Pd-Catalyzed Desulfitative Heck Coupling with Dioxygen as the Terminal Oxidant

Aerobic Copper-Catalyzed Oxysulfonylation of Vinylarenes with Sodium Sulfinates under Mild Conditions: A Modular Synthesis of β-Ketosulfones

An aerobic copper-catalyzed oxysulfonylation of vinylarenes with sodium sulfinates is described. This protocol features mild reaction conditions, convenient operation, and broad substrate scope with respect to vinylarenes and sodium sulfinates. Notably, the protocol demonstrates excellent tolerance of functional groups such as chloro, bromo, ester, cyano, and nitro groups. Mechanistic investigations indicated that the reaction should undergo radical cascades involving a sulfonyl radical generated from sodium sulfinate with air as the terminal oxidant, addition across alkene to deliver a benzylic radical, and subsequent cross-coupling with air.

Palladium-Catalyzed Tsuji-Trost-Type Reaction of 3-Indolylmethylacetates with O, and S Soft Nucleophiles

The chemical valorization of widespread molecules in renewable sources is a field of research widely investigated in the last decades. In this context, we envisaged that indole-3-carbinol, present in different Cruciferae plants, could be a readily available building block for the synthesis of various classes of indoles through a palladium-catalyzed Tsuji-Trost-type reaction with O and S soft nucleophiles. The regiochemical outcome of this high-yielding functionalization shows that the nucleophilic substitution occurs only at the benzylic position. Interestingly, with this protocol, the sulfonyl unit could be appended to the indole nucleus, providing convenient access to new classes of molecules with potential bioactivity.

Sulfonylpyrazole- and pyrazole-directed ortho-selective C-H functionalization/alkenylation and desulfenylative olefination of aryl(sulfonyl)pyrazoles

ortho-Selective C-H alkenylation of arenes was achieved using sulfonylpyrazoles and pyrazoles as directing groups, favored by a combination of a Pd(OAc)2 catalyst, Boc-Sar-OH and silver acetate. A wide variety of mono-alkenylated products of aryl-sulfonylpyrazoles and pyrazoles were synthesized with complete site-selectivity under mild reaction conditions. This transformation tolerated several electron-withdrawing and electron-donating groups on the aryl ring and the yields ranged from 52% to 70%, producing highly decorated/valuable alkenylated sulfonylpyrazole and pyrazole derivatives. Amazingly, switching of the oxidant, with the use of AgBF4 in place of AgOAc, offered cinnamic acid derivatives through de-sulfonylation followed by alkenylation at the same position with good yields in the case of aryl-sulfonylpyrazoles. These kinds of molecules have great biological importance and target predictions indicate that they may serve as potential antifungal and anti-tumor agents.

Three-Component Tandem Amidosulfenylation of Alkenes for the Synthesis of β-Succinimide Sulfides

An environmentally benign multicomponent strategy for the amidosulfenylation of alkenes for the synthesis of β-succinimide sulfides is disclosed. In this process, common disulfides smoothly act as a sulfur-based source, and N-iodosuccinimide (NIS) is used not only as a free radical initiator but also as an N-nucleophile. A broad range of functional groups are tolerated in this reaction system.

Effect of Arylazo Sulfones on DNA: Binding, Cleavage, Photocleavage, Molecular Docking Studies and Interaction with A375 Melanoma and Non-Cancer Cells

A set of arylazo sulfones, known to undergo N-S bond cleavage upon light exposure, has been synthesized, and their activity in the dark and upon irradiation towards DNA has been investigated. Their interaction with calf-thymus DNA has been examined, and the significant affinity observed (most probably due to DNA intercalation) was analyzed by means of molecular docking "in silico" calculations that pointed out polar contacts, mainly via the sulfonyl moiety. Incubation with plasmid pBluescript KS II revealed DNA cleavage that has been studied over time and concentration. UV-A irradiation considerably improved DNA damage for most of the compounds, whereas under visible light the effect was slightly lower. Moving to in vitro experiments, irradiation was found to slightly enhance the death of the cells in the majority of the compounds. Naphthylazosulfone 1 showed photo-disruptive effect under UV-A irradiation (IC50 ~13 μΜ) followed by derivatives 14 and 17 (IC50 ~100 μΜ). Those compounds were irradiated in the presence of two non-cancer cell lines and were found equally toxic only upon irradiation and not in the dark. The temporal and spatial control of light, therefore, might provide a chance for these novel scaffolds to be useful for the development of phototoxic pharmaceuticals.

