Regioselective Hydrothiolation of Alkenes Bearing Heteroatoms with Thiols Catalyzed by Palladium Diacetate

Thiyl Radical Trapped by Cobalt Catalysis: An Approach to Markovnikov Thiol-Ene Reaction

In the presence of a thiyl radical species, the catalytic Markovnikov thiol-ene reaction is challenging because it prefers to proceed via a radical pathway, thereby leading to anti-Markovnikov selectivity. In this work, a rare example of thiyl radical engaged in Markovnikov thiol-ene reaction enabled by cobalt catalysis is reported. This protocol features the avoidance of unique oxidants, exclusive regioselectivity, and broad substrate scope. Scalable synthesis and late-stage modification of complex molecules demonstrate the practicability of the protocol.

Transition-Metal-Catalyzed Addition of Organosulfur Compounds to Alkynes and Alkenes: Catalysis and Catalyst Poisons

The addition of heteroatom compounds to alkynes and alkenes is an atom-efficient method of carbon-heteroatom bond formation and is widely used as a fundamental synthetic method for the construction of functional molecules. Nevertheless, examples of transition-metal-catalyzed addition reactions of group 16 heteroatom compounds to carbon-carbon unsaturated bonds have been limited due to the widespread belief that organic sulfur and selenium compounds are representative catalyst poisons. In recent decades, however, several seminal catalytic reactions of sulfur compounds have been developed, providing important insights into catalysis and poisons. Therefore, this paper focuses on the transition-metal-catalyzed addition of organosulfur compounds to alkynes and alkenes, gains comprehensive insights into the catalysis and catalyst poisons, and proposes concepts for the development of transition-metal-catalyzed reactions of group 16 heteroatom compounds.

Visible light-driven photocatalytic thiol-ene/yne reactions using anisotropic 1D Bi2S3 nanorods: a green synthetic approach

Thiol-ene/yne click reactions play a significant role in creating carbon-sulfur (C-S) bonds, and there has been a growing interest in using visible-light photoredox catalysis for their formation. In this study, anisotropic 1D Bi2S3 nanorods were prepared using a simple polyol-assisted reflux method, and they were used as catalysts for the thiol-ene/yne click reactions under visible light irradiation. The developed protocol is highly compatible and tolerant to various substrates with excellent product yields. Also, thiol-ene and -yne reactions achieved maximum TONs of 93 and 95, respectively. Detailed mechanistic studies were conducted and supported by NMR studies, radical trapping utilizing TEMPO, and ESI-MS product analysis. The ability of Bi2S3 nanorods to catalyze thiol-ene/yne reactions is primarily due to the creation of photoexcited holes, which aid in the formation of thiyl radicals. This method can be scaled up to the gram-scale synthesis of benzyl styryl sulfide with an excellent chemical yield of 90%. The 1D Bi2S3 nanorods also demonstrated structural and morphological stability throughout five reaction cycles while maintaining a favorable photocatalytic activity. The developed methodology had the advantages of broad substrate scope, mild reaction conditions, scaled-up synthesis, and nonrequirement of free radical initiators.

Copper-Catalyzed Regio- and Stereoselective Hydrothiolation of Allenamides, Enamides, and Ynamides

We report a simple protocol for the copper-catalyzed hydrothiolation of N-unsaturated precursors, i.e., allenamides, enamides, and ynamides, under mild conditions. This method proceeds with a low loading of a commercially available Cu(CH₃CN)₄PF₆ catalyst and enables the room-temperature transformation of a wide range of aromatic and aliphatic thiols into allylic or vinylic thioethers, 1,3-dithioethers, and thioaminals with good regio- and stereoselectivity.

Synthesis of dithioacetals via gold-catalysed hydrothiolation of vinyl sulfides

The synthesis of unsymmetrical dithioacetals based on gold catalysis is described. Although many approaches to the preparation of symmetrical dithioacetals have been developed, the methods to access unsymmetrical ones remain limited. In this regard, we report a mild synthetic method with a broad substrate scope. Screening of various gold catalysts identified a catalyst, which allows the hydrothiolation of both activated and unactivated vinyl sulfides with high efficiency. Moreover, the reaction displays broad compatibility for both aryl and aliphatic thiols.

Green Catalytic Method for Hydrothiolation of Allylamines: An External Electric Field

Based on the idea of environmental friendliness, we first studied the hydrothiolation reactions of thiophenol with allylamine using a green catalyst-an external electric field (EEF). The hydrothiolation reactions could occur through Markovnikov addition (path M) and anti-Markovnikov addition (path AM) pathways. The calculation results demonstrated that when the EEF was oriented along F _-X , F _-Y , and F _+Z directions, path M was accelerated. However, it is favorable for path AM only when the EEF is oriented along the +X and -Y-axes. In addition, the introduction of the EEF further increased and lowered the differences of the reaction barrier as the EEF was oriented along F _-X , F _-Y , and F _+X directions. The solvent effects were also considered in this work. Hopefully, this unprecedented and green catalytic method for the hydrothiolation reactions of allylamine may provide guidance in the lab.

