Exploiting a "Beast" in Carbenoid Chemistry: Development of a Straightforward Direct Nucleophilic Fluoromethylation Strategy

Visible Light-Mediated Monofluoromethylation/Acylation of Olefins by Dual Organo-Catalysis

Monofluoromethyl (CH2F) motifs exhibit unique bioactivities and are considered privileged units in drug discovery. The radical monofluoromethylative difunctionalization of alkenes stands out as an appealing approach to access CH2F-containing compounds. However, this strategy remains largely underdeveloped, particularly under metal-free conditions. In this study, we report on visible light-mediated three-component monofluoromethylation/acylation of styrene derivatives employing NHC and organic photocatalyst dual catalysis. A diverse array of α-aryl-β-monofluoromethyl ketones was successfully synthesized with excellent functional group tolerance and selectivity. The mild and metal-free CH2F radical generation strategy from NaSO2CFH2 holds potential for further applications in fluoroalkyl radical chemistry.

Monofluoromethylation of N-Heterocyclic Compounds

The review focuses on recent advances in the methodologies for the formation or introduction of the CH2F moiety in N-heterocyclic substrates over the past 5 years. The monofluoromethyl group is one of the most versatile fluorinated groups used to modify the properties of molecules in synthetic medical chemistry. The review summarizes two strategies for the monofluoromethylation of N-containing heterocycles: direct monofluoromethylation with simple XCH2F sources (for example, ICH2F) and the assembly of N-heterocyclic structures from CH2F-containing substrates. The review describes the monofluoromethylation of pharmaceutically important three-, five- and six-membered N-heterocycles: pyrrolidines, pyrroles, indoles, imidazoles, triazoles, benzothiazoles, carbazoles, indazoles, pyrazoles, oxazoles, piperidines, morpholines, pyridines, quinolines and pyridazines. Assembling of 6-fluoromethylphenanthridine, 5-fluoromethyl-2-oxazolines, C5-monofluorinated isoxazoline N-oxides, and α-fluoromethyl-α-trifluoromethylaziridines is also shown. Fluoriodo-, fluorchloro- and fluorbromomethane, FCH2SO2Cl, monofluoromethyl(aryl)sulfoniummethylides, monofluoromethyl sulfides, (fluoromethyl)triphenylphosphonium iodide and 2-fluoroacetic acid are the main fluoromethylating reagents in recent works. The replacement of atoms and entire functional groups with a fluorine atom(s) leads to a change and often improvement in activity, chemical or biostability, and pharmacokinetic properties. The monofluoromethyl group is a bioisoster of -CH3, -CH2OH, -CH2NH2, -CH2CH3, -CH2NO2 and -CH2SH moieties. Bioisosteric replacement with the CH2F group is both an interesting task for organic synthesis and a pathway to modify drugs, agrochemicals and useful intermediates.

Base-mediated homologative rearrangement of nitrogen-oxygen bonds of N-methyl-N-oxyamides

Due to the well known reactivity of C(O)-N functionalities towards canonical C1-homologating agents (e.g. carbenoids, diazomethane, ylides), resulting in the extrusion of the N-centered fragment en route to carbonyl compounds, formal C1-insertions within N-O bonds still remain obscure. Herein, we document the homologative transformation of N-methyl-N-oxyamides - with high tolerance for diverse O-substituents - into N-acyl-N,O-acetals. Under controlled basic conditions, the N-methyl group of the same starting materials acts as a competent precursor of the methylene synthon required for the homologation. The logic is levered on the formation of an electrophilic iminium ion (via N-O heterolysis) susceptible to nucleophilic attack by the alkoxide previously expulsed. The procedure documents genuine chemocontrol and flexibility, as judged by the diversity of substituents placed on both amide and nitrogen linchpins. The mechanistic rationale was validated through experiments conducted on D-labeled materials which unambiguously attributed the origin of the methylene fragment to the N-methyl group of the starting compounds.

