HFIP-Assisted Single C-F Bond Activation of Trifluoromethyl Ketones using Visible-Light Photoredox Catalysis

Hexafluoroisopropanol Solvent Effects on Enantioselectivity of Dirhodium Tetracarboxylate-Catalyzed Cyclopropanation

In recent years, additives that modulate both reactivity and selectivity in rhodium-catalyzed reactions of aryldiazoacetates have become increasingly prominent. 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) has been shown to have a profound effect on rhodium carbene reactivity and selectivity, especially on enabling carbene cyclopropanation in the presence of various nucleophilic poisons. HFIP also has a variable influence on the enantioselectivity of the reactions catalyzed by chiral dirhodium tetracarboxylates, and this study examines the fundamental properties of the rhodium carbene/HFIP system through experimentation, density functional theory (DFT), and molecular dynamics (MD) simulations. These studies revealed that the C4-symmetric bowl-shaped catalysts, which have been previously considered to be relatively rigid, experience far greater flexibility in this hydrogen bonding media, resulting in distortion of the bowl-shaped catalysts. These studies explain why even though a majority of the catalysts have a drop in enantioselectivity in HFIP, some catalysts, such as Rh2(TCPTAD)4, lead to a switch in enantioselectivity, whereas others, such as Rh2(NTTL)4, lead to a considerably enhanced enantioselectivity.

Visible Light-Promoted Defluorinative Alkylation of Trifluoromethyl Ketones with α-Aminoalkyl Boron Species

In this study, we developed a photoredox-catalyzed defluorinative cross-coupling method for trifluoroketones and alkyl boronic acids. The reaction afforded a series of novel α,α-difluoroketone derivatives, and in vitro fungicidal activity revealed that some of these compounds exhibited moderate to excellent activity against Rhizoctonia solani and Botrytis cinerea. In particular, compound 3d showed an EC50 value of 4.27 μg/mL against B. cinerea and can be used as a fungicidal lead compound for further optimization.

Mild defluorinative N-acrylation of amines with (trifluoromethyl)alkenes: synthesis of α-arylacrylamides

A practical and efficient method for the N-acrylation of amines with (trifluoromethyl)alkenes is achieved via the cleavage of three C(sp3)-F bonds, affording a diverse range of useful tertiary and secondary α-arylacrylamides in high yields. This protocol features mild conditions, is transition-metal free, operationally simple, gram-scalable, and compatible with valuable functional groups, and has a broad substrate scope. Mechanistic studies indicate that exchange of an oxygen atom happens between H2O and NaOH, and that the oxygen atom is incorporated into the α-arylacrylamides via the ipso-defluorooxylation of the (trifluoromethyl)alkene. This method is also applied in the late-stage N-acrylation of pharmaceuticals.

Photoinduced Cross-Coupling of Trifluoromethylarenes with Heteroarenes via Unactivated C(sp3)-F and C(sp2)-H Selective Cleavage

The installation of gem-difluoromethylene groups into two adjacent aryl groups is a formidable synthetic challenge despite their attractive structural, physical, and biochemical properties. Herein, we disclose a photoredox-catalyzed selective defluoroarylation of heteroarenes through inert C(sp3)-F and C(sp2)-H selective cleavage, which provides a straightforward route to access medicinally relevant aryl-heteroaryl or heteroaryl-heteroaryl difluoromethane scaffolds. Salient features of this reaction include readily accessible starting materials, metal-free conditions, and broad substrate scope.

Synthesis of benzosultams via Ag(I)-catalyzed alkylative cyclization of vinyl sulfonamides

A convenient method to access benzo-fused-γ-sultams via alkyl radical induced cyclization of vinyl sulfonamides is presented. A wide range of carboxylic acids including sterically hindered adamantanes participated as alkyl donors in this Ag(I)-catalyzed decarboxylative alkylation. The reaction utilizes readily available starting materials and demonstrates a broad substrate scope.