Reactivity switch-over of 4-hydroxydithiocoumarins under various conditions and their application in organic synthesis

4-Hydroxydithiocoumarin is a valuable organic precursor to architect important heterocycles. The three different reactive nucleophilic sites in 4-hydroxydithiocoumarins display intriguing regioselectivity in their reaction towards various electrophiles. Previously, 4-hydroxydithiocoumarins have been used in the synthesis of heterocycles using Claisen and thio-Claisen reactions. Hetero-Diels-Alder reactions involving 4-hydroxydithiocoumarins have proven to be very convenient in assembling complex molecular organic frameworks from readily available feedstocks. Development of multicomponent reactions employing 4-hydroxydithiocoumarins has given rise to several important reaction protocols to access polycyclic compounds. Recently, this moiety has been used in forging some unusual S-S, S-N and S-O bonds under oxidative conditions which further explores its hidden reactivity in organic synthesis. Besides that, hydrothiolation of various alkynes and alkenes using 4-hydroxydithiocoumarins has led to the synthesis of some potential lead molecules. This mini-review provides an account of the reactivity pattern of 4-hydroxydithiocoumarins and their strategic applications in various reactions for the synthesis of several heterocycles and other important organic syntheses.

Directing-Group-Assisted Markovnikov-Selective Hydrothiolation of Styrenes with Thiols by Photoredox/Cobalt Catalysis

In contrast with the well-developed radical thiol-ene reaction to access anti-Markovnikov-type products, the research on the catalytic Markovnikov-selective hydrothiolation of alkenes is very restricted. Because of the catalyst poisoning of metal catalysts by organosulfur compounds, limited examples of transition-metal-catalyzed thiol-ene reactions have been reported. However, in this work, a directing-group-assisted hydrothiolation of styrenes with thiols by photoredox/cobalt catalysis is found to proceed smoothly to afford Markovnikov-type sulfides with excellent regioselectivity.

Catalysis and regioselectivity in hydrofunctionalization reactions of unsaturated carbon bonds. Part III

The review addresses the possibility of obtaining Markovnikov and anti-Markovnikov isomers in the reactions of unsaturated hydrocarbons with organophosphorus and organosulfur compounds having P–H and S–H bonds using metal salts or complexes as catalysts.

The bibliography includes 247 references.

Copper-catalyzed diastereoselective hydrothioetherification of oxa(aza)benzonorbornadienes

A novel copper-catalyzed hydrothioetherification of oxa(aza)bicyclic alkenes with potassium thioacetate and aryl or alkyl iodides to synthesize unsymmetrical thioethers has been developed. Notably, the reaction with complete diastereoselectivity went through a syn-selective addition process to give exo-adducts. In addition, this protocol exhibited high efficiency and good functional group tolerance to afford the target thioethers in moderate to good yields. Based on the results of mechanistic investigations, a plausible mechanism was proposed.

Thiol-Ene Cationic and Radical Reactions: Cyclization, Step-Growth, and Concurrent Polymerizations for Thioacetal and Thioether Units

Thiol-ene cationic and radical reactions were conducted for 1:1 addition between a thiol and vinyl ether, and also for cyclization and step-growth polymerization between a dithiol and divinyl ether. p-Toluenesulfonic acid (PTSA) induced a cationic thiol-ene reaction to generate a thioacetal in high yield, whereas 2,2'-azobisisobutyronitrile resulted in a radical thiol-ene reaction to give a thioether, also in high yield. The cationic and radical addition reactions between a dithiol and divinyl ether with oxyethylene units yielded amorphous poly(thioacetal)s and crystalline poly(thioether)s, respectively. Under high-dilution conditions, the cationic and radical reactions resulted in 16- and 18-membered cyclic thioacetal and thioether products, respectively. Furthermore, concurrent cationic and radical step-growth polymerizations were realized using PTSA under UV irradiation to produce polymers having both thioacetal and thioether linkages in the main chain.

Nickel-catalysed selective migratory hydrothiolation of alkenes and alkynes with thiols

Direct (utilize easily available and abundant precursors) and selective (both chemo- and regio-) aliphatic C–H functionalization is an attractive mean with which to streamline chemical synthesis. With many possible sites of reaction, traditional methods often need an adjacent polar directing group nearby to achieve high regio- and chemoselectivity and are often restricted to a single site of functionalization. Here we report a remote aliphatic C–H thiolation process with predictable and switchable regioselectivity through NiH-catalysed migratory hydrothiolation of two feedstock chemicals (alkenes/alkynes and thiols). This mild reaction avoids the preparation of electrophilic thiolation reagents and is highly selective to thiols over other nucleophilic groups, such as alcohols, acids, amines, and amides. Mechanistic studies show that the reaction occurs through the formation of an RS-Bpin intermediate, and THF as the solvent plays an important role in the regeneration of NiH species.

