Copper-Catalyzed Regioselective 1,4-Selenosulfonylation of 1,3-Enynes to Access Cyanoalkylsulfonylated Allenes

Recent Progress in Synthetic and Biological Application of Diorganyl Diselenides

Diorganyl diselenides have emerged as privileged structures because they are easy to prepare, have distinct reactivity, and have broad biological activity. They have also been used in the synthesis of natural products as an electrophile in the organoselenylation of aromatic systems and peptides, reductions of alkenes, and nucleophilic substitution. This review summarizes the advancements in methods for the transformations promoted by diorganyl diselenides in the main functions of organic chemistry. Parallel, it will also describe the main findings on pharmacology and toxicology of diorganyl diselenides, emphasizing anti-inflammatory, hypoglycemic, chemotherapeutic, and antimicrobial activities. Therefore, an examination detailing the reactivity and biological characteristics of diorganyl diselenides provides valuable insights for academic researchers and industrial professionals.

Four-Component Radical 1,2-Selenosulfonylation of Allenes

Selenosulfones, as pivotal pharmaceutical molecule frameworks, have become a research hotspot in modern organic synthesis due to their vital need for efficient preparation. Herein, we have developed an iron-catalyzed four-component controllable radical tandem reaction of allenes involving cycloketone oxime esters, 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct (DABSO), and diphenyl diselenides for the synthesis of complex selenosulfones. This is the first case of achieving the 1,2-selenosulfonylation of allenes via a radical process, wherein precise control of radical rates and polarity matching enhance high regioselective conversion. The reaction conditions are ecofriendly and mild with step-efficiency by forming two new C-S bonds and one C-Se bond in one pot. Moreover, the 1,2-selenosulfonylation of allenes can be achieved by replacing cycloketone oxime esters with aryldiazonium tetrafluoroborates in this system.

Photoinduced Alkylsulfonylation and Cyanoalkylsulfonylation of Morita-Baylis-Hillman Adducts via Multicomponent Insertion of Sulfur Dioxide

General and convenient visible-light-promoted alkylsulfonylation and cyanoalkylsulfonylation of MBH adducts have been developed through the multicomponent insertion of sulfur dioxide, enabling the assembly of two C-S bonds to generate structurally diverse allylic alkylsulfones (43 examples in total). The reaction of MBH adducts with potassium alkyltrifluoroborates and 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct afforded sulfones with generally good yields. Notably, the addition of N,N,N',N'-tetramethylethylenediamine as a base into the photocatalytic system led to yielding an alkyl sulfonyl unit and cyano group-anchored trisubstituted alkenes by utilizing cycloketone oxime esters as C-radical precursors. Both of these reactions have constructed two C-S bonds, and all desired products were obtained in moderate to excellent yields with complete stereospecificity.

Three-Component Synthesis of Multiple Functionalized Allenes via Copper/Photoredox Dual Catalyzed 1,4-Alkylcyanation of 1,3-Enynes

Efficient access to multiple functionalized allenes via a three component 1,4-alkylcyanation of enynes with cyclic alcohol derivatives in the presence of trimethylsilyl cyanide (TMSCN) under copper/photoredox dual catalysis has been developed. Both easily transformable aldehyde and cyano groups were introduced to tetra-substituted allenes through light-induced C-C bond cleavage of cyclic butanol and pentanol derivatives. The reactions proceeded smoothly under mild conditions with broad functional groups tolerance.

Synthesis of Functionalized Tetrasubstituted Allenes by the Addition of Bis(trimethylsilyl)ketene Acetals to Ynones Catalyzed by Gold(I)

We have developed a straightforward and rapid methodology for the synthesis of tetrasubstituted allenes bearing carboxylic acids in the 1,3-position through the gold(I)-catalyzed nucleophilic addition of bis(trimethylsilyl)ketene acetals to ynones. The reaction was evaluated with several substrates, and 21 allenes were obtained in moderate to good yields. Using DFT calculations, we studied the mechanism of the reaction, which suggested a nucleophilic 1,4-addition pathway. The potential of allenes to act as a source of highly functionalized lactones was also explored.

Regioselective Hydro(deutero)silylation of 1,3-Enynes Enabled by Photoredox/Nickel Dual Catalysis

In the presence of visible light irradiation, organophoto/nickel dual catalysts, and the mild base K2HPO4, 1,3-enynes react with silanecarboxylic acids to give the corresponding α-silylallenes with high selectivity. In this uniquely decarboxylative hydrosilylation of 1,3-enynes, a silyl radical process is involved and diverse electron-rich and -poor substrates proceed smoothly in moderate to excellent yields. This transformation is particularly synthetically worthwhile when using MeOD as the solvent, which furnishes new access to α-silyldeuteroallenes.

