α-Amino Radical-Mediated Diverse Difunctionalization of Alkenes: Construction of C–C, C–N, and C–S Bonds

Formally Stereoretentive SN1 Reactions of Homoallylic Tertiary Alcohols Via Nonclassical Carbocation

We present a stereoretentive nucleophilic substitution of homoallylic tertiary alcohols via the formation of a nonclassical cyclopropyl carbinyl (CPC) carbocation intermediate. This strategy enables the creation of highly congested tertiary centers with preserved stereocontrol, addressing the typical challenges of carbocation instability and reactivity in SN1 mechanisms. The stabilization of the CPC intermediate is crucial for achieving precise regio- and stereoselectivity, significantly enhancing the utility of SN1-type mechanisms in complex molecule synthesis.

The Vicinal-Diiodination of the HDDA-Benzynes by N-Iodo- succinimide (NIS) Through a Radical Pathway

The 1,2-diradical reactivity of the HDDA-benzynes (thermal) has not been explored well in comparison to their ionic reactivity. Accordingly, the radical trapping reactions of these reactive intermediates are very scarce in literature. Herein, we report the iodine-radical trapping reaction of the HDDA-benzynes for the construction of structurally divergent vicinal-diiodo arenes. The N-iodosuccinimide (NIS) has been employed as the source of radical iodine under thermal heating conditions. The existence of the arene-radical intermediates and the radical mechanism has been supported by the EPR spectral analysis of the reaction mixture. Several fruitful control experiments suggested that the 4-iodination (mono-) of the HDDA-benzynes is faster than the 5-iodiniation. The process is general in terms of substituents on the diynes as well as the nature of the tethering units. To the best of our knowledge, this is the first report on the vicinal-diiodination as well as radical diiodination of HDDA-benzynes.

Photocatalytic hydroalkylation of 3-methyleneisoindolin-1-ones with unactivated alkyl iodides

We report herein a simple method for hydroalkylation of 3-methyleneisoindolin-1-ones with unactivated iodoalkanes using visible light photocatalysis and a halogen atom transfer (XAT) process. This operationally simple method exhibits broad substrate scope and allows late-stage modifications of iodoalkanes derived from either active pharmaceutical ingredients or natural products, producing a range of structurally diverse and valuable corresponding hydroalkylation products in decent yields. The generation of alkyl radicals and carbanion intermediates was directly proven in the catalytic cycle through radical trapping/radical clock and isotope labeling studies, respectively.

Supramolecular Double-Helical Polymers: Supramolecular Chiral Induction and Asymmetric Catalysis

Seeking a supramolecular chiral system induced by trace chiral molecules instead of traditional complex and expensive chiral ligands to achieve high yield or ee value conversion of the products is of great significance in asymmetric synthesis but still remains a challenge. Herein, two types of double helical supramolecular chiral systems, (M)-Helix and (P)-Helix, with opposite chiral optics were constructed in situ using tyrosine-functionalized pillar[5]arene as inducers. These systems exhibit chiroptical stability and enable remarkable chirality amplification from 7 mol% chiral seeds. When applied to intermolecular olefin cyano-trifluoromethylation, (M)-Helix exhibits remarkable catalytic efficiency (yield up to 89%), whereas (P)-Helix achieves higher enantioselectivity (ee up to 84%). This research will provide new ideas for supramolecular chiral catalysts in organic asymmetric catalysis applications.

CO2•- Enabled Synthesis of Phenanthridinones, Oxindoles, Isoindolinones, and Spirolactams

We report herein that photoinduced CO2•- enabled reductive intramolecular radical cyclization of a variety of aryl iodide derivatives to the corresponding phenanthridinone, oxindole, isoindolinone, and spirolactam derivatives in good yields. Preliminary mechanistic studies suggested the generation of CO2•- through homolysis of cesium formate in the presence of light, and the further involvement of CO2•- and the aryl radical was directly proved by trapping with diphenyl styrene and TEMPO.

NBS-promoted regioselective thiocyanatothiolation of alkenes with free thiols and NH4SCN

An efficient NBS-promoted three-component thiocyanatothiolation of alkenes with free thiols and NH4SCN has been developed. This protocol avoids tedious preactivation of thiols and employs a diverse range of accessible thiols directly as sulfur sources. Moreover, the reaction exhibits regioselectivity and shows high compatibility with styrenes and unactivated alkenes. Preliminary mechanism studies revealed that both a radical pathway and thiol-oxidation-coupling were involved in this protocol.

