Hexafluoroisopropanol as a highly versatile solvent

Annulative Editing of Peptide Side Chains: N-Pyridination of Lysine via Chichibabin Pyridine Synthesis in Hexafluoroisopropanol

Modifying the lysine side chain through N-heteroaryl annulation offers a unique opportunity to tailor or edit the structure and properties of the parent peptides. Here, we report two new applications of the Chichibabin pyridine synthesis for lysine-specific peptide modification under mild conditions, employing two distinct classes of aldehyde reagents. Reactions with 2-arylacetaldehydes afforded symmetrical 3,5-diarylpyridinium products via an abnormal Chichibabin pathway, whereas reactions with 2-hydroxyacetaldehyde yielded unsymmetrical 3-hydroxy-4-hydroxylmethylpyridiniums (HHMP) products through an unusual, redox-neutral process. The use of a hexafluoroisopropanol (HFIP) solvent was crucial for the reactivity and selectivity in both reactions. Notably, these Lys-specific N-pyridination strategies demonstrated a rare tolerance toward highly nucleophilic cysteine residues.

Reductive alkylation of azoarenes to N-alkylated hydrazines enabled by hexafluoroisopropanol

A one-pot tandem approach to N-alkyl-N,N'-diarylhydrazines was developed using a sequence of reduction of azoarene to hydrazoarene followed by reductive alkylation by an aldehyde. The mild reaction conditions suppress N-N cleaved products and selectively provide trisubstituted hydrazine derivatives. The mechanistic study demonstrates that the iminium formation step is likely to be the rate-limiting step.

Electrophilic (Hetero)Arene C-H Nitration by Ferric Nitrate Nonahydrate in Hexafluoroisopropanol

In this article, we provide an extended substrate scope and more detailed mechanistic studies of an operationally simple and generally applicable arene nitration that we previously reported. This method utilizes safe and inexpensive Fe(NO3)3•9H2O as the nitro source in easily recyclable HFIP and obviates the need for corrosive acids (HNO3 + H2SO4). As a result, we speculated that it could serve as an effective substitute for the traditional mixed acid approach under most scenarios due to its operational simplicity. A general guidance for the application of this method was provided.

HFIP-Promoted Regioselective Hydrofunctionalization of Enamides and N-Vinyl Azoles

An efficient and regioselective method for the intermolecular hydrofunctionalization of enamides and N-vinyl azoles has been developed, enabling the formation of diverse C-S, C-O, C-N, and C-C bonds. This transition-metal-free, additive-free, and Brønsted acid-free protocol employs hexafluoroisopropanol (HFIP) as the sole reagent, which plays a dual role: formation of iminium carbocation intermediate and facilitating nucleophile generation through its hydrogen-bonding network. The reaction demonstrates exceptional substrate versatility, accommodating thiophenols, alcohols, heterocyclic amines, as well as NH-free indoles, pyrroles, and carbazoles as nucleophiles, proceeding via a Markovnikov-selective hydrofunctionalization pathway. The protocol is general and simple with broad substrate compatibility.

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.

Diluted alkaline pretreatment in hexafluoroisopropanol facilitates chemoenzymatic depolymerization of polyethylene terephthalate

Enzymatic PET degradation presents a sustainable and eco-friendly solution for recycling and upgrading PET materials. While various PET-degrading enzymes have proven effective in converting low-crystallinity PET into monomers, their efficiency decreases significantly for high-crystallinity PET. Given that most commercially available PET products are highly crystalline and have a limited specific surface area, conventional methods typically resort to heat treatment and ball milling to achieve decrystallization and micronization before enzymatic hydrolysis. However, these pretreatments often compromise environmental benefits due to their high energy consumption and dust pollution, and are difficult to scale up. In this study, we developed a chemoenzymatic strategy that efficiently depolymerizes waste PET materials into monomers in just 4 h. This process involves an alkaline treatment with diluted NaOH in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), followed by enzymatic hydrolysis of the PET nanosuspensions generated from solvent exchange. The alkaline treatment partially breaks down the PET molecular chains and mitigates recrystallization during the precipitation process. Importantly, the complete hydrolysis of PET is attributed to reduced crystallinity rather than particle size. Notably, this method eliminates the need for PET micronization and minimizes the usage of NaOH. The effectiveness of this method was demonstrated through the hydrolysis of various commercially available PET products, showcasing its potential to advance enzymatic degradation processes for PET recycling.

