Photoinduced Vicinal 1,2-Difunctionalization of Olefins for the Synthesis of Alkyl Sulfonamides

Photosensitized Imino-Sulfamoylation of Alkenes with Oxime Carbamates

In this study, we have devised a strategy that employs oxime carbamate as a bifunctional diamination reagent in combination with SO2 to realize imino-sulfamoylation of alkenes. This protocol is characterized by its mild conditions, operational simplicity, and metal-free nature, while demonstrating broad functional group tolerance for alkenes. Furthermore, the application of this method provides an accessible route to a diverse range of β-amino sulfonamide derivatives.

Visible-Light-Induced 4CzIPN-Catalyzed Alkylamination of Alkenes via Cyclobutanone Oxime Esters and Anilines

We disclosed an organophotoredox-catalyzed three-component oxidative radical-polar crossover strategy for constructing 1,2-alkylamination products. Cycloketone oxime derivatives were used as cyanoalkyl radical precursors and anilines were used as the nucleophiles. This facile protocol shows a good reaction yield and broad substrate scope.

Copper(I)-Photocatalyzed Addition of Trichloromethanesulfenyl Chloride to Olefinic Compounds

Atom transfer radical addition (ATRA) reactions are essential transformations in organic synthetic chemistry that enable the atom-economic difunctionalization of abundant olefin feedstocks. In this way, a rich chemical space can be opened up by well-planned combinations of simple starting materials. To build an efficient photocatalytic transformation, the reactivity of trichloromethanesulfenyl chloride toward alkenes and alkynes was investigated under photocatalytic Cu(I) reaction conditions. In this study, we found that trichloromethanesulfenyl chloride can be added to a series of olefins (such as styrenes and electron-rich and -poor olefins) in the presence of 1 mol% [Cu(dmp)2]BF4 photocatalyst and blue LED irradiation, producing α-chloro trichloromethylthioethers in good yields. Experimental and theoretical (DFT) mechanistic studies are consistent with the proposed radical chain mechanism of transformation. This study may serve as a valuable reference for the development of new coupling reactions that are economical and highly efficient processes.

Photoredox-Catalyzed Three-Component Sulfonaminoalkynylation of Alkenes via a Radial/Polar Crossover

We report a photoredox-catalyzed three-component sulfonaminoalkynylation of alkenes with N-aminopyridine salts and potassium alkynyltrifluoroborate salts. This aminoalkylation reaction underwent a radial/polar crossover mechanism, which was distinguished from the previous reports. A variety of β-alkynylated sulfonamides were obtained in moderate to excellent yields. The versatility of this method was further evidenced by its successful application in modifying biological molecules in advanced stages of development.

Visible-light-induced cascade radical cyclization to access sulfamoylated benzo[4,5]imidazo[2,1-a]isoquinolin-6(5H)-ones

We report, for the first time, a visible-light-induced cascade radical sulfamoylation and cyclization of 2-arylbenzoimidazoles using sulfamoyl chlorides as sulfamoylation reagents to access sulfamoylated benzo[4,5]imidazo[2,1-a]isoquinolin-6(5H)-ones. The readily available nature of sulfamoyl chlorides and the metal-free conditions make this method a promising strategy for the synthesis of these compounds.

Access to 1-aryl-pyrazolin-5-ones via photoinduced chemoselective cyclization of N-methacrylo aldehyde hydrazones

A photocatalytic sulfamoylation/5-endo-trig cyclization of (E)-N'-arylidene-N-phenylmethacrylohydrazides with sulfamoyl chlorides was developed. The chemoselective intramolecular addition of the carbon-centered radical intermediate to the CN bond in the hydrazone motif gave the sulfamoylated pyrazolin-5-one. Besides, sulfonyl chlorides are also suitable reaction partners to access sulfonylated pyrazolin-5-ones. This approach is characterized by mild reaction conditions, broad substrates scope, excellent selectivity and the late-stage modification of drug molecules.

Overcoming Selectivity Trade-Offs in Alkene Azidodifluoroalkylation: An Enlightening Synergistic Catalytic Approach

Recent advances in dual catalysis involving biomimetic conversion strategies that utilize radical ligand transfer (RLT) often rely on large doses of precious metal additives. The role of these additives within the mechanism remains ambiguous, leading to complex reaction conditions, uncertain pathways, and increased costs. These challenges complicate the study of the reaction process and are accompanied by potential safety risks. To address these issues, azide salt was used as an alternative to TMSN3. This replacement not only avoids the drawbacks associated with almost parallel research on alkene azidodifluoroalkylation but also eliminates the need for ligands. Comparative analysis indicates that existing biomimetic synergistic catalysis strategies require Ag2CO3 additives to enhance selectivity in alkene difunctionalization reactions, highlighting the superior simplicity, environmental friendliness, and operational ease of our developed synergistic catalysis strategy. Furthermore, under the guidance of our proposed mechanism, an alkene azidosulfonation was designed, validating the innovative and practical applicability of our synergistic catalysis approach.

