Silver-catalyzed generation of acyl radicals from α-imino-oxy acids: access to acylated 3-CF3-2-oxindoles

A unified strategy to generate acyl radicals from α-imino-oxy acids via selective C-C bond activation is reported. In the presence of a silver catalyst, α-imino-oxy acids could undergo decarboxylation and N-O and C-C bond homolysis to deliver the acyl radicals, which were subsequently captured by N-alkyl-N-aryl-2-(trifluoromethyl)acrylamides to access acylated 3-CF3-2-oxindoles.

Carbon Monoxide and Alkoxycarbonyl Radical Enabled Migration Strategy for the Carbonylative Functionalization of Unactivated Alkenes

Herein we report a "carbonylative migration" strategy for the acylation-esterification type double functionalization of unactivated alkenes using alkyloxalkyl chlorides and CO as the reagents. The transformation is proceeded by the alkoxycarbonyl radical addition to unactivated alkenes, followed by the insertion of carbon monoxide to induce intramolecular migration of heteroaryl groups, which is different from the traditional reaction modes. The reaction conditions were mild and well tolerated with varieties of functional groups. A variety of 1,4-dicarbonyl compounds with different ester groups were produced easily which has high potential applications in biology, medicine, and other fields.

Palladium-Catalyzed Cascade Distal C-H Methylation and Cyclization for the Construction of Spirooxindole Skeletons

Transition metal-catalyzed C-H methylation represents a straightforward approach for introducing methyl groups into organic molecules. Herein, we report a palladium-catalyzed alkene-relayed remote C-H methylation reaction that utilizes dimethyl carbonate as the methylation reagent. The aryl groups distal to a bromo group were dimethylated via C-H activation, leading to the formation of spirooxindoles as the final products through C(sp3)-H activation and C(sp3)-C(sp3) coupling. This cascade process involves the formation of four C-C bonds and the activation of three C-H bonds. The reaction not only provides a new approach to C-H methylation but also offers a novel method for constructing spirooxindole skeletons by merging skeleton construction and methylation into a single step.

Photo-Driven Regiodivergent Arylation/Cyclization and Arylation/Hydroxylation of N-Aryl Methacrylamides with Aryltriazenes: Access to Functionalized 3,3-Disubstituted Oxindoles and α-Hydroxylamides

A metal-free, light-induced regiodivergent functionalization of α,β-unsaturated amides with aryltriazenes under ambient conditions was developed. The visible light and B(C6F5)3 cocatalyzed radical cascade arylation/cyclization of N-alkyl-N-arylmethacrylamides can obtain functionalized 3,3-disubstituted oxindoles with the assistance of photocatalyst eosin Y-Na2. In the absence of any catalyst, with purple light irradiation and electron-donor-acceptor (EDA) complex initiation, the radical cascade arylation/hydroxylation of N-arylmethacrylamides affords α-hydroxylamides. This methodology highlights the arts in accessing different regioisomers by altering the substrates and photocatalytic strategies.

Photoredox-catalyzed alkylarylation of activated alkenes via a ring-opening/Truce-Smiles rearrangement cascade

A photoredox-catalyzed alkylarylation of activated alkenes via a radical C-C bond cleavage/Truce-Smiles rearrangement cascade is developed. The protocol features mild and redox-neutral conditions, broad substrate scope and excellent functional group compatibility, providing a facile and efficient approach to the long-chain distal keto-amides with all-carbon quaternary centers at the alpha position.

Photochemical C(sp3)-H Activation for Diversity-Oriented Synthesis of 3-Functionalized Oxindoles

Heteroatom-adjacent C(sp3) radical cyclization of N-arylacrylamides provides a straightforward pathway to synthesize valuable 3-functionalized oxindoles. Traditional cyclization reactions normally require harsh conditions or transition-metal catalysts. Here, we developed a metal-free, diversity-oriented synthesis of 3-functionalized oxindoles via photochemically induced selective cleavage of C(sp3)-H bonds. A variety of 3-substituted oxindoles with functionalities such as ethers, polyhalogens, benzyl, and formyl groups can be obtained by a rational design. This strategy is characterized by its simple operation and mild conditions, aligning well with the developmental requirements for sustainable chemistry. The gram-scale continuous-flow synthesis and efficient construction of bioactive molecules highlight its practical utility.