Three-Component Cross-Electrophile 1,4-Alkylarylation of 1,3-Enynes by Merging Nickel and Photoredox Catalysis

A three-component 1,4-alkylarylation of 1,3-enynes with organic halides through the combination of nickel and photoredox catalysis has been established, providing a novel and modular approach for the assembly of tetrasubstituted allenes. This reductive cascade cross-electrophile reaction obviates the need for air-sensitive organometallic reagents and stoichiometric metallic reductants. A diverse range of functional groups are very compatible under mild reaction conditions and give satisfactory yields. Moreover, a reasonable mechanism is presented according to a series of control experiments.

Carbon-Carbon Bond Cleavage for Late-Stage Functionalization

Late-stage functionalization (LSF) introduces functional group or structural modification at the final stage of the synthesis of natural products, drugs, and complex compounds. It is anticipated that late-stage functionalization would improve drug discovery's effectiveness and efficiency and hasten the creation of various chemical libraries. Consequently, late-stage functionalization of natural products is a productive technique to produce natural product derivatives, which significantly impacts chemical biology and drug development. Carbon-carbon bonds make up the fundamental framework of organic molecules. Compared with the carbon-carbon bond construction, the carbon-carbon bond activation can directly enable molecular editing (deletion, insertion, or modification of atoms or groups of atoms) and provide a more efficient and accurate synthetic strategy. However, the efficient and selective activation of unstrained carbon-carbon bonds is still one of the most challenging projects in organic synthesis. This review encompasses the strategies employed in recent years for carbon-carbon bond cleavage by explicitly focusing on their applicability in late-stage functionalization. This review expands the current discourse on carbon-carbon bond cleavage in late-stage functionalization reactions by providing a comprehensive overview of the selective cleavage of various types of carbon-carbon bonds. This includes C-C(sp), C-C(sp2), and C-C(sp3) single bonds; carbon-carbon double bonds; and carbon-carbon triple bonds, with a focus on catalysis by transition metals or organocatalysts. Additionally, specific topics, such as ring-opening processes involving carbon-carbon bond cleavage in three-, four-, five-, and six-membered rings, are discussed, and exemplar applications of these techniques are showcased in the context of complex bioactive molecules or drug discovery. This review aims to shed light on recent advancements in the field and propose potential avenues for future research in the realm of late-stage carbon-carbon bond functionalization.

Organoselenium Compounds: Chemistry and Applications in Organic Synthesis

Selenium, originally described as a toxin, turns out to be a crucial trace element for life that appears as selenocysteine and its dimer, selenocystine. From the point of view of drug developments, selenium-containing drugs are isosteres of sulfur and oxygen with the advantage that the presence of the selenium atom confers antioxidant properties and high lipophilicity, which would increase cell membrane permeation leading to better oral bioavailability. In this article, we have focused on the relevant features of the selenium atom, above all, the corresponding synthetic approaches to access a variety of organoselenium molecules along with the proposed reaction mechanisms. The preparation and biological properties of selenosugars, including selenoglycosides, selenonucleosides, selenopeptides, and other selenium-containing compounds will be treated. We have attempted to condense the most important aspects and interesting examples of the chemistry of selenium into a single article.

Visible-Light Photoredox Catalyzed Regioselective 1,4-Hydroalkylation of 1,3-Enyne

Described herein is a visible-light photoredox-catalyzed regioselective 1,4-hydroalkylation of 1,3-enynes. Various of di- and tri-substituent allenes were really accessible under the present reaction conditions. The visible-light photoredox activation of the carbon nucleophile to generate its radical species, allowing the addition with un-activated enynes. The synthetic utility for the present protocol was demonstrated by a large-scale reaction, as well as the derivatization of the allene product.

Copper-Catalyzed 1,4-Trifluoromethylthio-Arylsulfonylation of 1,3-Enynes via the Insertion of Sulfur Dioxide

A copper-catalyzed trifluoromethylthio-arylsulfonylation between 1,3-enynes, AgSCF3, aryldiazonium tetrafluoroborates, and SO2 (from SOgen) is presented, which could introduce sulfone, SCF3, and allene moieties into one molecule simultaneously. This strategy features mild reaction conditions, good substrate compatibility, and excellent regioselectivity. The products obtained have the potential for further conversion into other valuable compounds. Initial investigations into the reaction mechanism suggest that it may proceed via a radical pathway. Notably, SOgen was proven as a uniquely effective SO2 surrogate in this transformation.