Luminescent cyclometalated gold(iii) complexes covalently linked to metal-organic frameworks for heterogeneous photocatalysis

Phosphorescent gold(iii) complexes possess long-lived emissive excited states, making them ideal for use as molecular sensors and photosensitizers for organic transformations. Literature reports indicate that gold(iii) emitters exhibit good catalytic activity in homogeneous photochemical reactions. Heterogeneous metal-organic framework (MOF)-supported gold(iii) photocatalysts are considered to show high recyclability in photochemical reactions and potentially provide new selectivities. Here, we report the design and development of visible-light-absorbing MOF-covalently linked gold(iii) photocatalysts. A MOF-supported gold(iii) complex exhibits a longer phosphorescence lifetime than its homogeneous counterpart, reaching approximately 110 μs under argon and 12 μs under air when suspended in acetonitrile. This is attributed to the localization of the gold(iii) complex within the MOF nano-cages. The MOF-derived gold(iii) photosensitizer exhibits good catalytic performance in intramolecular and intermolecular [2 + 2] cycloaddition reactions to construct functionalized cyclobutanes and azetidines, both of which are important building blocks for pharmaceuticals. These photochemical [2 + 2] cycloaddition reactions catalyzed by the gold(iii)-MOF are governed by an energy transfer mechanism and do not require redox modulators. Under similar reaction conditions, the crossed [2 + 2] photocycloaddition reaction of two activated alkenes proceeds smoothly, and the cyclobutane product is obtained within 3 hours of irradiation under dilute conditions (0.2 mol dm-3 of alkene).

Photoredox-Catalyzed 1,4-Dichloromethyldimerization of Alkenes with Chloroform: Access to Polychlorinated Vicinal Diaryl Alkanes

A visible-light-mediated strategy is reported for the direct synthesis of polychlorinated vicinal diaryl alkanes from aryl alkenes and chloroform. In this approach, two haloalkyl radicals generated from chloroform via halogen atom transfer (XAT) and direct single electron transfer (SET) within the same photoredox catalysis cycle enable the 1,4-dichloromethyldimerization of alkenes. Besides chloroform, this strategy is applicable to carbon tetrachloride, bromotrichloromethane, and α-bromo carboxylic esters, yielding corresponding 1,4-disubstituted vicinal diaryl alkanes. Diverse polychlorinated structures containing highly congested vicinal quaternary carbon centers are effectively synthesized by this method. The potential of this reaction in late-stage drug modification is highlighted by the successful transformation of olefins with pharmaceutical structures.

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.

Carbonylation Reactions at Carbon-Centered Radicals with an Adjacent Heteroatom

Heteroatoms are essential to living organisms and present in almost all molecules with medicinal usage. The catalytic functionalization at the carbon-centered radical with an adjacent heteroatom provides an effective way to value added moiety while retaining the unique physicochemical and pharmacological properties of heteroatoms, which can promote the development of pharmaceutical and fine chemical production. Carbonylative transformation was discovered nearly a century ago which is an efficient method for the synthesis of carbonyl-containing molecules with potent applications in both industry and academia. Despite numerous advances in new reaction development, carbonylative transformation involving adjacent heteroatom carbon radical remain a subject that deserves to be discussed. In this minireview, we systematically summarized and discussed the recent advances in carbonylative transformations involving carbon-centered radicals with an adjacent heteroatom, including oxygen (O), nitrogen (N), phosphorus (P), silicon (Si), sulfur (S), boron (B), fluorine (F), and chlorine (Cl). The related reaction mechanism was also discussed.

Formal 1,1-Hydrocyanation Reaction of Alkynyl Halides with Isocyanides Enabled by Dual Nickel/Base Catalysis Relay

We herein describe a formal 1,1-hydrocyanation reaction of alkynyl halides with isocyanides enabled by a dual nickel/base catalysis relay. tert-Butyl isocyanide serves as a "HCN" precursor that is introduced to the α-position of alkynyl halides, and the halogen atom is moved to the β-position. As a result, a series of (Z)-3-bromo/iodo acrylonitrile derivatives could be obtained in moderate yields. Mechanistic experiments were carried out, and the collective data could support our proposal of the mechanism details.

