Selective Synthesis of ortho-Substituted Diarylsulfones by Using NHC-Au Catalysts under Mild Conditions

Gold-Catalyzed Cross-Coupling Reactions of Organoiodides with Disulfides: Access to Aryl Sulfides and Vinyl Sulfide Derivatives

Thioethers and their derivatives play important roles in synthetic chemistry, medicinal chemistry, and materials science. Herein, we report a hemilabile P,N-ligand-assisted gold-catalyzed C-S cross-coupling reaction of organoiodides with disulfides. In this reaction, alkyl or aryl disulfides react smoothly with aryl or vinyl iodides to afford a series of aryl sulfide and vinyl sulfide derivatives in good to excellent yields. The robust synthetic capabilities of thioether synthesis are exemplified by the readily available and easily handled reagents as well as the excellent compatibility with a wide range of functional groups.

Palladium-Catalyzed Site-Selective C-H Sulfonylation via Aryl Thianthrenium Salts to Access Diarylsulfones

We presented a highly efficient palladium-catalyzed site-selective C-H sulfonylation reaction via aryl thianthrenium salts. By utilizing readily available and cost-effective arenes along with sodium sulfinates, we achieved the C(sp2)-S cross-coupling with high efficiency, establishing a dependable method for synthesizing diarylsulfones with satisfactory yields. This method exhibits excellent tolerance toward functional groups, scalability, and the synthesis or late-stage functionalization of bioactive molecules, making it a valuable sulfonylation tool for drug modifications.

β-Thioamide Sulfone Enabled Copper-Catalyzed Ring-Opening/Sulfonylation of Cyclopropenes: Access to Alkyl Aryl Sulfones

Sulfone motifs play important roles in bioactive compounds and functional materials. The development of efficient methodologies for constructing sulfonyl-containing compounds has thus attracted considerable attention. Here, we introduce a protocol for the preparation of alkyl aryl sulfones under mild conditions. This protocol employs β-thioamide sulfone as a novel sulfone motif donor. It forms sulfinates in situ under basic conditions, which then undergo cross-coupling with the intermediates that were generated from ligand-free copper-catalyzed cyclopropenes (CPEs) ring opening.

Gold(I/III)-Catalyzed Sulfonylation of Aryl/Vinyl Iodides To Synthesize Aryl Sulfones

A gold-catalyzed sulfonylation of aryl/vinyl iodides to synthesize aryl sulfones facilitated by the ligand-enabled Au(I)/Au(III) redox catalysis was developed. In the reaction, aryl sodium sulfinates or sulphinic acids can react smoothly with aryl/vinyl iodides to directly construct various aryl sulfones. The strong synthetic capabilities of sulfone synthesis are demonstrated by its easily available and handled reagents, good functional group compatibility, and late-stage application of complicated biomolecules. Mechanistic studies suggest that the silver salt plays a crucial role in the transmetalation with the Au(I)/Au(III) intermediate, and the gold complex favors Au-S bond formation over Au-O bond formation.

Generation of perthiyl radicals for the synthesis of unsymmetric disulfides

Unsymmetric disulfides are prevalent in natural products and are essential in medicinal chemistry and materials science, but their robust synthesis poses significant challenges. In this paper, we report an expeditous transition-metal-free methodology for synthesizing unsymmetric disulfides through the addition of perthiyl radicals to alkenes. This study marks the use of generating perthiyl radicals by reacting SO2 with unactivated alkyl (pseudo)halides (Cl/Br/I/OTs). Various primary, secondary and tertiary alkyl (pseudo)halides substituted with different functional groups successfully function as suitable reactants. The formation of perthiyl radicals and their involvement in the reaction process are verified through mechanistic studies and DFT calculations. Overall, this method leverages readily available alkyl electrophiles and alkenes alongside SO2 in a single reaction setup to efficiently form both carbon-sulfur and sulfur-sulfur bonds simultaneously.