Non-directed oxidative annulation of 2-arylindazoles with electron deficient olefins via visible light photocatalysis

A new visible-light-mediated non-directed oxidative annulation between 2-arylindazoles and electron-deficient olefins using commercially available piperidine-1-sulfonyl chloride as the radical precursor to afford fused 5,6-dihydroindazolo[2,3-a]quinolines has been developed under mild reaction conditions. This transformation occurs via two consecutive C-H bond functionalizations. The mechanistic investigation results indicate that the reaction progresses through a radical pathway forming a 2-(2-aryl-2H-indazol-3-yl)-3-piperidin-1-ylsulfonyl derivative as an intermediate.

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.

Photoredox-Catalyzed Alkylamination of Alkenes via Oxidative Radical-Polar Crossover and Site-Selective 1,5-Hydrogen Atom Transfer

We reported the visible-light-mediated photoredox-catalyzed oxidative radical-polar crossover and 1,5-hydrogen atom transfer combined site-selective remote C(sp3)-N cross-coupling alkylamination of alkenes. Various anilines and hydroxamides (1,5-hydrogen atom transfer reagents) could be tolerated. The mechanistic studies indicated the radical nature of the reaction and the indispensability of light and photocatalyst. Stern-Volmer fluorescence quenching and cyclic voltammetry experiments have been used to outline the proposed reaction pathway.

Modular access to diarylmethyl sulfonamides via visible light-promoted cross-coupling reactions

We report a novel and efficient method for the preparation of diarylmethyl sulfonamide derivatives through visible-light-induced sulfamoylation of para-quinone methides with sulfamoyl chlorides under mild, metal-free conditions. This protocol demonstrates excellent tolerance toward a wide range of functional groups, affording the corresponding products in moderate to high yields. Preliminary mechanism studies revealed that the excited photocatalyst rhodamine 6G* was mainly quenched by para-quinone methides and the generated diarylmethyl radical intermediates then underwent radical-radical cross-coupling with sulfamoyl radicals to yield the diarylmethyl sulfonamides.

Photocatalytic Decarboxylative Functionalization of Cyclopropenes via Cyclopropenium Cation Intermediates

A photocatalytic decarboxylative functionalization of cyclopropenes is reported. Starting from a broad range of redox-active ester-substituted cyclopropenes, cyclopropenylphthalimides can be synthesized in the absence of a nucleophile. Alternatively, different carbon and heteroatom nucleophiles can be introduced. The transformation proceeds most probably through the formation of an aromatic cyclopropenium cation, followed by trapping with the nucleophiles.

Visible-Light-Induced Difunctionalization of 3-Butenoic Acid with Bromodifluoromethyl Heteroarylsulfones

Herein, we report a visible-light-induced iridium-promoted direct bifunctionalization of 3-butenoic acid with bromodifluoromethyl heteroarylsulfones. This methodology enables the concurrent introduction of difluoromethyl heteroarylsulfone and bromine groups into 3-butenoic acid under mild reaction conditions. Various α-substituted 3-butenoic acids and bromodifluoromethyl heteroarylsulfones were found to be compatible, yielding the corresponding products in moderate to good yields. This method opens a new route for the synthesis of fluorocarboxylic acid derivatives.

Photoinduced Vicinal Sulfamoyloximation of Alkenes: Harnessing Bifunctional Nitrosamines via a Rapid Radical Trapping Strategy

We developed a photoinduced method for vicinal sulfamoyloximation of alkenes using N-nitrosamines as bifunctional reagents, with DABSO serving as both a sulfonyl source and a rapid aminyl radical trap. This strategy prevents radical recombination, enabling bifunctional activation under neutral conditions to generate key sulfamoyl radicals. It accommodates broad substrate scope and functional group compatibility, enabling late-stage modifications of bioactive molecules and expanding sulfonamide diversity in organic synthesis.

SOMOphilic alkyne vs radical-polar crossover approaches: The full story of the azido-alkynylation of alkenes

We report the detailed background for the discovery and development of the synthesis of homopropargylic azides by the azido-alkynylation of alkenes. Initially, a strategy involving SOMOphilic alkynes was adopted, but only resulted in a 29% yield of the desired product. By switching to a radical-polar crossover approach and after optimization, a high yield (72%) of the homopropargylic azide was reached. Full insights are given about the factors that were essential for the success of the optimization process.

