Diversity-Oriented Synthesis of Aliphatic Fluorides via Reductive C(sp3 )-C(sp3 ) Cross-Coupling Fluoroalkylation

Modulation of metal species as control point for Ni-catalyzed stereodivergent semihydrogenation of alkynes with water

A base-assisted metal species modulation mechanism enables Ni-catalyzed stereodivergent transfer semihydrogenation of alkynes with water, delivering both olefinic isomers smoothly using cheap and nontoxic catalysts and additives. Different from most precedents, in which E-alkenes derive from the isomerization of Z-alkene products, the isomers were formed in orthogonal catalytic pathways. Mechanistic studies suggest base as a key early element in modulation of the reaction pathways: by adding different bases, nickel species with disparate valence states could be accessed to initiate two catalytic cycles toward different stereoisomers. The practicability of the method is showcased with nearly 70 examples, including internal and terminal triple bonds, enynes and diynes, affording semi-hydrogenated products in high yields and selectivity.

Photoredox-Catalyzed and Silane-Mediated Hydrofluoromethylation of Unactivated Alkenes with Fluoroiodomethane in Water

The first hydrofluoromethylation of unactivated alkenes with fluoroiodomethane and hydrosilanes is developed by merging photoredox catalysis and silane-mediated deiodination processes. The key to the success of this reaction is the use of water as the solvent to enhance the activity of CH₂F radical toward unactivated alkenes.

1-Fluoro-1-sulfonyloxylation of Alkenes by Sterically and Electronically Tuned Hypervalent Iodine: Regression Analysis toward 1,1-Heterodifunctionalization

In the heterodifunctionalization of alkenes, 1,1-regioselectivity remains elusive in sharp contrast to 1,2-regioselectivity. Herein, the 1-fluoro-1-sulfonyloxylation of styrenes with Bu₄NBF₄ and sulfonic acids using a hypervalent iodine ArI(OAc)₂ is reported. Regression analysis of substituents on ArI(OAc)₂ suggested that their electron-withdrawing ability and steric factor influence the 1,1-heterodifunctionalization. We designed o-{2,4-(CF₃)₂C₆H₃}- and p-NO₂-substituted ArI(OAc)₂ by the regression analysis to achieve high selectivity.

Unlocking geminal fluorohaloalkanes in nucleophilic fluoroalkylation chemistry: generation and trapping of lithiumfluorocarbenoids enabled by flow microreactors

A direct nucleophilic monofluoroalkylation strategy leveraging on lithium fluorocarbenoids has been developed. Flow microreactor technology allows capitalization of the synthetic potential of these scarcely explored short-lived intermediates - namely 1-fluoro-2-phenylethyllithium, 1-fluoro-3-phenylpropyllithium, and 1-fluorononyllithium - generated through lithium/iodine exchange reaction. This robust protocol was employed to prepare new fluorinated products, adopting various classes of electrophiles. The inherent advantages of microreactor technology contribute to rendering this approach a new valuable tool for direct fluoroalkylation chemistry.

A General and Efficient Solution to Monofluoroalkylation: Divergent Synthesis of Aliphatic Monofluorides with Modular Synthetic Scaffolds

Monofluoroalkanes are important in many pharmaceuticals, agrochemicals and functional materials. However, the lack of easily available and transformable monofluoroalkylating reagents that facilitate a broad array of transformations has hampered the application of monofluoroalkylation. Herein, we report a general and efficient method of preparing diverse aliphatic monofluorides with monofluoroalkyl triflate as the synthetic scaffold. Using both nickel-catalyzed hydromonofluoroalkylation of unactivated alkenes and copper-catalyzed C-C bond formation, the general diversification of the monofluoroalkylating scaffold has been exhibited. The broad utility of this monofluoroalkylating reagent is shown by concise conversion into various conventional fluoroalkylating reagents and construction of monofluoro-alkoxy, -alkylamino motifs with commercially available heteroatom-based coupling partners.

Recent ring distortion reactions for diversifying complex natural products

Covering: 2013-2022.Chemical diversification of natural products is an efficient way to generate natural product-like compounds for modern drug discovery programs. Utilizing ring-distortion reactions for diversifying natural products would directly alter the core ring systems of small molecules and lead to the production of structurally complex and diverse compounds for high-throughput screening. We review the ring distortion reactions recently used in complexity-to-diversity (CtD) and pseudo natural products (pseudo-NPs) strategies for diversifying complex natural products. The core ring structures of natural products are altered via ring expansion, ring cleavage, ring edge-fusion, ring spiro-fusion, ring rearrangement, and ring contraction. These reactions can rapidly provide natural product-like collections with properties suitable for a wide variety of biological and medicinal applications. The challenges and limitations of current ring distortion reactions are critically assessed, and avenues for future improvements of this rapidly expanding field are discussed. We also provide a toolbox for chemists for the application of ring distortion reactions to access natural product-like molecules.

