Metal-Free Visible-Light Radical Iodoperfluoroalkylation of Terminal Alkenes and Alkynes

10-Phenylphenothiazine-Organophotocatalyzed Bromo-Perfluoroalkylation of Unactivated Olefins

In this study, we have developed a smooth metal-free visible-light-induced bromo-perfluoroalkylation of unactivated olefins with the aid of 10-phenylphenothiazine (PTH) as an organic photoredox catalyst. The reaction is 100% atom-economic redox-neutral and proceeds with stoichiometric amounts of olefin and perfluoroalkyl bromide. To show the potential of these unexplored motifs, we carried out various postfunctionalizations taking advantage of the bromine atom, including gram-scale experiments.

Modulating β-Keto-enamine-Based Covalent Organic Frameworks for Photocatalytic Atom-Transfer Radical Addition Reaction

The atom-transfer radical addition (ATRA) reaction simultaneously forges carbon-carbon and carbon-halogen bonds. However, frequently-used photosensitizers such as precious transition metal complexes, or organic dyes have limitations in terms of their potential toxicity and recyclability. Three β-ketoenamine-linked covalent organic frameworks (COFs) from 1,3,5-triformylphloroglucinol and 1,4-phenylenediamines with variable transient photocurrent and photocatalytic activity have been prepared. A COF bearing electron-deficient Cl atoms displayed the highest photocatalytic activity toward the ATRA reaction of polyhalogenated alkanes to give halogenated olefins under visible light at room temperature. This heterogeneous photocatalyst exhibited good functional group tolerance and could be recycled without significant loss of activity.

Hydroxy- and Hydro-Perfluoroalkylation of Styrenes by Controlling the Quenching Cycle of Eosin Y

Fluoroalkyl compounds are widely used, underscoring a pressing need for the development of methods for their synthesis. However, reports on perfluoroalkylation to styrenes have been sparse. In this study, both hydroxy- and hydro-perfluoroalkylation of styrene were achieved using visible light reactions, catalyzed by eosin Y, by selecting appropriate additives and controlling the eosin Y quenching cycle. These reactions are heavy-metal free, use water as the hydroxyl or hydrogen source, and employ inexpensive and readily available reagents.

Synthesis of Selectively gem-Difluorinated Molecules; Chiral gem-Difluorocyclopropanes via Chemo-Enzymatic Reaction and gem-Difluorinated Compounds via Radical Reaction

The incorporation of fluorine atoms into an organic compound can alter the chemical reactivity or biological activity of the resulting compound due to the strong electron withdrawing nature of the fluorine atom. We have synthesized many original gem-difluorinated compounds and described the results in four sections. The first section describes the synthesis of optically active-gem-difluorocyclopropanes via the chemo-enzymatic reaction; we applied these compounds to liquid crystalline molecules, then further discovered a potent DNA cleavage activity for the gem-difluorocyclopropane derivatives. The second section describes the synthesis of selectively gem-difluorinated compounds via a radical reaction; we synthesized fluorinated analogues of a sex pheromone of the male African sugarcane borer, Eldana saccharina, and used the compounds as proof for investigating the origin of pheromone molecule recognition on the receptor protein. The third involves the synthesis of 2,2-difluorinated-esters by visible light-driven radical addition of 2,2-difluoroacetate with alkenes or alkynes in the presence of an organic pigment. The last section describes the synthesis of gem-difluorinated compounds via the ring-opening of gem-difluorocyclopropanes. We further developed a novel method of synthesizing gem-difluorohomoallylic alcohols via the ring-opening of gem-difluorocyclopropane and aerobic oxidation by photo-irradiation in the presence of an organic pigment. Since gem-difluorinated compounds that were prepared by the present method have two olefinic moieties with a different reactivity at the terminal position, we accomplished the synthesis of four types of gem-difluorinated cyclic alkenols via the ring-closing-metathesis (RCM) reaction.

