Synthesis of β-Hydroxysulfides via Multi-Component Cascade Hydroxysulfenylation of Styrenes with NH4 SCN and Water under Transition-metal-free Conditions

Transition-mental-free multi-component hydroxysulfenylation of styrenes with NH4 SCN and water to from β-hydroxysulfides is established. The reaction mechanism proceeded via a domino reaction after a radical addition to 2-phenylimidazo[1,2-a]pyridines. This approach features a wide substrate scope and functional group compatibility, providing 34 compounds in acceptable yields.

Base-Induced Decarboxylative 1,1-Alkoxy Thiolation via Hydrothiolation of Vinylene Carbonate

A base-mediated 1,1-difunctionalization of vinylene carbonate has been achieved using two different nucleophiles, namely, thiol and alcohol, with the assistance of air (O2). In alcoholic solvents, decarboxylation occurs at room temperature to provide a 1,1-difunctionalized product, where vinylene carbonate serves as an ethynol (C2) synthon in this three-component reaction. On the other hand, in acetonitrile, exclusive hydrothiolation occurs under the basic conditions at room temperature. This method offers a one-pot decarboxylative regioselective difunctionalization of vinylene carbonate at room temperature for the construction of α-alkoxy-β-hydroxy sulfide.

Three-Component Oxychalcogenation of Alkenes under Metal-Free Conditions: A Tetrabutylammonium Tribromide-Catalyzed System

A three-component oxychalcogenation reaction, from alkenes, diselenides/thiophenols, and H₂O/alcohols, has been realized herein. Tetrabutylammonium tribromide (TBATB) and dimethylsulfoxide (DMSO) are utilized as the catalyst and the terminal oxidant, respectively, to enable this difunctionalization transformation. The metal-free reaction system shows good functional group compatibility, providing a unified and practical approach to access β-hydroxyl or β-alkoxy organochalcogenides.

DMSO-Mediated Difunctionalization of Electron-Deficient Olefins to Access β-Hydroxysulfides with High Chemoselectivity

A novel and convenient method for the highly chemoselective synthesis of β-hydroxysulfides mediated by DMSO is reported. This eco-friendly reaction was amenable to a broad range of substrates and provided the desired β-hydroxysulfides in moderate to good yields with high selectivity via radical process. Moreover, several pharmaceutical and bioactive molecules were also suitable substrates for this reaction conditions to afford the targeted products in good yields.

External oxidant-free and selective thiofunctionalization of alkenes enabled by photoredox-neutral catalysis

A photoredox approach was reported to realize a highly selective three-component thiohydroxylation, thioalkoxylation and thioamination of vinylarenes towards valuable vicinal S,O- and S,N-disubstituted molecules under mild conditions.

Solvent-mediated switching between oxidative addition and addition–oxidation: access to β-hydroxysulfides and β-arylsulfones by the addition of thiols to olefins in the presence of Oxone

Solvent-switching allows formation of either β-hydroxy-2-arylethyl aryl sulfides or 2-arylethyl aryl sulfones exclusively in thiol–ene ‘click’ reactions conducted with Oxone.

Oxidative cross-coupling of thiols for S-X (X = S, N, O, P, and C) bond formation: mechanistic aspects

This review focuses on the reactive intermediates (disulfides, sulfenyl halides, thiyl radicals, sulfenium cations, and metal-organosulfur species) and the mechanisms of the recently reported oxidative couplings of thiols. These intermediates are generated by chemical oxidants, transition metal catalysts, electrochemistry, and photochemistry. Chemical oxidant-mediated reactions involve radical, halogenated, or cationic intermediates, or disulfides. Transition metal-catalyzed mechanisms proposed various metal-organosulfur intermediates to elucidate the reactivity and selectivity of metal catalysts. In electro- and photooxidation, direct oxidation/reduction mechanisms of reactants at the electrode or indirect oxidation/reduction of reactants in the presence of redox catalysts have been reported. The following sections are based on the products, thiosulfonates (S-S bond), sulfenamides, sulfinamides, and sulfonamides (S-N bond), sulfinates (S-O bond), thiophosphine oxides and thiophosphates (S-P bond), and sulfides, sulfoxides, and sulfones (S-C bond) and discuss the reaction mechanisms and the above-mentioned key intermediates for product formation. The contents of this review will provide helpful information, guiding the choice of oxidative coupling conditions for the synthesis of various organosulfur compounds with high yields and selectivity.

Brønsted Acid-Catalyzed Regioselective Hydrothiolation of Dienes: Solvent-Controlled Divergent Synthesis of Sulfides

A Brønsted acid-catalyzed 1,4-addition hydrothiolation of branched 1,3-dienes was explored for the first time. A solvent-controlled divergent synthesis of sulfides is also disclosed. Use of acetonitrile as a solvent gave allylic sulfides as hydrothiolation products, while thiochromane derivatives (hydrothiolation/Friedel-Crafts products) were obtained using dichloromethane as the solvent. The origin of the regioselectivity of hydrothiolation was explored through density functional theory calculations.

Light-Promoted and Tertiary-Amine-Assisted Hydroxysulfenylation of Alkenes: Selective and Direct One-Pot Synthesis of β-Hydroxysulfides

A light-promoted and tertiary-amine-assisted strategy for efficient hydroxysulfenylation of both electron-rich and electron-deficient alkenes with thiophenols to selectively and directly access β-hydroxysulfides in one pot is described herein. In contrast to the previously reported thiol-oxygen co-oxidation reactions, this simple and sustainable approach features mild reaction conditions, high efficiency, and excellent functional group tolerance.

