Fluorinated Sulfinates as Source of Alkyl Radicals in the Photo-Enantiocontrolled β-Functionalization of Enals

Zinc 1,1,2,2-Tetrafluoroethanesulfinate: A Synthetically Useful Oxidative and Photoredox Source of the 1,1,2,2-Tetrafluoroethyl Radical

1,1,2,2-Tetrafluoroethyl-containing molecules are of potential importance in drug discovery, but the efficient synthesis of such compounds is still relatively unexplored due to the lack of readily available reagents for the incorporation of the HCF2CF2 group. Herein, we introduce a new reagent, zinc 1,1,2,2-tetrafluoroethanesulfinate, which can be useful for the oxidative tetrafluoroethylation of arylboronic acids and heteroarenes as well as for a novel photoredox, three component hydro-tetrafluoroethylation of two alkenes of complementary reactivity.

Electrochemical Asymmetric Radical Functionalization of Aldehydes Enabled by a Redox Shuttle

Aminocatalysis is a well-established tool that enables the production of enantioenriched compounds under mild conditions. Its versatility is underscored by its seamless integration with various synthetic approaches. While the combination of aminocatalysis with metal catalysis, photochemistry, and stoichiometric oxidants has been extensively explored, its synergy with electrochemical activation remains largely unexplored. Herein, we present the successful merger of electrochemistry and aminocatalysis to perform SOMO-type transformations, expanding the toolkit for asymmetric electrochemical synthesis. The methodology harnesses electricity to drive the oxidation of catalytically generated enamines, which ultimately partake in enantioselective radical processes, leading to α-alkylated aldehydes. Crucially, mechanistic studies highlight how this electrochemical strategy is enabled by the use of a redox shuttle, 4,4'-dimethoxybiphenyl, to prevent catalyst degradation and furnishing the coveted compounds in good yield and high enantioselectivity.

Organophotoredox Catalysis: Switchable Radical Generation from Alkyl Sodium Sulfinates for Sulfonylation and Alkylative Activation of C-C Bonds of Cyclopropenes

Generating alkyl radicals from the sulfonyl radicals remains challenging in synthetic chemistry. Here, we report an efficient photocatalyzed strategy using alkyl sodium sulfinates as both sulfonylating and alkylating reagents by controlling the reaction temperature. This methodology provides a versatile protocol for synthesizing diastereoselective sulfonylated cyclopropanes and poly-substituted styrene derivatives. This methodology is successfully demonstrated with a wide variety of cyclopropenes and alkyl sulfinates, showcasing its broad substrate scope, high diastereo- and E/Z selectivity, and yielding good to excellent yields.

Photocatalyzed Hydroaminodifluoroalkylation of Alkenes

The synthesis of undescribed β-aminodifluoroethylsulfinates and their uses in the hydroaminodifluoroalkylation of alkenes is reported. This reaction is performed in the presence of a photocatalyst (4CzIPN, Ru complexes) and enables the direct incorporation of a β-difluoroamine moiety into vinylic aryls, unactivated alkenes, and electron-rich, or -deficient alkenes. The mechanism was studied, and the formation of a gem-difluoromethyl radical was observed after the selective oxidation of the sulfinate function.

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.

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.

Desulfinative Alkylation of Heteroarenes via an Electrostatic Electron Donor-Acceptor Complex

Functionalized pyridine and quinoline rings are important components of numerous bioactive molecules and natural products; however, diversification of these rings often requires de novo heterocycle ring synthesis or demanding reaction conditions. We report a method for desulfinative alkylation of pyridine and quinoline N-methoxide salts that operates under both photocatalytic and electrostatic electron donor-acceptor-mediated pathways. Unlike most EDA-mediated processes, this reaction operates in the absence of light and with the desulfination of the donor compound.

Radical hydrodifluoromethylation of unsaturated C-C bonds via an electroreductively triggered two-pronged approach

Due to its superior ability in controlling pharmaceutical activity, the installation of difluoromethyl (CF₂H) functionality into organic molecules has been an area of intensive research. In this context, difluoromethylation of C-C π bonds mediated by a CF₂H radical have been pursued as a central strategy to grant access to difluoromethylated hydrocarbons. However, early precedents necessitate the generation of oxidative chemical species that can limit the generality and utility of the reaction. We report here the successful implementation of radical hydrodifluoromethylation of unsaturated C-C bonds via an electroreductively triggered two-pronged approach. Preliminary mechanistic investigations suggest that the key distinction of the present strategy originates from the reconciliation of multiple redox processes under highly reducing electrochemical conditions. The reaction conditions can be chosen based on the electronic properties of the alkenes of interest, highlighting the hydrodifluoromethylation of both unactivated and activated alkenes. Notably, the reaction delivers geminal (bis)difluoromethylated products from alkynes in a single step by consecutive hydrodifluoromethylation, granting access to an underutilized 1,1,3,3-tetrafluoropropan-2-yl functional group. The late-stage hydrodifluoromethylation of densely functionalized pharmaceutical agents is also presented.

Recent Advances in Employing Catalytic Donors and Acceptors in Electron Donor-Acceptor Complex Photochemistry

Electron donor-acceptor (EDA) complexes provide a means to initiate radical reactions under visible light irradiation using substrates that do not absorb visible light individually. Catalytic approaches to complex formation are vital for advancing this synthetic strategy as it decouples the complexation and photogeneration of radicals from substrate functionalization, a limitation inherent to stoichiometric approaches that restricts structural diversity. This Synopsis highlights recent developments in EDA complex photochemistry in which either the donor or acceptor are employed catalytically.

Difluoromethylation of Unactivated Alkenes Using Freon-22 through Tertiary Amine-Borane-Triggered Halogen Atom Transfer

The application of abundant and inexpensive fluorine feedstock sources to synthesize fluorinated compounds is an appealing yet underexplored strategy. Here, we report a photocatalytic radical hydrodifluoromethylation of unactivated alkenes with an inexpensive industrial chemical, chlorodifluoromethane (ClCF₂H, Freon-22). This protocol is realized by merging tertiary amine-ligated boryl radical-induced halogen atom transfer (XAT) with organophotoredox catalysis under blue light irradiation. A broad scope of readily accessible alkenes featuring a variety of functional groups and drug and natural product moieties could be selectively difluoromethylated with good efficiency in a metal-free manner. Combined experimental and computational studies suggest that the key XAT process of ClCF₂H is both thermodynamically and kinetically favored over the hydrogen atom transfer pathway owing to the formation of a strong boron-chlorine (B-Cl) bond and the low-lying antibonding orbital of the carbon-chlorine (C-Cl) bond.

Continuous-flow synthesis of alkyl zinc sulfinates for the direct photofunctionalization of heterocycles

A sustainable strategy for the alkylation of heterocycles is presented. The protocol relies on the in situ generation and further in-line use of alkyl zinc sulfinates through a continuous-flow system. The environmentally friendly character of the protocol is assured by the use of a green solvent mixture, the presence of a metal free oxidant and low waste generation.

Nucleophilic strategies to construct –CF2– linkages using borazine-CF2Ar reagents

Using nucleophilic, boron-based –CF2Ar reagents, we demonstrate three methods to form C–CF bonds: (1) nucleophilic aromatic substitution, (2) palladium catalyzed cross-coupling, and (3) nucleophilic substitution.

Isothiourea-Catalysed Enantioselective Radical Conjugate Addition under Batch and Flow Conditions

The photocatalytic generation of α-amino radicals is combined with chiral isothiourea derived α,β-unsaturated acyl ammonium intermediates. The reaction proceeds via a [3+2] radical-polar crossover mechanism to generate γ-lactams in good...