Amine-catalyzed Synthesis of Fluorine-containing Polymers through Halogen Bonding

Fluorine-containing polymers are one of the most useful materials among various polymers. In this study, we have developed synthesis methods for fluorine-containing polymers through sequential and chain polymerization based on the generation of perfluoroalkyl radicals by photoirradiation halogen bonding of perfluoroalkyl iodide and amines. In sequential polymerization, fluoroalkyl-alkyl-alternating polymers were synthesized by the polyaddition of diene and diiodoperfluoroalkane. In chain polymerization, polymers with perfluoroalkyl terminals were synthesized by polymerization of general-purpose monomers, with perfluoroalkyl iodide as the initiating species. Block polymers were also synthesized by successive chain polymerization to the polyaddition product.

Metal-free visible-light-induced hydroxy-perfluoroalkylation of conjugated olefins using enamine catalyst

We developed a simple and sustainable method for the hydroxy-perfluoroalkylation of electron-deficient conjugated olefins and styrenes. In this protcol, in situ generated enamine forms electron-donor-accepter (EDA) complexes with perfluoroalkyl iodide, and reaction proceed with visible-light irradiation. Tertiary amine also interacts with perfluoroalkyl iodide via halogen-bonding, promoting the perfluoroalkyl radical generation. This reaction does not require any transition-metal or photoredox catalyst, and gaseous oxygen is used as the green hydroxy source. Moreover, various commercially available substrates and perfluoroalkyl iodides were tolerated, affording the desired hydroxy-perfluoroalkylated products in good to moderate yields (>50 examples, up to 90%).

Eosin Y-Catalyzed Visible-Light-Induced Hydroperfluoroalkylation of Electron-Deficient Alkenes

The eosin Y-catalyzed hydroperfluoroalkylation of electron-deficient alkenes is described herein. The reaction proceeded smoothly under visible light irradiation and selectively afforded a hydroperfluoroalkylated product. Various perfluoroalkyl bromides and electron-deficient olefins can be used in this reaction, and all chemicals required for this reaction are safe and readily available.

Copper-photocatalyzed ATRA reactions: concepts, applications, and opportunities

Atom transfer radical addition (ATRA) reactions are linchpin transformations in synthetic chemistry enabling the atom-economic difunctionalization of alkenes. Thereby a rich chemical space can be accessed through smart combinations of simple starting materials. Originally, these reactions required toxic and hazardous radical initiators or harsh thermal activation and thus, the recent resurgence and dramatic evolution of photocatalysis appeared as an attractive complement to catalyze such transformations in a mild and energy-efficient manner. Initially, this technique relied primarily on complexes of precious metals, such as ruthenium or iridium, to absorb the visible light. Hence, copper photocatalysis rapidly developed into a powerful alternative, not just from an economic point of view. Originally considered to be disadvantageous as a pathway for deactivation by quenching their excited state, the dynamic nature of Cu-complexes enables them to undergo facile ligand exchange and thus opens up special opportunities for transformations utilizing their inner-coordination sphere. Moreover, the ability of Cu(II), representing a persistent radical, to capture incipient radicals offers the possibility to access heretofore elusive two-component, but also three-component, ATRA reactions, not feasible with ruthenium or iridium catalysts. In this regard, the idea of using Cu(I)-substrate assemblies as active photocatalysts is an emerging field to achieve such 3-component coupling reactions even under enantioselective control, which is reflected by an increasing number of reports being covered in this review.

Co-Catalyzed atom transfer radical addition of bromodifluoroacetamides, expanding the scope of radical difluoroalkylation

The atom transfer radical addition (ATRA) of bromodifluoroacetamides to arylalkynes and terminal alkenes was conducted using von Wangelin's Co catalyst system (CoBr₂/1,2-bis(diphenylphosphino)benzene/Zn) in acetone/H₂O at 30 °C to afford the corresponding functionalized difluoroacetamides in 33-89% yields. Moreover, the Co catalyst was successfully applied to the tandem addition/cyclization of 1,6-diene and -enyne substrates and intramolecular ATRA of N-allyl and N-propargyl bromodifluoroacetamides, significantly expanding the scope of radical difluoroalkylation.

Iodoperfluoroalkylation of unactivated alkenes via pyridine-boryl radical initiated atom-transfer radical addition

The pyridine/bis(pinacolate)diboron combination has been found to be able to initiate the iodoperfluoroalkylation of unactivated alkenes with perfluoroalkyl iodides. Theoretical calculations and control experiments indicate that the atom transfer radical addition mechanism is responsible for the formation of iodoperfluoroalkylation products. This metal-free and photo-free strategy is applicable to a wide range of perfluoroalkyl iodides and unactivated alkenes with good functional group tolerance. Further applications in iodoperfluoroalkylation of organic semiconductor-relevant or bioactive molecules demonstrate the synthetic potential of this method.