Au(I)/Au(III)-Catalyzed Sulfonylation of Aryl Iodides for the Synthesis of Various Functionalized Aryl Sulfones

A gold-catalyzed sulfonylation reaction of aryl iodides with different sodium sulfinates facilitated by the ligand-enabled Au(I)/Au(III) redox catalysis was developed. In the reaction of gold-catalyzed C-S coupling, a variety of functionalized sodium sulfinates, such as CF3, CHF2, CH3, and alkyl groups, can react smoothly with aryl iodides to directly construct diversely functionalized aryl sulfones. This gold-catalyzed sulfonylation offers a complementary method for synthesizing functionalized aryl sulfones with electron-donating groups.

A Redox-neutral Nickel-catalysed Sulfonylation of (Hetero)aryl Boronic Acids with 2-Chlorothiazoles

A redox-neutral nickel-catalysed sulfonylation for arylsulfone synthesis was developed. (Hetero)aryl boronic acids reacted with potassium metabisulfite (K2 S2 O5 ) and readily available 2-chlorothiazoles in the presence of air-stable Ni(OTf)2 and 4,4-di-tert-butyl bipyridine (dtbpy) as a commercially available ligand to produce the corresponding 2-sulfonylthiazoles in moderate to excellent yields. This practical protocol tolerates a wide range of substrates including boronic acids and 2-chloro(benzo)thiazoles without additional bases, allowing the direct synthesis of functional arylsulfones.

Gold-catalyzed multicomponent reactions

Multicomponent reactions (MCRs) have emerged as an important branch in organic synthesis for the creation of complex molecular structures. This review is focused on gold-catalyzed MCRs with a special emphasis on the recent developments.

Scalable, Chemoselective Nickel Electrocatalytic Sulfinylation of Aryl Halides with SO2

Simple access to aryl sulfinates from aryl iodides and bromides is reported using an inexpensive Ni-electrocatalytic protocol. The reaction exhibits a broad scope, uses stock solution of simple SO2 as sulfur source, and can be scaled up in batch and recycle flow settings. The limitations of this reaction are clearly shown and put into context by benchmarking with state-of-the-art Pd-based methods.

Visible-Light-Mediated Three-Component Cascade Sulfonylative Annulation

Visible-light-promoted cascade radical cyclization for the synthesis of sulfonylated benzimidazo/indolo[2,1-a]iso-quinolin-6(5H)-ones has been reported. The reaction provides transition-metal-free and expeditious access to sulfonylated polyaromatics. The use of sodium metabisulfite as a SO₂ surrogate and the rapid generation of molecular complexity using a three-component photochemical protocol are the salient features of this reaction manifold.

Ligand-Enabled Gold-Catalyzed C(sp2)-S Cross-Coupling Reactions

Herein we report C(sp²)-S cross-coupling reactions of aryl iodides and arylsulfonyl hydrazides under ligand-enabled, Au(I)/Au(III) redox catalysis. This strategy operates under mild reaction conditions, requires no prefunctionalized aryl coupling partner, and works across several aryl iodides. The utility of this protocol is highlighted through the synthesis of various medicinally relevant biaryl sulfones. The reaction mechanism is supported with control experiments, mass spectrometry, and NMR studies.

Metal- and base-free tandem sulfonylation/cyclization of 1,5-dienes with aryldiazonium salts via the insertion of sulfur dioxide

A metal- and base-free 5-endo-trig sulfonylative cyclization between 1,5-dienes, aryldiazonium salts and SO₂ (from SOgen) is presented. This method could successfully produce sulfonylated pyrrolin-2-ones in one pot with excellent regioselectivity and good-to-excellent yields. This strategy features mild reaction conditions and broad substrate scope. Moreover, a scale-up reaction and three synthetic applications demonstrate the practicality of this method. Lastly, control experiments indicate that the 5-endo-trig sulfonylative cyclization may proceed in a radical pathway.

A new metal- and base-free method for synthesizing sulfonylated pyrrolin-2-ones from 1,5-dienes, aryldiazonium salts and SO₂ is presented. This transformation features mild reaction conditions and broad substrate scope.