Synthesis of Sulfilimines via Aryne and Cyclohexyne Intermediates

An efficient and metal-free approach for the synthesis of sulfilimines from sulfenamides with aryne and cyclohexyne precursors has been developed. The reaction proceeds through unusual S-C bond formation, which offers a novel and practical entry to access a wide range of sulfilimines in moderate to good yields with excellent chemoselectivity. Moreover, this protocol is amenable to gram-scale synthesis and is applicable to the transformation of the products into useful sulfoximines.

Metal-Free Chemoselective S-Arylation of Sulfenamides To Access Sulfilimines

A novel and efficient S-arylation of sulfenamides with diaryliodonium salts for the synthesis of sulfilimines is developed. The reaction proceeds smoothly under transition-metal-free and air conditions, giving rapid access to sulfilimines in good to excellent yields via selective S-C bond formation. This protocol is scalable and exhibits a broad substrate scope, good functional group tolerance, and excellent chemoselectivity.

Remote Radical 1,3-, 1,4-, 1,5-, 1,6- and 1,7-Difunctionalization Reactions

Radical transformations are powerful in organic synthesis for the construction of molecular scaffolds and introduction of functional groups. In radical difunctionalization reactions, the radicals in the first functionalized intermediates can be relocated through resonance, hydrogen atom or group transfer, and ring opening. The resulting radical intermediates can undertake the following paths for the second functionalization: (1) couple with other radical groups, (2) oxidize to cations and then react with nucleophiles, (3) reduce to anions and then react with electrophiles, (4) couple with metal-complexes. The rearrangements of radicals provide the opportunity for the synthesis of 1,3-, 1,4-, 1,5-, 1,6-, and 1,7-difunctionalization products. Multiple ways to initiate the radical reaction coupling with intermediate radical rearrangements make the radical reactions good for difunctionalization at the remote positions. These reactions offer the advantages of synthetic efficiency, operation simplicity, and product diversity.

Nickel-Catalyzed Three-Component Tandem Radical Cyclization 1,5-Difunctionalization of 1,3-Enynes and Alkyl Bromide

A nickel-catalyzed three-component tandem radical cyclization reaction of aryl bromides with 1,3-enynes and aryl boric acids to construct γ-lactam-substituted allene derivatives has been described. This protocol provides lactam alkyl radicals through the free radical cyclization process, which can be effectively used to participate in the subsequent multicomponent coupling reaction so that 1,3-enynes could directly convert into corresponding poly-substituted allene compounds. In addition, this efficient method enjoys a broad substrate scope and provides a series of 1,5-difunctionalized allenes in a one-pot reaction.

Construction of Non-Biaryl Atropisomeric Amide Scaffolds Bearing a C-N Axis via Enantioselective Catalysis

The significant scaffold offered by atropisomeric amides with a C–N chiral axis has been extensively utilized for pharmaceuticals, agricultural science, and organic syntheses. As a result, the field of atropisomer synthesis has attracted considerable interest within chemistry communities. To date, a range of catalytic atroposelective approaches has been reported for the efficient construction of these challenging scaffolds. However, greatly concise and highly useful methodologies for the synthesis of these atropisomeric compounds, focusing on transition-metal, chiral amine, and phosphoric acid catalysis reactions, etc., are still desirable. Hence, it is indispensable to succinctly and systematically present all such reports by means of disclosing the mechanistic analysis and application, as well as the challenges and issues associated with the establishment of these atropisomers. In this review, we summarize the development of catalytic asymmetric synthetic strategies to access non-biaryl atropisomers rotating around a C–N chiral axis, including the reaction methods, mechanism, late-stage transformations, and applications.

Switchable In Situ SO2 Capture and CF3 Migration of Enol Triflates with Peroxyl Compounds under Iron Catalysis

Switchable in situ SO₂ capture and CF₃ migration of enol triflates with peroxyl compounds under iron catalysis are presented. By regulating the structure of peroxides, a variety of keto-functionalized dialkyl sulfones and α-trifluoromethyl ketones were selectively synthesized in good yields under mild conditions.

Visible-Light-Promoted Cross-Coupling of O-Aryl Oximes and Nitrostyrenes to Access Cyanoalkylated Alkenes

A photoinduced, photocatalyst-free cyanoalkylation of nitrostyenes was explored, affording a series of cyanoalkylated alkenes in moderate to good yields. Mechanistic studies reveal that an electron donor-acceptor complex formed between O-aryl oximes and DIPEA is presumably involved in this process. The excellent functional group compatibility of this newly designed synthetic protocol allows for cyanoalkylation of structurally varied substrates, which offers an eco-friendly pathway for the assembly of cyanoalkylated alkenes.