External Flash Generation of Carbenoids Enables Monodeuteration of Dihalomethanes

In this study, incorporation of one deuterium atom was achieved by H-D exchange of one of the two identical methylene protons in various dihalomethanes (halogen=Cl, Br, and I) through a rapid-mixing microflow reaction of lithium diisopropylamide as a strong base and deuterated methanol as a deuteration reagent. Generation of highly unstable carbenoid intermediate and suppression of its decomposition were successfully controlled under high flow-rate conditions. Monofunctionalization of diiodomethane afforded various building blocks composed of boryl, stannyl, and silyl groups. The monodeuterated diiodomethane, which served as a deuterated C1 source, was subsequently subjected to diverted functionalization methods to afford various products including biologically important molecules bearing isotope labelling at specific positions and homologation products with monodeuteration.

Ex-situ generation and synthetic utilization of bare trifluoromethyl anion in flow via rapid biphasic mixing

Fluoroform (CF₃H) is the simplest reagent for nucleophilic trifluoromethylation intermediated by trifluoromethyl anion (CF₃^-). However, it has been well-known that CF₃^- should be generated in presence of a stabilizer or reaction partner (in-situ method) due to its short lifetime, which results in the fundamental limitation on its synthetic utilization. We herein report a bare CF₃^- can be ex-situ generated and directly used for the synthesis of diverse trifluoromethylated compounds in a devised flow dissolver for rapid biphasic mixing of gaseous CF₃H and liquid reagents that was designed and structurally optimized by computational fluid dynamics (CFD). In flow, various substrates including multi-functional compounds were chemoselectively reacted with CF₃^-, extending to the multi-gram-scale synthesis of valuable compounds by 1-hour operation of the integrated flow system.

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.

Preparation and Functionalization of Mono- and Polyfluoroepoxides via Fluoroalkylation of Carbonyl Electrophiles

We outline a new synthetic method to prepare mono- and polyfluoroepoxides from a diverse pool of electrophiles (ketones, acyl chlorides, esters) and fluoroalkyl anion equivalents. The initially formed α-fluoro alkoxides undergo subsequent intramolecular ring closure when heated. We demonstrated the versatility of the method through the isolation of 16 mono- and polyfluoroepoxide products. These compounds provide unique entry points for further diversification via either fluoride migration coupled with ring opening, or defluorinative functionalization reactions, the latter of which can be used as a late-stage method to install select bioactive moieties. The reaction sequences described herein provide a pathway to functionalize the commonly observed products formed from 1,2-addition into carbonyl electrophiles.

Early Clinical Development of Lufotrelvir as a Potential Therapy for COVID-19

Lufotrelvir was designed as a first in class 3CL protease inhibitor to treat COVID-19. Development of lufotrelvir was challenged by its relatively poor stability due to its propensity to epimerize and degrade. Key elements of process development included improvement of the supply routes to the indole and lactam fragments, a Claisen addition to homologate the lactam, and a subsequent phosphorylation reaction to prepare the prodrug as well as identification of a DMSO solvated form of lufotrelvir to enable long-term storage. As a new approach to preparing the indole fragment, a Cu-catalyzed C-O coupling using oxalamide ligands was demonstrated. The control of process-related impurities was essential to accommodate the parenteral formulation. Isolation of an MEK solvate followed by the DMSO solvate ensured that all impurities were controlled appropriately.

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.

Iron-Catalyzed Fluoromethylene Transfer from a Sulfonium Reagent

Herein, we report the first example of an iron porphyrin catalyzed fluoromethylene transfer from (2,4-dimethylphenyl)(fluoromethyl)(phenyl)sulfonium tetrafluoroborate to unactivated alkenes. The fluorocarbene or fluoromethylene synthon is the smallest "organic" node in a molecular graph of the organofluorine compounds. In this work, we present alternative solution to unavailable fluorodiazomethane (CHFN₂), a missing one-carbon C1 piece in fluorine chemistry, by using a fluoromethylsulfonium reagent.