Pd-Catalyzed desulfitative arylation of olefins by N-methoxysulfonamide

A novel Pd-catalyzed protocol for the desulfitative Heck-type reaction of N-methoxy aryl sulfonamides with alkenes was reported. The cross-coupling reaction was performed successfully with a variety of olefins to obtain aryl alkenes. Different substituents on the aromatic ring of N-methoxysulfonamides were also found to be compatible with the reaction conditions. Expectedly, the reaction proceeds through CuCl₂-promoted generation of the nitrogen radical and subsequent desulfonylation under thermal conditions to afford the aryl radical for the Pd-catalyzed coupling reaction. N-Methoxysulfonamide was further exploited for the synthesis of symmetrical biaryls in the presence of CuCl₂.

A three-component reaction of arynes, sodium sulfinates, and aldehydes toward 2-sulfonyl benzyl alcohol derivatives

A novel three-component reaction of arynes, sodium sulfinates, and aldehydes under mild reaction conditions is described. This transformation provides a direct synthetic approach to 2-sulfonyl benzyl alcohol derivatives, which could be rapidly converted to diverse arylsulfur compounds via the transformation of the corresponding hydroxyl groups. Various aryne precursors, sodium arenesulfinates, and aromatic aldehydes can be effectively converted to the desired products in 40-84% yields (29 examples).

Electrochemical Radical δ-H Sulfonylation Reaction for the Synthesis of 4-((Aryl,Arylsul fonyl)methylene)-2,5-Cyclohexadiene Derivatives

A novel and efficient electrochemical radical δ-H sulfonylation reaction of para-quinone methides (p-QMs) and sodium sulfinates has been achieved under common laboratory conditions. In this strategy, a new C(sp²)-S bond was constructed for the synthesis of 4-((aryl,arylsulfonyl)methylene)-2,5-cyclohexadiene derivatives with a broad substrate scope, good functional group tolerance, and mild conditions. Further studies showed that the reaction had an excellent regional selectivity.

Matsuda-Heck arylation of itaconates: a versatile approach to heterocycles from a renewable resource

Itaconic acid esters and hemiesters undergo Pd-catalyzed coupling reactions with arene diazonium salts in high to excellent yields. The coupling products of ortho-nitro arene diazonium salts can be converted in one or two steps to benzazepine-2-ones.

Palladium-catalyzed Tsuji-Trost-type reaction of benzofuran-2-ylmethyl acetates with nucleophiles

The palladium-catalyzed benzylic-like nucleophilic substitution of benzofuran-2-ylmethyl acetate with N, S, O and C soft nucleophiles has been investigated. The success of the reaction is dramatically influenced by the choice of catalytic system: with nitrogen based nucleophiles the reaction works well with Pd2(dba)3/dppf, while with sulfur, oxygen and carbo-nucleophiles [Pd(η3-C3H5)Cl]2/XPhos is more efficient. The regiochemical outcome shows that the nucleophilic substitution occurs only on the benzylic position of the η3-(benzofuryl)methyl complex. The high to excellent yields and the simplicity of the experimental procedure make this protocol a versatile synthetic tool for the preparation of 2-substituted benzo[b]furans.