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.

Transition-Metal-Free Radical Relay Cascade Annulation of Amides: Access to Antitumor Active Benzo[b]azepine and Oxindole Derivatives

Efficient transition-metal-free synthesis of benzo[b]azepines and oxindoles is achieved via a radical relay cascade strategy employing halogen atom transfer (XAT) for aryl radical generation followed by intramolecular hydrogen atom transfer (HAT). Optimization yielded moderate to substantial yields under visible light irradiation. Preliminary biological assessments revealed promising anti-tumor activity for select compounds. This study underscores the potential of XAT-mediated radical relay cascades in medicinal chemistry and anticancer drug discovery.

Access to Carbonyl Azides via Iodine(III)-Mediated Cross-Coupling

Herein, we present a prominent metal-free C-N cross-coupling platform that enables access to carbamoyl- and ketoazides from isocyanides or silyl enol ethers and trimethylsilyl azide (TMSN3) with an aid of iodine(III) promoter. This offers a rapid route to a diverse set of synthetically valuable azide decorated fragments with excellent substrate scope and good to excellent yields. The disclosed platform exemplifies the use of TMSN3 for incorporation of the azide fragment without the loss of N2.

TMSCN-Promoted Difunctionalization of Alkenes for the Synthesis of Alcohol Derivatives

A TMSCN-promoted difunctionalization of styrenes with CHCl3 and TBHP is reported via the radical addition/cross coupling process. A wide range of dichloromethyl-substituted alcohol derivatives were synthesized under transition-metal-free conditions. Besides, this method is also applicable to unactive alkenes. The key to this success lies in the role of TMSCN, which prevents the reaction toward dichloromethylperoxylation of olefins. This represents an alternative approach for synthesizing diverse alcohol derivatives using readily available substrates, holding significant promise in the fields of pharmaceutical chemistry and natural product synthesis.

A Radical Strategy for the Alkylation of Amides with Alkyl Halides by Merging Boryl Radical-Mediated Halogen-Atom Transfer and Copper Catalysis

Amide alkylation is a fundamental process in organic chemistry. However, the low nucleophilicity of amides means that divergent coupling with alkyl electrophiles is often not achievable. To circumvent this reactivity challenge, individual amine synthesis followed by amidation with standard coupling agents is generally required. Herein, we demonstrate a radical solution to this challenge by using an amine-borane complex and copper catalysis under oxidative conditions. While borohydride reagents are generally used as reducing agents in ionic chemistry, their conversion into amine-ligated boryl radicals diverts their reactivity toward halogen-atom transfer. This enables the conversion of alkyl halides into the corresponding alkyl radicals for amide functionalization via copper catalysis. The process is applicable to the N-alkylation of primary amides employing unactivated alkyl iodides and bromides, and it was also showcased in the late-state functionalization of both complex amide- and halide-containing drugs.

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.

Photocascade chemoselective controlling of ambident thio(seleno)cyanates with alkenes via catalyst modulation

Controlling the ambident reactivity of thiocyanates in reaction manifolds has been a long-standing and formidable challenge. We report herein a photoredox strategy for installing thiocyanates and isothiocyanates in a controlled chemoselective fashion by manipulating the ambident-SCN through catalyst modulation. The methodology allows redox-, and pot-economical 'on-demand' direct access to both hydrothiophene and pyrrolidine heterocycles from the same feedstock alkenes and bifunctional thiocyanomalonates in a photocascade sequence. Its excellent chemoselectivity profile was further expanded to access Se- and N-heterocycles by harnessing selenonitriles. Redox capability of the catalysts, which dictates the substrates to participate in a single or cascade catalytic cycle, was proposed as the key to the present chemodivergency of this process. In addition, detailed mechanistic insights are provided by a conjugation of extensive control experiments and dispersion-corrected density functional theory (DFT) calculations.