Straightforward Synthesis of Alkyl Fluorides via Visible-Light-Induced Hydromono- and Difluoroalkylations of Alkenes with α-Fluoro Carboxylic Acids

We herein report the first visible-light-induced hydromono- and difluoroalkylations of alkenes with inexpensive and easily accessible α-fluoro carboxylic acids. This metal-free protocol exhibits mild conditions, high efficiency, and excellent functional-group tolerance, providing a straightforward approach to mono- and difluoroalkylated alkanes. Moreover, the fluorine effect on the hydrofluoroalkylation reaction is discussed in detail.

The synthetic versatility of fluoroiodomethane: recent applications as monofluoromethylation platform

In recent years, fluoroiodomethane (CH₂FI) has emerged as an easy-to-handle, non-ozone depleting agent and readily available platform for monofluoromethylation strategies. Recent applications in nucleophilic substitutions, lithiation reactions, transition-metal catalyzed transformations, radical processes, and ¹⁸F-radiolabelling chemistry showcase the potential of this reagent for the preparation of organofluorine compounds. In this minireview, we provide an update to the field covering the recent relevant literature on the use of CH₂FI.

Homogeneous Organic Electron Donors in Nickel-Catalyzed Reductive Transformations

Many contemporary organic transformations, such as Ni-catalyzed cross-electrophile coupling (XEC), require a reductant. Typically, heterogeneous reductants, such as Zn⁰ or Mn⁰, are used as the electron source in these reactions. Although heterogeneous reductants are highly practical for preparative-scale batch reactions, they can lead to complications in performing reactions on process scale and are not easily compatible with modern applications, such as flow chemistry. In principle, homogeneous organic reductants can address some of the challenges associated with heterogeneous reductants and also provide greater control of the reductant strength, which can lead to new reactivity. Nevertheless, homogeneous organic reductants have rarely been used in XEC. In this Perspective, we summarize recent progress in the use of homogeneous organic electron donors in Ni-catalyzed XEC and related reactions, discuss potential synthetic and mechanistic benefits, describe the limitations that inhibit their implementation, and outline challenges that need to be solved in order for homogeneous organic reductants to be widely utilized in synthetic chemistry. Although our focus is on XEC, our discussion of the strengths and weaknesses of different methods for introducing electrons is general to other reductive transformations.

Noble metal-free bis-tridentate benzimidazole zinc(II) and iron(II) complexes for selective CO2 photoreduction

Three noble metal-free metal complexes [Fe(Me-bzimpy)₂]²⁺ (Fe1), [Fe(bzimpy)₂]²⁺ (Fe2) and [Zn(Me-bzimpy)₂]²⁺ (Zn1) were synthesized and studied in the visible light-driven CO₂ reduction, where ligands bzimpy and Me-bzimpy were 2,6-bis(1-methyl-1H-benzo[d]imidazol-2-yl)pyridine and 2,6-bis(1H-benzo[d]imidazol-2-yl)pyridine, respectively. It was found that Fe1 displayed the best photocatalytic performance with a turnover number (TON) of 878 and high selectivity up to 99.2% towards CO generation in the presence of an organic thermally activated delayed fluorescence (TADF) photosensitizer, which was more than 10 times that of Fe2 (TON_CO = 63) and Zn1 (TON_CO = 53). This is attributed to the much higher stability of Fe1 upon reduction, as proved by the cyclic voltammograms of the three complexes. These results highlight the cooperation of ligands and metals in molecular metal complexes for CO₂ photoreduction.

Diversity-Oriented Synthesis of Fluoromethylated Arenes via Palladium-Catalyzed C-H Fluoromethylation of Aryl Iodides

Herein we report the first versatile and expeditious method for the site-selective C-H fluoromethylation of aryl iodides via Pd/norbornene cooperative catalysis, which could work as a robust toolbox for the diversity-oriented synthesis (DOS) of fluoromethylated arenes. This methodology features the use of the low-cost industrial raw material CH₂IF as the fluoromethyl source, an excellent functional group tolerance, and a broad ipso termination scope and can be expanded to the late-stage modification of biorelevant molecules.

Photoredox-Catalyzed Oxidative Radical-Polar Crossover Enables the Alkylfluorination of Olefins

The three-component alkylfluorination of olefins via an oxidative radical-polar crossover under visible light-induced photocatalysis is disclosed. A key feature of this reaction is the incorporation of two synthetically meaningful components involving a three-dimensional alkyl group and a fluorine atom using easily preparable N-hydroxyphthalimide esters as the alkyl donors and a low-cost hydrogen fluoride as the fluorine source. Furthermore, a one-step procedure using commercially available carboxylic acids demonstrated the versatility of this new method.