Base-promoted synthesis of diarylsulfones from sulfonyl hydrazines and diaryliodonium salts

An efficient and concise method for the synthesis of diverse substituted sulfones was developed with high selectivity. Using n-PrOH as the solvent, diaryl sulfones are formed even on a gram scale via metal-free coupling from sulfonyl hydrazines with symmetrical or unsymmetrical diaryliodonium salts.

Aryldiazonium Salts and DABSO: a Versatile Combination for Three-Component Sulfonylative Cross-Coupling Reactions

A combination of aryldiazonium salts and DABSO provides a unique opportunity for sulfonylative multicomponent cross-coupling reactions. Here, a copper-catalyzed three-component cross-coupling of aryldiazonium salts, DABSO with arylboronic acids to obtain medicinally relevant unsymmetrical diarylsulfones is disclosed. Interestingly, a catalyst-free approach for the synthesis of arylvinylsulfones from the corresponding vinyl boronic acid or vinyl halides is explored under basic condition. Tethered aryldiazonium salts provided the corresponding annulated alkylvinylsulfones via alkene difunctionalization under the same transition metal-free condition. Mechanistically, these multicomponent reactions proceed through a single electron pathway by the formation of arylsulfonyl radical as a key intermediate.

Metal-free sulfonylation of arenes with N-fluorobenzenesulfonimide via cleavage of S-N bonds: expeditious synthesis of diarylsulfones

A novel metal-free sulfonylation of arenes with N-fluorobenzenesulfonimide (NFSI) toward the synthesis of diarylsulfones has been developed. The reaction represents a rare example of sulfonylation reaction using NFSI as an efficient sulfonyl donor and the first example of acid-mediated sulfonylation of unactivated arenes with NFSI via selective cleavage of S-N bonds. This protocol provides a concise approach for the construction of pharmaceutically and biologically important diarylsulfones. Applications in the functionalization of natural products (e.g., β-estradiol) and in the synthesis of a key intermediate to an inhibitor of farnesyl-protein transferase, as well as in the gram-scale synthesis of the EPAC2 antagonist, are demonstrated.

Copper-assisted preparation of pyridinyl sulfonate esters from hydroxypyridines and sodium sulfinates

An efficient and powerful copper-assisted method for the effective conversion of a broad range of hydroxypyridines and sodium sulfinates into their corresponding pyridinyl tosylates was developed. Key features of this base- and ligand-free protocol include using the cheap and readily available CuBr2 as a medium and the use of sodium sulfinates as formal sulfonylation reagents. A variety of functional pyridinyl tosylates could be formed with good yields, which can easily be converted into C-C and C-N bond-containing compounds.

Nickel(II)-Catalyzed Addition of Aryl and Heteroaryl Boroxines to the Sulfinylamine Reagent TrNSO: The Catalytic Synthesis of Sulfinamides, Sulfonimidamides, and Primary Sulfonamides

We report a redox-neutral Ni(II)-catalyzed addition of (hetero)aryl boroxines to N-sulfinyltritylamine (TrNSO). The reactions use a catalyst generated from the combination of commercial, air-stable NiCl₂·(glyme) and a commercially available bipyridine ligand, and deliver sulfinamide products. The scope of the reaction is established using a sulfonimidamide synthesis, in which the initially formed sulfinamides undergo oxidative chlorination with the inexpensive and safe chlorinating agent, trichloroisocyanuric acid (TCCA), to produce sulfonimidoyl chlorides as key intermediates. These are combined in situ with a range of amines to deliver sulfonimidamides. The sulfonimidoyl chlorides can also be elaborated into primary sulfonamides via hydrolysis, and sulfonimidoyl fluorides via treatment with fluoride. These transformations are all achieved using one-pot procedures. Unprotected, primary sulfinamides are also available. For larger-scale reactions, the catalyst loading can be reduced to 1 mol %.