Confinement Effect in Metal-Organic Framework Cu3()2 for Enhancing Shape Selectivity of Radical Difunctionalization of Alkenes

The radical difunctionalization of alkenes plays a vital role in pharmacy, but the conventional homogeneous catalytic systems are challenging in selectivity and sustainability to afford the target molecules. Herein, the famous readily available metal-organic framework (MOF), Cu3(BTC)2, has been applied to cyano-trifluoromethylation of alkenes as a high-performance and recyclable heterogeneous catalyst, which possesses copper(II) active sites residing in funnel-like cavities. Under mild conditions, styrene derivatives and various unactivated olefins could be smoothly transformed into the corresponding cyano-trifluoromethylation products. Moreover, the transformation brought about by the active copper center in confined environments achieved regio- and shape selectivity. To understand the enhanced selectivity, the activation manner of the MOF catalyst was studied with control catalytic experiments such as FT-IR and UV-vis absorption spectroscopy of substrate-incorporated Cu3(BTC)2, which elucidated that the catalyst underwent a radical transformation with the intermediates confined in the MOF cavity, and the confinement effect endowed the method with pronounced selectivities.

Thiocyanate promoted difunctionalization and cyclization of unsaturated C-C bonds to construct 1-sulfur-2-nitrogen-functionalized alkenes and 2-thiocyanate indolines

An unprecedented one-pot route to achieve highly regioselective 1-sulfur-functionalized 2-nitrogen-functionalized alkenes and 2-thiocyanate indolines from unsymmetrical ynamides (readily and generally available amides) using the commercially available inexpensive iodobenzene diacetate (PIDA) as the oxidant and potassium thiocyanate (KSCN) as the thiocyanate (SCN) source has been developed. The interconversion of thiocyanate (SCN) and isothiocyanate (NCS) groups simultaneously forms C-N and C-S bonds in this metal-free approach, while introducing important functional groups into homemade alkynes. A radical-chain mechanism, involving competing kinetically controlled chain transfer at the S atom and sterically-controlled chain transfer at the N atom of the thiocyanogen molecule in this mild approach, is proposed.

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.

Copper-catalyzed trichloromethylative carbonylation of ethylene

Difunctionalization of alkenes is an efficient strategy for the synthesis of complex compounds from readily available starting materials. Herein, we developed a copper-catalyzed visible-light-mediated trichloromethylative carbonylation of ethylene by employing commercially available CCl4 and CO as trichloromethyl and carbonyl sources, respectively. With this protocol, various nucleophiles including amines, phenols, and alcohols can be rapidly transformed into β-trichloromethyl carboxylic acid derivatives with good functional-group tolerance. Bis-vinylated γ-trichloromethyl amides can also be obtained by adjusting the pressure of carbon monoxide and ethylene. In addition, this photocatalytic system can be successfully applied in the late-stage functionalization of bioactive molecules and pharmaceutical derivatives as well.

Highly Diastereoselective Preparation of Tertiary Alkyl Thiocyanates en Route to Thiols by Stereoinvertive Nucleophilic Substitution at Nonclassical Carbocations

An effective InBr3-catalyzed nucleophilic thiocyanation of cyclopropyl alcohols has been developed. The reaction takes place at the quaternary carbon stereocenter of the cyclopropyl carbinol with a complete inversion of configuration, offering a novel pathway for the creation of complex tertiary alkyl thiocyanates with high diastereopurity. These substitution reactions proceed under mild reaction conditions and tolerate several functional groups. Additionally, thiocyanates were converted to thiols using lithium aluminum hydride.

Organophotocatalyzed Mono- and Bis-Alkyl/Difluoroalkylative Thio/Selenocyanation of Alkenes

Organophotocatalyzed three-component 1,2-difluoroacetyl/alkyl/perfluoroalkylative thio/selenocyanation of styrene derivatives under stoichiometric, transition metal-, oxidant-, and additive-free, and mild redox-neutral conditions is reported. Organophotocatalyst 4CzIPN operates the overall radical-polar-crossover mechanistic cycle via initial oxidative luminescence quenching, and the key intermediates were experimentally detected. Selective mono-alkylative thiocyanation of alkenes using dibromoalkanes is also demonstrated. This one-pot synthetic methodology is suitable for primary, secondary, and tertiary alkyl halides and also extended for double alkylative thiocyanation of the dibromoalkanes with excellent yields.

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.

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

Herein, we report a mild and practical protocol for the α-perchloroalkyl β-heteroarylation of alkenes using available chloroform as the dichloromethyl source via α-amino radical-mediated halogen-atom transfer. Various substrates are compatible under mild reaction conditions, providing the corresponding products in moderate to good yields. This strategy gives an efficient and convenient method for the introduction of chloroalkyl motifs into N-heteroarenes. The control experiment demonstrates that the α-amino radical generated in situ is a key intermediate in the transformation.

