Copper(II)-Catalyzed Alkene Aminosulfonylation with Sodium Sulfinates For the Synthesis of Sulfonylated Pyrrolidones

Aerobic Copper-Catalyzed Hydroxysulfonylation of Vinylarenes with Sodium Sulfinates

A novel and efficient method for the intermolecular hydroxysulfonylation of vinylarenes using sodium sulfinates has been achieved through aerobic copper catalysis. This transformation proceeded smoothly with green air as the terminal oxidant in the presence of Cu (I)/1,10-phenanthroline as an efficient catalytic system, leading to an array of β-hydroxysulfones in moderate to high yields. The significant advantages of this protocol are the mild reaction conditions, readily available starting materials, good functional-group compatibility, synthetic convenience, and practicability. Preliminary mechanistic investigation suggested that the catalytic process should undergo a cascade of radical events involving the initial generation of sulfonyl radical followed by sulfonyl radical addition across alkenes and subsequent cross-coupling with air.

Sulfonyl Radical-Induced Regioselective Cyclization of Enamide-Olefin To Form Sulfonylated 6-7-Membered Cyclic Enamines

Remarkable progress has been made in the radical cascade cyclization of heteroaryl- or aryl-tethered alkenes to construct benzene-fused frameworks via the cracking of aryl C-H bonds. In contrast, the radical cascade cyclization of linear dienes through the cracking of vinyl C-H bonds to construct nonbenzene-fused ring frameworks with endocyclic double bonds has significantly lagged behind, and major advances have largely been restricted to the generation of 5-membered heterocycles, such as pyrrolinones. Herein, we report the silver-mediated regioselective sulfonylation-cyclization of linear dienes with sodium sulfinates to form sulfonylated 6- and 7-membered cyclic enamines.

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.

Nickel-Catalyzed Direct Sulfonylation of Styrenes and Unactivated Aliphatic Alkenes with Sulfonyl Chlorides

A nickel-catalyzed direct sulfonylation of alkenes with sulfonyl chlorides has been developed using 1,10-phenanthroline-5,6-dione as the ligand. Unactivated alkenes and styrenes including 1,1-, 1,2-disubstituted alkenes can be subjected to the protocol, and a wide range of vinyl sulfones was obtained in high to excellent yields with good functional group compatibility. Notably, the process did not allow the desulfonylation of sulfonyl chloride or chlorosulfonylation of alkenes. Radical-trapping experiment supported that a sulfonyl free-radical was likely produced and triggered subsequent transformation in the process.

Cu(II)-Mediated Sulfonylation of (Hetero)arenes with TosMIC Using Monodentate Directing Groups

Monodentate chelation-assisted direct ortho-C-H sulfonylation of (hetero)arenes using TosMIC as the novel sulfonylating reagent has been developed. A broad range of substrates, including indolines, indoles, 2-phenylpyridines, and others were well tolerated to afford the corresponding products in moderate to good yields. Mechanistic studies revealed that the sulfonyl radical might be involved. Inspired by the above discovery, preliminary para-C-H sulfonylation of naphthalene substrate was also successfully realized. The current protocol featured with cheap metal catalysis, good functional group compatibility, and operational convenience.

Photo-induced imino functionalizations of alkenes via intermolecular charge transfer

A catalyst-free photosensitized strategy has been developed for regioselective imino functionalizations of alkenes via the formation of an EDA complex. This photo-induced protocol facilitates the construction of structurally diverse β-imino sulfones and vinyl sulfones in moderate to high yields. Mechanistic studies reveal that the reaction is initiated with an intermolecular charge transfer between oximes and sulfinates, followed by fragmentation to generate a persistent iminyl radical and transient sulfonyl radical. This catalyst-free protocol also features excellent regioselectivity, broad functional group tolerance and mild reaction conditions. The late stage functionalization of natural product derived compounds and total synthesis of some bioactive molecules have been demonstrated to highlight the utility of this protocol. Meanwhile, the compatibility of different donors has proved the generality of this strategy.