Modular Synthesis of α-Aryl Acrylamido Carboxylic Acids by Triple C-F Bond Cleavage of (Trifluoromethyl)alkenes with Unprotected Amino Acids

A straightforward and efficient strategy for the construction of tertiary and secondary α-aryl acrylamido carboxylic acids is reported. This N-acrylation protocol of unprotected amino acids is achieved by triple C-F bond cleavage of (trifluoromethyl)alkenes. This method features mild conditions, is operationally simple, is free of transition metals and racemization, can be used on a gram scale, and is compatible with various functional moieties. Mechanistic studies indicate that oxygen atom exchange happens among H2O, NaOH, and amino acids, and the oxygen atom of the amide moiety of the product is incorporated by the ipso-defluorooxylation of (trifluoromethyl)alkene.

Catalyst-free regioselective sulfonylation of phenoxazine with sulfonyl hydrazides in H2O/HFIP

A facile catalyst-free sulfonylation of phenoxazine with sulfonyl hydrazides was efficiently developed in H2O/HFIP without any catalyst. This metal- and catalyst-free protocol is suitable for aromatic and aliphatic reagents to afford the corresponding sulfones in moderate to high yields. A gram-scale experiment was performed to assess the practicability of the method.

Defluorinative Haloalkylation of Unactivated Alkenes Enabled by Dual Photoredox and Copper Catalysis

A three-component defluorinative haloalkylation of alkenes with trifluoromethyl compounds and TBAX (X = Cl, Br) via dual photoredox/copper catalysis is reported. The mild conditions are compatible with a wide array of activated trifluoromethyl aromatics bearing diverse substituents, and various nonactivated terminal and internal alkenes, enabling straightforward access to synthetically valuable γ-gem-difluoroalkyl halides with high efficiency. Mechanistic studies indicate that the [Cu] complexes not only serve as XAT catalysts but also facilitate the SET reduction of trifluoromethyl groups by photocatalysts. Additionally, the resulting alkyl halide products can serve as versatile conversion intermediates for the synthesis of a diverse range of γ-gem-difluoroalkyl compounds.

General Defluoroalkylation of Trifluoromethylarenes with Both Electron-Donating and -Withdrawing Alkenes

The incorporation of gem-difluoromethylene units into organic molecules remains a formidable challenge. Conventional methodologies for constructing aryldifluoromethyl derivatives relied on the use of high-functional fluorinating regents under harsh conditions. Herein, we report general and efficient photoredox catalytic systems for defluoroalkylation of readily available trifluoromethylarenes through selective C-F cleavage to deliver gem-difluoromethyl radicals which proceed through reductive addition to both electron-donating and withdrawing alkenes under transition-metal free conditions. Mechanistic studies reveal that thiol serves as both photocatalyst and HAT reagent under visible light irradiation. This synergistic photocatalysis and HAT catalysis protocol exhibits ample and salient features such as high chemo- and regioselectivity, broad substrate scope, amenable gram-scale synthesis and late-stage modification of bioactive molecules.

Electrochemical Dehydrogenative [3 + 2]/[5 + 2] Annulation of N-Arylacrylamides with γ,σ-Unsaturated Malonates via Direct C(sp3)-H/C(sp2)-H Functionalization

Herein, we introduce an electrochemical dehydrogenative [3 + 2]/[5 + 2] annulation of easily available N-arylacrylamides with γ,σ-unsaturated malonates through C(sp3)-H/C(sp2)-H functionalization. The employment of inexpensive ferrocene as the redox catalyst allows access to diverse benzo[b]azepin-2-ones in moderate to excellent yields without stoichiometric oxidants. This protocol features broad substrate scope and excellent selectivity, and mechanistic studies indicated that the reaction proceeded through the oxidation of a C(sp3)-H bond to generate an alkyl radical, radical addition across the C═C bond, [3 + 2]/[5 + 2] annulations, and C(sp2)-H functionalization cascades.

Photoreduction of Trifluoromethyl Group: Lithium Ion Assisted Fluoride-Coupled Electron Transfer from EDA Complex

Photoinduced single-electron reduction is an efficient method for the mono-selective activation of the C-F bond on a trifluoromethyl group to construct a difluoroalkyl group. We have developed an electron-donor-acceptor (EDA) complex mediated single-electron transfer (EDA-SET) of α,α,α-trifluoromethyl arenes in the presence of lithium salt to give α,α-difluoroalkylarenes. The C-F bond reduction was realized by lithium iodide and triethylamine, two common feedstock reagents. Mechanistic studies revealed the generation of a α,α-difluoromethyl radical by single-electron reduction and defluorination, followed by the radical addition to alkenes. Lithium salt interacted with the fluorine atom to promote the photoinduced reduction mediated by the EDA complex. Computational studies indicated that the lithium-assisted defluorination and the single-electron reduction occurred concertedly. We call this phenomenon fluoride-coupled electron transfer (FCET). FCET is a novel approach to C-F bond activation for the synthesis of organofluorine compounds.