A Visible-Light-Induced α-Aminoalkyl-Radical-Mediated Halogen-Atom Transfer Process: Modular Synthesis of Phenanthridinone Alkaloids

A halogen-atom transfer (XAT) strategy utilizing α-aminoalkyl radicals allows the generation of aryl radicals at room temperature, which is applied for intramolecular cyclization reactions en route to biologically relevant alkaloids. Starting from simple halogen-substituted benzamides under visible light irradiation in the presence of an organophotocatalyst (4CzIPN) and nBu₃N allows the modular construction of the phenanthridinone core, which gives facile access to drug analogs and alkaloids, e.g., from the Amaryllidaceae family. The reaction pathway most likely involves a quantum mechanical tunneling enabled transfer event to achieve aromatization-halogen-atom transfer.

Transition-metal free C-N bond formation from alkyl iodides and diazonium salts via halogen-atom transfer

Construction of C-N bond continues to be one part of the most significant goals in organic chemistry because of the universal applications of amines in pharmaceuticals, materials and agrochemicals. However, E2 elimination through classic SN2 substitution of alkyl halides lead to generation of alkenes as major side-products. Thus, formation of a challenging C(sp3)-N bond especially on tertiary carbon center remains highly desirable. Herein, we present a practical alternative to prepare primary, secondary and tertiary alkyl amines with high efficiency between alkyl iodides and easily accessible diazonium salts. This robust transformation only employs Cs2CO3 promoting halogen-atom transfer (XAT) process under transition-metal-free reaction conditions, thus providing a rapid method to assemble diverse C(sp3)-N bonds. Moreover, diazonium salts served as alkyl radical initiator and amination reagent in the reaction. Mechanism studies suggest this reaction undergo through halogen-atom transfer process to generate active alkyl radical which couples with diazonium cations to furnish final products.

Iron-Catalyzed Sulfonylthiocyanation of α,β-Unsaturated Amides/Esters via the Insertion of Sulfur Dioxide

An iron-catalyzed four-component sulfonylthiocyanation between α,β-unsaturated amides/esters, TMSNCS, aryldiazonium tetrafluoroborates, and sulfur dioxide (from SOgen) is demonstrated. This protocol is characterized by mild reaction conditions, good functional group compatibility, broad substrate scope, and good to excellent yields, providing a feasible method for the preparation of β-thiocyanated sulfone compounds. The preliminary mechanism investigation shows that a radical pathway may be involved in the process.

Synthesis of β-Polychlorinated Alkynes Enabled by Copper-Catalyzed Multicomponent Reaction

Functional molecules bearing polychlorinated moieties usually play versatile roles in organic synthesis and biochemistry. A copper-catalyzed multicomponent polychloro-carboalkynylation of alkenes presents an efficient and operationally simple approach for the synthesis of β-polychlorinated alkynes. Mechanistic experiments were conducted demonstrating that an in situ generated copper acetylide complex was the real catalyst and reactive intermediate during the copper-catalytic cycle. And enantioselective exploration demonstrated potential application for the synthesis of chiral β-polychlorinated alkynes.

Synthesis of Benzimidazo[2,1-a]isoquinoline and Indolo[2,1-a]isoquinoline Derivatives via Copper-Catalyzed Silylation/Methylation of 2-Arylindoles and 2-Arylbenzimidazoles

A one-pot method for the synthesis of silylsubstituted/methylsubstituted indolo[2,1-a]isoquinolin-6(5H)-ones and benzimidazo[2,1-a]isoquinoline-6(5H)-ones via copper(II)-initiated silylation/methylation of 2-arylindoles and 2-arylbenzimidazoles was developed. In this procedure, the C-Si bond and C-C bond were constructed by radical addition and cyclization. A series of 2-arylindole and 2-arylbenzimidazole derivatives were facilely transformed to indolo[2,1-a]isoquinolines and benzimidazo[2,1-a]isoquinolines in 39-83% yields.

