Mechanochemical Conversion of Aromatic Amines to Aryl Trifluoromethyl Ethers

Nitrogen-Based Organofluorine Functional Molecules: Synthesis and Applications

Fluorine and nitrogen form a successful partnership in organic synthesis, medicinal chemistry, and material sciences. Although fluorine-nitrogen chemistry has a long and rich history, this field has received increasing interest and made remarkable progress over the past two decades, driven by recent advancements in transition metal and organocatalysis and photochemistry. This review, emphasizing contributions from 2015 to 2023, aims to update the state of the art of the synthesis and applications of nitrogen-based organofluorine functional molecules in organic synthesis and medicinal chemistry. In dedicated sections, we first focus on fluorine-containing reagents organized according to the type of fluorine-containing groups attached to nitrogen, including N-F, N-RF, N-SRF, and N-ORF. This review also covers nitrogen-linked fluorine-containing building blocks, catalysts, pharmaceuticals, and agrochemicals, underlining these components' broad applicability and growing importance in modern chemistry.

Ru-Catalyzed Deoxygenative Functionalization of Phenols via π-Coordination Activation: Mechanochemical Access to N-Aryl Amides and α-Aryl Carbonyls

Given the vast occurrence and availability of both primary amides and phenols, the synthesis of N-aryl amides via direct coupling between these starting materials would be much attractive. Herein, we report an efficient method for the mechanochemical synthesis of N-aryl amides via ruthenium-catalyzed direct amidation of unprotected phenols with primary amides with water as the sole byproduct. Unexpectedly, replacing amides with methyl carboxylic acids, esters, or ketones, the same reaction led to the formation of α-aryl carbonyl derivatives instead of the anticipated aryl carboxylates. The synthetic strategy accepts a wide scope of primary amides, alkyl carbonyls, and phenolic substrates to deliver 28 expected N-aryl amides and 14 unexpected α-aryl carbonyl derivatives with good to excellent yields. The developed synthetic approach would serve as the better alternative to the classical cross-coupling reactions in context to the PASE (pot, atom, and step economy) synthesis and late-stage modification of structurally complex molecules, including natural products and pharmaceuticals.

Advances in Mechanochemical Methods for One-Pot Multistep Organic Synthesis

Mechanochemical synthesis has emerged as a powerful and more sustainable alternative to conventional solution-based methods, offering advantages such as no or only minimal solvent use, reduced reaction times, and simplified operational conditions. The integration of multiple steps into a single reaction vessel further enhances these benefits by eliminating workup and purification steps, reducing waste, and often improving overall efficiency. This review highlights recent advancements in mechanochemical one-pot multistep reactions in organic synthesis, focusing on protocols with sequential one-pot operation. Diverse transformations are covered, including heterocycle formation, functional group interconversions, and the synthesis of active pharmaceutical ingredients, while discussing both the operational and environmental advantages of these methodologies, along with their remaining challenges. Overall, mechanochemical one-pot synthesis has the potential to streamline transformations and therefore contribute to more sustainable approaches in modern organic synthetic chemistry.

Mechanochemically Enabled Formal Reductive Cross-Coupling Reaction Between Aryl Ethers and Aryl Fluorides

Reductive cross-coupling reactions involving two electrophilic reagents have become increasingly important in modern synthetic chemistry. Previous studies have investigated electrophilic reagents featuring zero or one inactive bond; however, reactions involving electrophilic reagents with two inactive bonds remain unexplored. This study presents the first nickel-catalyzed reductive cross-coupling reaction under mechanical conditions, involving aryl ethers and aryl fluorides, both of which contain inactive bonds. The reaction successfully synthesized a series of multifunctional biphenyl compounds, specifically including several sparingly soluble substrates that are challenging to prepare in a solvent system. Mechanistic studies have demonstrated that nickel and magnesium play a crucial role in the activation of C─F bonds. This novel coupling reaction offers a beneficial approach for polymer degradation and the development of luminescent materials.

Mechanochemical Sequential Deoxygenative Cross-Coupling Reactions of Phenols Under Ruthenium-Nickel Catalysis

Herein, we report the first mechanochemical strategy for the Ru-catalyzed deoxygenative borylation of free phenols via C-O bond cleavage. This Ru-catalyzed phenolic borylation approach has been successfully extended to the Suzuki-Miyaura-type cross-coupling of phenols with aryl bromides. The protocol accepts a wide scope of phenolic substrates, allowing the synthesis of aryl pinacolboranes and biphenyl structures in excellent yields and serving as a better alternative to classical cross-coupling reactions in the context of pot, atom, and step economy synthesis.