Selective Mono-Defluorinative Cross-Coupling of Trifluoromethyl arenes via Multiphoton Photoredox Catalysis

A new cross-coupling of trifluoromethyl arenes has been realized via multiphoton photoredox catalysis. Trifluoromethyl arenes were demonstrated to undergo selective mono-defluorinative alkylation under mild reaction conditions providing access to a series of valuable α,α-difluorobenzylic compounds. The reaction shows broad substrate scope and general functional group tolerance. In addition to the electron-deficient trifluoromethyl arenes that are easily reduced to the corresponding radical anion, more challenging electron-rich substrates were also successfully applied. Steady-State Stern-Volmer quenching studies indicated that the trifluoromethyl arenes were reduced by the multiphoton excited Ir-based photocatalyst.

C-F Bond Insertion: An Emerging Strategy for Constructing Fluorinated Molecules

C-F Insertion reactions, where an organic fragment formally inserts into a carbon-fluorine bond in a substrate, are highly attractive, yet largely unexplored, methods to prepare valuable fluorinated molecules. The inherent strength of C-F bonds and the resulting need for a large thermodynamic driving force to initiate C-F cleavage often leads to sequestering of the released fluoride in an unreactive by-product. Recently, however, several groups have succeeded in overcoming this challenge, opening up the study of C-F insertion as an efficient and highly atom-economical approach to prepare fluorinated compounds. In this article, the recent breakthroughs are discussed focusing on the key conceptual advances that allowed for both C-F bond cleavage and subsequent incorporation of the released fluoride into the product.

Sequential C-F Bond Transformation of the Difluoromethylene Unit in Perfluoroalkyl Groups: A Combination of Fine-Tuned Phenothiazine Photoredox Catalyst and Lewis Acid

A sequential process via photoredox catalysis and Lewis acid mediation for C-F bond transformation of the CF2 unit in perfluoroalkyl groups has been achieved to transform perfluoroalkylarenes into complex fluoroalkylated compounds. A phenothiazine-based photocatalyst promotes the defluoroaminoxylation of perfluoroalkylarenes with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) under visible light irradiation, affording the corresponding aminoxylated products. These products undergo a further defluorinative transformation with various organosilicon reagents mediated by AlCl3 to provide highly functionalized perfluoroalkyl alcohols. Our novel phenothiazine catalyst works efficiently in the defluoroaminoxylation. Transient absorption spectroscopy revealed that the catalyst regeneration step is crucial for the photocatalytic aminoxylation.

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.

C-F bond activation enables synthesis of aryl difluoromethyl bicyclopentanes as benzophenone-type bioisosteres

Bioisosteric design has become an essential approach in the development of drug molecules. Recent advancements in synthetic methodologies have enabled the rapid adoption of this strategy into drug discovery programs. Consequently, conceptionally innovative practices would be appreciated by the medicinal chemistry community. Here we report an expeditous synthetic method for synthesizing aryl difluoromethyl bicyclopentane (ADB) as a bioisostere of the benzophenone core. This approach involves the merger of light-driven C-F bond activation and strain-release chemistry under the catalysis of a newly designed N-anionic-based organic photocatalyst. This defluorinative coupling methodology enables the direct conversion of a wide variety of commercially available trifluoromethylaromatic C-F bonds (more than 70 examples) into the corresponding difluoromethyl bicyclo[1.1.1]pentanes (BCP) arenes/difluoromethyl BCP boronates in a single step. The strategy can also be applied to [3.1.1]and [4.1.1]propellane systems, providing access to analogues with different geometries. Moreover, we have successfully used this protocol to rapidly prepare ADB-substituted analogues of the bioactive molecule Adiporon. Biological testing has shown that the ADB scaffold has the potential to enhance the pharmacological properties of benzophenone-type drug candidates.