Access to CF2COR-Containing Quinazolinones via Visible-Light-Induced Domino Difluoroalkylation/Cyclization of N-Cyanamide Alkenes

A green and highly efficient visible-light-induced radical cascade difluoroalkylation/cyclization reaction of N-cyanamide alkenes has been developed. A variety of CF2COR-containing quinazolinones have been obtained in high yields with cheap non-metallic 4CzIPN as the photocatalyst. This photocatalytic reaction provides rapid, facile, and practical access to valuable polycyclic quinazolinone, and it is amenable to the gram scale.

Direct synthesis of N-functionalized indoles through isomerization of azomethine ylides

An unexpected isomerization of azomethine ylides generated in situ from isatin with indoline-2-carboxylic acid has been disclosed, providing direct access to N-functionalized indole scaffolds. This protocol has good functional group tolerance and provides various 3-(1H-indol-1-yl)indolin-2-one derivatives in moderate to high yields simply by using alcohol as the solvent, with no additional additive being required.

Cp2Fe-Mediated Electrochemical Synthesis of Phosphorylated Oxindoles and Indolo[2,1-a]isoquinolin-6(5H)-ones

An efficient and environmentally friendly electrochemical synthesis of phosphorylated oxindoles and indolo[2,1-a]isoquinolin-6(5H)-ones mediated by readily available Cp2Fe has been developed, which illustrated a broad substrate scope and diverse functional group compatibility. This protocol featured an external oxidant-free process and was at room temperature, which was proposed to be driven by the anodic oxidation of Cp2Fe.

Electrochemical Fe-catalysed radical cyclization for the synthesis of oxindoles

We report an efficient and sustainable electrocatalytic approach for the synthesis of 3,3-disubstituted 2-oxindoles bearing ester groups from readily accessible N-arylacrylamides and carbazates. The reaction proceeds through an electrochemical iron-catalyzed radical addition/cyclization sequence with a commercially available iron catalyst and carbazates as alkoxycarbonyl radical precursors. This mild and operationally simple method transforms a wide range of structurally diverse N-arylacrylamides into oxindole derivatives in good yields and can be smoothly scaled up for the preparation of synthetically valuable oxindoles that are key intermediates for the synthesis of natural products.

Synthesis of Tetrahydro-indolones through Rh(III)-Catalyzed [3 + 2] Annulation of Enaminones with Iodonium Ylides

An unprecedented protocol for a Rh(III)-catalyzed [3 + 2] annulation from simple and readily available enaminones and iodonium ylides has been developed. The novel strategy allows for access to a new class of structurally diverse tetrahydro-indolones with high efficiency and a broad substrate scope. In addition, this transformation represents the first example of the selective Rh(III)-catalyzed alkenyl C-H bond functionalization and annulation of enaminones. Finally, the potential applications of this protocol are demonstrated through gram-scale reaction and late-stage modification.

Persulfate promoted carbamoylation of N-arylacrylamides and N-arylcinnamamides with 4-carbamoyl-Hantzsch esters

Carbamoyl-Hantzsch esters were used as carbamoyl radical precursors for oxidative carbamoylation of N-arylacrylamides and N-arylcinnamamides in the presence of inexpensive persulfates. This protocol can be applied to a broad range of substrates with various functional groups, providing a variety of 3,3-disubstituted oxindoles and 3,4-disubstituted dihydroquinolin-2(1H)-ones in moderate to good yields via an intermolecular addition/cyclization process.

Metal-Catalyst-Free One-Pot Aqueous Synthesis of trans-1,2-Diols from Electron-Deficient α,β-Unsaturated Amides via Epoxidation Using Oxone as a Dual Role Reagent

In organic synthesis, incorporating two functional groups into the carbon-carbon double bond of α,β-unsaturated amides is challenging due to the electron-deficient nature of the olefin moiety. Although a few examples of dihydroxylation of α,β-unsaturated amides have been demonstrated, producing cis-1,2-diols using either highly toxic OsO4 or other specialized metal reagents in organic solvents, they are limited to several specific amides. We describe herein a general and one-pot direct synthesis of trans-1,2-diols from electron-deficient α,β-unsaturated amides through dihydroxylation using oxone as a dual-role reagent in water. This reaction does not require any metal catalyst and produces non-hazardous and nontoxic K2 SO4 as the sole byproduct. Moreover, epoxidation products could also be selectively formed by adjusting the reaction conditions. By the strategy, the intermediates of Mcl-1 inhibitor and antiallergic bioactive molecule can be synthesized in one pot. The gram-scale synthesis of trans-1,2-diol which is isolated and purified by recrystallization further shows the potential applications of this new reaction in organic synthesis.