Recent Advances in Photoinduced Perfluoroalkylation Using Perfluoroalkyl Halides as the Radical Precursors

Perfluoroalkylation is one of the most important methods for the introduction of multiple fluorine atoms into organic molecules in a single step. The use of photoinduced technology is a common strategy that uses the outstanding oxidation or reduction ability of a photo­redox catalyst in its excited state to generate perfluoroalkyl radicals from perfluoroalkyl halides. The perfluoroalkyl radicals thus obtained can undergo various subsequent reactions under mild conditions, such as ATRA reaction of alkenes, alkynes, and 1,n-enynes; carbo/heteroperfluoroalkylation of alkenes and isocyanides; and C–H/F perfluoroalkyl­ation. This allows the expedient incorporation of various perfluoroalkyl groups into the molecular motifs. Perfluorinated functional groups are still in demand in pharmaceutical and material sciences; this short review discusses recent advances in photoinduced perfluoroalkylation methodologies and technologies.

1 Introduction

2 Photocatalytic Perfluoroalkylation of Alkenes, Alkynes, and 1,n- Enynes

3 Photocatalytic Carboperfluoroalkylation or Heteroperfluoro­alkylation of Alkenes, Alkynes, Isocyanides, and Hydrazones

4 Photocatalytic ATRE Reactions of Alkenes with Perfluoroalkyl Halides­

5 Photocatalytic C–X (X = H, F) Bond Perfluoroalkylation

6 Continuous Flow Strategies in Photocatalytic Perfluoroalkylation

7 Conclusions

Rose Bengal-photocatalyzed perfluorohexylation reactions of organic substrates in water. Applications to late-stage syntheses

The Rose Bengal-photocatalyzed perfluorohexylation of olefins, alkynes, and electron-rich aromatic compounds in water was achieved employing perfluorohexyl iodide as fluoroalkyl source and TMEDA as sacrificial donor under green LED irradiation. Alkenes and alkynes rendered products derived from the atom transfer radical addition (ATRA) pathway, and in the case of alkynes, exclusively as E-stereoisomers. These are the first examples of photocatalyzed ATRA reactions carried out excursively in water alone. The reactions of aromatic compounds under the current protocol in water present the advantage of employing a perfluoroalkyl iodide (C₆F₁₃-I) as source of perfluorohexyl radicals. Examples of photocatalytic late-stage incorporations of fluoroalkyl moieties into two commercial drugs of widespread use are reported.

Photoactive perylenediimide metal–organic framework for boosting iodoperfluoroalkylation of alkenes and oxidative coupling of amines

A novel photoactive MOF was prepared based on an electron-deficient perylenediimide derivative, which exhibits excellent photocatalytic activities towards the iodoperfluoroalkylation of alkenes and the oxidation of amines to imines.

Water facilitated photolysis of perfluoroalkyl iodides via halogen bonding

A strategy for the efficient water facilitated photolysis of perfluoroalkyl iodide has been established for the synthesis of various perfluoroalkylated products.

Construction of sterically congested oxindole derivatives via visible-light-induced radical-coupling

The oxindole scaffold represents an important structural feature in many natural products and pharmaceutically relevant molecules. Herein, we report a visible-light-induced modular methodology for the synthesis of complex 3,3'-disubstituted oxindole derivatives. A library of valuable fluoroalkyl-containing highly sterically congested oxindole derivatives can be synthesized by a catalytic three-component radical coupling reaction under mild conditions (metal & photocatalyst free, >80 examples). This strategy shows high functional group tolerance and broad substrate compatibility (including a wide variety of terminal or non-terminal alkenes, conjugated dienes and enynes, and a broad array of polyfluoroalkyl iodide and oxindoles), which enables modular modification of complex drug-like compounds in one chemical step. The success of solar-driven transformation, large-scale synthesis, and the late-stage functionalization of bioactive molecules, as well as promising tumor-suppressing biological activities, highlights the potential for practical applications of this strategy. Mechanistic investigations, including a series of control experiments, UV-vis spectroscopy and DFT calculations, suggest that the reaction underwent a sequential two-step radical-coupling process and the photosensitive perfluoroalkyl benzyl iodides are key intermediates in the transformation.