Photo- and electro-chemical strategies for the activations of strong chemical bonds

The employment of light and/or electricity - alternatively to conventional thermal energy - unlocks new reactivity paradigms as tools for chemical substrate activations. This leads to the development of new synthetic reactions and a vast expansion of chemical spaces. This review summarizes recent developments in photo- and/or electrochemical activation strategies for the functionalization of strong bonds - particularly carbon-heteroatom (C-X) bonds - via: (1) direct photoexcitation by high energy UV light; (2) activation via photoredox catalysis under irradiation with relatively lower energy UVA or blue light; (3) electrochemical reduction; (4) combination of photocatalysis and electrochemistry. Based on the types of the targeted C-X bonds, various transformations ranging from hydrodefunctionalization to cross-coupling are covered with detailed discussions of their reaction mechanisms.

Defluorinative Alkylboration of Alkenes Enabled by Dual Photoredox and Copper Catalysis

A regioselectivity reversed three-component defluorinative alkylboration of alkenes with trifluoromethyls and bis(pinacolato)diboron via dual photoredox/copper catalysis is reported. The mild conditions are compatible with a wide array of nonactivated trifluoromethyl aromatics bearing electron-donating or electron-neutral substituents, trifluoroacetamides, and various nonactivated terminal and internal alkenes, enabling straightforward access to synthetically valuable γ-gem-difluoroalkyl boronates with high efficiency. Furthermore, this protocol is applicable to alkene-tethered trifluoromethyl aromatics to furnish gem-difluoromethylene-containing cyclic compounds. Synthetic applications and preliminary mechanistic studies are also presented.

Selective Defluoroalkylation and Hydrodefluorination of Trifluoromethyl Groups Photocatalyzed by Dihydroacridine Derivatives

The selective functionalization of trifluoromethyl groups through C-F cleavage poses a significant challenge due to the high bond energy of the C(sp3)-F bonds. Herein, we present dihydroacridine derivatives as photocatalysts that can functionalize the C-F bond of trifluoromethyl groups with various alkenes under mild conditions. Mechanistic studies and DFT calculations revealed that upon irradiation, the dihydroacridine derivatives exhibit high reducibility and function as photocatalysts for reductive defluorination. This process involves a sequential single-electron transfer mechanism. This research provides valuable insights into the properties of dihydroacridine derivatives as photocatalysts, highlighting the importance of maintaining a planar conformation and a large conjugated system for optimal catalytic activity. These findings facilitate the efficient catalytic reduction of inert chemical bonds.

Catalyst- and Additive-free, Regioselective 1,6-Hydroarylation of para-Quinone Methides with Anilines in HFIP

A simple and efficient method for the synthesis of diarylmethyl-functionalized anilines through the hexafluoroisopropanol (HFIP)-mediated regioselective 1,6-hydroarylation reaction of para-quinone methides (p-QMs) with anilines under catalyst- and additive-free conditions is reported. Various kinds of p-QMs and amines (e. g. primary, secondary and tertiary amines) are well tolerated in this transformation without the pre-protection of amino group, and the corresponding products could be generated with good to excellent yields and satisfactory regioselectivity under the optimized reaction conditions. In addition to adaptable amine compounds, indoles and their derivatives are also compatible with this reaction system. This transformation can be easily extended to a gram scale-synthesis level to synthesize the target product. Furthermore, it is worth noting that some complex small aniline molecules with biological activity can be selectively modified using this method. The possible reaction mechanism is proposed through the step-by-step control experiments and DFT calculations, showing that the key process for achieving the regioselective 1,6-hydroarylation of p-QMs is the hydrogen bonding effect of HFIP to substrates.

Visible-Light-Promoted C(sp3)-C(sp3) Cross-Coupling of Amino Acids and Aryl Trifluoromethyl Ketones Through Simultaneous Decarboxylation and Defluorination

A photoredox-catalyzed approach for the difluoroalkylation of amino acids was achieved through simultaneous decarboxylation and defluorination processes. This innovative protocol employs commonly available amino acids and trifluoroacetophenones as the primary starting materials, eliminating the necessity for preactivation. This strategy has enabled the synthesis of several difluoroketone functionalized amines in moderate to impressive yields. These synthesized compounds are presented as foundational molecules for subsequent modification. The underlying mechanism for the transformation is anchored in a single electron transfer (SET) radical pathway.