Photoredox-Catalyzed Synthesis of 3-Sulfonylated Pyrrolin-2-ones via a Regioselective Tandem Sulfonylation Cyclization of 1,5-Dienes

A mild, visible-light-induced, regioselective cascade sulfonylation-cyclization of 1,5-dienes with sulfonyl chlorides through the intermolecular radical addition/cyclization of alkenes C(sp²)-H was developed. This procedure proceeds well and affords a mild and efficient route to a range of monosulfonylated pyrrolin-2-ones at room temperatures.

Regiodivergent synthesis of sulfone-tethered lactam-lactones bearing four contiguous stereocenters

Sulfone-tethered lactones/amides/amines display a diverse spectrum of biological activities, including anti-psychotic and anti-hypertensive. Sulfones are also widely present in functional materials and fragrances. We therefore reasoned that a regiodivergent and stereocontrolled strategy that merges the sulfone, lactone, and lactam motifs would likely lead to the discovery of new pharmacophores and functional materials. Here, we report mild conditions for the sulfonyllactonization of γ-lactam-tethered 5-aryl-4(E)-pentenoic acids. The annulation is highly modular, chemoselective, and diastereoselective. With respect to regioselectivity, trisubstituted alkenoic acids display a preference for 5-exo-trig cyclization whereas disubstituted alkenoic acids undergo exclusive 6-endo-trig cyclization. The lactam-fused sulfonyllactones bear angular quaternary as well as four contiguous stereocenters. The products are post-modifiable, especially through a newly developed Co-catalyzed reductive cross-coupling protocol.

Copper-Catalyzed Sulfonylation/Cyclization of Pent-4-ynamides toward Sulfonyl-Functionalized Pyrrol-2-ones

A domino sulfonylation/intramolecular C-N coupling/dehydrogenation reaction was realized between pent-4-ynamides and sulfonyl chlorides by catalysis of Cu(acac)₂ and 2,2'-bis(diphenylphosphanyl)-1,1'-binaphthalene. The reaction provides a convenient approach to sulfonyl-functionalized pyrrol-2-ones. This method can also be applied to the synthesis of 3-alkylidene isoindolinones from 2-ethynyl-benzamides.

Electrochemically Enabled Intramolecular Amino- and Oxysulfonylation of Alkenes with Sodium Sulfinates to Access Sulfonylated Saturated Heterocycles

A practical and efficient electrochemical intramolecular amino- or oxysulfonylation of internal alkenes equipped with pendant nitrogen or oxygen-centered nucleophiles with sodium sulfinate was developed. Under undivided electrolytic cell conditions, a variety of sulfonylated N-heterocycles and O-heterocycles, such as tetrahydrofurans, tetrahydropyrans, oxepanes, tetrahydropyrroles, piperidines, δ-valerolactones, etc., were efficiently prepared from easily accessible unsaturated alcohols, carboxylic acids, and N-tosyl amines without the need for additional metal or exogenous oxidant. The robust electrochemical transformation features excellent redox economy, high diastereoselectivity, and broad substrate specificity, which provide a general and practical access to sulfone-containing heterocycles and would facilitate the related synthetic and biological studies based on this electrosynthesis.

Computational Chemistry-Assisted Highly Selective Radical Cascade Cyclization of 1,6-Enynes with Thiols: Access to Sulfur-Substituted 4-Enyl-2-Pyrrolidones

In this study, an efficient method for the synthesis of sulfur-substituted 4-enyl-2-pyrrolidones was successfully developed through AIBN-promoted highly selective 5-exo-dig radical cascade cyclization of 1,6-enynes with sulfur sources with the aid of theoretical and computational chemistry. This protocol enables the first practical and green synthesis of an array of 4-enyl-2-pyrrolidones in moderate-to-good yields with broad substrate scopes and high regioselectivities (>20:1). Moreover, excellent stereoselectivities have also been achieved (up to >20:1, Z/E). Most interestingly, when the sulfur source is electron-rich thiophenol, reverse stereoselectivities were discovered. In addition, the control experiments indicate that the cascade cyclization is realized by radical reactions, and the detailed reaction mechanism and regioselectivities have also been explained by theoretical studies.