Photocatalyst-Free Activation of Sulfamoyl Chlorides for Regioselective Sulfamoyl-Oximation of Alkenes via Hydrogen Atom Transfer (HAT) and Halogen-Atom Transfer (XAT) Relay Strategy

The use of readily available and diverse sulfamoyl chlorides for synthesizing sulfonamide compounds presents an intriguing, yet significantly underexplored strategy. Activating sulfamoyl chlorides via single-electron reduction poses challenges due to their high reduction potential. Alternatively, the SO2-Cl bond in sulfamoyl chlorides could be readily cleaved by XAT. However, the existing methodologies have been limited to either the use of photocatalyst or the monofunctionalization of activated alkenes. Here, we report a regioselective sulfamoyl-oximation of alkenes by involving the activation of sulfamoyl chlorides through a HAT and XAT relay strategy in a photocatalyst-free way. The key to this success lies in the dual roles of tert-butyl nitrite (TBN), which not only serves as the source of oximes but also acts as the HAT reagent to generate the crucial XAT reactive species. The exclusion of metal catalysts or photosensitizers for utilizing light energy renders this protocol versatile and universally applicable for synthesizing a broad range of structurally diverse oxime-containing alkyl sulfonamides.

Photosensitized 1,2-Difunctionalization of Alkenes to Access β-Amino Sulfonamides

A metal-free photosensitized 1,2-imino-sulfamoylation of olefins by employing a tailor-made sulfamoyl carbamate as the difunctionalization reagent has been established. This protocol exhibits versatility across a broad substrate scope, including aryl and aliphatic alkenes, leading to the synthesis of diverse β-imino sulfonamides in moderate to good yields. This method is characterized by its metal-free reaction system, mild reaction conditions, excellent regioselectivity, and high atom economy, serving as a promising platform for the preparation of β-amino sulfonamide-containing molecules, particularly in the context of drug discovery.

New chemistry of alkynyl trifluoroborates under transition metal catalyst-free conditions

This review summarizes recent advances in alkynyl trifluoroborate chemistry, emphasizing their unique reactivity and stability in organic synthesis and biological applications under transition metal catalyst-free conditions.

Visible-Light-Promoted Intermolecular β-Acyl Difunctionalization of Alkenes via Oxidative Radical-Polar Crossover

A visible-light-induced β-acyl difunctionalization of alkenes with acyl oxime esters and various nucleophiles was developed to achieve molecular complexity from readily available raw materials via oxidative radical-polar crossover. A variety of nucleophiles, including NH-sulfoximines, indoles, indazole, and trimethoxybenzene, were all effectively applicable to the sustainable reaction system. The novel synthetic strategy features mild reaction conditions, a broad substrate scope (39 examples), easy scale-up, and excellent regioselectivity.

Synthesis of α-Trifluoromethyl Alkynes through Fluoroalkynylation of gem-Difluoroalkenes

A trifluoromethylalkynylation reaction of gem-difluoroalkenes with alkynyl sulfoxide by photoredox radical addition with good functional group tolerance in moderate to high yields, is developed for the synthesis of α-trifluoromethyl alkyne. This reaction features simple operation and inexpensive raw materials and provides an expeditious route to synthesize biologically relevant fluorine-containing alkynyl compounds with diverse structural skeletons.

Azido-alkynylation of alkenes through radical-polar crossover

We report an azido-alkynylation of alkenes allowing a straightforward access to homopropargylic azides by combining hypervalent iodine reagents and alkynyl-trifluoroborate salts. The design of a photocatalytic redox-neutral radical polar crossover process was key to develop this transformation. A variety of homopropargylic azides possessing electron-rich and -poor aryls, heterocycles or ether substituents could be accessed in 34-84% yield. The products are synthetically useful building blocks that could be easily transformed into pyrroles or bioactive amines.

Multicomponent Reactions between Heteroatom Compounds and Unsaturated Compounds in Radical Reactions

In this mini-review, we present our concepts for designing multicomponent reactions with reference to a series of sequential radical reactions that we have developed. Radical reactions are well suited for the design of multicomponent reactions due to their high functional group tolerance and low solvent sensitivity. We have focused on the photolysis of interelement compounds with a heteroatom-heteroatom single bond, which readily generates heteroatom-centered radicals, and have studied the photoinduced radical addition of interelement compounds to unsaturated compounds. First, the background of multicomponent radical reactions is described, and basic concepts and methodology for the construction of multicomponent reactions are explained. Next, examples of multicomponent reactions involving two interelement compounds and one unsaturated compound are presented, as well as examples of multicomponent reactions involving one interelement compound and two unsaturated compounds. Furthermore, multicomponent reactions involving intramolecular cyclization processes are described.