Photoinduced radical cascade domino Heck coupling of N-aryl acrylamide with vinyl arenes enabled by palladium catalysis

Here, a redox-neutral palladium-catalyzed photo-induced radical cascade domino Heck reaction of N-aryl acrylamide with vinyl arenes is described. A diverse range of bioactive oxindoles, featuring an all-carbon quaternary center, were synthesized. The reaction is proposed to proceed via an open-shell intermediate and occurs under mild reaction conditions, exhibiting excellent functional group tolerance. Importantly, the synthesized products can be readily transformed into biologically active molecules, including (±)-physostigmine and (±)-physovenine.

Photoinduced Alkyl/Aryl Radical Cascade for the Synthesis of Quaternary CF3-Containing Oxindoles and Indoline Alkaloids

Metal- and additive-free, photoinduced decarboxylative radical alkylation-cyclization of CF₃-acrylamides with alkyl redox-active esters provided the corresponding quaternary CF₃-oxindole derivatives in good yields. Notably, diaryliodonium salts also efficiently participated in the arylation-cyclization of CF₃-acrylamides in environmentally benign H₂O as a solvent. The present approach has been extended for the concise synthesis of CF₃-attached indoline alkaloid analogues, i.e., CF₃-(±)-desoxyeseroline, CF₃-(±)-esermethole, and CF₃-(±) progesterone receptor antagonists. The preliminary mechanistic studies revealed that the reaction is likely to proceed through initial photoexcitation of redox-active ester/diaryliodonium salts followed by the SET process with acrylamide.

Ligand-to-Copper Charge-Transfer-Enabled C-H Sulfoximination of Arenes

Herein, we report a photoinduced sulfoximine-to-copper charge-transfer-enabled generation of sulfoximinyl radicals directly from NH-sulfoximines for C-H sulfoximination of arenes via radical addition. Through copper-LMCT, N-arylation of NH-sulfoximines was achieved for the first time using arenes of different electronic structures as the aryl donors.

TBHP-mediated photochemical coupling/cyclization of N-arylacrylamides with thiols

The effective photoredox-mediated oxidative thiolation and cyclization of N-arylacrylamides with thiols leads to biologically interesting 3-thionated oxindoles through C-S and C-C bond formation. This process represents a straightforward reaction that starts from non-prefunctionalized thiolating reagents. Mechanistic studies demonstrated that the TBHP serves as a key radical initiator with visible-light catalysis.

Practical, scalable, and transition metal-free visible light-induced heteroarylation route to substituted oxindoles

The synthetic application of (hetero)aryl radicals in organic synthesis has been known since the last century. However, their applicability has significantly suffered from ineffective generation protocols. Herein, we present a visible-light-induced transition metal-free (hetero)aryl radical generation from readily available (hetero)aryl halides for the synthesis of 3,3'-disubstituted oxindoles. This transformation is amenable to a wide range of (hetero)aryl halides as well as several easily accessible acrylamides, and it is also scalable to multigram synthesis. Finally, the versatility of the oxindole products is demonstrated through their conversion to a variety of useful intermediates applicable to target-directed synthesis.

NaI/PPh3-catalyzed visible-light-mediated decarboxylative radical cascade cyclization of N-arylacrylamides for the efficient synthesis of quaternary oxindoles

A practical NaI/PPh3-catalyzed decarboxylative radical cascade cyclization of N-arylacrylamides with redox-active esters is described, which is mediated by visible light irradiation. A wide range of substrates bearing different substituents and derived from ubiquitous carboxylic acids, including α-amino acids, were synthesized and examined under this very mild, efficient, and cost effective transition-metal-free synthetic method. These afforded various functionalized oxindoles featuring a C3 quaternary stereogenic center. Mechanistic experiments suggest a radical mechanism.