Copper-Catalyzed Enantioselective Oxysulfenylation of Alkenols: Synthesis of Arylthiomethyl-Substituted Cyclic Ethers

Saturated heterocycles containing oxygen and sulfur are found in biologically significant molecules. The enantioselective oxysulfenylation of alkenols provides a straightforward synthesis route. To date, organocatalytic methods have dominated this approach. Herein, a complementary approach via copper catalysis is presented. This exoselective method provides enantioenriched arylthiomethyl-substituted tetrahydrofurans, phthalans, isochromans, and morpholines from acyclic alkenols. This method provides the largest scope to date for the exocyclization mode, and with generally high enantioselectivity. The enantioselectivity of this copper-catalyzed oxysulfenylation is rationalized by a proposed mechanism involving alkene oxycupration followed by C─S bond formation via radical-mediated atom transfer.

Regioselective Radical-Relay Sulfonylation/Cyclization Protocol to Sulfonylated Pyrrolidones under Transition-Metal-Free Conditions

A simple and low-cost tandem sulfonylation/cyclization of 1,5-diene, aryldiazonium salt, and DABCO·(SO₂)₂ is disclosed. This base-promoted multicomponent reaction can provide a "green" and economic synthesis of sulfonylated pyrrolidones under transition-metal-free and moisture/oxygen-insensitive reaction conditions, thus delivering a wide range of sulfonylated pyrrolidones in moderate to high yields with excellent functional group compatibility. A plausible mechanism involving a radical process is proposed, which demonstrates highly chemoselective trapping of the aryl radical with "SO₂" species, and a regioselective sulfonylation/cyclization protocol in this reaction.

Complementary Copper-Catalyzed and Electrochemical Aminosulfonylation of O-Homoallyl Benzimidates and N-Alkenyl Amidines with Sodium Sulfinates

A complementary copper-catalyzed and electrochemical aminosulfonylation of O-homoallyl benzimidates and N-alkenyl amidines with sodium sulfinates was developed. The terminal alkene substrate produced sulfone-containing 1,3-oxazines and tetrahydropyrimidines in the presence of Cu(OAc)₂, Ag₂CO₃, and DPP, and under similar reaction conditions, sulfonylated tetrahydro-1,3-oxazepines were prepared from 1-aryl-substituted O-homoallyl benzimidates in moderate to good yields. For certain electron-rich 1,1-diaryl-substituted alkene substrates, the corresponding tetrahydro-1,3-oxazepines could also be obtained in similar or even higher yields via a green electrochemical technique.

Iodine-Promoted Formal [3+2] Cycloaddition of Enaminone: Access to 2-Hydroxy-1,2-dihydro-pyrrol-3-ones with Quaternary Carbon Center

A novel iodine promoted cyclization of enaminone with aryl methyl ketones has been developed as a straightforward method for constructing 2-hydroxy-pyrrol-3(2H)-ones. This strategy affords structurally diverse 2-hydroxy-pyrrol-3(2H)-ones rings in high yields. Moreover, a quarternary alcohol has been constructed efficiently in the reaction. Product purification required only washing with CH₂Cl₂ solvent, thereby avoiding traditional chromatography and recrystallization, making this an example of group-assisted purification chemistry.

Visible-Light Photoredox-Catalyzed Sulfonyl Lactonization of Alkenoic Acids with Sulfonyl Chlorides for Sulfonyl Lactone Synthesis

A visible-light photoredox-catalyzed sulfonyl lactonization of unsaturated carboxylic acids with sulfonyl chlorides is described. This reaction features good functional group tolerance and a broad substrate scope, providing a simple and efficient protocol to access a wide range of sulfonyl lactones in high to excellent yields. Preliminary mechanistic investigations suggested that a free-radical pathway should be involved in the process.

Copper-Catalyzed Aminosulfonylation of O-Homoallyl Benzimidates with Sodium Sulfinates to Access Sulfonylated 1,3-Oxazines

A facile copper-catalyzed aminosulfonylation of O-homoallyl benzimidates with sodium sulfinates in the presence of tert-butyl peroxybenzoate (TBPB) and XPhos ligand has been developed. By using this protocol, a variety of potentially bioactive 1,3-oxazines were directly synthesized. This method has the merits of a cheap catalyst, easily available and stable sulfone reagents, and simple operation.