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.

Straightforward synthesis of bench-stable heteroatom-centered difluoromethylated entities via controlled nucleophilic transfer from activated TMSCHF2

The commercially available and experimentally convenient (bp 65 °C) difluoromethyltrimethylsilane (TMSCHF₂) is proposed as a valuable difluoromethylating transfer reagent for delivering the CHF₂ moiety to various heteroatom-based electrophiles. Upon activation with an alkoxide, a conceptually intuitive nucleophilic displacement directly furnishes in high yields the bench-stable analogues.

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.

29th Annual GP2A Medicinal Chemistry Conference

The 29th Annual GP₂A (Group for the Promotion of Pharmaceutical chemistry in Academia) Conference was a virtual event this year due to the COVID-19 pandemic and spanned three days from Wednesday 25 to Friday 27 August 2021. The meeting brought together an international delegation of researchers with interests in medicinal chemistry and interfacing disciplines. Abstracts of keynote lectures given by the 10 invited speakers, along with those of the 8 young researcher talks and the 50 flash presentation posters, are included in this report. Like previous editions, the conference was a real success, with high-level scientific discussions on cutting-edge advances in the fields of pharmaceutical chemistry.

Consecutive and Selective Double Methylene Insertion of Lithium Carbenoids to Isothiocyanates: A Direct Assembly of Four-Membered Sulfur-Containing Cycles

A formal CH₂−CH₂ homologation conducted with C1 carbenoids on a carbon electrophile for the obtainment of a four‐membered cycle is reported. The logic proposes the consecutive delivery of two single nucleophilic CH₂ units to an isothiocyanate—as competent electrophilic partner—resulting in the assembling of a rare imino‐thietane cluster. The single synthetic operation procedure documents genuine chemocontrol, as indicated by the tolerance to various reactive elements decorating the starting materials. Significantly, the double homologation protocol is accomplished directly on a carbon electrophile, thus not requiring the installation of heteroatom‐centered manifolds (e.g. boron).

Innovative Strategies for the Construction of Diverse 1'-Modified C-Nucleoside Derivatives

Modified C-nucleosides have proven to be enormously successful as chemical probes to understand fundamental biological processes and as small-molecule drugs for cancer and infectious diseases. Historically, the modification of the glycosyl unit has focused on the 2'-, 3'-, and 4'-positions as well as the ribofuranosyl ring oxygen. By contrast, the 1'-position has rarely been studied due to the labile nature of the anomeric position. However, the improved chemical stability of C-nucleosides allows the modification of the 1'-position with substituents not found in conventional N-nucleosides. Herein, we disclose new chemistry for the installation of diverse substituents at the 1'-position of C-nucleosides, including alkyl, alkenyl, difluoromethyl, and fluoromethyl substituents, using the 4-amino-7-(1'-hydroxy-d-ribofuranosyl)pyrrolo[2,1-f][1,2,4]triazine scaffold as a representative purine nucleoside mimetic.

Visible light-mediated radical fluoromethylation via halogen atom transfer activation of fluoroiodomethane

Incorporation of the fluoromethyl group can profoundly influence the physicochemical properties of organic molecules, offering a promising strategy for the discovery of novel pharmaceutical agents. Direct fluoromethylation of unfunctionalized C(sp2) centres can be achieved using fluoromethyl radicals, but current methods for their generation usually rely on the activation of non-commercial or expensive radical precursors via inefficient single electron transfer pathways, which limits their synthetic application. Here we report the development of a fluoromethylation strategy based on the generation of fluoromethyl radicals from commercially available fluoroiodomethane via halogen atom transfer. This mode of activation is orchestrated by visible light and tris(trimethylsilyl)silane, which serves as both a hydrogen- and halogen atom transfer reagent to facilitate the formation of C(sp3)-CH2F bonds via a radical chain process. The utility of this metal- and photocatalyst-free transformation is demonstrated through the multicomponent synthesis of complex α-fluoromethyl amines and amino acid derivatives via radical addition to in situ-formed iminium ions, and the construction of β-fluoromethyl esters and amides from electron-deficient alkene acceptors. These complex fluoromethylated products, many of which are inaccessible via previously reported methods, may serve as useful building blocks or fragments in synthetic and medicinal chemistry both in academia and industry.

