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

Nickel-Catalyzed Reductive 1,4-Alkylacylation of 1,3-Enynes Enabling Synthesis of Allenyl Ketones

A nickel-catalyzed reductive 1,4-alkylacylation of 1,3-enynes has been established using nonactivated tertiary alkyl bromides and aromatic anhydrides as dual electrophiles. This protocol enables efficient assembly of tetrasubstituted allenyl ketones with high chemo- and regioselectivity. Mechanistic insights reveal the radical relay process involving the synergistic interactions of nickel and zinc. The allenyl ketone products serve as modular building blocks, particularly for constructing fully carbon-substituted furans via Au-catalyzed cycloisomerization with selective 1,2-aryl migration, enhancing the synthetic practicality.

Synthesis of fluoroalkenes and fluoroenynes via cross-coupling reactions using novel multihalogenated vinyl ethers

In this study, we develop the synthesis methods of fluoroalkenes and fluoroenynes via Suzuki-Miyaura and Sonogashira cross-coupling reactions using novel multihalogenated fluorovinyl ethers, which are easily prepared from the reaction between phenols and 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane). These reactions make use of the unique structure of multihalogenated fluorovinyl ethers, which contains a reactive bromine atom, to afford a series of fluoroalkenes and fluoroenynes in moderate to high yields.

Photoreductive 1,4-Dicarbofunctionalization of 1,3-Enynes with Organoiodides and Cyanoarenes via Halogen-Atom Transfer

A photoreductive halogen-atom transfer (XAT) strategy for 1,4-dicarbofunctionalization of 1,3-enynes with organoiodides and cyanoarenes is disclosed, enabling access to functionalized allenes in a highly regio-, chemo-, and stereoselective manner. Upon the photoredox catalysis and the activation of Et3N XAT agents, the mild conditions and high functional group tolerance of this protocol enable the formation of two C-C bonds, including a C(sp3)-C(sp3) bond and a C(sp2)-C(sp2) bond, in a single reaction step, and provides a general avenue to polysubstituted allenes and late-stage modification of bioactive compounds.

Nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes to access allenes and dienes

The radical-mediated difunctionalization of 1,3-enynes facilitates rapid access to structurally diverse allenes and dienes. Whereas, owing to the existence of multiple active sites in conjugated 1,3-enynes, regulating selectivity in difunctionalized addition via a single transition-metal-catalyzed radical tandem process remains elusive. Herein, we disclose an intriguing protocol of substrate-controlled nickel-catalyzed regiodivergent sulfonylarylation of 1,3-enynes with the assistance of sulfonyl chlorides and arylboronic acids. This valuable synthetic utility respectively delivers a series of highly functionalized and synthetically challenging allenyl sulfones and dienyl sulfones from fine-tuned 1,3-enynes by one step, which provides a facile approach for complex sulfone-containing drug molecules synthesis.

Dual Nickel/Photoredox-Catalyzed Arylsulfonylation of Allenes

The nickel/photoredox dual catalysis system is an efficient conversion platform for the difunctionalization of unsaturated hydrocarbons. Herein, we disclose the first dual nickel/photoredox-catalyzed intramolecular 1,2-arylsulfonylation of allenes, which can accurately construct a C(sp2)-C(sp2) bond and a C(sp3)-S bond. The reaction exhibits excellent chemoselectivity and regioselectivity, allowing modular conformations of a diverse series of 3-sulfonylmethylbenzofuran derivatives. Control experiments showed that the bipyridine ligand is crucial for the formation of a stable σ-alkyl nickel intermediate, providing the possibility for sulfonyl radical insertion. Meanwhile, the electrophilic sulfonyl radical facilitates further oxidative addition of the σ-alkyl nickel intermediate and inhibits addition with allenes. In addition, control experiments, cyclic voltammetry tests, Stern-Volmer experiments, and density functional theory calculations afford evidence for the Ni(0)/Ni(I)/Ni(II)/Ni(III) pathway in this 1,2-arylsulfonylation.

Visible-Light-Induced Regioselective Radical-Polar Crossover 1,4-Hydrophosphinylation of 1,3-Enynes: Access to Trisubstituted Allenes Bearing a Phosphine Oxide Group

The radical 1,4-functionalizations of 1,3-enynes have emerged as a powerful strategy for the synthesis of multisubstituted allenes. However, the phosphorus-centered radical-initiated transformations remain largely elusive. Herein, visible-light photoredox catalytic regioselective radical hydrophosphinylation of 1,3-enynes with diaryl phosphine oxides as phosphinoyl radical precursors has been realized. This protocol features mild conditions, a wide substrate scope, and good functional group tolerance, producing a diverse range of phosphinoyl-substituted allenes in moderate to good yields with high atom economy. Detailed mechanistic experiments revealed a radical-polar crossover process in the reaction.

Photoredox-Catalyzed 1,4-Peroxidation-Sulfonylation of Enynones: A Three-Component Radical Coupling Approach for the Synthesis of Highly Functionalized Allenes

An Eosin Y-catalyzed visible light-promoted 1,4-peroxidation-sulfonylation of enynones was achieved to give tetrasubstituted allenes. The photoredox catalysis of Eosin Y allowed the concomitant formation of peroxy and sulfonyl radicals, where the preferential peroxy radical addition to the alkene moiety of enynones resulted in the subsequent α-keto radical-sulfonyl radical cross couplings. The developed photoredox catalysis of Eosin Y demonstrates a regioselective 1,4-diradical addition strategy, opening up a new possibility of diradical functionalization of conjugate systems.