Rapid and Additive-Free Synthesis of β-Sulfido Sulfonyl Fluorides through N-Methyl-2-pyrrolidinone (NMP)-Promoted Thia-Michael Addition

β-Sulfido sulfonyl fluorides, incorporating a clickable sulfonyl fluoride and a thioether motif, are valuable intermediates in chemical biology, materials science, and drug discovery. Herein, we developed a rapid and additive-free synthesis of these compounds via N-methyl-2-pyrrolidinone (NMP)-promoted thia-Michael addition of thiols to ethene sulfonyl fluoride (ESF). The reaction proceeds smoothly under neutral conditions without the need for a base or catalyst, achieving high efficiency within 20 min. This method demonstrates a broad substrate scope, tolerating thiophenols, alkylthiols, thioglycosides, and cysteine-containing peptides. The resulting β-sulfido sulfonyl fluorides enable diverse transformations, such as sulfur(VI) fluoride exchange (SuFEx) reaction and thioether oxidation, facilitating applications in drug conjugates and materials, such as additives for lithium-ion battery electrolyte components.

Simultaneous Activation of Bicyclobutanes and Indolyl Alcohols with HFIP: Access to Indole-Fused Bicyclo[3.1.1]Heptanes

The concept of strain release to unleash unique reactivity that drives a wide range of synthetically valuable transformations has long intrigued chemists. Among the various strained systems, highly reactive bicyclo[1.1.0]butanes (BCBs) have recently emerged as versatile building blocks for constructing bicyclic scaffolds. Despite the existence of various activation pathways for BCBs, the use of 1,1,1,3,3,3-hexafluoroisopropan-2-ol (HFIP) to activate BCBs has not been realized so far. Herein, we report the first HFIP-promoted (3 + 3) annulation of BCBs with indolyl alcohols through the simultaneous activation of both partners, facilitating the metal- and photocatalyst-free synthesis of indole-fused bicyclo[3.1.1]heptanes. Mechanistic studies reveal the role of HFIP in activating both components, and the reaction proceeds by an initial (3 + 2) annulation followed by a ring expansion/aromatization cascade.

Hexafluoroisopropanol Solvent Effects on Enantioselectivity of Dirhodium Tetracarboxylate-Catalyzed Cyclopropanation

In recent years, additives that modulate both reactivity and selectivity in rhodium-catalyzed reactions of aryldiazoacetates have become increasingly prominent. 1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) has been shown to have a profound effect on rhodium carbene reactivity and selectivity, especially on enabling carbene cyclopropanation in the presence of various nucleophilic poisons. HFIP also has a variable influence on the enantioselectivity of the reactions catalyzed by chiral dirhodium tetracarboxylates, and this study examines the fundamental properties of the rhodium carbene/HFIP system through experimentation, density functional theory (DFT), and molecular dynamics (MD) simulations. These studies revealed that the C4-symmetric bowl-shaped catalysts, which have been previously considered to be relatively rigid, experience far greater flexibility in this hydrogen bonding media, resulting in distortion of the bowl-shaped catalysts. These studies explain why even though a majority of the catalysts have a drop in enantioselectivity in HFIP, some catalysts, such as Rh2(TCPTAD)4, lead to a switch in enantioselectivity, whereas others, such as Rh2(NTTL)4, lead to a considerably enhanced enantioselectivity.

Chiral Spirobipyridine Synthesis by Cobalt-Catalyzed Enantioselective Double [2 + 2 + 2] Cycloaddition

Chiral spirobiindanes are recognized as the privileged structures in the field of asymmetric catalysis. However, the structurally similar chiral spirobipyridines have not yet been explored as chiral ligands or organocatalysts due to the absence of efficient synthetic methods. Herein, we report a cobalt-catalyzed enantioselective synthesis of spirobipyridines via double [2 + 2 + 2] cycloaddition reaction. Spirobipyridines with ortho- or meta-substituents could be obtained with exclusive regioselectivity and up to 99% ee in the presence of cobalt and bisoxazolinephosphine ligands. Spirobipyridines coordinate with transition metals as chiral ligands. Spirobipyridine dioxides can be applied as chiral organocatalysts in the asymmetric allylation of aldehydes.

α-N-phthalimido-oxy isobutyrate-mediated deoxygenative arylation: total synthesis of alanenses A and B

Inspired by a biosynthetic hypothesis of alanense A, we developed two distinct methods for the deoxygenative arylation of α-N-phthalimido-oxy isobutyrate (NPIB), derived from hydroxyl groups adjacent to or conjugated with a carbonyl moiety. One approach utilizes photoredox catalysis to achieve a radical-mediated arylation reaction. The other approach involves an acid-mediated arylation method that proceeds through a cationic intermediate. The acid-mediated approach was successfully applied to the total syntheses of alanenses A, B, and O7'-methyllacinilene E.