Selective Fluoromethyl Couplings of Alkynes via Nickel Catalysis*

We describe here a Ni-catalyzed intermolecular carbo-fluoromethylation of alkynes with aliphatic halides and fluoromethyl halides (BrCF 2 H and ICH 2 F) in the presence of zinc, enabling the facile and selective access to a diverse range of biologically valuable CF 2 H/CH 2 F-incorporated alkenes with excellent regio- and stereo-selectivity. Notably, merging intramolecular radical cyclization with fluoromethyl coupling enables the expedient constructions of CF 2 H/CH 2 F-incorporated lactones and lactams with high efficiency and selectivity. Mechanistic studies disclose that this catalytic protocol proceeds via a radical addition to an alkyne followed by selective coupling with the fluoromethyl unit.

Transition-Metal-Catalyzed Monofluoroalkylation: Strategies for the Synthesis of Alkyl Fluorides by C-C Bond Formation

Alkyl fluorides modulate the conformation, lipophilicity, metabolic stability, and p K a of compounds containing aliphatic motifs and, therefore, have been valuable for medicinal chemistry. Despite significant research in organofluorine chemistry, the synthesis of alkyl fluorides, especially chiral alkyl fluorides, remains a challenge. Most commonly, alkyl fluorides are prepared by the formation of C-F bonds (fluorination), and numerous strategies for nucleophilic, electrophilic, and radical fluorination have been reported in recent years. Although strategies to access alkyl fluorides by C-C bond formation (monofluoroalkylation) are inherently convergent and complexity-generating, they have studied less than methods based on fluorination. This Review provides an overview of recent developments in the synthesis of chiral (enantioenriched or racemic) secondary and tertiary alkyl fluorides by monofluoroalkylation catalyzed by transition-metal complexes. We expect this contribution will illuminate the potential of monofluoroalkylations to simplify the synthesis of complex alkyl fluorides and suggest further research directions in this growing field.

Fluorinated S-Adenosylmethionine as a Reagent for Enzyme-Catalyzed Fluoromethylation

Strategic replacement of protons with fluorine atoms or functional groups with fluorine-containing fragments has proven a powerful strategy to optimize the activity of therapeutic compounds. For this reason, the synthetic chemistry of organofluorides has been the subject of intense development and innovation for many years. By comparison, the literature on fluorine biocatalysis still makes for a slim chapter. Herein we introduce S-adenosylmethionine (SAM) dependent methyltransferases as a new tool for the production of fluorinated compounds. We demonstrate the ability of halide methyltransferases to form fluorinated SAM (S-adenosyl-S-(fluoromethyl)-L-homocysteine) from S-adenosylhomocysteine and fluoromethyliodide. Fluorinated SAM (F-SAM) is too unstable for isolation, but is accepted as a substrate by C-, N- and O-specific methyltransferases for enzyme-catalyzed fluoromethylation of small molecules.

Hydrofluoromethylation of alkenes with fluoroiodomethane and beyond

A process for the direct hydrofluoromethylation of alkenes is reported for the first time. This straighforward silyl radical-mediated reaction utilises CH₂FI as a non-ozone depleting reagent, traditionally used in electrophilic, nucleophilic and carbene-type chemistry, but not as a CH₂F radical source. By circumventing the challenges associated with the high reduction potential of CH₂FI being closer to CH₃I than CF₃I, and harnessing instead the favourable bond dissociation energy of the C–I bond, we demonstrate that feedstock electron-deficient alkenes are converted into products resulting from net hydrofluoromethylation with the intervention of (Me₃Si)₃SiH under blue LED activation. This deceptively simple yet powerful methodology was extended to a range of (halo)methyl radical precursors including ICH₂I, ICH₂Br, ICH₂Cl, and CHBr₂F, as well as CH₃I itself; this latter reagent therefore enables direct hydromethylation. This versatile chemistry was applied to ¹⁸F-, ¹³C-, and D-labelled reagents as well as complex biologically relevant alkenes, providing facile access to more than fifty products for applications in medicinal chemistry and positron emission tomography.

Herein, we report the direct hydro(halo)methylation of alkenes from a variety of (halo)methyl iodides (including F-18, C-13, D-2 isotopologues), enabling the incorporation of a plethora of C-1 fragments into complex biologically active molecules.

Nickel-catalyzed reductive monofluoroakylation of alkyl tosylate with bromofluoromethane to primary alkyl fluoride

A nickel-catalysed direct terminal monofluoromethlyation between alkyl tosylates and a low-cost, industrial raw material bromofluoromethane has been developed. This transformation has demonstrated high efficiency, mild conditions, and good functional-group compatibility. The key to success of this transformation lies in the ligand and mild base selection, ensuring the generation of various terminal monofluormethylation products.