Selective C(sp2)-H bond functionalization of olefins via visible-light-induced photoredox-quinuclidine dual catalysis

The site selective C(sp²)-H bond functionalization of olefins has been achieved through a visible-light-induced photoredox-quinuclidine dual catalysis upon merging the quinuclidinium radical cation addition to alkene strategy and the distal heteroaryl ipso-migration strategy. This synthetic protocol features a simple operation with readily available starting materials in good step-economy to access alkenylheteroaromatic products in moderate to good yields under mild conditions. A plausible cascade catalytic reaction mechanism is also proposed.

Oxindole synthesis via polar-radical crossover of ketene-derived amide enolates in a formal [3 + 2] cycloaddition

Herein we introduce a simple, efficient and transition-metal free method for the preparation of valuable and sterically hindered 3,3-disubstituted oxindoles via polar-radical crossover of ketene derived amide enolates. Various easily accessible N-alkyl and N-arylanilines are added to disubstituted ketenes and the resulting amide enolates undergo upon single electron transfer oxidation a homolytic aromatic substitution (HAS) to provide 3,3-disubstituted oxindoles in good to excellent yields. A variety of substituted anilines and a 3-amino pyridine engage in this oxidative formal [3 + 2] cycloaddition and cyclic ketenes provide spirooxindoles. Both substrates and reagents are readily available and tolerance to functional groups is broad.

Free Radical Cascade Carbochloromethylations of Activated Alkenes

Free radical carbochloromethylations of ortho-cyanoarylacrylamides and N-(arylsulfonyl)acrylamides have been developed by employing simple alkyl chlorides as the chloromethyl source. The transformations are characterized by wide functional group compatibility and utilizing readily available reagents, thus providing efficient methods for constructing polychloromethyl-substituted quinoline-2,4-diones and α-aryl-β-polychloromethylated amides.

Copper-promoted difunctionalization of unactivated alkenes with silanes

An efficient copper-catalyzed cascade difunctionalization of N-allyl anilines toward the synthesis of silylated indolines using commercially available silanes has been reported. This strategy provides a new avenue for the synthesis of a diverse array of indolines in reasonable yields. Preliminary mechanistic investigations indicate that the reaction probably proceeds via a radical pathway with unactivated alkenes as radical acceptors and simple silanes as radical precursors. This protocol is distinguished by its atom economy, broad substrate scope and readily available starting materials.

Radical coupling reactions of hydrazines via photochemical and electrochemical strategies

Hydrazines are versatile building blocks in organic synthesis.

Visible light-mediated radical-cascade addition/cyclization of arylacrylamides with aldehydes to form quaternary oxindoles at room temperature

The visible light-induced oxidative radical cascade coupling of N-arylacrylamides with aldehydes using bromide as the hydrogen atom transfer agent to synthesize functional oxindoles is described.

Palladium-Catalyzed Sequential Heck Coupling/C-C Bond Activation Approach to Oxindoles with All-Carbon-Quaternary Centers

Catalytic construction of oxindoles bearing all-carbon-quaternary centers draws wide attentions from synthetic community. Herein, we report a Palladium-catalyzed sequential Heck coupling/C-C bond activation of aryl halide-tethered alkenes with benzocyclobutenols affording...

Intermolecular 1,2-Difunctionalization of Alkenes Enabled by Fluoroamide-Directed Remote Benzyl C(sp3)-H Functionalization

A copper-catalyzed remote benzylic C-H functionalization strategy enabling 1,2-difunctionalization of alkenes with 2-methylbenzeneamides and nucleophiles, including alcohols, indoles, pyrroles, and the intrinsic amino groups, is reported, which is characterized by its redox-neutral conditions, exquisite site-selectivity, broad substrate scope, and wide utilizations of late-stage modifying bioactive molecules. This reaction proceeds through nitrogen-centered radical generation, hydrogen atom transfer, benzylic radical addition across the alkenes, single-electron oxidation, and carbocation electrophilic course cascades. While using external nucleophiles manipulates three-component alkene alkylalkoxylation and alkyl-heteroarylation with 2-methylbenzeneamides to access dialkyl ethers, 3-alkylindoles, and 3-alkylpyrroles, omitting the external nucleophiles results in two-component alkylamidation ([5+2] annulation) of alkenes with 2-methylbenzeneamides to benzo-[f][1,2]thiazepine 1,1-dioxides.

