N-Difluoromethylation of Imidazoles and Benzimidazoles Using the Ruppert–Prakash Reagent under Neutral Conditions

Rhodium-Catalyzed Synthesis of Trifluoromethyl-Containing Allylic Alcohols Via Z-Alkenyl Transfer with High Stereochemistry Retention

Herein, we report the rhodium-catalyzed Z-alkenyl transfer from tertiary allylic alcohols to aryl trifluoromethyl ketones, which provided an efficient way of preparation of trifluoromethyl-containing Z-allylic alcohols via β-Z-alkenyl elimination. The key Z-alkenyl-rhodium species were generated with a high degree of stereochemical retention. This reaction featured a broad substrate scope and good functional tolerance and would offer a fascinating approach for the synthesis of Z-alkenes.

Synthesis of α,α-Difluoromethylene Amines from Thioamides Using Silver Fluoride

We developed a mild, rapid process employing AgF and thioamides to produce α,α-difluoromethylene amines efficiently. This method exhibited remarkable tolerance toward various functional groups present in N-sulfonylthioamides, thereby broadening the scope of difluoromethylene sulfonamides through a straightforward approach. Additionally, we applied this approach to synthesize various perfluoroalkyl amines, establishing practical synthetic routes for exploring these compounds in pharmaceutical chemistry and materials science.

Difluorocarbene-Promoted O-O Bond Activation of Peroxy Acids for Electrophilic Carboxylation of Boronic Acids

In this study, a difluorocarbene-promoted O-O bond activation of peroxy acids is developed through the insertion of difluorocarbene into O-H bond. This activation strategy in synergy with O-B coordination with boronic acids/ester greatly polarizes the O-O bond for in-situ generation of carboxylium species that reacts with the nucleophilic part of boronic acids in a concerted way to produce carboxylic esters. Good efficiency and functional group tolerance are demonstrated. Application of this method to the functionalization of a boronic acid drug used as HSL enzyme inhibitor produces smoothly the ester derivative. This difluorocarbene-mediated O-O bond activation strategy is conceptually different from traditional radical type methods, and is also complementary to conventional esterification methods with a distinct retro-synthetic disconnection.

Making Full Use of TMSCF3: Deoxygenative Trifluoromethylation/Silylation of Amides

As one of the most powerful trifluoromethylation reagents, (trifluoromethyl)trimethylsilane (TMSCF3) has been widely used for the synthesis of fluorine-containing molecules. However, to the best of our knowledge, the simultaneous incorporation of both TMS- and CF3- groups of this reagent onto the same carbon of the products has not been realized. Herein, we report an unprecedented SmI2/Sm promoted deoxygenative difunctionalization of amides with TMSCF3, in which both silyl and trifluoromethyl groups are incorporated into the final product, yielding α-silyl-α-trifluoromethyl amines with high efficiency. Notably, the silyl group could be further transformed into other functional groups, providing a new method for the synthesis of α-quaternary α-CF3-amines.

Synthesis of N-Difluoromethyl Carbonyl Compounds from N-Difluoromethylcarbamoyl Fluorides

Fluorinated small molecules are commonly used in functional small-molecule chemistry, and N-difluoromethyl (N-CF2H) compounds are particularly intriguing due to their unique and unexplored physiochemical properties. However, despite limited progress, a general methodological approach to the synthesis of N-CF2H compounds remains elusive. Here, guided by computation, we present a simple and practical protocol to access N-CF2H amides and related carbonyl derivatives. The protocol involves a one-pot conversion of thioformamides through desulfurization-fluorination and acylation, providing N-difluoromethylcarbamoyl fluoride building blocks that can be further diversified to a variety of unexplored N-CF2H carbonyl compounds with rich functionality. Additionally, preliminary studies on their properties and stability showcased their potential application in pharmaceuticals and agrochemicals.

Cu-Catalyzed Carbocyclization for General Synthesis of N-Containing Heterocyclics Enabled by BrCF2COOEt as a C1 Source

A practical and efficient copper-catalyzed carbocyclization of 2-functionalized anilines with ethyl bromodifluoroacetate has been developed. Ethyl bromodifluoroacetate is employed as the C1 source via quadruple cleavage in this transformation. This reaction can afford a variety of N-containing heterocyclics with satisfactory yields and excellent functional group compatibility.

Access to N-Difluoromethyl Amides, (Thio)Carbamates, Ureas, and Formamides

The first efficient access to N-difluoromethyl amides, carbamates, thiocarbamates, ureas, formamides, and their derivatives is reported herein. The synthetic strategy relies on the initial synthesis and straightforward derivatization of N-CF2H carbamoyl fluorides, which were prepared through a desulfurization-fluorination of thioformamides (─NH─C(H)═S) coupled with carbonylation. The newly made N-CF2H carbonyl compounds proved to be highly robust and compatible with numerous chemical transformations and downstream derivatizations, underscoring the potential of this novel motif as a building block in complex functional molecules.