Eosin: a versatile organic dye whose synthetic uses keep expanding

Organic dyes, which absorb light in the visible region of the electromagnetic spectrum, offer a lower cost, greener alternative to precious metals in photocatalysis. In this context, the organic dye eosin's uses are currently expanding at a significant rate. For a long time, its action as an energy transfer agent dominated, more recently, however, there has been a growing interest in its potential as an electron transfer agent. In this short review, we highlight some recent (from 2016 onwards) contributions to the field with a focus on the breadth of the reactions eosin can catalyse.

Recent advancements in the development of molecular organic photocatalysts

Research in the development of molecular organic photocatalysts for applications in chemical syntheses has burgeoned in recent years. While organic photosensitizers have been known for over a century, tuning the properties of these molecules to increase photocatalytic efficiencies is now of growing importance. The properties that help improve the performance of organic photocatalysts include: a wider range of redox potentials, increased molar absorptivity (ε) in the visible spectrum, increased quantum yields (Φ), long-lived excited-state lifetimes (ns to μs), and increased chemical stability. This review examines some of the recent advancements in the development of molecular organic photocatalysts, specifically cyanoarenes, acridinium dyes, phenazines, thiazines, oxazines, and xanthenes, with respect to these properties and examines the chemical synthesis routes now achieved by organic photocatalysts.

Application of Bifunctional 2-Amino-1,4-naphthoquinones in Visible-Light-Promoted Photocatalyst-Free Alkene Perfluoroalkyl-Alkenylation

A simple and practical photochemical strategy for intermolecular perfluoroalkyl-alkenylation of alkenes with 2-amino-1,4-naphthoquinones and perfluoroalkyl iodides has been demonstrated under visible-light irradiation. Mechanistic studies reveal that easily available 2-amino-1,4-naphthoquinone substrates can serve as efficient photosensitizers to activate perfluoroalkyl iodides through a photoredox process. Therefore, the developed radical relay reaction proceeds smoothly without additional transition metals and photocatalysts.

Selective nickel-catalyzed fluoroalkylations of olefins

Mild and selective nickel-catalyzed trifluoromethylation and perfluoroalkylation reactions of alkenes were developed to provide fluorinated olefins, including natural products, pharmaceuticals, and variety of synthetic building blocks in good to excellent yields (38 examples). Control experiments, kinetic measurements and in situ EPR studies reveal the importance of radical species and the formation of 1,2-adducts as intermediates.

Visible light photocatalytic cross-coupling and addition reactions of arylalkynes with perfluoroalkyl iodides

Visible light photocatalytic cross-coupling and addition reactions of arylalkynes with perfluoroalkyl iodides have been developed. Through slight modifications of the reaction conditions, reactions that are selective for the preparation of the C-C coupling product (perfluoroalkyl alkynes) and the addition products (iodo-perfluoroalkyl substituted alkenes) can be achieved. These reactions work well with different types of alkynes and perfluoroalkyl iodides. As the iodide generated from the reaction can serve as a reductant to regenerate the photocatalyst from its oxidized form, no sacrificial electron donor is required.

Light-driven, heterogeneous organocatalysts for C-C bond formation toward valuable perfluoroalkylated intermediates

The favorable exploitation of carbon nitride (CN) materials in photocatalysis for organic synthesis requires the appropriate fine-tuning of the CN structure. Here, we present a deep investigation of the structure/activity relationship of CN in the photocatalytic perfluoroalkylation of organic compounds. Four types of CN bearing subtle structural differences were studied via conventional characterization techniques and innovative nuclear magnetic resonance (NMR) experiments, correlating the different structures with the fundamental mechanistic nexus and especially highlighting the importance of the halogen bond strength between the reagent and the catalyst surface. The optimum catalyst exhibited an excellent performance, with a very wide reaction scope, and could prominently trigger the model reaction using natural sunlight. The work lays a platform for establishing a new approach in the development of heterogeneous photocatalysts for organic synthesis related to medical, agricultural, and material chemistry.