Ruthenium Catalyzed Mechanochemical Transformation of Sulfonamide Group to Fluoro, Trifluoromethyl, and Trifluoromethoxy Functionalities

A convenient route for the mechanochemical synthesis of fluorinated aromatic compounds, that is, fluoro, trifluoromethyl, and trifluoromethoxy arenes, has been developed via pyrylium tetrafluoroborate (Pyry-BF4)-mediated desulfonamidative cross-coupling of primary sulfonamides under the synergy of a piezoelectric material BaTiO3, and Ru-catalysis. This is the first-ever report on the selective transformation of sulfonamide (SO2NH2) functionality to CF3/OCF3/F group in a single step under mechanochemical ball-milling conditions. Considering the importance of primary sulfonamides as the valuable pharmacophores, the present desulfonamidative cross-coupling approach could have potential to get synthetic utility in pharmaceutical industries for the late-stage functionalization of sulfonamide drugs and related active pharmaceutical ingredients (APIs).

Elemental Germanium Activation and Catalysis Enabled by Mechanical Force

In the realm of materials science and chemical industry, germanium emerges as a strategic resource with distinctive properties that extend its applicability beyond traditional electronics and optics into the promising field of chemical catalysis. Despite its significant role in advanced technological applications, the potential of elemental germanium as a catalyst remains unexplored. Leveraging recent developments in mechanochemistry, this study introduces a groundbreaking approach to activate elemental germanium via mechanical force, facilitating the Reformatsky reaction without the reliance on external reducing agents. Meanwhile, we have also demonstrated, for the first time, the catalytic activity of elemental germanium, successfully achieving this through the bromoalkylation of alkenes. These achievements mark a significant advancement in the field of catalysis and open up a new promising avenue for both academic research and industrial applications.

Rhodium-Catalyzed Trifluoromethoxylation of Allenylic Trichloroacetimidates

The first rhodium-catalyzed trifluoromethoxylation of allenylic trichloroacetimidates has been reported. The products were obtained through a procedure using trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxy source with a yield up to 76% by identifying the ligand of diene. The reaction proceeds under mild reaction conditions with excellent functional group tolerance and complete regiocontrol.

Ru-catalyzed activation of free phenols in a one-step Suzuki-Miyaura cross-coupling under mechanochemical conditions

Activation of phenols by a Ru-catalyst allows for the resulting η5-phenoxo complex to selectively react with a variety of nucleophiles under mechanochemical conditions. Conversion of phenolic hydroxy groups without derivatization is important for late-stage modifications of pharmaceuticals and in the context of lignin-material processing. We present a one-step, Ru-catalyzed cross-coupling of phenols with boronic acids, aryl trialkoxysilanes and potassium benzoyltrifluoroborates under mechano-chemical conditions. The protocol accepts a wide scope of starting materials and allows for gram-scale synthesis in excellent yields. The developed approach constitutes a very interesting and waste-limiting alternative to the known methods.

Mechanochemical synthesis of aromatic ketones: pyrylium tetrafluoroborate mediated deaminative arylation of amides

A new method has been introduced that is able to tackle the complexities of N-C(O) activation in amide moieties through utilization of pyrylium tetrafluoroborate in a mechanochemical setting, where amide bonds undergo activation and subsequent conversion to biaryl ketones. Due to the employment of a mechanochemical setting, the reaction conforms to green chemistry principles, offering an environmentally friendly approach to traditional amide derivatization techniques that rely on transition metals to achieve further functionalization.

Indium Promotes Direct Sulfonamidation of Unactivated Alcohols

An improved protocol has been developed for the direct sulfonamidation of unactivated alkyl alcohols using In(OTf)3 as a Lewis acid catalyst. Although the established methods using Lewis or Brønsted acids have been well-studied for the direct functionalization of alcohols, their substrate scope mainly focuses on the π-activated alcohols. In this reaction, unactivated aliphatic alcohols were evaluated and afforded the desired sulfonamide products with good to excellent yields.

Unexpected side reactions dominate the oxidative transformation of aromatic amines in the Co(II)/peracetic acid system

Aromatic amines (AAs), ubiquitous in industrial applications, pose significant environmental hazards due to their resistance to conventional wastewater treatments. Peracetic acid (PAA)-based advanced oxidation processes (AOPs) have been proposed as effective strategies for addressing persistent AA contaminants. While the organic radicals generated in these systems are believed to be selective and highly oxidative, acetate residue complicates the evaluation of AA removal efficiency. In this work, we explored transformation pathways of AAs in a representative Co(II)-catalyzed PAA system, revealing five side reactions (i.e. nitrosation, nitration, coupling, dimerization, and acetylation) that yield 17 predominantly stable and toxic by-products. The dominant reactive species was demonstrated as Co-OOC(O)CH3, which hardly facilitated ring-opening reactions. Our findings highlight the potential risks associated with PAA-based AOPs for AA degradation and provide insights into selecting suitable catalytic systems aimed at efficient and by-product-free degradation of pollutants containing aromatic -NH2.