Photoredox-Catalyzed α-Sulfonylation of Ketones from Sulfur Dioxide and Thianthrenium Salts

A photoredox-catalyzed sulfonylation of silyl enol ethers with DABCO·(SO₂)₂ and thianthrenium salts is achieved, providing diverse β-keto sulfones in moderate to good yields. This protocol features easily accessible starting materials and good functional group compatibility, enabling the introduction of various functionalized sulfonyl groups into ketones. Furthermore, as one of the important industrial raw materials, methanol can be employed as the methyl source to prepare α-methylsulfonated ketones through a methyl thianthrenium intermediate for the first time.

Merging C-C σ-bond activation of cyclobutanones with CO2 fixation via Ni-catalysis

A carboxylative Ni-catalyzed tandem C-C σ-bond activation of cyclobutanones followed by CO₂-electrophilic trapping is documented as a direct route to synthetically valuable 3-indanone-1-acetic acids. The protocol shows an adequate functional group tolerance and useful chemical outcomes (yield up to 76%) when AlCl₃ is adopted as an additive. Manipulations of the targeted cyclic scaffolds and a mechanistic proposal based on experimental evidence complete the investigation.

Radical modulated regioselective difunctionalization of vinyl enynes: tunable access to naphthalen-1(2H)-ones and allenic alcohols

A novel and efficient radical-modulated difunctionalization of vinyl enynes has been disclosed using TEMPO as a radical regulator. Facile access to structurally diverse 3-bromo-naphthalen-1(2H)-ones and 4-bromo-allenic alcohols was realized via 1,2-addition/1,2-migration or 1,4-addition, respectively. This protocol represents the first example of radical-modulated metal-free difunctionalization of 1,3-enynes with high regioselectivity.

Palladium-catalyzed radical cascade cyanoalkylsulfonylation/cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with cyclobutanone oxime esters and DABSO

A palladium-catalyzed radical cascade cyanoalkylsulfonylation/cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with DABCO·(SO₂)₂ and cyclobutanone oxime esters via cleavage of a C-C single bond and insertion of SO₂ was described. A series of cyanoalkylsulfone-containing cyclopenta[gh]phenanthridines were obtained in moderate-to-good yields, thus featuring mild reaction conditions, a broad substrate scope, and a high functional group tolerance.

Photoredox-catalyzed reaction of thianthrenium salts, sulfur dioxide and hydrazines

A photoredox-catalyzed reaction of thianthrenium salts, hydrazines and DABCO·(SO2)2 is accomplished, providing diverse arenesulfonohydrazides in moderate to good yields under mild reaction conditions.

Ni and Fe Catalyzed Cascade Radical Reactions of Oxime Esters with Diselenides

A radical cyclization and ring-opening of oxime esters with diselenides was developed. Both Ni(0) and Fe(II) catalysts could be employed for the selenylation of olefin-containing and cyclic oxime ester derivatives....

Copper-Catalyzed Regioselective 1,4-Sulfonylcyanation of 1,3-Enynes with Sulfonyl Chlorides and TMSCN

A novel and practical copper-catalyzed reaction for the 1,4-sulfonylcyanation of 1,3-enynes under mild conditions is described. This protocol provides efficient and straightforward access to a variety of 5-sulfonylpenta-2,3-dienenitrile derivatives with...

Exploring the regioselectivity of the cyanoalkylation of 3-aza-1,5-dienes: photoinduced synthesis of 3-cyanoalkyl-4-pyrrolin-2-ones

Regioselective cyanoalkylalkenylation of 3-aza-1,5-dienes with oxime esters induced by visible light.

An iron-catalyzed multicomponent reaction of cycloketone oxime esters, alkenes, DABCO·(SO2)2 and trimethylsilyl azide

The synthesis of β-azidosulfones starting from alkenes, cycloketone oxime esters, trimethylsilyl azide and a sulfur dioxide surrogate of DABCO·(SO2)2 under iron catalysis is developed.

Nickel-catalysed SET-reduction-based access to functionalized allenes via 1,4-carbohydrogenation of 1,3-enynes with alkyl bromides

Allene synthesis: Using reductive radical–polar crossover as the strategy, functionalized allenes could be easily accessed via the reactions of 1,3-enynes with alkyl bromides enabled by nickel catalysis.

