From Styrenes to Fluorinated Benzyl Bromides: A Photoinduced Difunctionalization via Atom Transfer Radical Addition

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.

N-Heterocyclic Carbene and Manganese Synergistic Catalysis: A Three-Component Radical Acylmonofluoroalkylation of Alkenes

Despite the importance of monofluoroalkyl groups in pharmaceutically relevant molecules, catalytic protocols for their incorporation into alkenes remain limited. We describe herein a three-component acylmonofluoroalkylation of alkenes for the introduction of such moieties through an unprecedented cooperativity between the N-heterocyclic carbene catalyst and earth-abundant Mn(II) complex. This general method can be applied to a variety of alkenes, including styrenes, 1,3-enynes, and allenes, as well as complex substrates containing natural product and drug motifs.

Highlights on U.S. FDA-approved fluorinated drugs over the past five years (2018-2022)

The objective of this review is to provide an update on the fluorine-containing drugs approved by U.S. Food and Drug Administration in the span of past five years (2018-2022). The agency accepted a total of fifty-eight fluorinated entities to diagnose, mitigate and treat a plethora of diseases. Among them, thirty drugs are for therapy of various types of cancers, twelve for infectious diseases, eleven for CNS disorders, and six for some other diseases. These are categorized and briefly discussed based on their therapeutic areas. In addition, this review gives a glimpse about their trade name, date of approval, active ingredients, company developers, indications, and drug mechanisms. We anticipate that this review may inspire the drug discovery and medicinal chemistry community in both industrial and academic settings to explore the fluorinated molecules leading to the discovery of new drugs in the near future.

Thio(seleno)cyano-difluoroalkylation of Alkenes Using Visible-Light Photocatalysis

A mild and efficient three-component thio(seleno)cyano-difluoroalkylation of simple alkenes is demonstrated using an iridium(ruthenium) photocatalyst. This protocol provides a direct and regioselective installation of both C-S(Se)CN [thio(seleno)cyanation] and C-C_F (difluoroalkylation) bonds.

Transition metal-free photochemical C-F activation for the preparation of difluorinated-oxindole derivatives

The development of strategies for single and selective C-F bond activation represents an important avenue to overcome limitations in the synthesis of valuable fluorine-containing compounds. The synthetic and medicinal research communities would benefit from new routes that access such relevant molecules in a simple manner. Herein we disclose a straightforward and mechanistically distinct pathway to generate gem-difluoromethyl radicals and their installation onto N-arylmethacrylamides for the preparation of valuable difluorinated oxindole derivatives. To achieve operational simplicity, the use of a readily available benzenethiol as a photocatalyst under open-to-air conditions was developed, demonstrating the facile multigram preparation of the targeted fluorinated molecules. Additionally, dispersion-corrected density functional theory (DFT) and empirical investigations provide a new basis to support the proposed reaction pathway, indicating that arene thiolate is an efficient organophotocatalyst for this transformation.

Visible-Light-Promoted Hydrogenation of Azobenzenes to Hydrazobenzenes with Thioacetic Acid as the Reductant

A catalyst- and metal-free hydrogenation of azobenzenes to hydrazobenzenes in the presence of thioacetic acid was achieved under visible light irradiation. The transformation was carried out under mild conditions in an air atmosphere at ambient temperature, generating a variety of hydrazobenzenes with yields up to 99%. The current process is compatible with a variety of substituents and is highly chemoselective for azo reduction when other unsaturated functionalities (carbonyl, alkenyl, alkynyl, etc.) are contained. Preliminary mechanistic study indicated that the transformation could be a radical process.

Synthesis of Alkyl Fluorides and Fluorinated Unnatural Amino Acids via Photochemical Decarboxylation of α-Fluorinated Carboxylic Acids

Leveraging α-fluoroalkyl or fluorobenzyl radicals to introduce fluorinated motifs allows for the rapid preparation of fluorine-containing building blocks. Herein, we report the generation of α-fluoroalkyl or fluorobenzyl radicals from readily available α-fluorocarboxylic acids under mild reaction conditions and their utilization in the Giese-type addition on Michael acceptors and dehydroamino acids, resulting in the preparation of mono- and difluorinated Michael addition adducts and unnatural fluorinated amino acids.

Syn-Selective Chlorosulfonylation of Alkynes via a Copper-Powder-Initiated Atom Transfer Radical Addition Reaction and Mechanistic Studies

Copper-powder-catalyzed syn-selective chlorosulfonylation of readily available alkynes by an atom transfer radical addition (ATAR) process has been developed, providing straightforward access to a broad range of (Z)-β-chlorovinylsulfones in good yields under mild conditions. In addition, this method is ligand-free and features excellent stereoselectivity and high atom economy. Moreover, the product was obtained without an apparent loss of yield when the reaction was performed on the gram scale at a low catalyst loading. In this reaction, the copper powder not only acts as a sulfone radical initiator but also produces the catalytically active CuCl species. Mechanistic investigations and DFT calculation studies revealed that the stereoselectivity is controlled by the thermodynamic stabilities of the in situ-generated cyclic alkenyl Cu^II complex intermediate, which can serve as a chlorine atom transfer agent.

Visible-Light-Induced C-F Bond Activation for the Difluoroalkylation of Indoles

An aryl disulfide mediated C-F bond activation of the trifluoromethyl group to generate valuable gem-difluoroalkylindoles is described. This method relies on readily available commodity reagents under mild reaction conditions and represents the first transition-metal-free redox-neutral C-F bond activation strategy. The reaction employs various substituted indoles and α-fluoro-substituted esters. Further, this mode of C-F activation was also amenable to the activation of trifluoromethylated arenes for the preparation of bis-benzylic gem-difluoromethylenes between indole and arene substructures, providing access to a unique chemical space.

A three-component difunctionalization of N-alkenyl amides via organophotoredox radical-polar crossover

Herein, we report a three-component organophotoredox coupling of N-alkenyl amides with α-bromocarbonyls and various nucleophiles. This transition metal-free difunctionalization protocol installs sequential C-C and C-Y (Y = S/O/N) bonds in alkenes. This reaction works with terminal and internal alkenes containing both cyclic and acyclic amides via radical-polar crossover.

Visible-Light-Induced Difluoroalkylation of 1-(Allyloxy)-2-(1-arylvinyl)benzenes and 1-(1-Arylvinyl)-2-(vinyloxy)benzenes: Synthesis of Bis-Difluoroalkylated Benzoxepines and 2H-Chromenes

A novel visible-light-mediated difluoroalkylation of 1-(allyloxy)-2-(1-arylvinyl)benzenes and 1-(1-arylvinyl)-2-(vinyloxy)benzenes for the synthesis of bis-difluoroalkylated benzoxepines and 2H-chromenes is developed. This method features mild reaction conditions, good regioselectivity, a wide substrate scope, good functional-group compatibility, and late-stage modification. Preliminary mechanistic studies reveal that the generation of the CF₂CO₂Et radical is more prone to reaction with the double bond of the aryl group.