Skeletal rearrangement through photocatalytic denitrogenation: access to C-3 aminoquinolin-2(1H)-ones

The addition of an amine group to a heteroaromatic system is a challenging synthetic process, yet it is an essential one in the development of many bioactive molecules. Here, we report an alternative method for the synthesis of 3-amino quinolin-2(1H)-one that overcomes the limitations of traditional methods by editing the molecular skeleton via a cascade C-N bond formation and denitrogenation process. We used TMSN3 as an aminating agent and a wide variety of 3-ylideneoxindoles as synthetic precursors for the quinolin-2(1H)-one backbone, which demonstrates remarkable tolerance of sensitive functional groups. The control experiments showed that the triazoline intermediate plays a significant role in the formation of the product. The spectroscopic investigation further defined the potential reaction pathways.

Mechanochemical arylative detrifluoromethylation of trifluoromethylarenes

The stoichiometric defluorinative functionalization of ArCF3 is a conceptually appealing research target. It enables the challenging late-stage functionalization of CF3-containing aromatic molecules and contributes to the remedy of environmental risks resulting from the accumulation of relatively inert ArCF3-containing molecules. Similarly, Ar-CN bond features limit their utilization in cross-coupling reactions. Thus, the employment of benzonitriles in decyanative Suzuki-Miyaura type coupling remains in high demand in the field of C-C bond formation. Herein, we report mechanochemically induced and ytterbium oxide (Yb2O3)-mediated defluorinative cyanation of trifluoromethylarenes. In addition, we describe a facile mechanochemically facilitated and nickel-catalyzed decyanative arylation of benzonitriles to access biphenyls. Combining both processes in a one-pot multicomponent protocol to achieve a concise direct arylative detrifluoromethylation of ArCF3 is described herein. This work is the first hitherto realization of C-C coupling with CF3 as a formal leaving group.

Synthesis and Biological Evaluation of a Library of Sulfonamide Analogs of Memantine to Target Glioblastoma

A library of 34 lipophilic sulfonamides based upon the memantine core has been synthesized to identify potential drug candidates to cross the blood-brain barrier and target glioblastoma. The library was screened for in vitro activity against 4 mammalian cell lines, including U-87 (glioblastoma). Additional synthetic variation of the active compounds has validated the importance of specific regions of the pharmacophore, with the sulfonamide functionality and S-aryl unit displaying the most significant impact. In silico investigations suggest the active compounds might target DDR1 or RET proteins. The investigation has resulted in several compounds that warrant further development for lead optimization.

Bio-Inspired Deaminative Hydroxylation of Aminoheterocycles and Electron-Deficient Anilines

Among the tools available to chemists for drug design of bioactive compounds, the bioisosteric replacement of atoms or groups of atoms is the cornerstone of modern strategies. Despite the undeniable interest in amino-to-hydroxyl interchange, enzymatic deaminative hydroxylation remains unmatched. Herein, we report a user friendly and safe procedure to selectively convert aminoheterocycles to their hydroxylated analogues by means of a simple pyrylium tetrafluoroborate salt. The hydroxylation step relies on a Lossen-type rearrangement under mild conditions thus avoiding the use of strong hydroxide bases. In addition to biorelevant heterocycles, the deaminative hydroxylation of electron-deficient anilines was also demonstrated. Finally, mechanistic experiments allowed the identification of the key intermediates, thus unveiling a rather unusual mechanism for this formal aromatic substitution.

Mechanochemical Defluorinative Arylation of Trifluoroacetamides: An Entry to Aromatic Amides

The amide bond is prominent in natural and synthetic organic molecules endowed with activity in various fields. Among a wide array of amide synthetic methods, substitution on a pre-existing (O)C-N moiety is an underexplored strategy for the synthesis of amides. In this work, we disclose a new protocol for the defluorinative arylation of aliphatic and aromatic trifluoroacetamides yielding aromatic amides. The mechanochemically induced reaction of either arylboronic acids, trimethoxyphenylsilanes, diaryliodonium salts, or dimethyl(phenyl)sulfonium salts with trifluoroacetamides affords substituted aromatic amides in good to excellent yields. These nickel-catalyzed reactions are enabled by C-CF₃ bond activation using Dy₂O₃ as an additive. The current protocol provides versatile and scalable routes for accessing a wide variety of substituted aromatic amides. Moreover, the protocol described in this work overcomes the drawbacks and limitations in the previously reported methods.