Visible Light-Induced Homolytic Cleavage of Perfluoroalkyl Iodides Mediated by Phosphines

In an effort to explain the experimentally observed variation of the photocatalytic activity of t Bu 3 P, n Bu 3 P and (MeO) 3 P in the blue-light regime [Helmecke et al., Org. Lett. 21 (2019) 7823], we have explored the absorption characteristics of several phosphine- and phosphite-IC 4 F 9 adducts by means of relativistic density functional theory and multireference configuration interaction methods. Based on the results of these computational and complementary experimental studies, we offer an explanation for the broad tailing of the absorption of t Bu 3 P-IC 4 F 9 and (MeO) 3 P-IC 4 F 9 into the visible-light region. Larger coordinate displacements of the ground and excited singlet potential energy wells in n Bu 3 P-IC 4 F 9 , in particular with regard to the P-I-C bending angle, reduce the Franck-Condon factors and thus the absorption probability compared to t Bu 3 P-IC 4 F 9 . Spectroscopic and computational evaluation of conformationally flexible and locked phosphites suggests that the reactivity of (MeO) 3 P may be the result of oxygen lone-pair participation and concomitant broadening of absorption. The proposed mechanism for the phosphine-catalyzed homolytic C-I cleavage of perfluorobutane iodide involves S₁ ← S₀ absorption of the adduct followed by intersystem crossing to the photochemically active T 1 state.

Visible-light Promoted Atom Transfer Radical Addition-Elimination (ATRE) Reaction for the Synthesis of Fluoroalkylated Alkenes Using DMA as Electron-Donor

Here, we describe a mild, catalyst-free and operationally-simple strategy for the direct fluoroalkylation of olefins driven by the photochemical activity of an electron donor−acceptor (EDA) complex between DMA and fluoroalkyl iodides. The significant advantages of this photochemical transformation are high efficiency, excellent functional group tolerance, and synthetic simplicity, thus providing a facile route for further application in pharmaceuticals and life sciences.

Photo-induced 1,2-carbohalofunctionalization of C–C multiple bonds via ATRA pathway

Carbohalofunctionalization of C–C multiple bonds via atom transfer radical processes constitutes an efficient method for the construction of halogenated building blocks with complete atom economy. This review summarizes the recent advancements.

Towards a practical perfluoroalkylation of (hetero)arenes with perfluoroalkyl bromides using cobalt nanocatalysts

This paper report a convenient methodology for perfluoroalkylation including trifluoromethylation of (hetero)arenes with perfluoroalkyl bromides using a specific cobalt-based nanocatalyst.

A general and green fluoroalkylation reaction promoted via noncovalent interactions between acetone and fluoroalkyl iodides

The first example of visible light promoted fluoroalkylation reactions initiated via noncovalent interactions between solvents and R_FI is presented.

Radical fluoroalkylation reactions of (hetero)arenes and sulfides under red light photocatalysis

Fluoroalkylation reactions of (hetero)aromatics have been accomplished through the low-power illumination from red LEDs (λmax = 635 nm) of commercially available perfluoroalkyl iodides RF-I and phthalocyanine zinc salt as photocatalyst in MeCN : DMF solvent mixture. This methodology has been extended to the perfluorobutylation of sulfides. As far as we are concerned, this is the first report on a perfluoroalkylation reaction of (hetero)aromatics and sulfides under red-light photocatalysis.

Metal-free visible-light synthesis of quaternary α-perfluoroalkyl aldehydes via an enamine intermediate

Visible-light induced perfluoroalkylation of the α-position of aldehydes via enamines was developed. The reaction proceeds by electron donor-acceptor complexation of the enamine and perfluoroalkyl iodide without any additional redox catalyst. A variety of perfluoroalkyl groups are tolerated to give various quaternary α-perfluoroalkyl aldehydes. An example using proline-derived chiral amine gives high enantioselectivity.

Visible light promoted fluoroalkylation of alkenes and alkynes using 2-bromophenol as a catalyst

A simple, mild and efficient approach for the fluoroalkylation of alkenes and alkynes using 2-bromophenol as a catalyst is presented.