Photocatalytic redox-neutral selective single C(sp3)-F bond activation of perfluoroalkyl iminosulfides with alkenes and water

Visible-light-promoted site-selective and direct C-F bond functionalization of polyfluorinated iminosulfides was accomplished with alkenes and water under redox-neutral conditions, affording a diverse array of γ-lactams with a fluoro- and perfluoroalkyl-substituted carbon centre. A variety of perfluoroalkyl units, including C2F5, C3F7, C4F9, and C5F11 underwent site-selective defluorofunctionalization. This protocol allows high chemoselectivity control and shows excellent functional group tolerance. Mechanistic studies reveal that the remarkable changes of the electron geometries during the defluorination widen the redox window between the substrates and the products and ensure the chemoselectivity of single C(sp3)-F bond cleavage.

Palladium-Catalyzed Fluorinative Bifunctionalization of Aziridines and Azetidines with gem-Difluorocyclopropanes

An unprecedented Pd-catalyzed fluorinative bifunctionalization of aziridines and azetidines was successfully developed via regioselective C-C and C-F bond cleavage of gem-difluorocyclopropanes, leading to various β,β'-bisfluorinated amines and β,γ-bisfluorinated amines. This reaction was achieved by incorporating a 2-fluorinated allyl group and a fluorine atom scissored from gem-difluorocyclopropane in 100 % atom economy for the first time. The mechanistic investigations indicated that the reaction underwent amine attacking 2-fluorinated allyl palladium complex to generate η2 -coordinated N-allyl aziridine followed by fluoride ligand transfer affording the final β- and γ-fluorinated amines.

α-Difluoroalkylation of Benzyl Amines with Trifluoromethylarenes

An α-difluoroalkylation of benzyl amines with trifluoromethylarenes is disclosed herein. This protocol is characterized by its operational simplicity, excellent chemoselectivity and broad scope-even with advanced synthetic intermediates-, thus offering a new entry point to medicinally-relevant α-difluoroalkylated amines from simple, yet readily accessible, precursors.

C-F Transformations of Benzotrifluorides by the Activation of Ortho-Hydrosilyl Group

Single C-F transformations of aromatic trifluoromethyl compounds are challenging issues due to the strong C-F bond. We have recently developed selective methods for single C-F transformations such as allylation of o-hydrosilyl-substituted benzotrifluorides through the hydride abstraction with trityl cations. Single C-F thiolation and azidation of o-(hydrosilyl)benzotrifluorides were achieved using trityl sulfides and trityl azide catalyzed by Yb(OTf)3 . Treatment of o-(hydrosilyl)benzotrifluorides with trityl chloride resulted in single C-F chlorination. The resulting fluorosilyl group served in further transformations including protonation, halogenation, and Hiyama cross-coupling with C-Si cleavage. We also synthesized benzyl fluorides by LiAlH4 -reduction of the resulting fluorosilanes and further C-F transformations. These methods enabled us to prepare a broad range of organofluorines from simple benzotrifluorides through C-F and C-Si transformations.

Selective and Controllable Defluorophosphination and Defluorophosphorylation of Trifluoromethylated Enones: An Auxiliary Function of the Carbonyl Group

The auxiliary function of a carbonyl group in the tunable defluorophosphination and defluorophosphorylation of trifluoromethylated enones with P(O)-containing compounds was demonstrated. Controlled replacement of one or two fluorine atoms in trifluoromethylated enones while maintaining high chemo- and stereoselectivity was achieved under mild conditions, thus enabling diversity-oriented synthesis of skeletally diverse organophosphorus libraries─(Z)-difluoro-1,3-dien-1-yl phosphinates, (1Z,3E)-4-phosphoryl-4-fluoro-buta-1,3-dien-1-yl phosphinates, and (E)-4-phosphoryl-4-fluoro-1,3-but-3-en-1-ones─in good yields with excellent functional group tolerance.

