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

Photoredox Iron-Catalyzed Decarboxylative Radical Cyclization for the Synthesis of Oxindoles and Chroman-4-ones

A sustainable, photocatalytic approach for the synthesis of oxindoles and chroman-4-ones was developed using carboxylate salts as radical precursors and FeCl3 as a catalyst. The reaction proceeds via a decarboxylative radical cyclization mechanism triggered by ligand-to-metal charge transfer under visible light irradiation, operating efficiently at room temperature. This method demonstrates excellent substrate scope, including the use of various alkyl carboxylates, and functional group tolerance and offers a scalable pathway for gram-scale synthesis, highlighting its practical application.

A unified approach to meta-selective methylation, mono-, di- and trifluoromethylation of arenes

Matched molecular series (MMS) are series of molecules that differ only by a single modification at a specific site. The synthesis of MMS is a desirable strategy in drug discovery campaigns. Small aliphatic motifs, notably methyl, mono-, di- and trifluoromethyl substituents (C1 units), are known to have profound effects on the physiochemical properties and/or potency of drug candidates. In this context, we herein report a unique strategy for achieving direct meta-selective methylation, mono-, di-, and trifluoromethylation from the same parent compound. This approach takes advantage of a highly meta-selective ruthenium(ii)-catalyzed alkylation, followed by a subsequent photocatalyzed protodecarboxylation or silver-mediated fluorodecarboxylation to reveal the (fluoro)methyl moiety. This method enables the late-stage access to MMS in small molecules bearing a variety of orienting groups as well as bio-relevant molecules containing complex functionalities, bypassing the need for de novo synthesis to access individual compounds in a series. Moreover, key physiochemical properties of drug candidates were successfully modulated, highlighting opportunities to accelerate medicinal chemistry programs in a sustainable fashion.

Photo-induced decarboxylative radical cascade cyclization of unactivated alkenes: access to CF- and CF2-substituted ring-fused imidazoles

A mild and effective visible-light-induced decarboxylative radical cascade reaction of olefin-containing imidazoles with α-fluorinated carboxylic acids as building blocks containing CF or ArCF2 moieties, has been developed to afford a series of monofluoromethylated or aryldifluoromethylated polycyclic imidazoles in medium to excellent yields with features of simple operation, available raw materials, and wide substrate scopes. In addition, the mechanistic experiments indicated that the methodology involved a radical pathway.

Continuous Flow Decarboxylative Monofluoroalkylation Enabled by Photoredox Catalysis

Herein, we report a scalable and mild strategy for the monofluoroalkylation of a wide array of Giese acceptors via visible-light-mediated photoredox catalysis in continuous flow. The use of flow technology significantly enhances productivity and scalability, whereas mildness of conditions and functional group tolerance are ensured by leveraging 4CzIPN, a transition-metal-free organic photocatalyst. Structurally diverse secondary and tertiary monofluoroalkyl radicals can thus be accessed from readily available α-monofluorocarboxylic acids. Given the mild reaction conditions, this protocol is also amenable to the late-stage functionalization of biologically relevant molecules such as menthol, amantadine, bepotastine, and estrone derivatives, rendering it suitable for application to drug discovery programs, for which the introduction of fluorinated fragments is highly sought after. This method was also extended to enable a reductive multicomponent radical-polar crossover transformation to rapidly increase the complexity of the assembled fluorinated architectures in a single synthetic operation.

Photocatalyzed Imino-Difluoromethylation of Alkenes with Bifunctional Oxime Esters

Herein, we report a simple and versatile difluoromethylene-imide reaction in which a series of olefins can undergo a difluoromethylenimine reaction under photocatalytic conditions through an energy transfer (EnT) process. The reaction has mild conditions and a wide range of applicability. We successfully synthesized 27 molecules containing difluoromethylene units, featuring easily accessible starting materials and operational simplicity.

Pioneering Metal-Free Late-Stage C-H Functionalization Using Acridinium Salt Photocatalysis

Using organic dyes as photocatalysts is an innovative approach to photocatalytic organic transformations. These dyes offer advantages such as widespread availability, adaptable absorption properties, and diverse chemical structures. Recent progress has led to the development of organic photocatalysts that can utilize visible light to modify chemically inert C-H bonds. These catalysts are sustainable, selective, and versatile, enabling mild reactions, late-stage functionalization, and various transformations in line with green chemistry principles. As catalysts in photoredox chemistry, they contribute to the development of efficient and environmentally friendly synthetic pathways. Acridinium-based organic photocatalysts have proved valuable in late-stage C-H functionalization, enabling transformative reactions under mild conditions. This review emphasizes their innovative features, such as organic frameworks, efficient light absorption properties, and their applications in modifying complex molecules. It provides an overview of recent advancements in the use of acridinium-based organic photocatalysts for late-stage C-H bond functionalization without the need for transition metals, showcasing their potential to expedite the development of new molecules and igniting excitement about the prospects of this research in the field.

Electrochemical Radical Tandem Difluoroethylation/Cyclization of Unsaturated Amides to Access MeCF2-Featured Indolo/Benzoimidazo [2,1-a]Isoquinolin-6(5H)-ones

A metal-free electrochemical oxidative difluoroethylation of 2-arylbenzimidazoles was accomplished, which provided an efficient strategy for the synthesis of MeCF2-containing benzo[4,5]imidazo[2,1-a]-isoquinolin-6(5H)-ones. In addition, the method also enabled the efficient construction of various difluoroethylated indolo[2,1-a]isoquinolin-6(5H)-ones. Notably, this electrochemical synthesis protocol proceeded well under mild conditions without metal catalysts or exogenous additives/oxidants added.

Visible-Light-Induced Cascade Cyclization of 1-Acryloyl-2-cyanoindole: Access of Difluoroalkylated Pyrrolo[1,2-a]indolediones

An effective method for accessing diverse difluoroalkylated pyrrolo[1,2-a]indolediones via visible-light-induced PhI(OAc)2-promoted cascade difluoroalkylation/cyclization reaction under mild conditions has been established. This method is noteworthy for its use of DMSO-H2O as a green medium at room temperature and avoidance of photocatalysts. The reactions are straightforward to execute and convenient to expand on, provide good to excellent yields, and have good functional group tolerance.

Fluoroalkylation of Activated Allylic Acetates through Radical-Radical Coupling: Organophotoredox/DABCO Catalytic System

A novel organophotoredox/DABCO catalytic system for the fluoroalkylation of activated allylic acetates via radical-radical coupling is described. The method offers mild reaction conditions, high selectivity, and broad substrate compatibility and enabled diverse bioactive molecules, FDA-approved drugs, and amino acid derivatives to be incorporated into transformation. This study expands the synthetic toolbox for the construction of fluorine-containing molecules.

Electrosynthesis of Protected Dehydroamino Acids

A NaCl-mediated electrochemical oxidation of amino acid carbamates (R¹ = Boc, Cbz) afforded α-methoxylated α-amino acids. Subsequent acid-catalyzed elimination delivered valuable dehydroamino acid derivatives. The simplicity of our setup using graphite-electrodes was showcased, producing N-Boc-ΔAla-OMe on a decagram scale.