Evaluation of Aliphatic Alcohols for CO2 Capture Using the Characteristic Carbonate Frequency

Control over CO2 capture and utilization are important scientific and technological challenges. Although a variety of amine absorbents are used for capture, releasing the captured CO2 is often difficult and limits their recyclability. Therefore, it is crucial to control the strength of the CO2 bond with the absorbent. Furthermore, it is desirable to use a method that can conveniently report the strength of this bond. This motivates exploring adducts of CO2 with alcohols in the presence of a base, using vibrational spectroscopy to report on the bond strength. Although reactions of alcohols with CO2 to form alkyl carbonates are known, a systematic study of these adducts has not been conducted. Here we show formation of alkyl carbonates by a series of alcohols spanning the pKa range 9.5 to 16.8. We show experimental and computational results for the frequency of the characteristic asymmetric stretch of the carbonate and demonstrate that it correlates inversely with the pKa of the alcohol. Based on computations of the bond lengths and previous work, we propose that this frequency also correlates inversely with the adduct strength. This work extends the scope of CO2 capture reagents and inspires further research in tuning alcohols as reversible absorbents.

Syntheses of Unsymmetric (Sulfoxylidene)ureas from NH-Sulfoximines and Dioxazolones Assisted by 2,2,2-Trifluoroethanol

Ureas and sulfoximines are relevant as natural products and pharmaceuticals. The fusion of these two frameworks results in (sulfoxylidene)ureas. Herein, we present a convenient method to access such compounds from NH-sulfoximines and dioxazolones. The reactions are assisted by 2,2,2-trifluoroethanol (TFE), yielding the desired products in moderate to good yields under mild reaction conditions. The process, which involves a Curtius rearrangement, is characterized by its simplicity and the absence of any additional activator rendering it appealing for applications in medicinal chemistry.

Rotational and vibrational spectroscopy of a weakly bound hexafluoroisopropanol⋯dinitrogen complex: 14N hyperfine splittings, molecular geometry, and experimental benchmarks

The rotational spectrum of a weakly bound binary complex of hexafluoroisopropanol (HFIP) with molecular nitrogen was measured using chirped-pulse and cavity-based Fourier transform microwave spectrometers. In addition, its infrared spectrum was measured in the OH stretching region. An extensive conformational search identified multiple binding sites on HFIP, with the global minimum structure featuring a trans-HFIP conformation and nitrogen weakly bound at the acidic proton (HtNH). Good agreement between the experimentally determined rotational constants and the relative intensity patterns of a-, b-, and c-type transitions with theoretical predictions conclusively identified the HtNH conformer. This assignment is further corroborated by an analysis of the 14N nuclear quadrupole hyperfine structure. The non-equivalence of the two 14N nuclei in HtNH is confirmed through a detailed molecular symmetry group analysis, as well as the 14N nuclear quadrupole hyperfine analysis. Examination of the experimental nuclear quadrupole coupling constants offers additional insights into the orientation and large-amplitude vibrational motions of the N2 subunit. Furthermore, the experimentally derived rotational constants and the OH stretching band position of the complex, compared with previously known values for the isolated monomer, serve as complementary benchmarks for evaluating the systematic quality of predictions from electronic structure calculations across several levels of theory. This combined examination of vibrational energy levels and structural parameters aids in distinguishing fortuitously accurate predictions of individual properties.

Unlocking Hexafluoroisopropanol as a Practical Anion-Binding Catalyst for Living Cationic Polymerization

Living cationic polymerization (LCP) is a classical technique for precision polymer synthesis; however, due to the high sensitivity of cationic active species towards chain-transfer/termination events, it is notoriously difficult to control polymerization under mild conditions, which inhibits its progress in advanced materials engineering. Here, we unlock a practical anion-binding catalytic strategy to address the historical dilemma in LCP. Our experimental and mechanistic studies demonstrate that commercially accessible hexafluoroisopropanol (HFIP), when used in high loading, can create higher-order HFIP aggregates to tame dormant-active species equilibrium via non-covalent anion-binding principle, in turn inducing distinctive polymerization kinetics behaviors that grant efficient chain propagation while minimizing competitive side reactions. This unique control mechanism delivers unprecedented polymerization activity and controllability across various electron-rich vinyl monomers under mild conditions, and provides easy access to high molecular weight polymers, block copolymers, and end-functionalized telechelic polymers. Also, the minimalistic structure of HFIP coupled with its convenient removal and recycle renders this approach easy to scale up, without concern for cost, sustainability and complicated work-up processes associated with previous systems. This study presents another universal and sustainable strategy for cationic macromolecular engineering, and will also stimulate further exploration of innovative non-covalent catalysis that enables more challenging living polymerization systems.

HFIP-Promoted Friedel-Crafts Allenylation of Imidazopyridines with Propargyl Alcohols at Room Temperature

Herein, we report an efficient synthetic protocol for the Friedel-Crafts reaction of imidazo[1,2-a]pyridines with propargyl alcohols in HFIP. Notably, this FC allenylation works without any additional solvent or catalyst and requires neither inert conditions nor heating. In this method, HFIP, besides offering hydrogen bonding with propargyl alcohol, also stabilizes the resultant carbocation, thus forming the product. This method also enables the straightforward synthesis of 1,3-enynes. The current method offers a large substrate diversity with good to excellent yields. We also demonstrated gram-scale synthesis and synthetic modifications.