Photoredox Catalyzed Single C-F Bond Activation of Trifluoromethyl Ketones: A Solvent Controlled Divergent Access of gem-Difluoromethylene Containing Scaffolds

Selective defluorinative functionalization of trifluoromethyl ketones is a long-standing challenge owing to the exhaustive mode of the process. To meet the demands for the installation of the gem-difluoromethylene unit for the construction of the molecular architectures of well-known pharmaceuticals and agrochemicals, a distinct pathway is thereby highly desirable. Here, a protocol is introduced that allows the divergent synthesis of gem-difluoromethylene group containing tetrahydrofuran derivatives and linear ketones via single C-F bond activation of trifluoromethyl ketones using visible-light photoredox catalysis in the presence of suitable olefins as trapping partner. The choice of appropriate solvent and catalyst plays a significant role in controlling the divergent behavior of this protocol. Highly reducing photo-excited catalysts are found to be responsible for the generation of α,α-difluoromethyl ketone (DFMK) radicals as the key intermediate via a SET process. This protocol also results in a high diastereoselectivity towards the formation of partially fluorinated cyclic ketal derivatives with simultaneous construction of one C-C and two C-O bonds. State-of-the-art DFT calculations are performed to address the origin of diastereoselectivity as well as the divergence of this protocol.

Visible-Light-Mediated Photoredox Carbon Radical Formation from Aqueous Sulfoxonium Ylides

The visible-light-induced photoredox carbon radical formation from aqueous sulfoxonium ylides has been demonstrated for the first time. While direct reduction of sulfoxonium ylides by H₂O efficiently generates the corresponding hydrocarbon compounds, the use of additional alkenes as radical acceptors alters the chemical reactivity to achieve alkene carboarylation of N-arylacrylamides. Mechanistic studies reveal two different reaction pathways involved in the carbon radical formation from aqueous sulfoxonium ylides resulting in reduction to release dimethyl sulfone and carboarylation to form DMSO.

Defluorinative Transformation of (2,2,2-Trifluoroethyl)arenes Catalyzed by the Phosphazene Base t-Bu-P2

In this study, we demonstrated that 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-Bu-P2) catalyzes the defluorinative functionalization reactions of (2,2,2-trifluoroethyl)arenes with alkanenitriles to produce monofluoroalkene products. The reaction proceeds through HF elimination from a (2,2,2-trifluoroethyl)arene to form a gem-difluorostyrene intermediate, which is followed by nucleophilic addition of an alkanenitrile and elimination of a fluoride anion. The catalysis is compatible with a variety of functional groups.

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.

Catalytic and Chemodivergent Synthesis of 1-Substituted 9H-Pyrrolo[1,2-a]indoles via Annulation of β-CF3 Enones with 3-Substituted Indoles

Chemodivergent reactions are more advantageous in organic synthesis that yield diversely functionalized scaffolds from common starting materials. Herein, we report an efficient metal-free chemodivergent protocol for the synthesis of 1-substituted 9H-pyrrolo[1,2-a]indole derivatives in the presence of catalytic amounts of Lewis acid/Brønsted acid conditions using 3-substituted indoles and β-trifluoromethyl-α,β-unsaturated ketones. Fine-tuning of the catalyst and solvent system in the reaction conditions deliver the trifluoromethyl, trifluoroethylcarboxylate, or carboxylic acid substituents on the C1-position of 9H-pyrrolo[1,2-a]indole derivatives in situ. It is postulated that the solvent and LA/BA catalyst interaction was found to be crucial for the catalytic C-F activation in these transformations.

Development of Carbazole-Cored Organo-Photocatalyst for Visible Light-Driven Reductive Pinacol/Imino-Pinacol Coupling

Benzoperylenocarbazole (BPC), a unique carbazole-based organophotocatalyst, is reported herein as a potent organo-photoreductant. Lower excited state oxidation potential (-2.0 V vs SCE) and reasonable excited state lifetime (4.61 ns) render BPC an effective photosensitizer. Under irradiation of blue light employing low catalyst loading (0.5 mol %), a plethora of vicinal diols and diamines were synthesized in excellent yields through reductive coupling of carbonyls and imines, respectively. Insight about the electronic structure of BPC was obtained by DFT calculations.

Visible-Light-Induced Cascade Cyclization of 3-(2-(Ethynyl)phenyl)quinazolinones to Phosphorylated Quinolino[2,1-b]quinazolinones

3-(2-(Ethynyl)phenyl)quinazolinones were designed and synthesized as a class of novel and efficient skeletons for phosphorylation/cyclization reactions. Under visible light irradiation, a series of phosphorylated quinolino[2,1-b]quinazolinones (35 examples, up to 87% yield) were first synthesized from 3-(2-(ethynyl)phenyl)quinazolinones and diarylphosphine oxides by using 4CzIPN as a photocatalyst under mild conditions. This reaction was also applicable under sunlight irradiation. Moreover, the reaction efficiency could be significantly improved under continuous-flow conditions.