One-Carbon Ring Expansion of Indoles and Pyrroles: A Straightforward Access to 3-Fluorinated Quinolines and Pyridines

3-Fluorinated quinolines and pyridines are prevalent pharmacophores, yet their synthesis is often challenging. Herein, we demonstrate that dibromofluoromethane as bromofluorocarbene source enables the one-carbon ring expansion of readily available indoles and pyrroles to structurally diverse 3-fluorinated quinolines and pyridines. This straightforward protocol requires only a short reaction time of ten minutes and can be performed under air atmosphere. Preliminary investigations reveal that this strategy can also be applied to the synthesis of other valuable azines by using different 1,1-dibromoalkanes as bromocarbene sources.

Metal-Free C-H Difluoromethylation of Imidazoles with the Ruppert-Prakash Reagent

The reaction of trimethyl(trifluoromethyl)silane-tetrabutylammonium difluorotriphenylsilicate (CF₃SiMe₃-TBAT) with a series of imidazoles gives products of the formal difluorocarbene insertion into the C-H bond at the C-2 position (i.e., C-difluoromethylation). According to NMR spectra, the corresponding 2-(trimethylsilyl)difluoromethyl-substituted derivatives are likely formed as the intermediates in the reaction, and then, they slowly convert to 2-difluoromethyl-substituted imidazoles. Quantum chemical calculations of two plausible reaction mechanisms indicate that it proceeds through the intermediate imidazolide anion stabilized through the interaction with solvent molecules and counterions. In the first proposed mechanism, the anion reacts with difluorocarbene without an activation barrier, and then, the CF₂ moiety of the adduct attacks the CF₃SiMe₃ molecule. After the elimination of the CF₃ anion, 2-(trimethylsilyl)difluromethyl-substituted imidazole is formed. Another possible reaction pathway includes silylation of imidazolide anion at the N-3 atom, followed by the barrierless addition of difluorocarbene at the C-2 atom and then by 1,3-shift of the SiMe₃ group from N-3 to the carbon atom of the CF₂ moiety. Both proposed mechanisms do not include steps with high activation barriers.

Microwave-assisted Synthesis of Fluorinated Heterocycles

Abstract:

The diverse biological applications of fluorinated heterocycles make them crucial chemical compounds. Several synthetic processes have been developed for their synthesis. Microwave-assisted synthesis has emerged as an important technique for generating fluorinated heterocycles in an eco-friendly and energy-efficient manner. It provides several benefits like less reaction time, high reaction yield, homogeneous heat distribution leading to lower side reaction, and better control of reaction temperature. Recently there has been significant progress in microwave use for heterocycle synthesis. This article discusses the applications of microwave irradiation in the synthesis of oxygen- and nitrogen-containing fluorinated heterocycles.

N-Difluoromethylation of N-pyridyl-substituted anilines with ethyl bromodifluoroacetate

A general protocol for N-difluoromethylation of aniline derivatives is developed. Commercially available ethyl bromodifluoroacetate serves as a difluorocarbene source in the presence of a base. This carbene surrogate is attractive owing to its favorable stability, environmental friendliness and inexpensiveness. This reaction system features notable operational simplicity (bench top-grade solvents can be used without any pre-drying and do not require inert atmosphere protection). A wide range of functional groups in aniline derivatives are well-tolerated, and good-to-excellent product yields are generally obtained.

Chemoselective N- and O-Difluoromethylation of 2-Pyridones, Isoquinolinones, and Quinolinones with TMSCF2Br

An operationally simple protocol for direct N- and O-difluoromethylation of 2-pyridones, quinolinones, and isoquinolinones using commercially available TMSCF₂Br is disclosed. The chemoselectivity is modulated by simple variations in temperature, solvent, and strength of the base. Diverse, synthetically relevant functional groups are tolerated, including functional groups that have reported reactivity with TMSCF₂Br. Gram-scale reactions to prepare both N- and O-difluoromethyl compounds are included.

Metal-Free Difunctionalization of Pyridines: Selective Construction of N-CF2H and N-CHO Dihydropyridines

The reactivity of N-difluoromethylpyridinium salts is seldom explored because of their instability and low availability. Here we present a novel nucleophilic addition of N-difluoromethylpyridinium salts with nitroalkanes to synthesize N-CF₂H-dihydropyridines and N-CHO-dihydropyridines in a highly efficient and regioselective pathway. This protocol exhibits good functional group tolerance and good to excellent yields.