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.

Borane-Catalyzed, Chemoselective Reduction and Hydrofunctionalization of Enones Enabled by B-O Transborylation

The use of stoichiometric organoborane reductants in organic synthesis is well established. Here these reagents have been rendered catalytic through an isodesmic B-O/B-H transborylation applied in the borane-catalyzed, chemoselective alkene reduction and formal hydrofunctionalization of enones. The reaction was found to proceed by a 1,4-hydroboration of the enone and B-O/B-H transborylation with HBpin, enabling catalyst turnover. Single-turnover and isotopic labeling experiments supported the proposed mechanism of catalysis with 1,4-hydroboration and B-O/B-H transborylation as key steps.

Direct and straightforward transfer of C1 functionalized synthons to phosphorous electrophiles for accessing gem-P-containing methanes

The direct transfer of different α-substituted methyllithium reagents to chlorinated phosphorous electrophiles of diverse oxidation state (phosphates, phosphine oxides and phosphines) is proposed as an effective strategy to synthesize geminal P-containing methanes. The methodology relies on the efficient nucleophilic substitution conducted on the P-chlorine linkage. Uniformly high yields are observed regardless the specific nature of the carbanion employed: once established the conditions for generating the competent nucleophile (LiCH₂Hal, LiCHHal₂, LiCH₂CN, LiCH₂SeR etc.) the homologated compounds are obtained via a single operation. Some P-containing formal carbanions have been evaluated in transferring processes, including the carbonyl-difluoromethylation of the opioid agent Hydrocodone.

Fluoromethyl-2,4,6-trinitrophenylsulfonate: A New Electrophilic Monofluoromethylating Reagent

Fluoromethyl-2,4,6-trinitrophenylsulfonate has been prepared for the first time and qualified as a simple to use monofluoromethylating reagent. Its molecular structure in the solid state has been determined by single-crystal X-ray diffraction studies. This reagent proves to be effective for the electrophilic introduction of a CH₂F group into selected chalcogen and nitrogen nucleophiles. Monofluoromethyl derivatives of various bifunctional N,O-nucleophiles have been synthesized using fluoromethyl-2,4,6-trinitrophenylsulfonate. Due to the good crystallizing properties of the anion, the fluoromethylated products as well as side products that are difficult to identify by nuclear magnetic resonance spectroscopy can readily be characterized by X-ray crystallographic techniques.

Taking advantage of lithium monohalocarbenoid intrinsic α-elimination in 2-MeTHF: controlled epoxide ring-opening en route to halohydrins

The intrinsic degradative α-elimination of Li carbenoids somehow complicates their use in synthesis as C1-synthons. Nevertheless, we herein report how boosting such an α-elimination is a straightforward strategy for accomplishing controlled ring-opening of epoxides to furnish the corresponding β-halohydrins. Crucial for the development of the method is the use of the eco-friendly solvent 2-MeTHF, which forces the degradation of the incipient monohalolithium, due to the very limited stabilizing effect of this solvent on the chemical integrity of the carbenoid. With this approach, high yields of the targeted compounds are consistently obtained under very high regiocontrol and, despite the basic nature of the reagents, no racemization of enantiopure materials is observed.

Optimized Monofluoromethylsulfonium Reagents for Fluoromethylene-Transfer Chemistry

An investigation of the properties and reactivity of fluoromethylsulfonium salts resulted in the redesign of the reagents for fluoromethylene transfer chemistry. The model reaction, fluorocyclopropanation of nitrostyrene, turned out to be a suitable platform for the discovery of more streamlined fluoromethylene transfer reagents. The incorporation of halides on one aryl ring increased the reactivity, and 2,4-dimethyl substitution on the other aryl ring provided a balance between the reactivity/crystallinity of the reagent as well as the atom economy. The utility of new reagents was demonstrated by the development of an efficient fluorocyclopropanation protocol to access a range of monofluorinated cyclopropane derivatives.

