α-Amino Radical-Mediated Difunctionalization of Alkenes with Polyhaloalkanes and N-Heteroarenes

Access to quaternary-carbon-containing β-alkyl amides via persulfate-promoted domino alkylation/smiles rearrangement of alkenes

In this study, we present an efficient approach for synthesizing all-carbon quaternary-centered β-alkyl amides. This method entails a persulfate-promoted cascade alkylative annulation/arylation of N-(arylsulfonyl)acrylamide with 4-alkyl-1,4-dihydropyridines (DHP). The reaction mechanism comprises four consecutive steps: (1) in situ generation of alkyl radical intermediates, (2) radical addition to the alkene moiety, (3) 1,4-aryl migration, and (4) finally desulfonylation.

Synthesis of 3,4-unsubstituted isoquinolone derivatives from benzimidates and vinylene carbonate via cobalt(III)-catalyzed C-H activation/cyclization

A cobalt(III)-catalyzed C-H activation/cyclization of benzimidates and vinylene carbonate has been developed. Various benzimidates showed good compatibility, providing isoquinolone derivatives in moderate to good yields. This strategy employs the inexpensive Co(III) as the catalyst and provides an efficient and practical solution for the synthesis of medicinally valuable 3,4-unsubstituted isoquinolone derivatives.

MeOH-Triggered Halogen-Atom Transfer of Unactivated Alkyl Bromides Enabling the Photoredox Giese Addition

Herein, a nickel-catalyzed, photoredox Giese addition reaction with readily accessible alkyl bromides, driven by readily available feedstock MeOH as the halogen-atom transfer (XAT) reagent, was successfully achieved under mild conditions. The versatility of this protocol was demonstrated through a range of structurally varied alkyl bromides and Giese-type acceptors with moderate to good yields. Mechanistic investigation highlights that the formation of alkyl radicals through the XAT of alkyl bromides was tentatively prompted by •CH2OH, which was derived from the sequential photo-oxidation/1,2-hydrogen-atom transfer of MeOH.

Computational and Experimental Studies on the α-Functionalization of Ketones Using Domino Reactions: A Strategy to Increase Chemoselectivity at the α-Carbon of Ketones

A facile strategy to increase the chemoselectivity of domino reactions was proposed and successfully applied in the α-functionalization of ketones. The strategy involved widening the activation energy of the main reaction and side reaction through intermolecular interactions, thereby increasing the chemoselectivity of the domino reaction. In the proposed α-functionalization reaction, TMSCF3 acted as an excellent reagent which increased the nucleophilicity of DMF through the Van der Waals force and reduced the nucleophilicity of H2O through a hydrogen bond. We found that TMSCF3 can increase the activation energy difference between the main reaction and side reaction using DFT calculations, which greatly increased chemoselectivity and avoided the formation of by-products. TMSCF3 was recycled by rectification, and the average recovery rate was 87.2%. DFT calculations, XRD experiments, and control experiments were performed to support this mechanism. We are confident that this strategy has the potential to deliver significant practical advancements while simultaneously fostering broader innovation in the field of domino synthesis.

Visible-Light-Induced C(sp3)-H Activation for Minisci Alkylation of Pyrimidines Using CHCl3 as Radical Source and Oxidant

A highly efficient Minisci reaction of pyrimidines with alkyl radical generated from visible-light-induced activation of simple C(sp3)-H feedstocks such as (cyclo)alkanes, ethers, alcohols, esters, and amides is reported. A mechanistic study revealed that alkyl radical was generated via hydrogen atom transfer (HAT) of C(sp3)-H with dichloromethyl radical (·CHCl2), which was generated by photoreduction of chloroform.

Photocatalytic Hydrodichloromethylation of Unactivated Alkenes with Chloroform

A visible-light-induced method for the hydrodichloromethylation of unactivated alkenes using chloroform (CHCl3) was developed, employing pyridine·BH3 as the halogen atom transfer (XAT) reagent. The strategy showed a broad functional group tolerance, and 29 examples of unactivated alkenes, including complex natural products or drug derivatives, have been established with good yields. Mechanistic studies indicated that CHCl3 serves as both the source of a dichloromethyl radical and a hydrogen atom transfer (HAT) reagent, and the borane short-chain reaction process was involved in this system. This method represents a novel approach for hydrodichloromethylation of unactivated alkenes without using an additional HAT reagent.

