally functionalized C-C double bond can be chemoselectively defunctionalized or further processed by cross-coupling reactions with the alkene configuration retained. The procedure is also applicable to the regio- and diastereoselective thiosilylation of terminal allenes to arrive at allylic thioethers containing a vinylsilane unit. These reactions involve the electrophilic activation of the S-Si reagent, both a silylated thiophenol and even alkylthiol derivative, by an in situ-generated carbocation intermediate. The catalytic cycle is maintained by a bissilylated aryl- or alkylsulfonium ion as a shuttle for the cationic silicon electrophile. Its independent preparation and structural characterization by X-ray diffraction are also reported.

Facile synthesis of dibenzothiophene S-oxides from sulfinate esters

An efficient method to prepare dibenzothiophene S-oxides is disclosed. Suzuki-Miyaura cross-coupling of 2-bromoaryl sulfinate esters with arylboronic acids selectively at the bromo group followed by electrophilic cyclization of the resulting sulfinate ester moiety provides diverse dibenzothiophene S-oxides. Further transformations including Pummerer-type C-H propargylation and aryne reactions realize to synthesize highly functionalized dibenzothiophene derivatives.

Development of 3-triazenylaryne and its application to iterative aryne reactions via o-triazenylarylboronic acids

Herein, a novel aryne species, 3-triazenylaryne, was developed and its regioselectivity was revealed. Based on the regioselectivity, various alkyne moieties were introduced by iodoalkynylation, and further derivatization to o-triazenylarylboronic acids as 3-alkynylaryne precursors was enabled. Therefore, 3-triazenylaryne was developed as a divergent platform for the generation of various 3-alkynylarynes.

Synthesis of Multisubstituted Aromatics via 3-Triazenylarynes

An efficient method for generating 3-triazenylarynes from ortho-iodoaryl triflate-type precursors was developed. The generated arynes reacted with various arynophiles with high regioselectivity because of the triazenyl group. The 3-triazenylaryne precursors functioned as useful intermediates of diverse multisubstituted aromatic compounds through the transformation of the remaining triazenyl group of aryne adducts and triazenyl group-directed ortho-C-H functionalization.

Synthesis of Sulfur-Containing Analogues of Hedychenone, a Labdane Diterpenoid from Hedychium spicatum

The labdane diterpene hedychenone, isolated from Hedychium spicatum, is an example of a furan-containing natural product. Herein, a new and efficient method for the synthesis of 19 new thio analogues of hedychenone is reported. The present methodology exhibits a broad substrate scope with good to excellent yields without metal or base under mild reaction conditions. The natural compound 1 and four semisynthetic derivatives (3a, 3b, 3i, and 3j) exhibited strong α-glucosidase inhibition activity with IC₅₀ values of 15.93 ± 0.29, 9.70 ± 0.33, 11.82 ± 0.06, 12.23 ± 0.33, and 12.15 ± 0.14 μg/mL, respectively. In addition, compound 3e (6.0 ± 0.04 mm; zone of inhibition) displayed antibacterial activity against Staphylococcus aureus. This study increases the chemical diversity of bioactive hedychenone derivatives and provides a direction for the development of antidiabetic agents.

Synthesis of Multisubstituted Benzenes from Phenols via Multisubstituted Benzynes

A new method to synthesize multifunctionalized arenes from simple phenols through aryne intermediates is described. Multisubstituted aryne precursors were prepared from phenols by Ir-catalyzed C–H borylation, deborylthiolation, O-triflylation, S-oxidation, and further modification through ortho-deprotonation directed by the sulfoxide moiety. Various multisubstituted arenes were synthesized by transformations of highly functionalized aryne intermediates generated from the o-sulfinylaryl triflates.

Regioselective transformation of 3-phosphoryl benzyne intermediates to diverse phosphorus-substituted arenes

Pre-functionalized benzyne precursors 5, 6 and 10 bearing a phosphoryl group were efficiently synthesized via a phospho-Fries rearrangement reaction on gram scales, and directly proceed various transformations to poly-substituted organophosphorus arenes in high regioselectivity.

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%.

The Aryne-Abramov Reaction as a 1,2-Benzdiyne Platform for the Generation and Solvent-Dependent Trapping of 3-Phosphonyl Benzynes

Synthetic methodology utilizing two aryne intermediates (i.e., a formal benzdiyne) enables the rapid generation of structurally complex molecules with diverse functionality. This report describes the sequential generation of two ortho-benzyne intermediates for the synthesis of 2,3-disubstituted aryl phosphonates. Aryl phosphonates have proven useful in medicinal chemistry and materials science, and the reported methodology provides a two-step route to functionally dense variants by way of 3-phosphonyl benzyne intermediates. The process begins with regioselective trapping of a 3-trifloxybenzyne intermediate by an O-silyl phosphite in an Abramov-like reaction to bond the strained Csp carbons with phosphorus and silicon. Standard aryne-generating conditions follow to convert the resulting 2-silylphenyl triflate into a 3-phosphonyl benzyne, which readily reacts with numerous aryne trapping reactants to form a variety of 2,3-difunctionalized aryl phosphonate products. DFT computational studies shed light on important mechanistic details and revealed that 3-phosphonyl benzynes are highly polarizable. Specifically, the distortion in the internal bond angles at each of the Csp atoms was strongly influenced by both the electronegativity of the phosphonate ester groups as well as the dielectric of the computational solvation model. These effects were verified experimentally as the regioselectivity of benzyl azide trapping increased with more electronegative esters and/or increasingly polar solvents. Conversely, replacing the conventional solvent, acetonitrile, with nonpolar alternatives provided attenuated or even inverted selectivities. Overall, these studies showcase new reactivity of benzyne intermediates and extend the aryne relay methodology to include organophosphonates. Furthermore, this work demonstrates that the regioselectivity of aryne trapping reactions could be tuned by simply changing the solvent.