Photocatalyzed Defluorinative Dichloromethylation of α-CF3 Alkenes Using CHCl3 as the Radical Source

A visible-light-induced defluorinative dichloromethylation of α-CF₃ alkenes was developed with cheap and readily accessible chloroform simultaneously as a dichloromethylation reagent and reaction medium, leading to the facile preparation of new polyhalogenated scaffolds. Notably, the change from CHCl₃ to CDCl₃ offers a straightforward pathway for accessing the deuterated analogues with excellent degrees of D incorporation. Mechanistic studies suggested the reaction underwent a radical addition of the dichloromethyl radical with alkenes, followed by sequential single-electron transfer and defluorination. This protocol features mild conditions, easy operation, facile scalability, and high efficiency, allowing convenient access to dichloronated gem-difluoroalkenes.

Enantioselective construction of spiro-tetrahydroquinoline scaffolds through asymmetric catalytic cascade reactions

An efficient and concise strategy has been successfully developed for merging spiro-tetrahydroquinoline with spiro-benzofuranone into a single new skeleton through asymmetric catalytic cascade reactions catalyzed by quinine-derived chiral bifunctional squaramide organocatalysts. In this approach, differently substituted spiro-tetrahydroquinoline derivatives were smoothly obtained with high yields, and excellent diastereoselectivities and enantioselectivities (up to 99% yield, up to >20 : 1 dr, up to >99% ee, 40 examples) under mild reaction conditions.

Electrochemical Benzylic C(sp3)-H Isothiocyanation

Selective C(sp³)-H isothiocyanation represents a significant strategy for the synthesis of isothiocyanate derivatives. We report herein an electrochemical benzylic isothiocyanation in a highly chemo- and site-selective manner under external oxidant-free conditions. The high chemoselectivity is attributed to the facile in situ isomerization of benzylic thiocyanates to isothiocyanates. Notably, the method exhibits high functional group compatibility and is suitable for late-stage functionalization of bioactive molecules.

Cu-Catalyzed alkylation-cyanation type difunctionalization of styrenes with aliphatic aldehydes and TMSCN via decarbonylation

A copper-catalyzed decarbonylative alkylation-cyanation of styrene derivatives with aliphatic aldehydes and trimethylsilyl cyanide to provide chain elongated nitriles is reported. Using TBHP as an oxidant and free radical initiator, the reaction can smoothly convert abundant α-di-substituted, α-mono-substituted and linear aliphatic aldehydes into the corresponding 3°, 2° and 1° alkyl radicals to initiate the subsequent radical-type difunctionalization of various styrenes.

Application of α-Aminoalkyl Radicals as Reaction Activators

α-Aminoalkyl radicals are easily accessible through multiple pathways from various precursors. Apart from their utilization as nitrogen-containing building blocks, they have recently been used as halogen atom abstraction reagents or single-electron reductants to transform organic halides or sulfonium salts into their corresponding highly reactive radical species. Benefiting from the richness of various halides and the diverse reactivity of radical intermediates, new transformations of halides and sulfonium salts have been developed. This short review summarizes this emerging chemistry that uses α-aminoalkyl radicals as the reaction activators.

1 Introduction

2 Activation of Halides as Halogen-Atom Transfer Agents

2.1 Addition to Unsaturated Bonds

2.1.1 Addition to C=C Bonds

2.1.2 Addition to C=O Bonds

2.2 Substitution Reactions

2.2.1 Deuteration

2.2.2 Olefination

2.2.3 Allylation

2.2.4 Aromatic Substitution

2.2.5 Amination

3 Activation of Sulfonium Salts as Single-Electron Reductants

4 Conclusion and Outlook

Merging Halogen-Atom Transfer (XAT) and Copper Catalysis for the Modular Suzuki–Miyaura-Type Cross-Coupling of Alkyl Iodides and Organoborons

We report here a mechanistically distinct approach to achieve Suzuki–Miyaura-type cross-couplings between alkyl iodides and aryl organoborons. This process requires a copper catalyst but, in contrast with previous approaches based on palladium and nickel systems, does not utilizes the metal for the activation of the alkyl electrophile. Instead, this strategy exploits the halogen-atom-transfer ability of α-aminoalkyl radicals to convert secondary alkyl iodides into the corresponding alkyl radicals that then are coupled with aryl, vinyl, alkynyl, benzyl, and allyl boronate species. These novel coupling reactions feature a simple setup and conditions (1 h at room temperature) and facilitate access to privileged motifs targeted by the pharmaceutical sector.