Visible-Light-Induced Cascade Cyclization of 1-(2-(Arylethynyl)benzoyl)indoles into Sulfonated Benazepino[1,2-a]indolones

1-(2-(Arylethynyl)benzoyl)indoles were developed as an innovative scaffold for radical cascade cyclization under visible-light and mild conditions, enabling efficient synthesis of sulfonated benazepino[1,2-a]indolones. This method operates at room temperature and demonstrates broad substrate compatibility and scalability, with promising potential for sunlight-driven reactions.

Solvent Dictated Organic Transformations

Solvent plays an important role in many chemical reactions. The C-H activation has been one of the most powerful tools in organic synthesis. These reactions are often assisted by solvents which not only provide a medium for the chemical reactions but also facilitate reaching to the product stage. The solvent helps the reaction profile both chemically and energetically to reach the targeted product. Organic transformations via C-H activation from the solvent assistance perspective has been discussed in this review. Various solvents such as tetrahydrofuran (THF), MeCN, dichloromethane (DCM), dimethoxyethane (DME), 1,2-dichloroethane (1,2-DCE), dimethylformamide (DMF), dimethylsulfoxide (DMSO), isopropyl nitrile (iPrCN), 1,4-dioxane, AcOH, trifluoroacetic acid (TFA), Ac2O, PhCF3, chloroform (CHCl3), H2O, N-methylpyrrolidone (NMP), acetone, methyl tert-butyl ether (MTBE), toluene, p-xylene, alcohols, MeOH, 1,1,1-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), tert-amyl alcohol and their roles are discussed. The exclusive role of the solvent in various transformations has been deliberated by highlighting the substrate scope, along with the proposed mechanisms. For easy classification, the review has been divided into three parts: (i) solvent-switched divergent C-H activation; (ii) C-H bond activation with solvent as the coupling reagent, and (iii) C-H activation with solvent caging and solvent-assisted electron donor acceptor (EDA) complex formation and autocatalysis.

Iron-Catalyzed Perfluoroalkylarylation of Styrenes with Arenes and Alkyl Iodides Enabled by Halogen Atom Transfer

A new iron-catalyzed three-component perfluoroalkylarylation of styrenes with alkyl halides and arenes has been established. Alkyl halides undergo halogen atom transfer with methyl radicals to form alkyl radicals in reactions initiated by a combination of tert-butyl peroxybenzoate and an iron catalyst, thus adducting to the olefins, which results in alkylarylation products. The protocol is compatible with a wide range of perfluoroalkyl and non-perfluoroalkyl halides, features excellent functional group tolerance, and enables the synthesis of structurally diverse 1,1-diaryl fluoro-substituted alkanes.

Light-Induced Difunctionalization of Alkenes with Polyhaloalkanes and Quinoxalin-2(1H)-ones

Herein, we report a metal-free light-induced three-component reaction for the synthesis of polychloroalkyl-substituted quinoxalin-2(1H)-ones using commercially available alkenes, polyhalo alkanes, and quinoxalin-2(1H)-ones. Preliminary mechanistic studies suggested the generation of radical intermediates via an EDA-complex, single electron transfer, or halogen atom transfer pathway. Under mild reaction conditions, various alkenes and quinoxalin-2(1H)-ones containing different functional groups are compatible, providing the corresponding polychloroalkyl-substituted quinoxalin-2(1H)-ones in moderate to good yields.

Visible-light-induced alkyl-arylation of olefins via a halogen-atom transfer process

Visible-light-induced three-component 1,2-alkyl-arylation of alkenes and alkyl radical addition/cyclization of acrylamides have been realized via a photocatalytic halogen-atom transfer (XAT) process. This metal-free protocol utilizes readily available tertiary alkylamine as both an electron donor and an XAT reagent for the activation of alkyl halides using naphthalimide (NI)-based organic photocatalysts. This process features broad substrate scope and good functional group tolerance under mild conditions, and could be effectively applied to a variety of medicinally relevant substrates.

Decennary Update on Oxidative-Rearrangement Involving 1,2-Aryl C-C Migration Around Alkenes: Synthetic and Mechanistic Insights

In recent years, numerous methodologies on oxidative rearrangements of alkenes have been investigated, that produce multipurpose synthons and heterocyclic scaffolds of potential applications. The present review focused on recently established methodologies for oxidative transformation via 1,2-aryl migration in alkenes (2013-2023). Special emphasis has been placed on mechanistic pathways to understand the reactivity pattern of different substrates, challenges to enhance selectivity, the key role of different reagents, and effect of different substituents, and how they affect the rearrangement process. Moreover, synthetic limitations and future direction also have been discussed. We believe, this review offers new synthetic and mechanistic insight to develop elegant precursors and approaches to explore the utilization of alkene-based compounds for natural product synthesis and functional materials.

