Photoredox Activation of Anhydrides for the Solvent-Controlled Switchable Synthesis of gem-Difluoro Compounds

Divergent functionalization of alkenes enabled by photoredox activation of CDFA and α-halo carboxylic acids

Herein we present our studies on the solvent-controlled difunctionalization of alkenes utilizing chlorodifluoroacetic acid (CDFA) and α-halo carboxylic acids for the synthesis of γ-lactones, γ-lactams and α,α-difluoroesters. Mechanistic insights revealed that photocatalytic reductive mesolytic cleavage of the C-X bond delivers elusive α-carboxyl alkyl radicals. In the presence of an olefin molecule, this species acts as a unique bifunctional intermediate allowing for stipulated formation of C-O, C-N and C-H bonds on Giese-type adducts via single electron transfer (SET) or hydrogen atom transfer (HAT) events. These protocols exhibit great efficiency across a broad spectrum of readily available α-halo carboxylic acids and are amenable to scalability in both batch and flow. To demonstrate the versatility of this concept, the synthesis of (±)-boivinianin A, its fluorinated analog and eupomatilone-6 natural products was successfully accomplished.

Reversal of the Regioselectivity of Iron-Promoted Hydrogenation and Hydrohalogenation of gem-Difluoroalkenes

The reaction regioselectivity of gem-difluoroalkenes is dependent on the intrinsic polarity. Thus, the reversal of the regioselectivity of the addition reaction of gem-difluoroalkenes remains a formidable challenge. Herein, we described an unprecedented reversal of regioselectivity of hydrogen atom transfer (HAT) to gem-difluoroalkenes triggered by Fe-H species for the formation of difluoroalkyl radicals. Hydrogenation of the in situ generated radicals gave difluoromethylated products. Mechanism experiments and theoretical studies revealed that the kinetic effect of the irreversible HAT process resulted in the reversal of the regioselectivity of this scenario, leading to the formation of a less stable α-difluoroalkyl radical regioisomer. On basis of this new reaction of gem-difluoroalkene, the iron-promoted hydrohalogenation of gem-difluoroalkenes for the efficient synthesis of aliphatic chlorodifluoromethyl-, bromodifluoromethyl- and iododifluoromethyl-containing compounds was developed. Particularly, this novel hydrohalogenation of gem-difluoroalkenes provided an effect and large-scale access to various iododifluoromethylated compounds of high value for synthetic application.

Mechanochemistry Drives Alkene Difunctionalization via Radical Ligand Transfer and Electron Catalysis

A general and modular protocol is reported for olefin difunctionalization through mechanochemistry, facilitated by cooperative radical ligand transfer (RLT) and electron catalysis. Utilizing mechanochemical force and catalytic amounts of 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO), ferric nitrate can leverage nitryl radicals, transfer nitrooxy-functional group via RLT, and mediate an electron catalysis cycle under room temperature. A diverse range of activated and unactivated alkenes exhibited chemo- and regioselective 1,2-nitronitrooxylation under solvent-free or solvent-less conditions, showcasing excellent functional group tolerance. Mechanistic studies indicated a significant impact of mechanochemistry and highlighted the radical nature of this nitrative difunctionalization process.

Solvation Structure and Derived Interphase Tuning for High-Voltage Ni-Rich Lithium Metal Batteries with High Safety Using Gem-Difluorinated Ionic Liquid Based Dual-Salt Electrolytes

Stabilizing electrolytes for high-voltage lithium metal batteries (LMBs) is crucial yet challenging, as they need to ensure stability against both Li anodes and high-voltage cathodes (above 4.5 V versus Li/Li+ ), addressing issues like poor cycling and thermal runaway. Herein, a novel gem-difluorinated skeleton of ionic liquid (IL) is designed and synthesized, and its non-flammable electrolytes successfully overcome aforementioned challenges. By creatively using dual salts, fluorinated ionic liquid and dimethyl carbonate as a co-solvent, the solvation structure of Li+ ions is efficiently controlled through electrostatic and weak interactions that are well unveiled and illuminated via nuclear magnetic resonance spectra. The as-prepared electrolytes exhibit high security avoiding thermal runaway and show excellent compatibility with high-voltage cathodes. Besides, the solvation structure derives a robust and stable F-rich interphase, resulting in high reversibility and Li-dendrite prevention. LiNi0.6 Co0.2 Mn0.2 O2 /Li LMBs (4.5 V) demonstrate excellent long-term stability with a high average Coulombic efficiency (CE) of at least 99.99 % and a good capacity retention of 90.4 % over 300 cycles, even can work at a higher voltage of 4.7 V. Furthermore, the ultrahigh Ni-rich LiNi0.88 Co0.09 Mn0.03 O2 /Li system also delivers excellent electrochemical performance, highlighting the significance of fluorinated IL-based electrolyte design and enhanced interphasial chemistry in improving battery performance.

Divergent Synthesis of Fluoroalkyl Ketones through Controlling the Reactivity of Organoboronate Complexes

Herein, we report a divergent synthesis of fluoroalkyl ketones through visible-light-induced reactions between readily available organoboronic esters and fluoroalkyl acylsilanes. Selective control of the reactivity of the in situ generated organoboronate complexes is the key to achieving divergent transformations. Under basic conditions, the organoboronate complexes undergo deboronative fluoride elimination, resulting in the formation of enol silyl ethers as intermediates that react with various electrophiles to generate defluorinated ketones as the products. Moreover, in combination with peroxide, a 1,2-shift of fluoroalkyl group is favored over deboronative fluoride elimination to generate ketal intermediates, leading to the formation of ketones as the products. This transition-metal-free reaction is operationally simple, and aryl, alkenyl, and alkyl boronic esters are all suitable substrates. The synthetic potential has been demonstrated by gram-scale reactions and facile synthesis of bioactive molecules including zifrosilone and its fluoroalkyl analogs.