Aminolactonization of Unactivated Alkenes Catalyzed by Aryl Iodine

A one-step protocol of the aryl iodine-catalyzed aminolactonization of unactivated alkenes under oxidation conditions was first reported to efficiently construct diverse amino lactones in a short time using HNTs₂ as the compatible nitrogen source. In addition, we investigated the influence of the reaction rate based on the structure of the iodoarene precatalyst, which revealed the selective adjustment effect on aminolactonization and oxylactonization. Finally, preliminary experiments verified the feasibility of asymmetric aminolactonization catalyzed by a chiral iodoarene precatalyst.

Practical Electro-Oxidative Sulfonylation of Phenols with Sodium Arenesulfinates Generating Arylsulfonate Esters

A practical and sustainable synthesis of arylsulfonate esters has been developed through electro-oxidation. This reaction employed the stable and readily available phenols and sodium arenesulfinates as the starting materials and took place under mild reaction conditions without additional oxidants. A wide range of arylsulfonate esters including those bearing functional groups were produced in good to excellent yields. This reaction could also be conducted at a gram scale without a decrease of reaction efficiency. Those results well demonstrated the potential synthetic value of this reaction in organic synthesis.

Synthesis and applications of sodium sulfinates (RSO2Na): a powerful building block for the synthesis of organosulfur compounds

This review highlights the preparation of sodium sulfinates (RSO2Na) and their multifaceted synthetic applications. Substantial progress has been made over the last decade in the utilization of sodium sulfinates emerging as sulfonylating, sulfenylating or sulfinylating reagents, depending on reaction conditions. Sodium sulfinates act as versatile building blocks for preparing many valuable organosulfur compounds through S-S, N-S, and C-S bond-forming reactions. Remarkable advancement has been made in synthesizing thiosulfonates, sulfonamides, sulfides, and sulfones, including vinyl sulfones, allyl sulfones, and β-keto sulfones. The significant achievement of developing sulfonyl radical-triggered ring-closing sulfonylation and multicomponent reactions is also thoroughly discussed. Of note, the most promising site-selective C-H sulfonylation, photoredox catalytic transformations and electrochemical synthesis of sodium sulfinates are also demonstrated. Holistically, this review provides a unique and comprehensive overview of sodium sulfinates, which summarizes 355 core references up to March 2020. The chemistry of sodium sulfinate salts is divided into several sections based on the classes of sulfur-containing compounds with some critical mechanistic insights that are also disclosed.

The Three-Component Synthesis of 4-Sulfonyl-1,2,3-triazoles via a Sequential Aerobic Copper-Catalyzed Sulfonylation and Dimroth Cyclization

4-Sulfonyl-1,2,3-triazole scaffolds possess promising bioactivities and applications as anion binders. However, these structures remain relatively unexplored and efficient synthetic procedures for their synthesis remain desirable. A practical room-temperature, aerobic copper-catalyzed three-component reaction of aromatic ketones, sodium sulfinates, and azides is reported. This procedure allows for facile access to 4-sulfonyl-1,5-disubstituted-1,2,3-triazoles in yields ranging from 34 to 89%. The reaction proceeds via a sequential aerobic copper(II)chloride-catalyzed oxidative sulfonylation and the Dimroth azide–enolate cycloaddition.

Copper(II)-Catalyzed Domino Synthesis of 4-Benzenesulfonyl Isoxazoles from 2-Nitro-1,3-enynes, Amines, and Sodium Benzenesulfinate

A simple and effective method for the synthesis of fully substituted 4-benzenesulfonyl isoxazoles through a copper(II)-catalyzed three-component reaction of 2-nitro-1,3-enynes, amines, and sodium benzenesulfinate is described. The reaction proceeds smoothly under mild conditions and provides the benzenesulfonyl isoxazoles with high chemoselectivity.

Transition-metal-free sulfonylations of methylthiolated alkynones to synthesize 3-sulfonylated thioflavones

A set of transition-metal-free NaI/TBHP-mediated sulfonylation cyclization reactions of methylthiolated alkynones with sulfonyl hydrazides was developed, by which various 3-sulfonylated thioflavones were prepared under mild reaction conditions.

Copper-catalyzed regioselective sulfonylcyanations of vinylarenes

A set of copper-catalyzed sulfonylcyanations of vinylarenes with readily accessible arylsulfonyl chlorides and trimethyl cyanide was achieved, providing a streamlined route to various decorated β-sulfonyl nitriles with good regioselectivity and functional group tolerance.