Acenaphthene-Based N-Heterocyclic Carbene Metal Complexes: Synthesis and Application in Catalysis

N-Heterocyclic carbene (NHC) ligands have become a privileged structural motif in modern homogenous and heterogeneous catalysis. The last two decades have brought a plethora of structurally and electronically diversified carbene ligands, enabling the development of cutting-edge transformations, especially in the area of carbon-carbon bond formation. Although most of these were accomplished with common imidazolylidene and imidazolinylidene ligands, the most challenging ones were only accessible with the acenaphthylene-derived N-heterocyclic carbene ligands bearing a π-extended system. Their superior σ-donor capabilities with simultaneous ease of modification of the rigid backbone enhance the catalytic activity and stability of their transition metal complexes, which makes BIAN-NHC (BIAN—bis(imino)acenaphthene) ligands an attractive tool for the development of challenging reactions. The present review summarizes synthetic efforts towards BIAN-NHC metal complexes bearing acenaphthylene subunits and their applications in modern catalysis, with special emphasis put on recently developed enantioselective processes.

The Renaissance of Alkali Metabisulfites as SO2 Surrogates

The upsurge of interest in the development of methodologies for the construction of sulfur-containing compounds via the use of expedient reagents has established sustainable tools in organic chemistry. This review focuses on sulfonylation reactions using inorganic sulfites (Na2S2O5 or K2S2O5) as the sulfur dioxide surrogates. Compared to the bis-adduct with DABCO, which is an excellent surrogate of gaseous SO2, the use of sodium or potassium metabisulfites as SO2 surrogates are equally efficient. The objective of the current review is to exemplify recent sulfonylation reactions using inorganic sulfites. For better understanding, the review is categorized according to the mode of reactions: transition-metal-catalyzed SO2 insertion, metal-free SO2 insertion, and visible-light-mediated SO2 insertion. All the reactions in each of the sections are illustrated with selected examples with a pertinent explanation of the proposed mechanism.

1 Introduction

2 Outlines of the Reactions Involving SO2 Insertion

2.1 Transition-Metal-Catalyzed SO2 Insertion

2.2 Transition-Metal-Free SO2 Insertion

2.3 Visible-Light-Mediated SO2 Insertion

3 Conclusion and Outlook

Optimizing Catalyst and Reaction Conditions in Gold(I) Catalysis-Ligand Development

This review considers phosphine and N-heterocyclic carbene complexes of gold(I) that are used as (pre)catalysts for a range of reactions in organic synthesis. These are divided according to the structure of the ligand, with the narrative focusing on studies that offer a quantitative comparison between the ligands and readily available or widely used existing systems.

Copper-Catalyzed Chloro-Arylsulfonylation of Styrene Derivatives via the Insertion of Sulfur Dioxide

A copper-catalyzed four-component chloro-arylsulfonylation of styrene derivatives with aryldiazonium tetrafluoroborates, lithium chloride, and ex-situ generated sulfur dioxide (from SOgen) is presented. This sulfonylation features good functional group compatibility, mild reaction conditions, excellent regioselectivity, and good yields. The robustness and potential of this method have also been successfully demonstrated by a gram-scale reaction. Based on experimental study, a radical-involved mechanism is proposed for the transformation.

Metal- and Base-Free C(sp2)-H Arylsulfonylation of Enamides for Synthesis of (E)-β-Amidovinyl Sulfones via the Insertion of Sulfur Dioxide

A metal- and base-free C(sp²)-H direct arylsulfonylation of secondary and tertiary enamides with aryldiazonium salts and ex situ generated SO₂ (from SOgen) is presented. This method runs smoothly to produce β-amidovinyl sulfones with excellent stereoselectivities in moderate to excellent yields. Moreover, this strategy features good functional group tolerance and environmentally benign reaction conditions. Mechanistic experiments indicate that this sulfonylation may proceed in a radical pathway.