Chemoselective oxidative addition of vinyl sulfones mediated by palladium complexes bearing picolyl-N-heterocyclic carbene ligands

The manifold interactions of (E)- or (Z)-1,2-ditosylethene with a palladium(0) centre bearing picolyl-NHC carbene ligands have been studied thoroughly. (E)-1,2-Ditosylethene produces the expected and stable η²-olefin palladium complexes, whereas the coordination of the Z derivative alternatively promotes the isomerization of the olefin itself or an oxidative addition process depending on the steric bulkiness of carbene substituents and/or the adopted synthetic procedure. Remarkably, the oxidative addition pathway involves a selective S-vinyl (not S-aryl) breaking and produces selectively the S- rather than O-coordinated sulfinate. A mechanistic study has clarified the reasons of the chemoselectivity of the process, which was proved to be kinetically controlled. All the involved species have been isolated and exhaustively characterized. In particular, we report the first example of the X-ray crystal structure of a complex bearing one vinyl and one S-sulfinate fragment coordinated to palladium.

Mechanistic Studies of the Palladium-Catalyzed Desulfinative Cross-Coupling of Aryl Bromides and (Hetero)Aryl Sulfinate Salts

Pyridine and related heterocyclic sulfinates have recently emerged as effective nucleophilic coupling partners in palladium-catalyzed cross-coupling reactions with (hetero)aryl halides. These sulfinate reagents are straightforward to prepare, stable to storage and coupling reaction conditions, and deliver efficient reactions, thus offering many advantages, compared to the corresponding boron-derived reagents. Despite the success of these reactions, there are only scant details of the reaction mechanism. In this study, we use structural and kinetic analysis to investigate the mechanism of these important coupling reactions in detail. We compare a pyridine-2-sulfinate with a carbocyclic sulfinate and establish different catalyst resting states, and turnover limiting steps, for the two classes of reagent. For the carbocyclic sulfinate, the aryl bromide oxidative addition complex is the resting state intermediate, and transmetalation is turnover-limiting. In contrast, for the pyridine sulfinate, a chelated Pd(II) sulfinate complex formed post-transmetalation is the resting-state intermediate, and loss of SO2 from this complex is turnover-limiting. We also investigated the role of the basic additive potassium carbonate, the use of which is crucial for efficient reactions, and deduced a dual function in which carbonate is responsible for the removal of free sulfur dioxide from the reaction medium, and the potassium cation plays a role in accelerating transmetalation. In addition, we show that sulfinate homocoupling is responsible for converting Pd(OAc)2 to a catalytically active Pd(0) complex. Together, these studies shed light on the challenges that must be overcome to deliver improved, lower temperature versions of these synthetically important processes.

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 Regioselective One-Pot Synthesis of Aryl Sulfones from Sodium Sulfinates via Quinone Imine Ketal

A novel, efficient, and regioselective transition-metal-free one-pot synthesis of aryl sulfones via the reactive quinone imine ketal intermediate is demonstrated using easily accessible bench-stable sulfinate salts. A broad range of functionality on p-anisidine substrates as well as sulfinate salts was tolerated under mild reaction conditions to provide the corresponding aryl sulfones in good to excellent yields.

PdII Immobilized on Ferromagnetic Multi-Walled Carbon Nanotubes Functionalized by Aminated 2-Chloroethylphosphonic Acid with S-Methylisothiourea (FMMWCNTs@CPA@SMTU@PdII NPs) Applied as a Highly Efficient and Recyclable Nanostructured Catalyst for Suzuki–Miyaura and Mizoroki–Heck Cross-Coupling Reactions in Solvent-Free Conditions

The new ferromagnetic nanostructured FMMWCNTs@CPA@SMTU@PdII NPs (IV) as an eco-friendly heterogeneous nanocatalyst with a particle size of ~20–30nm reported earlier by our group has been found to be very effective for Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions at ambient temperature. The procedure has been applied for a wide range of aryl halides, arylboronic acids, and alkenes. The magnetic separation by an external magnetic field, mild reaction conditions, and catalyst reusability up to four times without significant decrease in catalytic activity (reduced catalytic activity from 11 to 18% in the fifth, sixth, and seventh cycles) made the present method sustainable and economically viable for C–C cross-coupling reactions.

