Visible-light-induced direct hydrodifluoromethylation of alkenes with difluoromethyltriphenylphosphonium iodide salt

Halogen Bonding Promoted Photoinduced Synthesis of 3,3-Disubstituted Oxindoles

A photoinduced and catalyst-free radical cyclization process for the synthesis of 3,3-disubstituted oxindoles is reported. This method utilizes readily available α-bromoanilides as substrates, showcasing a broad substrate scope. The reaction mechanism is facilitated by a photoactivated charge transfer complex based on the halogen bonding of α-bromoanilide with TMG and alcohol.

Photoredox-Catalyzed Direct C(sp2)-H Difluoromethylation of Hydrazones with Difluoromethyltriphenylphosphonium Salt via Aminyl Radical/Polar Crossover

This study describes an efficacious and generally applicable synthetic strategy for the incorporation of biologically and physiologically prominent difluoromethyl entity into synthetically crucial hydrazone scaffolds with bench-stable and easily accessible difluoromethyltriphenylphosphonium bromide. The broad substrate scope, excellent functional group compatibility, feasibility of step and atom economical one-pot synthetic manipulation, and environmentally benign and mild reaction conditions rendered this methodology an efficient tool for the preparation of synthetically and pharmaceutically prominent fluorine-containing imino compounds.

Pnictogen bonding enabled photosynthesis of chiral selenium-containing pyridines from pyridylphosphonium salts

Pyridylphosphonium salts, which are readily available and air and thermally stable, have been used to effectively synthesize structurally diverse pyridines. Herein, we report the pnictogen bonding (PnB) enabled photoactivation of pyridylphosphonium salts with catalytic potassium carbonate to generate pyridyl radical for pyridine synthesis. Remarkably, this light-driven transformation allowed chiral pool synthesis with excellent chirality retention, giving a wide range of chiral selenium-containing pyridines. On the basis of our combined computational and experimental studies, we propose that the PnB between pyridylphosphonium salts and potassium carbonate enables access to the photoactive charge transfer complex, which is able to undergo single electron transfer to generate pyridyl radical for its transformation.

Expanding tracer space for positron emission tomography with high molar activity 18F-labeled α,α-difluoromethylalkanes

Positron emission tomography (PET) is an advanced biomedical imaging modality that relies on well-designed radiotracers to report on specific protein targets and processes occurring in living animals and humans. Cyclotron-produced short-lived fluorine-18 (t1/2 = 109.8 min) is widely used to radiolabel tracers for PET. Herein we aim to expand the chemical space available for PET tracer development to include structures with 18F-labeled α,α-difluoromethylalkyl groups. We report an efficient and broad-scope method for labeling such groups with high molar activities based on a single-step radiofluorination of α-bromo-α-fluoroalkanes. The method is applicable to bioactive compounds and drug-like molecules, and is readily automated for radiotracer production. The unique physical and biochemical features of the α,α-difluoromethyl group can now be exploited in the design of new PET tracers.

N-Phenylphenothiazine-based Hyper-cross-linked Polymers for Recyclable, Heterogeneous Photocatalysis of Organic Transformations: A Strategy to Access 6-Difluoromethyl-phenanthridines

Herein, a N-phenylphenothiazine-based hyper-cross-linked polymer (PTH-HCP) was finely designed and constructed, which serves as a metal-free heterogeneous photocatalyst for organic transformations. Characterization experiments have shown that this polymer demonstrates outstanding stability, extensive surface area, and exceptional photoelectric response properties. Moreover, PTH-HCP showed good catalytic efficiency and recyclability in the photochemically driven difluoromethylation/cyclization reactions. This work provides a strategy for the design and construction of polymer photocatalysts and offers support for their broad prospects in synthetic applications.

Visible Light-Induced Organophotoredox-Catalyzed β-Hydroxytrifluoromethylation of Unactivated Alkenes

Herein, we report a mild transition metal-free organophotoredox-catalyzed approach for β-hydroxytrifluoromethylation of unactivated alkenes using CF3SO2Na and acridinium salt. The protocol is compatible with various mono-, di-, and trisubstituted aliphatic unactivated alkenes containing numerous functional groups and natural product derivatives. Further, the postsynthetic modifications of the synthesized trifluoromethylated products have been demonstrated through cross-coupling and functional group interconversion reactions. The method proved to be scalable and it works smoothly under the direct exposure of sunlight. A plausible mechanism has been proposed based on the fluorescence quenching experiment and cyclic voltammetry analysis.