Construction of C–S bonds via C–H functionalization is an attractive route to organosulfur compounds. Here, the authors show the synergistic combination of NiH-catalysed alkene isomerization and subsequent thiolation to afford remote hydrothiolation products from alkenes (or alkynes) and thiols under mild conditions.

Catalytic Hydrothiolation: Counterion-Controlled Regioselectivity

In this Article, we expand upon the catalytic hydrothiolation of 1,3-dienes to afford either allylic or homoallylic sulfides with high regiocontrol. Mechanistic studies support a pathway in which regioselectivity is dictated by the choice of counterion associated with the Rh center. Non-coordinating counterions, such as SbF6-, allow for η4-diene coordination to Rh complexes and result in allylic sulfides. In contrast, coordinating counterions, such as Cl-, favor neutral Rh complexes in which the diene binds η2 to afford homoallylic sulfides. We propose mechanisms that rationalize a fractional dependence on thiol for the 1,2-Markovnikov hydrothiolation while accounting for an inverse dependence on thiol in the 3,4- anti-Markovnikov pathway. Through the hydrothiolation of an essential oil (β-farnesene), we achieve the first enantioselective synthesis of (-)-agelasidine A.

Catalytic Hydrothiolation: Regio- and Enantioselective Coupling of Thiols and Dienes

We report a Rh-catalyzed hydrothiolation of 1,3-dienes, including petroleum feedstocks. Either secondary or tertiary allylic sulfides can be generated from the selective addition of a thiol to the more substituted double bond of a diene. The catalyst tolerates a wide range of functional groups, and the loading can be as low as 0.1 mol %.

Organoactinides in catalytic transformations: scope, mechanisms and Quo Vadis

The last decade has witnessed brilliant and remarkable advances in the chemistry of the early actinides in stoichiometric and in challenging catalytic processes. This canvas of knowledge allows the design of chemical reactivities reaching a high level of sophistication. This review highlights the latest results obtained since 2008 on those catalytic processes.

Single-Electron Transfer between CuX2 and Thiols Determined by Extended X-Ray Absorption Fine Structure Analysis: Application in Markovnikov-Type Hydrothiolation of Styrenes

Transition-metal mediated C-S bond formation using thiol compounds has been widely used in recent years. However, there has been less focus on the interaction between the metal and thiol compounds. In this work, we have successfully evidenced the single-electron transfer between CuX₂ and thiophenol utilizing EXAFS. The fitting EXAFS results reveal that two halide anions are coordinated with the Cu^I center, whereas no sulfur atom is observed in the first coordination sphere. This Cu^I ate complex serves as the key intermediate for the proton transfer in the application of Markovnikov-type hydrothiolation reactions.

Palladium-Catalyzed Markovnikov-Selective Hydroselenation of N-Vinyl Lactams with Selenols Affording N,Se-Acetals

The highly regioselective hydroselenation of N-vinyl lactams has been revealed to successfully afford the corresponding N,Se-acetals as Markovnikov adducts. In the case of terminal N-vinyl lactams, Markovnikov-selective hydroselenation proceeds efficiently in the absence of any catalyst (or additive), owing to the acidity of the selenols. In contrast, the self-promoted hydroselenation is inefficient with internal N-vinyl lactams. In the presence of palladium diacetate (Pd(OAc)2), however, the desired hydroselenation of internal N-vinyl lactams proceeds efficiently to afford the corresponding N,Se-acetals.

The air-stable carbocation salt [(MeOC6H4)CPh2][BF4] in Lewis acid catalyzed hydrothiolation of alkenes

Markovnikov hydrothiolation of 1,1-disubstituted and trisubstituted olefins (20 examples) is catalyzed by Lewis acids, including the air-stable trityl-cation salt [(MeOC₆H₄)CPh₂][BF₄] 3.

Selective Thiolative Lactonization of Internal Alkynes Bearing a Hydroxyl Group with Carbon Monoxide and Organic Disulfides Catalyzed by Transition-Metal Complexes

Although many transition-metal catalysts are ineffective for the addition and carbonylative addition of organic disulfides to internal alkynes, dicobalt octacarbonyl and palladium complexes such as Pd(PPh3)4 and Pd(OAc)2 were found to exhibit excellent catalytic activity for the thiolative lactonization of internal alkynes bearing a hydroxyl group. In the presence of the cobalt or palladium catalyst, internal alkynes bearing a hydroxy group, such as homopropargyl alcohol derivatives, successfully undergo thiolative carbonylation with carbon monoxide and an organic disulfide regio- and stereoselectively to afford the corresponding thio group bearing-lactones in good yields. In the Co-catalyzed reaction, the cobalt-alkyne complex from dicobalt octacarbonyl and internal alkyne acts as a key species, making it possible to attain thiolative lactonization of internal alkynes with a hydroxyl group. In the Pd-catalyzed reaction, the coordination of the hydroxy group to the palladium catalyst plays an important role for the thiolative lactonization.