Iodine-promoted stereoselective amidosulfenylation of electron-deficient alkynes

Iodine-promoted three-component synthesis of substituted β-amino sulfides has been developed starting from a propargyl ester, aliphatic secondary amine, and disulfide. This protocol provides a step-economic and highly regioselective entry to trisubstituted olefins with good substrate scope and functional group tolerance.

Halo-substituted benzenesulfonyls and benzenesulfinates: convenient sources of arenes in metal-catalyzed C–C bond formation reactions for the straightforward access to halo-substituted arenes

The use of halo-substituted ArSO₂R as an aryl source in metal-catalyzed C–C bond formation reactions presents several advantages, as the reaction often proceeds without cleavage of the C–halo bonds.

Platinum-catalyzed syn-stereocontrolled ring-opening of oxabicyclic alkenes with sodium arylsulfinates

A new efficient platinum-catalyzed ring-opening reaction of oxabicyclic alkenes with a wide range of sodium arylsulfinates was developed.

Pd-catalyzed desulfitative arylation for the synthesis of 2,5-diarylated oxazole-4-carboxylates using dioxygen as the terminal oxidant

A novel palladium-catalyzed approach for constructing 2,5-diarylated oxazole-4-carboxylates using sodium arylsulfinates as the aryl source has been demonstrated.

Acid-promoted denitrogenative Pd-catalyzed addition of arylhydrazines with nitriles at room temperature

Pd(TFA)₂-catalyzed denitrogenative addition proceeded with selective C–N bond cleavage of arylhydrazines with nitriles under air at room temperature.

Copper-Free Palladium-Catalysed Desulfinative Homocoupling of Sodium Arylsulfinates under Mild and Aerobic Conditions

A Pd(II)-catalysed homocoupling of sodium arylsulfinates has been successfully achieved under mild conditions. This transformation is a new method for the homocoupling reaction of sodium arylsulfinates, thus providing an alternative synthesis of symmetric biaryls. The reported homocoupling reaction is tolerant to many common functional groups, such as ester, halo, cyano and nitro and works well in the presence of electron-donating and electron-withdrawing substituents. Notably, the reported desulfinative homocoupling does not require Cu salts, ligands and bases, making this newly developed transformation attractive.

Palladium-catalyzed C-3 desulfitative arylation of indolizines with sodium arylsulfinates and arylsulfonyl hydrazides

Derivatized indolizines were efficiently prepared by direct C-3 arylation of indolizines using sodium arylsulfinates and arylsulfonyl hydrazides in good yields.

Open-air oxidative Mizoroki–Heck reaction of arylsulfonyl hydrazides with alkenes

A palladium(ii)-catalyzed oxidative Mizoroki–Heck reaction of arylsulfonyl hydrazides with alkenes was developed employing Pd(OAc)₂ and pyridine ligand L9 as a catalyst system and ​atmospheric air as the sole oxidant in an open-vessel manner.

Structure–activity relationships in Pd catalysed C–S activation of thioesters

The structure–activity relationship of thioesters promoted by Pd(0) complex has been studied using the density functional theory calculation methods.

Palladium-Catalyzed Desulfitative Oxidative Coupling between Arenesulfinic Acid Salts and Allylic Alcohols: A Strategy for the Selective Construction of β-Aryl Ketones and Aldehydes

An efficient palladium-catalyzed desulfitative oxidative coupling of sodium arylsulfinites for highly region-selective Heck-type reaction of allylic alcohols has been developed. The compatibility of the functionalities of -I, -Br, and -F would explore further postfunctionalization of the C-X bonds. This method provides a new and straightforward protocol for the synthesis of β-aryl ketones and aldehydes. The deuterium labeling experiments indicated that this transformation may proceed via a [1, 2-H] shift process.