Radical Replacement Process for Ligated Boryl Radical-Mediated Activation of Unactivated Alkyl Chlorides for C(sp3)-C(sp3) Bond Formation

The ligated boryl radical (LBR) has emerged as a potent tool for activating alkyl halides in radical transformations through halogen-atom transfer (XAT). However, unactivated alkyl chlorides still present an open challenge for this strategy. We herein describe a new activation mode of the LBR for the activation of unactivated alkyl chlorides to construct a C(sp3)-C(sp3) bond. Mechanistic studies reveal that the success of the protocol relies on a radical replacement process between the LBR and unactivated alkyl chloride, forming an alkyl borane intermediate as the alkyl radical precursor. Aided with the additive K3PO4, the alkyl borane then undergoes one-electron oxidation, generating an alkyl radical. The incorporation of the radical replacement activation model to activate unactivated alkyl chlorides significantly enriches LBR chemistry, which has been applied to activate alkyl iodides, alkyl bromides, and activated alkyl chlorides via XAT.

Near-Infrared-Light-Induced Iron(I) Dimer-Enabled Radical Cascade Reactions of Fluoroalkyl Bromides for the Synthesis of Ring-Fused Quinazolinones

The use of an earth-abundant and inexpensive iron complex as a catalyst, coupled with near-infrared (NIR) light as the energy source, for radical reactions with alkyl halides has been far less developed. In this study, we report NIR light-mediated iron(I) dimer-catalyzed radical cascade reactions of fluoroalkyl bromides for the synthesis of ring-fused quinazolinones bearing a difluoromethyl group. In this process, the 3-bromo-1,10-phenanthroline ligand facilitates the reactivity of [CpFe(CO)2]2, thereby improving the efficiency of the reaction.

Divergent Generation of the Difluoroalkyl Radical and Difluorocarbene via Selective Cleavage of C-S Bonds of the Sulfox-CF2SO2Ph Reagent

A new difluoroalkylation reagent Sulfox-CF2SO2Ph bearing both sulfoximine and sulfone moieties was prepared from commercially available SulfoxFluor and PhSO2CF2H. On one hand, the Sulfox-CF2SO2Ph reagent could act as a (phenylsulfonyl)difluoromethyl radical source under photoredox catalysis, in which the arylsulfoximidoyl group is selectively removed. On the other hand, under basic conditions, Sulfox-CF2SO2Ph could serve as a difluorocarbene precursor for S- and O-difluoromethylations with S- and O-nucleophiles, respectively, in which the phenylsulfonyl group in Sulfox-CF2SO2Ph is selectively removed (followed by α-elimination of the arylsulfoximidoyl group).

Difluoromethylation-Carboxylation and -Deuteration of Alkenes Triggered by Electroreduction of Difluoromethyltriphenylphosphonium Bromide

It is significant to develop novel difluoromethylation methods because of the important roles of difluoromethyl groups in the medicinal chemistry and material industries. Here, we developed a novel difluoromethylation-carboxylation and difluoromethylation-deuteration method triggered by a difluoromethyl radical generated by electroreduction of stable and easily available difluoromethyltriphenylphosphonium bromide. Various molecules containing difluoromethyl and carboxyl or deuterium groups can be synthesized through this method. The establishment of this method will provide an alternative to radical difluoromethylation reactions.

Cross-Electrophile C-PIII Coupling of Chlorophosphines with Organic Halides: Photoinduced PIII and Aminoalkyl Radical Generation Enabled by Pnictogen Bonding

Pnictogen bonding (PnB) has gained recognition as an appealing strategy for constructing novel architectures and unlocking new properties. Within the synthetic community, the development of a straightforward and much simpler protocol for cross-electrophile C-PIII coupling remains an ongoing challenge with organic halides. In this study, we present a simple strategy for photoinduced PnB-enabled cross-electrophile C-PIII couplings using readily available chlorophosphines and organic halides via merging single electron transfer (SET) and halogen atom transfer (XAT) processes. In this photomediated transformation, the PnB formed between chlorophosphines and alkyl amines facilitates the photogeneration of PIII radicals and α-aminoalkyl radicals through SET. Subsequently, the resulting α-aminoalkyl radicals activate C-X bonds via XAT, leading to the formation of carbon radicals. This methodology offers operational simplicity and compatibility with both aliphatic and aromatic chlorophosphines and organic halides.