Metal-free radical bicyclization/chloroalkylarylation of 1,6-enynes with chloroalkanes

Free radical initiated bicyclization of 1,6-enynes with chloralkanes, is achieved via selective activation of the C(sp3)-H bond of the chloralkane, resulting in diverse polychlorinated/chlorinated polyheterocycles. Two kinds of transformations and a scaled-up experiment were performed to test the synthetic importance of the organic chlorides. Finally, a range of radical inhibition operations and radical clock tests were explored to support the reaction process.

Synergistic Merger of Ketone, Halogen Atom Transfer (XAT), and Nickel-Mediated C(sp3)-C(sp2) Cross-Electrophile Coupling Enabled by Light

In the present manuscript, we have developed a unique catalytic system by merging photoexcited ketone catalysis, halogen atom transfer (XAT), and nickel catalysis to forge C(sp3)-C(sp2) cross-electrophile coupling products from unactivated iodoalkanes and (hetero)aryl bromides. The synergistic catalytic system works under mild reaction conditions and tolerates a variety of functional groups; moreover, this strategy allows the late-stage modification of medicinally relevant molecules. Preliminary mechanistic studies reveal the role of the α-aminoalkyl radical, which further participates in the XAT process with alkyl iodides to generate the desired alkyl radical, which eventually intercepts with the nickel catalytic cycle to liberate the products in good to excellent yields.

Visible-Light-Induced Three-Component 1,2-Alkylpyridylation of Alkenes via a Halogen-Atom Transfer Process

Visible-light-induced three-component 1,2-alkylpyridylation of alkenes with unactivated alkyl iodides and aryl cyanides is reported via a photocatalytic halogen-atom transfer (XAT) strategy. This metal-free protocol utilizes readily available tertiary alkylamine as the terminal reductant to smoothly convert alkyl iodides into the corresponding carbon radical species. The reaction features a broad substrate scope, excellent functional group tolerance, high efficiency, and mild reaction conditions. The practicability of this methodology is further demonstrated in the late-stage difunctionalization of bioactive molecules.

Direct alkylation of quinoxalinones with electron-deficient alkenes enabled by a sequential paired electrolysis

The metal-free alkylation of N-heterocycles with alkenes has remained a synthetic challenge. We report here the successful implementation of metal-free alkylation of quinoxalinones with electron-deficient alkenes enabled by a sequential paired electrolysis. This protocol provides a mechanistically distinct approach to prepare a variety of C-3 alkylated quinoxalinones that are otherwise quite difficult to synthesize by other means.

Metal-free polychloromethylation/cyclization of unactivated alkenes towards ring-fused tricyclic indolones and benzoimidazoles

Polychloromethylative cyclization of N-alkenyl indoles was developed under metal-free conditions to afford tricyclic pyridoindolones and pyrroloindolones in moderate to good yields. In the reaction, commercially available CHCl3 and CH2Cl2 were employed as tri- and dichloromethyl radical sources. Moreover, tri- and dichloromethylated polycyclic benzoimidazoles can also be obtained under standard conditions.

Enantioselective Chemodivergent Three-Component Radical Tandem Reactions through Asymmetric Photoredox Catalysis

Chemodivergent synthesis has been achieved in asymmetric photocatalysis. Under a dual catalyst system consisting of a chiral phosphoric acid and DPZ as a photosensitizer, different inorganic bases enabled the formation of two sets of valuable products from the three-component radical tandem transformations of 2-bromo-1-arylenthan-1-ones, styrenes, and quinoxalin-2(1H)-ones. The key to success was the distinct pKa environment, in which the radicals that formed on the quinoxalin-2(1H)-one rings after two radical addition processes underwent either single-electron oxidation or single-electron reduction. In addition, this work represents the first use of quinoxalin-2(1H)-ones in asymmetric photoredox catalysis.

Photocatalytic, Intermolecular Olefin Alkylcarbofunctionalization Triggered by Haloalkyl Radicals Generated via Halogen Atom Transfer

A visible-light-mediated, haloalkyl-radical-initiated, three-component olefin difunctionalization is reported. The application of haloalkyl radicals generated via halogen atom abstraction by α-aminoalkyl radicals has been demonstrated for accessing a new halogenated chemical space. Overall, the alkylcarbofunctionalization of styrenes was accomplished by employing them as (poly)haloalkyl radical acceptors and subsequent C-C bond formation with quinoxalinones.