Carbodefluorination of fluoroalkyl ketones via a carbene-initiated rearrangement strategy

The C-F bond cleavage and C-C bond formation (i.e., carbodefluorination) of readily accessible (per)fluoroalkyl groups constitutes an atom-economical and efficient route to partially fluorinated compounds. However, the selective mono-carbodefluorination of trifluoromethyl (CF3) groups remains a challenge, due to the notorious inertness of C-F bond and the risk of over-defluorination arising from C-F bond strength decrease as the defluorination proceeds. Herein, we report a carbene-initiated rearrangement strategy for the carbodefluorination of fluoroalkyl ketones with β,γ-unsaturated alcohols to provide skeletally and functionally diverse α-mono- and α,α-difluoro-γ,δ-unsaturated ketones. The reaction starts with the formation of silver carbenes from fluoroalkyl N-triftosylhydrazones, followed by nucleophilic attack of a β,γ-unsaturated alcohol to form key silver-coordinated oxonium ylide intermediates, which triggers selective C-F bond cleavage by HF elimination and C-C bond formation through Claisen rearrangement of in situ generated difluorovinyl ether. The origin of chemoselectivity and the reaction mechanism are determined by experimental and DFT calculations. Collectively, this strategy by an intramolecular cascade process offers significant advances over existing stepwise strategies in terms of selectivity, efficiency, functional group tolerance, etc.

Defluorinative Alkylation of Trifluoromethylbenzimidazoles Enabled by Spin-Center Shift: A Synergistic Photocatalysis/Thiol Catalysis Process with CO2•

We describe a catalytic strategy for direct single C(sp³)-F bond alkylation of trifluoromethylbenzimidazoles under a photoinduced thiol catalysis process. The CO₂ radical anion (CO₂^•-) proved to be the most efficient single-electron reductant to realize such a transformation. The spin-center shift of the generated radical anion intermediate is the key step in realizing C-F bond activation under mild conditions with high efficiency.

Chemodivergent Csp3─F bond functionalization and cross-electrophile alkyl-alkyl coupling with alkyl fluorides

The widespread use of fluorinated organic compounds in the health, agrochemical, and materials sciences is sustained by a steadily growing pool of commercially available fine chemicals. The synthetic utility of the increasingly ubiquitous Csp³─F bond, however, remains to be fully exploited, which is often a difficult task because of its paramount stability and chemical inertness. Here, we demonstrate chemodivergent activation of monofluoroalkyl compounds toward either nucleophilic or electrophilic intermediates. This is accomplished under conditions that are compatible with several reaction types and many functional groups, which drastically widens the current scope of organofluorine chemistry and sets the stage for carbon-carbon and carbon-heteroatom bond formations, stereoselective construction of bisoxindole alkaloid scaffolds via in situ Umpolung, and cross-electrophilic coupling methodology. The selective generation of either nucleophilic or electrophilic species and the possibility of doing so simultaneously or, alternatively, switching molecular polarity enable previously unidentified synthetic opportunities that recognize alkyl fluorides as chemodivergent building blocks.

Recent advances in C-F bond activation of trifluoromethylated carbonyl compounds and derivatives

The selective activation of the inert C-F bonds is one of the most challenging topics in modern organic chemistry. Trifluoromethylketones represent a class of versatile building blocks, which are inexpensive...

Photoredox-Catalyzed Defluorinative Functionalizations of Polyfluorinated Aliphatic Amides and Esters

Selective C-F bond functionalization of perfluoalkyl units has huge potential towards accessing functionalized organofluorinated compounds, but remains chanllenging due to the high C-F bond strength and inherent selectivity challenges. We report a new catalytic approach for the selective functionalization of the strong C-F bonds in polyfluorinated aliphatic esters and amides. This simple reaction proceeds in mild and operationally fashion with divergent conversions, including hydrodefluorination, defluoroalkylation, and defluoroalkenlylation, affording a diverse array of important partially fluorinated motifs. Straightforward downstream chemistry towards fluorinated alcohols, amines and drug derivatives highlights the potential of the protocol.