Photoredox-catalyzed synthesis of sulfonated oxazolines from N-allylamides through the insertion of sulfur dioxide

Photoredox-catalyzed generation of sulfonated oxazolines starting from N-allylamides, DABCO·(SO2)2, and aryldiazonium salts has been developed and a range of sulfonated oxazolines were obtained in moderate to good yields.

Direct selenosulfonylation of unsaturated compounds: a review

In this review, we have discussed recent developments on the direct selenosulfonylation of unsaturated compounds which lead to the formation of two new carbon-sulfur and carbon-selenium bonds in a single operation. The reactions were classified based on the type of starting unsaturated compound and product. Thus, the review is divided into three major sections. The first describes the current literature on selenosulfonylation of alkenes. The second section covers the available literature on selenosulfonylation of alkynes. The third focuses exclusively on selenosulfonylation of allenes.

In this review, we have discussed recent developments on the direct selenosulfonylation of unsaturated compounds which lead to the formation of two new carbon-sulfur and carbon-selenium bonds in a single operation.

Fe-catalyzed denitrative cyanoalkylation of nitroalkenes with cycloketone oxime esters via reductive C–C bond formation

An iron catalyzed reductive denitrative cyanoalkylation of nitroalkenes with cycloketone oxime esters using Zn as the reductant has been successfully established in which the NO2 of nitroalkenes eventually acts as a leaving group.

Construction of sulfonated spiro[5,5]trienones from sulfur dioxide via iron-catalyzed dearomative spirocyclization of biaryls

An iron-catalyzed dearomative spirocyclization of biaryl ynones with sodium metabisulfite and cycloketone oxime esters is developed. By using sodium metabisulfite as the source of sulfur dioxide, this approach enables the...

Radical transformations for allene synthesis

Allenes are valuable organic molecules that feature unique physical and chemical properties. They are not only often found in natural products, but also act as versatile building blocks for the access of complex molecular targets, such as natural products, pharmaceuticals, and functional materials. Therefore, many remarkable and elegant methodologies have been established for the synthesis of allenes. Recently, more and more methods for radical synthesis of allenes have been developed, clearly emphasizing the associated great synthetic values. In this perspective, we will discuss recent important advances in the synthesis of allenes via radical intermediates by categorizing them into different types of substrates as well as distinct catalytic systems. The mechanistic studies and synthetic challenges will be highlighted.

Recent important advances in the synthesis of allenes via radical strategies are highlighted.

N-Heterocyclic Carbene-Catalyzed 1,4-Alkylacylation of 1,3-Enynes

The radical relay coupling reaction recently emerged as a powerful synthetic strategy for producing tetrasubstituted allenes. However, bond-forming processes involving the allenyl radical intermediate are mostly limited to those promoted by transition metals. In this report, we describe that a ketyl radical generated from single-electron oxidation of the Breslow intermediate is an excellent coupling partner of allenyl radicals. An organocatalytic 1,4-alkylacylation of 1,3-enynes occurred smoothly in the presence of an aldehyde, a radical precursor, and an N-heterocyclic carbene catalyst. This transformation showed remarkable tolerance to both aromatic and aliphatic aldehydes, enyne substitution, and diversified radical precursors.

Synthesis of β-cyanoalkylsulfonylated vinyl selenides through a four-component reaction

A mild copper-catalyzed four-component selenosulfonylation of alkynes, cycloketone oxime esters, DABCO (SO₂)₂ and diselenides has been developed. This method enables the rapid assembly of β-cyanoalkylsulfonylated vinyl selenides in moderate to good yields. Advantages of this protocol include a broad substrate scope, good functional group tolerance and the late-stage functionalization of complex molecules. Moreover, the potential utility of this methodology is demonstrated through simple oxidation of the products to access synthetically important alkynyl sulfones. Mechanistic studies suggest that a cyanoalkylsulfonyl radical intermediate is involved in this process.

Dual Photoredox/Nickel-Catalyzed 1,4-Sulfonylarylation of 1,3-Enynes with Sulfinate Salts and Aryl Halides: Entry into Tetrasubstituted Allenes

A radical-mediated three-component 1,4-sulfonylarylation of 1,3-enynes with aryl iodides and sulfinate salts using cooperative photoredox/nickel catalysis is described. This protocol enables the synthesis of tetrasubstituted sulfonyl-containing allenes under redox-neutral conditions and provides a versatile 1,3-enyne 1,4-difunctionalization platform for the synthesis of a diverse range of tetrasubstituted allenes with high chemo- and regioselectivities, excellent functional group tolerance, and a broad substrate scope.