Late-stage difluoromethylation: concepts, developments and perspective

This review describes the conceptual advances that have led to the multiple difluoromethylation processes making use of well-defined CF₂H sources.

Synthesis of purines and adenines containing the hexafluoroisopropyl group

Several new derivatives of adenine, purine, and theophylline containing the (CF₃)₂CH group connected to a nitrogen atom of the imidazole ring were prepared by the reaction of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane (1) with the corresponding substrates, resulting in the selective alkylation of one of the nitrogen atoms of the imidazole ring. The reaction proceeds under mild conditions in a polar solvent, giving the alkylated products in 47–78% yield. While for purine and 4- and 5-azabenzimidazole, the reaction led to a mixture of two isomers, the reaction of adenine and the corresponding 2-fluoro derivative was regioselective, resulting in the formation of only one isomer in each case. The alkylation of theophylline led to the formation of a new derivative of caffeine.

Defluorosilylation of trifluoromethane: upgrading an environmentally damaging fluorocarbon

The rapid, room-temperature defluorosilylation of trifluoromethane, a highly potent greenhouse gas, has been achieved using a simple silyl lithium reagent. An extensive computational mechanistic analysis provides a viable reaction pathway and demonstrates the unexpected electrophilic nature of LiCF₃. The reaction generates a bench stable fluorinated building block that shows promise as an easy-to-use difluoromethylating agent. The difluoromethyl group is an increasingly important bioisostere in active pharmaceutical ingredients, and therefore our methodology creates value from waste. The potential scalability of the process has been demonstrated by achieving the reaction on a gram-scale.

Slicing and Splicing of Bromodifluoro-N-arylacetamides: Dearomatization and Difunctionalization of Pyridines

Copper-catalyzed dearomatization and difunctionalization of pyridines have been disclosed, in which bromodifluoro-N-arylacetamide was sliced into five fragments and three or four of them were transferred to pyridine partners. Through this reaction, novel N-difluoromethyl-2-imine dihydropyridine derivatives can be conveniently accessed from commercially available 4-amino substituted pyridines. This strategy demonstrates a novel fluorination method featuring high atom economy, environmental friendliness, an easily available catalyst, and simple operation.

Photocatalytic Difluoromethylation Reactions of Aromatic Compounds and Aliphatic Multiple C-C Bonds

Among the realm of visible light photocatalytic transformations, late-stage difluoromethylation reactions (introduction of difluoromethyl groups in the last stages of synthetic protocols) have played relevant roles as the CF2X group substitutions exert positive impacts on the physical properties of organic compounds including solubility, metabolic stability, and lipophilicity, which are tenets of considerable importance in pharmaceutical, agrochemical, and materials science. Visible-light-photocatalyzed difluoromethylation reactions are shown to be accomplished on (hetero)aromatic and carbon-carbon unsaturated aliphatic substrates under mild and environmentally benign conditions.

Insertion of Carbenes into Deprotonated nido-Undecaborane, B11H13(2-)

We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2- dianion to form the [closo-1-CB11H12]- anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient and scalable and proceeds with 70-90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14]- to [closo-1-CB11H12]-, and CCl2 and CBr2, which require more.

Transition-metal-free N-difluoromethylation of hydrazones with TMSCF2Br as the difluoromethylation reagent

A transition-metal-free N-difluoromethylation protocol is developed to synthesize a series of N-difluoromethyl hydrazones with TMSCF₂Br as the difluoromethylation reagent.