Construction of 3-Sulfonyl Naphthalenes via Tandem Reaction of 1,4-Diyn-3-yl Esters with Sodium Sulfinates

Polysubstituted 3-sulfonyl naphthalenes were constructed in good to high yields by AlCl₃-mediated tandem reaction of 1,4-diyn-3-yl esters and sodium sulfinates. This reaction proceeded under mild reaction conditions and tolerated a variety of functional groups. Moreover, the mechanistic studies indicated that the initial formation of allene under DBU from 1,4-diyn-3-yl ester and a sequence of nucleophilic addition of sodium sulfinate, the formation of allene, and intramolecular cyclization might be involved.

BIAN-NHC Ligands in Transition-Metal-Catalysis: A Perfect Union of Sterically Encumbered, Electronically Tunable N-Heterocyclic Carbenes?

The discovery of NHCs (NHC = N-heterocyclic carbenes) as ancillary ligands in transition-metal-catalysis ranks as one of the most important developments in synthesis and catalysis. It is now well-recognized that the strong σ-donating properties of NHCs along with the ease of scaffold modification and a steric shielding of the N-wingtip substituents around the metal center enable dramatic improvements in catalytic processes, including the discovery of reactions that are not possible using other ancillary ligands. In this context, although the classical NHCs based on imidazolylidene and imidazolinylidene ring systems are now well-established, recently tremendous progress has been made in the development and catalytic applications of BIAN-NHC (BIAN = bis(imino)acenaphthene) class of ligands. The enhanced reactivity of BIAN-NHCs is a direct result of the combination of electronic and steric properties that collectively allow for a major expansion of the scope of catalytic processes that can be accomplished using NHCs. BIAN-NHC ligands take advantage of (1) the stronger σ-donation, (2) lower lying LUMO orbitals, (3) the presence of an extended π-system, (4) the rigid backbone that pushes the N-wingtip substituents closer to the metal center by buttressing effect, thus resulting in a significantly improved control of the catalytic center and enhanced air-stability of BIAN-NHC-metal complexes at low oxidation state. Acenaphthoquinone as a precursor enables facile scaffold modification, including for the first time the high yielding synthesis of unsymmetrical NHCs with unique catalytic properties. Overall, this results in a highly attractive, easily accessible class of ligands that bring major advances and emerge as a leading practical alternative to classical NHCs in various aspects of catalysis, cross-coupling and C-H activation endeavors.

A photoredox- or metal-catalyzed three-component cyanoalkylsulfonylation reaction of 1-(allyloxy)-2-(1-arylvinyl)benzenes, potassium metabisulfite, and cycloketone oxime esters: synthesis of cyanoalkylsulfonylated benzoxepines

A visible light photocatalyzed or metal-catalyzed three-component cyanoalkylsulfonylation of 1-(allyloxy)-2-(1-arylvinyl)benzenes, potassium metabisulfite and cyclobutanone oxime esters is developed.

Synergistic photoredox and tertiary amine catalysis: generation of allylic sulfones from Morita–Baylis–Hillman acetates and sulfur dioxide

The first example of the synthesis of allylic sulfones through synergistic photoredox and tertiary amine catalysis, starting from MBH acetates, DABCO·(SO₂)₂ and 4-substituted Hantzsch esters or potassium alkyltrifluoroborates via a radical pathway, is reported.

A visible-light photoredox-catalyzed four-component reaction for the construction of sulfone-containing quinoxalin-2(1H)-ones

A visible-light photoredox-catalyzed four component reaction of quinoxalin-2(1H)-ones, alkenes, aryldiazonium, and sodium metabisulfite leading to sulfone-containing quinoxalin-2(1H)-ones has been developed.

Generation and precise control of sulfonyl radicals: visible-light-activated redox-neutral formation of sulfonates and sulfonamides

An efficient protocol to direct sulfonamidation or sulfonation of electron-deficient alkenes for furnishing alkylsulfonamides or sulfonates has been achieved.

Metal-free sulfonylative annulations of alkyl diiodides with sulfur dioxide: synthesis of cyclic aliphatic sulfones

A straightforward protocol for cyclic aliphatic sulfones is effectively established via sulfonylative annulations of alkyl diiodides and gaseous sulfur dioxide. Five- to nine-membered cyclic aliphatic sulfones were afforded in this manner.