Selective oxidative intermolecular carbosulphenylation of aryl alkenes with thiols and nucleophiles via a 1,2-dithioethane intermediate

A periodate lithium-oxidized difunctionalisation of aryl alkenes with thiols and electron-rich aromatics was achieved, selectively affording more than thirty carbosulphenylated products. Both experiments and quantum chemical calculations demonstrated the radical-polar nature of the processes, and that 1,2-dithioethane and thiiranium ions might play the role of intermediates.

Intermolecular difunctionalization of alkenes: synthesis of β-hydroxy sulfides

Direct difunctionalization of carbon-carbon double bonds is one of the most powerful tools available for concomitant introduction of two functional groups into olefinic substrates. In this context, vicinal hydroxysulfenylation of unactivated alkenes has emerged as a novel and straightforward strategy for the fabrication of β-hydroxy sulfides, which are extremely valuable starting materials in constructing various natural products, pharmaceuticals, and fine chemicals. The aim of this review is to summarize the most representative and important reports on the preparation of β-hydroxy sulfides through intermolecular hydroxysulfenylation of the corresponding alkenes with special emphasis on the mechanistic features of the reactions.

Metal-free C–S coupling of thiols and disulfides

A literature overview on C–S coupling reactions using thiols or disulfides as sulfur surrogates under metal-free conditions is presented. Reagents for the transformations include polyvalent iodines, peroxides, tert-butyl nitrite (TBN), DDQ, and aerial oxygen, among others.

A Mild and Direct C(sp3)-S Cross-Coupling of Oxindoles with Thiols: Synthesis of Unsymmetrical 3-Thiooxindoles

Herein, an operationally simple and mild strategy to construct sulfenation of oxindoles with a series of thiols in the absence of transition metals was developed. This methodology provides an efficient way to directly form a C-S bond at the C-3 position of oxindoles under mild reaction conditions with a cheap and common solvent and base in moderate to good yields.

Aerobic conversion of benzylic sp3 C–H in diphenylmethanes and benzyl ethers to CO bonds under catalyst-, additive- and light-free conditions

Catalyst-, additive- and light-free aerobic conversion of benzylic C–H to CO bonds is, for the first time, reported.

Decarbonylative Formation of Homoallyl Radical Capable of Annulation with N-Arylpropiolamides via Aldehyde Auto-oxidation

A new metal-free aldehyde auto-oxidation strategy that allows the decarbonylative formation of homoallyl radical capable of cascade annulations with alkynes is described. By using various N-arylpropiolamides, the oxidative radical [3 + 2]/[5 + 2] cascade annulation reaction was achieved to produce benzo[ b]cyclopenta[ e]azepin-4(1 H)-ones, which represent a powerful new platform for the intermolecular cycloadditions of alkyne with broad substrate scope and high selectivity.

An expeditious and efficient bromomethylation of thiols: enabling bromomethyl sulfides as useful building blocks

A facile and highly efficient method for the bromomethylation of thiols, using paraformaldehyde and HBr/AcOH, has been developed, which advantageously minimizes the generation of highly toxic byproducts. The preparation of 22 structurally diverse α-bromomethyl sulfides illustrates the chemo-tolerant applicability while bromo-lithium exchange and functionalization sequences, free radical reductions, and additions of the title compounds demonstrate their synthetic utility.

A new method for the bromomethylation of thiols using paraformaldehyde and HBr/AcOH, minimizes the generation of toxic byproducts. Synthetic utility of α-bromomethyl sulfides was demonstrated through umpolung and free radical chemistry.

Air promoted annulation of thiophenols with alkynes leading to benzothiophenes

Air promoted intermolecular annulation of thiophenols with alkynes, leading to complex benzothiophenes, is reported.

Auto-oxidation promoted sp3 C–H arylation of glycine derivatives

An auto-oxidation promoted sp³ C–H arylation reaction between N-aryl glycine derivatives and electron-rich arenes, leading to the formation of N-aryl α-aryl α-amino acid derivatives, is described. This atom-economical and environmentally benign reaction proceeds smoothly under mild reaction conditions and requires only Brønsted acid and oxygen (balloon). A plausible radical involved mechanism is proposed.

Direct construction of benzimidazo[l,2-c]quinazolin-6-ones via metal-free oxidative C–C bond cleavage

A highly regioselective protocol has been developed for the synthesis of benzimidazo[l,2-c]quinazolin-6-ones via C–C bond cleavage and triple C–N bond formation.

Visible-light-mediated iodine-catalyzed α-hydroxylation of α-methylene ketones under aerobic conditions

A visible-light-mediated α-hydroxylation of α-methylene ketones using atmospheric oxygen as a green oxidant has been developed with novel substrate selectivity.

One-Pot Synthesis of β-Hydroxysulfones and Its Application in the Preparation of Anticancer Drug Bicalutamide

An efficient one-pot multistep strategy has been developed, comprising auto-oxidative difunctionalization of alkenes, oxidation of sulfides, and a further reduction of peroxides for the synthesis of complex β-hydroxysulfone derivatives from phenthiols and alkenes. This method has several advantageous characteristics, including readily available substrates, low-cost and environmental benign reagents, nontoxic and renewable solvents, and mild reaction conditions. The application of this transformation to the multigram-scale preparation of the anticancer drug bicalutamide is accomplished.

Tandem radical cyclization to construct poly-brominated 2-oxindoles

A metal-free aerobic way to construct tribromomethylated poly-brominated 2-oxindoles from reaction of N-arylacrylamides with CBr₄via a tandem radical cyclization process was discovered. The formation of the 1,1-dibromoolefin derivatives was also realized at higher temperature.

Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

Multiple radical reaction steps have been observed in a continuous sequence with sub-picosecond to microsecond transient absorption spectroscopy.

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.