Difluorocarbene as a Building Block for Consecutive Bond-Forming Reactions

Compounds containing a difluoromethylene unit have gained increasing attention due to their utility in drug design. Classic methods for the synthesis of these compounds rely on either harsh deoxofluorination reactions or laborious functional group manipulation sequences. In 2013, we proposed a method for assembling gem-difluorinated molecules from a difluorocarbene, a nucleophile, and an electrophile. In this process, a difluorocarbene can be considered an equivalent of a bipolar CF₂ unit. Performing consecutive bond-forming reactions by sequential attachment of a nucleophile and an electrophile to a difluorocarbene provides the opportunity for the synthesis of a wide variety of organofluorine compounds. Silicon reagents were the most effective sources of the difluoromethylene fragment, and among them (bromodifluoromethyl)trimethylsilane (Me₃SiCF₂Br) is the reagent of choice. Mildly basic activators such HMPA, DMPU, bromide and acetate ions can initiate the decomposition of the silane with concomitant generation of a difluorocarbene. Organozinc reagents can be employed as nucleophiles, and the CF₂ fragment can insert into the carbon-zinc bond. Primary and secondary benzyl and alkyl organozinc compounds work well. Generally, organozinc reagents tolerate a variety of functional groups. The resulting fluorinated organozinc species can be coupled with heteroatom- or carbon-centered electrophiles. Halogenation of the carbon-zinc bond leads to compounds with bromo- or iododifluoromethyl fragments, which are difficult to access by other means, whereas protonation of that bond generates a valuable difluoromethyl group. Despite the decrease in the reactivity of the carbon-zinc bond caused by the adjacent fluorines, organozinc compounds can effectively participate in copper-catalyzed cross-couplings with allylic and propargyl halides, 1-bromoalkynes, and S-acyl dithiocarbamates. Difluorocarbene can be inserted into the carbon-silicon bond of trimethylsilyl cyanide, and the resulting silane can react with aldehydes and imines to furnish difluorinated nitriles. Interactions of difluorocarbene with heteroatom nucleophiles, such as phosphines or halide ions, are reversible, but the adduct can be trapped by an electrophile. The use of halide ions allows the direct nucleophilic bromo- and iododifluoromethylation of aldehydes and iminium ions. The combination of triphenylphosphine with difluorocarbene generates a difluorinated phosphorus ylide, which can interact with a wide range of π-electrophiles (aldehydes, ketones, acyl chlorides, azomethines, and Michael acceptors) to provide gem-difluorinated phosphonium salts. In the latter species, the carbon-phosphorus bond can be readily cleaved under basic conditions, affording the difluoromethylation products. Primary products resulting from three-component couplings can subsequently be used for further transformations. Single-electron reduction of carbon-phosphorus or carbon-iodine bonds can be conducted under photocatalytic conditions to generate gem-difluorinated radicals. These radicals can be trapped by silyl enol ethers leading to β,β-difluorinated ketones as the primary products. Fluorinated radicals can also undergo intramolecular attacks adjacent to an aromatic ring or a double bond.

An electrophilic reagent for the synthesis of OCHFMe-containing molecules

Herein the synthesis of a novel and bench stable electrophilic reagent to construct the OCFHMe motif from O-nucleophiles has been described. This sulfonium salt, readily obtained in 5 steps, reacted with various phenols and alcohols. The resulting products, including complex molecules, were obtained in good yields. This reagent was also used for the functionalization of thiol derivatives.

19F-NMR Diastereotopic Signals in Two N-CHF₂ Derivatives of (4S,7R)-7,8,8-Trimethyl-4,5,6,7-tetrahydro-4,7-methano-2H-indazole

In this paper, we report the anisochrony of the fluorine atoms of a CHF₂ group when linked to a pyrazole ring. The pyrazole is part of (4S,7R)-7,8,8-trimethyl-4,5,6,7-tetrahydro-4,7-methano-2H-indazole also known as (4S,7R)-campho[2,3-c]pyrazole, which has two stereogenic centers. Gauge-Independent Atomic Orbital (GIAO)/Becke, 3-parameter, Lee-Yang-Parr (B3LYP)/6-311++G(d,f) calculated 19F chemical shifts of the minimum energy conformations satisfactorily agree with the experimental data. The energy differences between minima need to consider solvent effects (continuum model) to be satisfactorily reproduced.

CF2H, a Hydrogen Bond Donor

The CF₂H group, a potential surrogate for the OH group, can act as an unusual hydrogen bond donor, as confirmed by crystallographic, spectroscopic, and computational methods. Here, we demonstrate the bioisosterism of the OH and CF₂H groups and the important roles of CF₂-H···O hydrogen bonds in influencing intermolecular interactions and conformational preferences. Experimental evidence, corroborated by theory, reveals the distinctive nature of CF₂H hydrogen bonding interactions relative to their normal OH hydrogen bonding counterparts.

Silver-mediated fluorination of alkyl iodides with TMSCF3 as the fluorinating agent

The first example of a silver-mediated fluorination of alkyl iodides with the Ruppert–Prakash reagent (TMSCF₃) as the fluorinating agent is reported.

Fluorescent probes for the selective detection of chemical species inside mitochondria

This feature article systematically summarizes the development of fluorescent probes for the selective detection of chemical species inside mitochondria.

Difluorocarbene-Derived Trifluoromethylthiolation and [(18)F]Trifluoromethylthiolation of Aliphatic Electrophiles

The first trifluoromethylthiolation and [(18)F]trifluoromethylthiolation of alkyl electrophiles with in situ generated difluorocarbene in the presence of elemental sulfur and external (radioactive) fluoride ion is described. This transition-metal-free approach is high yielding, compatible with a variety of functional groups, and operated under mild reaction conditions. The conceptual advantage of this exogenous-fluoride-mediated transformation enables unprecedented syntheses of [(18)F]CF3S-labeled molecules from most commonly used [(18)F]fluoride ions. The rapid radiochemical reaction time (≤1 min) and high functional-group tolerance allow access to a variety of aliphatic [(18)F]CF3S compounds in high yields.