N-Heterocyclic Nitrenium-Catalyzed Photohomolysis of CF3SO2Cl for Alkene Trifluoromethylation

N-Heterocyclic nitreniums (NHNs) have been utilized as Lewis acid catalysts to activate substrates with lone pairs. Alternative to their conventional applications, we have discovered that NHNs can also serve as charge transfer complex catalysts. Herein, we present another potential of NHNs by utilizing a weak interaction between NHNs and CF3SO2Cl. The method promotes CF3SO2Cl to undergo photohomolysis, resulting in the CF3 radical. Mechanistic studies suggested that the weak interaction could be due to the π-hole effect of NHNs.

Charge Transfer Complex-Enabled Synthesis of (Hetero)arylated m-Carboranes from m-Carborane Phosphonium Salts

A photoinduced charge transfer complex (CTC)-enabled photoreduction of carborane phosphonium salts for the cage carbon (hetero)arylation of carboranes was developed. It offers a convenient approach for introducing a wide range of aryl and heteroaryl groups, such as pyrroles, thiophenes, indoles, thianaphthenes, benzofurans, pyridines, and benzenes, into carboranes. This strategy offers operational simplicity, mild reaction conditions, and a broad substrate scope, making it highly advantageous.

Nickel-Catalyzed Markovnikov-Selective Hydrodifluoromethylation of Alkynes Using BrCF2 H

A Markovnikov-selective hydrodifluoromethylation of alkynes with BrCF2 H via nickel catalysis is described. This protocol proceeds via a migratory insertion of nickel hydride to alkyne followed by a CF2 H-coupling, enabling straightforward access to diverse branched CF2 H-alkenes with high efficiency and exclusive regioselectivity. The mild condition applies to a wide array of aliphatic and aryl alkynes with good functional group compatibility. Mechanistic studies are presented to support the proposed pathway.

Photoinduced halogen-bonding enabled synthesis of oxindoles and isoindolinones from aryl iodides

We report the use of halogen bonding (XB) for the generation of aryl radicals from aryl halides under blue light irradiation and applied it in radical generation/1,5-hydrogen-atom transfer/radical cyclization cascade reactions for the synthesis of oxindoles and isoindolinones. On the basis of experimental studies, we propose that DBU can serve as a suitable XB acceptor with aryl halides for the formation of a photoactive electron donor and acceptor complex.

Catalytic charge transfer complex enabled difluoromethylation of enamides with difluoromethyltriphenylphosphonium bromide

A catalytic charge transfer complex strategy that enabled difluoromethylation and ethoxycarbonylmonofluoromethylation of enamides with phosphonium bromine salts has been reported. This strategy also provides a convenient approach for the synthesis of functionalized oxindoles and 1,1-diphenylethylenes with easily available phosphonium bromine salts and a catalytic amount of iodine anion.

N-Heterocyclic Nitreniums Can Be Employed as Photoredox Catalysts for the Single-Electron Reduction of Aryl Halides

N-Heterocyclic nitrenium (NHN) salts, the analogues of N-heterocyclic carbenes, have attracted considerable interest. However, relatively little is known about their catalytic ability beyond their Lewis acid catalysis. Herein, we describe that NHNs can serve as catalytic electron acceptors for charge transfer complex photoactivations. We showcase that, under blue light irradiation, the NHN salts could catalyze the generation of aryl radicals from aryl halides.

Charge Transfer Complex Enabled Photoreduction of Wittig Phosphonium Salts

A photoinduced charge transfer complex strategy enabled (alkoxycarbonyl)methylation reaction of alkenes with phosphonium salts has been reported. This strategy provides a convenient strategy to functionalize indoles, 1,1-diphenylethylenes, enamides and N-phenyl...