High-Safety Electrolytes with an Anion-Rich Solvation Structure Tuned by Difluorinated Cations for High-Voltage Lithium Metal Batteries

As next-generation energy storage devices, lithium metal batteries (LMBs) must offer high safety, high-voltage resistance, and a long life span. Electrolyte engineering is a facile strategy to tailor the interfacial chemistry of LMBs. In particular, the solvation structure and derived solid electrolyte interphase (SEI) are crucial for a satisfactory battery performance. Herein, a novel middle-concentrated ionic liquid electrolyte (MCILE) with an anion-rich solvation structure tuned by difluorinated cations is demonstrated to achieve ultrahigh safety, high-voltage stability, and excellent ternary-cathode compatibility. Novel gem-difluorinated cations first synthesized for prestoring fluorine on positively charged species, not only preferentially adsorb in the inner-Helmholtz layers, but also participate in regulating the Li+ solvation structure, resulting in a robust interphase. Moreover, these weak interactions in the Li+ solvation structure including anion-solvent and ionic liquid (IL) cation-solvent pairs are first revealed, which are beneficial for promoting an anion-dominated solvation structure and the desolvation process. Benefiting from the unique anion-rich solvation structure, a stable hetero-SEI structure is obtained. The designed MCILE exhibits compatibility with Li metal anode and the high-voltage ternary cathode at high temperatures (60 °C). This work provides a new approach for regulating the solvation structure and electrode interphase chemistry of LMBs via difluorinated IL cations.

Photoredox/Copper-Catalyzed One-Pot Aminoalkylation/Cyclization of Alkenes with Primary Amines to Synthesize Polysubstituted γ-Lactams

Visible-light-driven chemical transformation has emerged as a powerful tool for the synthesis of γ-lactams. However, during this transformation, the α-bromoimides need to be pre-prepared. Herein, we report a photoreodox/copper-catalyzed one-pot three-component reaction of alkenes with primary amines for the construction of γ-lactams. In this transformation, the orthoquinones were generated via a photocatalytic pathway, followed by attack by Cu-amido complexes and intramolecular cyclization to give the γ-lactams. This method represents a simple synthetic route displaying broad functional group tolerance, including substrates bearing alcohols, ketones, heterocycles, esters, halides, alkynes, nitriles, ethers, etc.

Understanding and Controlling Fluorinated Diacyl Peroxides and Fluoroalkyl Radicals in Alkene Fluoroalkylations

The demand for practical methods for the synthesis of novel fluoroalkyl molecules is increasing owing to their diverse applications. Our group has achieved efficient difunctionalizing fluoroalkylations of alkenes using fluorinated carboxylic anhydrides as user-friendly fluoroalkyl sources. Fluorinated diacyl peroxide, prepared in situ from carboxylic anhydrides, enables the development of novel reactions when used as a radical fluoroalkylating reagent. In this account, we aim to provide an in-depth understanding of the structure, bonding, and reactivity of fluorinated diacyl peroxides and radicals as well as their control in fluoroalkylation reactions. In the first part of this account, the physical properties and reactivity of diacyl peroxides and fluoroalkyl radicals are described. In the subsequent part, we categorize the reactions into copper-catalyzed and metal-free methods utilizing the oxidizing properties of fluorinated diacyl peroxides. We also outline examples and mechanisms.

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.

Trifluoromethylations of (Hetero)arenes and Polarized Alkenes Using Trifluoroacetic Anhydride under Photoredox Catalysis

A novel trifluoromethylation of (hetero)arenes and polarized alkenes using simple trifluoroacetic anhydride (TFAA) as the low price CF₃ source under photoredox catalysis was developed without using additives such as bases, hyperstoichiometric oxidant, or auxiliaries. The reaction showed excellent tolerance, including to some important natural products and prodrugs, even on the gram scale and extended to ketones. This simple protocol provides a practical utilization of TFAA. Several perfluoroalkylations and trifluoromethylation/cyclizations were successfully achieved under identical conditions.

Coupling of α-bromoamides and unactivated alkenes to form γ-lactams through EDA and photocatalysis

γ-Lactams are prevalent in small-molecule pharmaceuticals and provide useful precursors to highly substituted pyrrolidines. Despite numerous methods for the synthesis of this valuable motif, previous redox approaches to γ-lactam synthesis from α-haloamides and olefins require additional electron withdrawing functionality as well as N-aryl substitution to promote electrophilicity of the intermediate radical and prevent competitive O-nucleophilicity about the amide. Using α-bromo imides and α-olefins, our strategy enables the synthesis of monosubstituted protected γ-lactams in a formal [3 + 2] fashion. These species are poised for further derivatization into more complex heterocyclic scaffolds, complementing existing methods. C-Br bond scission occurs through two complementary approaches, the formation of an electron donor-acceptor complex between the bromoimide and a nitrogenous base which undergoes photoinduced electron transfer, or triplet sensitization with photocatalyst, to furnish an electrophilic carbon-centered radical. The addition of Lewis acids allows for further increased electrophilicity of the intermediate carbon-centered radical, enabling tertiary substituted α-Br-imides to be used as coupling partners as well as internal olefins.

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.