Design, synthesis and biological evaluation of Tozadenant analogues as adenosine A2A receptor ligands

With the aim to obtain potent adenosine A_2A receptor (A_2AR) ligands, a series of eighteen derivatives of 4-hydroxy-N-(4-methoxy-7-morpholin-4-yl-1,3-benzo[d]thiazol-2-yl)-4-methylpiperidine-1-carboxamide (SYN-115, Tozadenant) were designed and synthesized. The target compounds were obtained by a chemical building block principle that involved reaction of the appropriate aminobenzothiazole phenyl carbamates with either commercially available or readily synthesized functionalized piperidines. Their affinity and subtype selectivity with regard to human adenosine A₁-and A_2A receptors were determined using radioligand binding assays. K_i values for human A_2AR ranged from 2.4 to 38 nM, with more than 120-fold selectivity over A₁ receptors for all evaluated compounds except 13k which had a K_i of 361 nM and 18-fold selectivity. The most potent fluorine-containing derivatives 13e, 13g and 13l exhibited K_i values of 4.9 nM, 3.6 nM and 2.8 nM for the human A_2AR. Interestingly, the corresponding values for rat A_2AR were found to be four to five times higher. Their binding to A_2AR was further confirmed by radiolabeling with ¹⁸F and in vitro autoradiography in rat brain slices, which showed almost exclusive striatal binding and complete displacement by the A_2AR antagonist ZM 241385. We conclude that these compounds represent potential candidates for the visualization of the A_2A receptor and open pathways to novel therapeutic treatments of neurodegenerative disorders or cancer.

Pseudo-Dipeptide Bearing α,α-Difluoromethyl Ketone Moiety as Electrophilic Warhead with Activity against Coronaviruses

The synthesis of α-fluorinated methyl ketones has always been challenging. New methods based on the homologation chemistry via nucleophilic halocarbenoid transfer, carried out recently in our labs, allowed us to design and synthesize a target-directed dipeptidyl α,α-difluoromethyl ketone (DFMK) 8 as a potential antiviral agent with activity against human coronaviruses. The ability of the newly synthesized compound to inhibit viral replication was evaluated by a viral cytopathic effect (CPE)-based assay performed on MCR5 cells infected with one of the four human coronaviruses associated with respiratory distress, i.e., hCoV-229E, showing antiproliferative activity in the micromolar range (EC₅₀ = 12.9 ± 1.22 µM), with a very low cytotoxicity profile (CC₅₀ = 170 ± 3.79 µM, 307 ± 11.63 µM, and 174 ± 7.6 µM for A549, human embryonic lung fibroblasts (HELFs), and MRC5 cells, respectively). Docking and molecular dynamics simulations studies indicated that 8 efficaciously binds to the intended target hCoV-229E main protease (M^pro). Moreover, due to the high similarity between hCoV-229E M^pro and SARS-CoV-2 M^pro, we also performed the in silico analysis towards the second target, which showed results comparable to those obtained for hCoV-229E M^pro and promising in terms of energy of binding and docking pose.

Synthesis of Weinreb amides using diboronic acid anhydride-catalyzed dehydrative amidation of carboxylic acids

The first successful example of the direct synthesis of Weinreb amides using catalytic hydroxy-directed dehydrative amidation of carboxylic acids using the diboronic acid anhydride catalyst is described. The methodology is applicable to the concise syntheses of eight α-hydroxyketone natural products, namely, sattabacin, 4-hydroxy sattabacin, kurasoins A and B, soraphinols A and B, and circumcins B and C.