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.

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.

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.

Amino Acid Sulfinate Salts as Alkyl Radical Precursors

A general approach to the synthesis of amino acid sulfinate salts from commercially available α-chiral hydroxylated amino acids is reported. These reagents are shown to be valuable precursors to alkyl radicals under mild photochemical oxidation conditions. The photochemically generated amino acid radicals engage readily with alkyl and aryl disulfide radical traps to afford a diverse suite of modified amino acids.

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.

Catalyst-Free Electrochemical Sulfonylation of Organoboronic Acids

A simple and efficient electrochemical sulfonylation of organoboronic acids with sodium arylsulfinate salts has been reported for the first time. A variety of aryl, heteroaryl, and alkenylsulfones were obtained in good to excellent yields via a simple electrochemical sulfonylation of various arylboronic acids, heterocyclic boronic acids, or alkenylboronic acids with sodium arylsulfinate at room temperature in 5 h under the catalyst-free and additive-free conditions. A plausible mechanism has been proposed based on various radical-trapping and CV control experiments.

Ni-catalyzed C-S bond construction and cleavage

Sulfur-containing compounds have attracted considerable interest due to their wide-ranging applications in pharmaceuticals, agriculture, natural products, and organic materials. The development of efficient and rapid methods for the construction and transformation of sulfur-containing compounds is of great importance. Since nickel is inexpensive and has a variety of valence states, strong nucleophilicity and low energy barriers for oxidative addition, the construction and transformation of sulfur-containing compounds by nickel-catalyzed cross-coupling have become important strategies. In addition, sulfur-containing compounds have also been playing increasingly important roles in the field of cross-coupling due to their thermodynamically stable but dynamic activity. This review will focus on nickel-catalyzed construction and transformation of various sulfide-containing compounds, such as sulfides, disulfides, and hypervalent sulfur-containing compounds.

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.

Photo and copper dual catalysis for allene syntheses from propargylic derivatives via one-electron process

Different from the traditional two-electron oxidative addition-transmetalation-reductive elimination coupling strategy, visible light has been successfully integrated into transition metal-catalyzed coupling reaction of propargylic alcohol derivatives highly selectively forming allenenitriles: specifically speaking, visible light-mediated Cu-catalyzed cyanation of propargylic oxalates has been realized for the general, efficient, and exclusive syntheses of di-, tri, and tetra-substituted allenenitriles bearing various synthetically versatile functional groups. A set of mechanistic studies, including fluorescence quenching experiments, cyclic voltammetric measurements, radical trapping experiments, control experiments with different photocatalyst, and DFT calculation studies have proven that the current reaction proceeds via visible light-induced redox-neutral reductive quenching radical mechanism, which is a completely different approach as compared to the traditional transition metal-catalyzed two-electron oxidative addition processes.

NHC and visible light-mediated photoredox co-catalyzed 1,4-sulfonylacylation of 1,3-enynes for tetrasubstituted allenyl ketones

The modulation of selectivity of highly reactive carbon radical cross-coupling for the construction of C-C bonds represents a challenging task in organic chemistry. N-Heterocyclic carbene (NHC) catalyzed radical transformations have opened a new avenue for acyl radical cross-coupling chemistry. With this method, highly selective cross-coupling of an acyl radical with an alkyl radical for efficient construction of C-C bonds was successfully realized. However, the cross-coupling reaction of acyl radicals with vinyl radicals has been much less investigated. We herein describe NHC and visible light-mediated photoredox co-catalyzed radical 1,4-sulfonylacylation of 1,3-enynes, providing structurally diversified valuable tetrasubstituted allenyl ketones. Mechanistic studies indicated that ketyl radicals are formed from aroyl fluorides via the oxidative quenching of the photocatalyst excited state, allenyl radicals are generated from chemo-specific sulfonyl radical addition to the 1,3-enynes, and finally, the key allenyl and ketyl radical cross-coupling provides tetrasubstituted allenyl ketones.

Visible-Light-Induced Dual Acylation of Alkenes for the Construction of 3-Substituted Chroman-4-ones

Heterocyclic compounds, especially oxygen-containing heterocyclic compounds, are crucial moieties in bioactive compounds and drug leads. Substituted chroman-4-ones are a kind of the most significant structural skeletons. Herein, we report a visible-light-induced dual acylation of alkenes for constructing 3-substituted chroman-4-ones, which undergoes a radical tandem cyclization reaction through carbon-carbon bond cleavage of oxime esters by a nitrogen-centered radical strategy. A series of 3-substituted chroman-4-ones were prepared with up to 86% yield.

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...

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.

Selective 1,4-arylsulfonation of 1,3-enynes via photoredox/nickel dual catalysis

A photoredox/nickel-catalyzed selective 1,4-arylsulfonation of 1,3-enynes to access structurally diverse sulfone-containing allenes has been established with low catalyst loading.