Site-selective electrochemical thiocyanation of benzylic C–H bonds

Direct benzylic C(sp3)−H thiocyanation is explored as a straightforward strategy toward the synthesis of thiocyanate derivatives. We report herein an electrochemical protocol for site-selective benzylic C(sp3)−H thiocyanation under mild reaction...

Metal-free photocleavage of C(non-acyl)-S bond of thioesters for regioselective pyridylthioesterification of styrenes

Transformation of thioesters via transition-metal-mediated C(acyl)−S bond cleavage is an emerging method to forge C-C and C-heteroatom bonds. Herein, we report the first activation of stronger C(non-acyl)–S bond of thioesters...

Three-component 1,2-dicarbofunctionalization of alkenes involving alkyl radicals

1,2-Dicarbofunctionalization of alkenes represents an appealing strategy for chemical bond formation in organic synthesis, which could enable the rapid construction of molecular complexity from simple and readily available starting materials by incorporating two functional groups onto a carbon-carbon double bond in one step. In this field, the dicarbofunctionalization of alkenes with different alkyl radicals in a controlled manner represents an elegant and versatile strategy to access structurally diverse functionalized alkanes, which have witnessed significant progress over the last five years. Due to the importance of alkyl radicals in organic synthesis and medicinal chemistry, this review provides a comprehensive perspective on the development of alkyl radical precursors including electrophilic precursors such as alkyl halides, alkyl peroxides, alkyl NHP esters, cycloketone oxime esters, and Katritzky pyridinium salts, and nucleophilic precursors such as alkyl acids, alkyl oxalates, alkylborates, alkylsilicates, and unactivated hydrocarbons, which generate alkyl radicals by photocatalysis or transition metal catalysis to engage in dicarbofunctionalization under oxidative reaction conditions, redox-neutral conditions, or reductive conditions. The mechanisms of these dicarbofunctionalization reactions have also been discussed in detail.

Precise Introduction of the -CHnX3-n (X = F, Cl, Br, I) Moiety to Target Molecules by a Radical Strategy: A Theoretical and Experimental Study

Addition of halomethyl radicals to form bioactive molecules has recently become an efficient strategy. The reaction has a bottleneck, however, which is the effective and selective generation of the proper halomethyl ^•CH_nX_3-n radical by combining CH_nX_4-n with a carbon radical. Understanding the reactivity and selectivity of carbon radicals in the hydrogen atom transfer (HAT) and halogen atom transfer (XAT) reactions of CH_nX_4-n is key to the development of such an attractive method. With the help of the emerging data-driven strategy, DFT calculations were used to explore various correlations. For selectivity, the relative energy barriers between HAT and XAT reactions (ΔG^⧧_H - ΔG^⧧_X) correlate reasonably well with the three parameters ΔG_H, ΔG_X, and IP, and the correlation studies reveal that the calculated IP_inver and the experimental ΔBDE can be used to conveniently predict the selectivity. Predicted selectivities are consistent with experimental determinations. This work not only provides a possibility for selecting carbon radicals with the known or easily obtained physicochemical data but also demonstrates that the informatic workflow such as generating data and identifying correlations has potential applications in mining reaction rules.

Iron-Catalyzed Enantioselective Radical Carboazidation and Diazidation of α,β-Unsaturated Carbonyl Compounds

Azidation of alkenes is an efficient protocol to synthesize organic azides which are important structural motifs in organic synthesis. Enantioselective radical azidation, as a useful strategy to install a C-N₃ bond, remains challenging due to the inherently instability and unique structure of radicals. Here, we disclose an efficient enantioselective radical carboazidation and diazidation of α,β-unsaturated ketones and amides catalyzed by chiral N,N'-dioxide/Fe(OTf)₂ complexes. An array of substituted alkenes was transformed to the corresponding α-azido carbonyl derivatives in good to excellent enantioselectivities, benefiting the preparation of chiral α-amino ketones, vicinal amino alcohols, and vicinal diamines. Control experiments and mechanistic studies proved the radical pathway in the reaction process. The DFT calculations showed that the azido transferred to the radical intermediate via an intramolecular five-membered transition state with the internal nitrogen of the Fe-N₃ species.