A Synthetic Approach to Dimetalated Arenes Using Flow Microreactors and the Switchable Application to Chemoselective Cross-Coupling Reactions

In spite of their potential utility, the chemistry of dimetalated arenes is still in its infancy because they are extremely difficult to synthesize. We report a novel method of synthesizing arenes bearing a boryl group and a metallic substituent, such as boryl, silyl, stannyl, or zincyl groups, in an integrated flow microreactor based on the generation and reactions of aryllithiums bearing a trialkyl borate moiety. The bimetallic arenes showed a remarkable chemoselectivity in palladium-catalyzed cross-coupling reactions. The selectivity was switched by the selection of the metal species that constitutes the dimetalated arenes as well as appropriate catalysts.

Chemoselective Homologation-Deoxygenation Strategy Enabling the Direct Conversion of Carbonyls into (n+1)-Halomethyl-Alkanes

The sequential installation of a carbenoid and a hydride into a carbonyl, furnishing halomethyl alkyl derivatives, is reported. Despite the employment of carbenoids as nucleophiles in reactions with carbon-centered electrophiles, sp³-type alkyl halides remain elusive materials for selective one-carbon homologations. Our tactic levers on using carbonyls as starting materials and enables uniformly high yields and chemocontrol. The tactic is flexible and is not limited to carbenoids. Also, diverse carbanion-like species can act as nucleophiles, thus making it of general applicability.

Carbenoid-Mediated Homologation Tactics for Assembling (Fluorinated) Epoxides and Aziridines

Homologation strategies provide highly versatile tools in organic synthesis for the introduction of a CH2 group into a given carbon skeleton. The operation can result in diverse structural motifs by tuning of the reaction conditions and the nature of the homologating agent. In this Account, concisely contextualizing our work with lithium carbenoids (LiCH2X, LiCHXY etc) for homologating carbon-centered electrophiles, we focus on the assembly of three-membered cycles featuring fluorinated substituents. Two illustrative case studies are considered: (1) the development and employment of fluorinated carbenoids en route to rare α-fluoroepoxides and aziridines, and (2) the installation of up to halomethylenic groups on trifluoroimidoylacetyl chlorides (TFAICs) for preparing CF3-containing halo- and halomethylaziridines. Collectively, we demonstrate that the initial homologation event generated by the installation of the carbenoid, upon modulation of the conditions, serves as a tool for creating fluorinated building blocks in a single operation.

Reagents for Selective Fluoromethylation: A Challenge in Organofluorine Chemistry

The introduction of a monofluoromethyl moiety has undoubtedly become a very important area of research in recent years. Owing to the beneficial properties of organofluorine compounds, such as their metabolic stability, the incorporation of the CH2 F group as a bioisosteric substitute for various functional groups is an attractive strategy for the discovery of new pharmaceuticals. Furthermore, the monofluoromethyl unit is also widely used in agrochemistry, in pharmaceutical chemistry, and in fine chemicals. The problems associated with climate change and the growing need for environmentally friendly industrial processes mean that alternatives to the frequently used CFC and HFBC fluoromethylating agents (CH2 FCl and CH2 FBr) are urgently needed and also required by the Montreal Protocol. This has recently prompted many researchers to develop alternative fluoromethylation agents. This Minireview summarizes both the classical and new generation of fluoromethylating agents. Reagents that act via electrophilic, nucleophilic, and radical pathways are discussed, in addition to their precursors.

Flow Microreactor Technology for Taming Highly Reactive Chloroiodomethyllithium Carbenoid: Direct and Chemoselective Synthesis of α-Chloroaldehydes

A straightforward flow synthesis of α-chloro aldehydes has been developed. The strategy involves, for the first time, the thermal unstable chloroiodomethyllithium carbenoid and carbonyl compounds. A batch versus flow comparative study showcases the superb capability of flow technology in prolonging the lifetime of the lithiated carbenoid, even at -20 °C. Remarkably, the high chemoselectivity realized in flow allowed for preparing polyfunctionalized α-chloro aldehydes not easily accessible with traditional batch procedures.