Nickel-Catalyzed Arylcarbamoylation of Alkenes of N-(o-Iodoaryl)acrylamides with Nitroarenes via Reductive Aminocarbonylation: Facile Synthesis of Carbamoyl-Substituted Oxindoles

Nickel-catalyzed arylcarbamoylation reactions of alkenes of N-(o-haloaryl)acrylamides with CO and nitroarenes via reductive aminocarbonylation to produce carbamoyl-substituted oxindoles with an all-carbon quaternary stereogenic center are presented. Starting with N-(o-haloaryl)acrylamides, simple CO, and inexpensive nitroarenes and using a Ni catalyst, a dinitrogen-based ligand, a Zn reductant, a TMSCl additive, and a base system, this protocol enables the synthesis of various carbamoyl-substituted oxindoles and allows the efficient late-stage derivatization of valuable molecules.

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile: synthesis of diverse nitrogenous heterocyclic compounds

A visible light-mediated heterogeneous photocatalytic cyanomethylarylation of alkenes with acetonitrile has been established using K-modified carbon nitride (CN-K) as a recyclable semiconductor photocatalyst. This protocol, employing readily accessible alkyl N-hydroxyphthalimide (NHPI) ester as a radical initiator, allows the efficient construction of a broad array of structural diverse nitrogenous heterocyclic compounds including indolines, oxindoles, isoquinolinones, and isoquinolinediones.

Cu-Catalyzed Oxidative Dual Arylation of Active Alkenes: Preparation of Cyanoarylated Oxindoles through Denitrogenation of 3-Aminoindazoles

A novel and mild Cu-catalyzed oxidative dual arylation of carbon-carbon double bonds in acrylamides with 3-aminoindazoles is proposed for the synthesis of cyanoarylated oxindoles. Notably, 3-aminoindazoles are employed as efficient arylating agents via the cleavage of two C-N bonds. This oxidative dual arylation of active alkenes involves a radical process and undergoes a sequence of 3-aminoindazole oxidation, two-C-N-bond cleavage, cyanoaryl radical addition, and intramolecular cyclization.

Copper(i)–catalyzed intramolecular asymmetric C-arylation of acyclic β-ester amides: enantioselective formation of chiral oxindoles

A highly efficient intramolecular asymmetric C-arylation of acyclic β-ester amides is demonstrated.

Visible light-induced aerobic dioxygenation of α,β-unsaturated amides/alkenes toward selective synthesis of β-oxy alcohols using rose bengal as a photosensitizer

The first visible light-induced aerobic dioxygenation of alkenes for the selective synthesis of β-oxy alcohols was developed using non-toxic rose bengal as a photosensitizer.

Brønsted acid-promoted hydroamination of unsaturated hydrazones: access to biologically important 5-arylpyrazolines

A novel and efficient Brønsted acid-promoted hydroamination of hydrazone-tethered olefins has been developed. A variety of pyrazolines have been easily obtained in good to excellent yields with high chemo- and regioselectivity under simple and mild conditions. This method represents a straightforward, facile, and practical approach toward biologically important 5-arylpyrazolines, which are difficult to access by previously reported radical hydroamination of β,γ-unsaturated hydrazones.

An efficient, chemo- and regioselective Brønsted acid-promoted hydroamination reaction of hydrazone-tethered olefins towards 5-arylpyrazolines was developed.

Multicomponent, Tandem 1,3- and 1,4-Bisarylation of Donor-Acceptor Cyclopropanes and Cyclobutanes with Electron-Rich Arenes and Hypervalent Arylbismuth Reagents

A tandem catalytic process for 1,3- and 1,4-bisarylation of donor-acceptor (D-A) cyclopropanes and cyclobutanes is disclosed. This strategy capitalizes on the use of two distinct sources of nucleophilic and electrophilic arylating agents, affording the formation of two new C-C bonds in an orchestrated multicomponent fashion with the aid of a catalytic Lewis acid. Mechanistic investigations have revealed it to be a stereoselective process, and products could be easily elaborated into other useful compounds.

Access to cyano-substituted pyrazolines through copper-catalyzed cascade cyanation/cyclization of unactivated olefins

A mild copper-catalyzed cascade cyanation/cyclization of hydrazone-tethered unactivated olefins was developed for the efficient and practical synthesis of cyano-containing pyrazolines.