Transition-Metal-Free Synthesis of N-Arylphenothiazines through an N- and S-Arylation Sequence

An efficient synthetic method of N-arylphenothiazines from o-sulfanylanilines under transition-metal-free conditions is disclosed. An N- and S-arylation sequence of o-sulfanylanilines enabled us to synthesize a wide variety of N-arylphenothiazines. In particular, one-pot synthesis of N-arylphenothiazines was accomplished from easily available modules through preparation of o-sulfanylanilines by thioamination of aryne intermediates and following N- and S-arylation sequence.

Diverse diaryl sulfide synthesis through consecutive aryne reactions

An efficient method to synthesize diaryl sulfides with structural diversity is disclosed. Demethylative hydrothiolation of aryne intermediates generated from o-iodoaryl triflates with methylthio-substituted o-silylaryl triflates and further aryne reactions afford diverse diaryl sulfides.

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.

Aryne Precursors for Selective Generation of 3-Haloarynes: Preparation and Application to Synthetic Reactions

The synthesis and reaction of new 3-haloaryne precursors 2a-2h were studied. The ortho-(trimethylsilyl)aryl triflate precursors 2a-2h were prepared by a simple procedure involving O-trimethylsilylation and migration of a trimethylsilyl group followed by triflation. The remarkable feature of new precursors is the selective generation of 3-haloarynes by suppressing the competitive thia-Fries rearrangement, which is the problem in the reaction using the well-known 3-haloaryne precursors. The advantage of new precursor 2a over a typical precursor 1 was confirmed by the direct comparisons in several reactions. The application of precursors 2a-2h to the syntheses of heterocycles was also reported.

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.

Sulfoxide synthesis from sulfinate esters under Pummerer-like conditions

A facile synthetic method for the preparation of allyl sulfoxides by S-allylation of sulfinate esters proceeds through sulfonium intermediates without [3,3]-sigmatropic rearrangement and further Pummerer-type reactions of the resulting allyl sulfoxides. On the basis of the plausible reaction mechanism involving sulfonium salt intermediates, S-alkynylation and S-arylation were also accomplished.

Strategies toward Aryne Multifunctionalization via 1,2-Benzdiyne and Benzyne

Polysubstituted arenes are prevalent in numerous natural products, medicines, agrochemicals, and organic functional materials. Among methods to prepare polysubstituted arenes, pathways involving benzyne intermediates are particularly attractive given they can readily assemble highly diverse vicinal difunctionalized benzenes in a step-economical manner under transition-metal-free conditions. In order to incorporate more than two substituents on a benzene ring via a benzyne intermediate, methodologies involving benzdiyne and benztriyne have been developed, which significantly expand the current difunctionalization strategies in benzyne chemistry. In the past years, our group has been focusing on pushing the frontier of traditional benzyne chemistry and exploring new applications. In an aim to efficiently and conveniently construct polysubstituted arenes, we developed several aryne multifunctionalization strategies. The first strategy is through the 1,2-benzdiyne processes, which can be divided into a domino aryne approach and stepwise 1,2-benzdiyne approach. In our domino aryne study, we developed three domino aryne reagents as "sesquibenzyne" synthons, which are complementary in terms of reactivity and could adapt different modes of cascade transformations. By employing these domino aryne precursors, we were able to accomplish several cascade transformations, including double nucleophilic reactions, i.e., the reaction with carbonyl protected benzothioamides, 1,2-diamination, and 1,3-diamination. In addition, two cascade processes involving nucleophilic and pericyclic reactions, namely, domino aryne annulation via nucleophilic-ene cascade and domino aryne nucleophilic, Diels-Alder process, were successfully achieved as well. Meanwhile, with our desire to expand the scope of 1,2-benzdiyne transformations, we employed stepwise 1,2-benzdiyne tactics to access polysubstituted arenes. Depending on the property of the substituent on the C3-position of a benzyne intermediate, either an electron-withdrawing or electron-donating group, the incoming ortho groups were chosen accordingly. Consequently, we realized a [2 + 2] cycloaddition-Grob fragmentation process using 3-triflyloxybenzyne and a 1,2-benzdiyne process using 3-(trimethylsilyl)benzyne. Our second research strategy is to use single benzyne to access trisubstituted arenes, which represents a more atom- and step-economical protocol. With our deliberate design, we discovered a tandem benzyne S═O bond insertion/C-H functionalization process using single benzyne and aryl allyl sulfoxides, furnishing three chemical bonds of different types in a single process. This transformation is the first 1,2,3-trisubstitution example using single benzyne intermediate. At last, we developed an oxidative dearomatization strategy on Kobayashi benzyne precursors, which led to the preparation of various cyclohexenynone precursors with diverse substituents in highly efficient manner. In this study, we also demonstrated a new reaction mode of these cyclohexenynones with allyl sulfoxides, which involves a deeper utilization of the cyclohexyne triple bond. This work is the first example of successful connection of precursors of benzyne with cyclohexyne together, revealing a new research direction in the field of cyclohexyne.

Recent advances in the synthesis of fluorinated compounds via an aryne intermediate

In this review, the usefulness of aryne intermediates for the synthesis of various fluorinated organic compounds during the last decade has been demonstrated.

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.