One-Pot NIS-Promoted Cyclization/Palladium-Catalyzed Carbonylation for the Selective Synthesis of HFIP Ester-Containing Indenes and Thiochromenes

Practical and atom-economic procedures for the selective synthesis of HFIP ester-containing indenes/thiochromenes from the same propargylic thioethers and HFIP have been developed via one-pot NIS-promoted cyclization/palladium-catalyzed carbonylation. Solvent plays an important role in this transformation, and the reactions proceed selectively and efficiently to afford a variety of HFIP ester-containing indenes and thiochromenes in moderate to excellent yields. In addition, the use of formic acid as the CO source could avoid manipulation of toxic CO gas.

Thioether-Functionalized Cellulose for the Fabrication of Oxidation-Responsive Biomaterial Coatings and Films

Biomaterial coatings and films can prevent premature failure and enhance the performance of chronically implanted medical devices. However, current hydrophilic polymer coatings and films have significant drawbacks, including swelling and delamination. To address these issues, hydroxyethyl cellulose is modified with thioether groups to generate an oxidation-responsive polymer, HECMTP. HECMTP readily dissolves in green solvents and can be fabricated as coatings or films with tunable thicknesses. HECMTP coatings effectively scavenge hydrogen peroxide, resulting in the conversion of thioether groups to sulfoxide groups on the polymer chain. Oxidation-driven, hydrophobic-to-hydrophilic transitions that are isolated to the surface of HECMTP coatings under physiologically relevant conditions increase wettability, decrease stiffness, and reduce protein adsorption to generate a non-fouling interface with minimal coating delamination or swelling. HECMTP can be used in diverse optical applications and permits oxidation-responsive, controlled drug release. HECMTP films are non-resorbable in vivo and evoke minimal foreign body responses. These results highlight the versatility of HECMTP and support its incorporation into chronically implanted medical devices.

HFIP-Promoted Aromatic Electrophilic Amidation of Indoles and Pyrroles with Isocyanates

A mild and practical method for synthesizing amidoindoles and amidopyrroles was described via the direct amidation of indoles or pyrroles with isocyanates promoted by 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). In this reaction, HFIP acted as a strong hydrogen bond-donating solvent to activate isocyanates, enabling the amidation of electron-rich nitrogen-containing heterocycles.

Quantifying hexafluoroisopropanol's hydrogen bond donor ability: infrared photodissociation spectroscopy of halide anion HFIP complexes

We report on the gas phase vibrational spectroscopy (3500-950 cm-1) of halide anion complexes with 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and its partially deuterated analogue (HFIP-d 1). Infrared photodissociation spectra of messenger-tagged X-(HFIP/HFIP-d 1), with X- = Cl-, Br-, and I-, together with electronic structure calculations reveal O-H(D) stretching fundamentals that are red-shifted twice as much as those for the corresponding complexes with isopropanol and water, directly reflecting HFIP's enhanced hydrogen-bond donor ability. The harmonic analysis of the bands in the fingerprint region reveals that HFIP assumes a synperiplanar conformation in the complexes. The consideration of anharmonic effects is necessary to recover the efficient coupling between stretching and bending modes in the OH stretching region. An energy decomposition analysis shows that the roughly twice as large binding energy in the HFIP complexes vs. i-PrOH and water is determined mainly by differences in the electrostatic attraction. The observed red-shifts, which reflect the extent of charge transfer along the coordinate of the proton transfer reaction X- + HM → XH + M-, correlate qualitatively with the difference in the proton affinities ΔPA = PA(X-) - PA(M-). A more quantitative agreement requires also considering differences in the hydrogen bond angle.

Total synthesis of breviscapin B via intramolecular dehydrative etherification

The total synthesis of breviscapin B, a norlignan natural product having an unusual 2,2-diaryltetrahydrofuran skeleton, has been achieved via intramolecular dehydrative Williamson ether synthesis as a key step. The use of a combination of p-TsOH·H2O and polyfluorinated alcohol was found as an effective method for the synthesis of 2-aryl-substituted saturated oxygen heterocycles.

Hydrogen-Bonding Network-Enabled Terminal Selective Heteroarylation of Allenamides in Hexafluoroisopropanol

Hexafluoroisopropanol (HFIP)-mediated terminal selective heteroarylation of allenamides has been accomplished through H-bonding network-enabled substrate activation in a robust fashion. This strategy features a cascade process involving sequential nucleophilic addition followed by electrophilic heteroaromatic substitution and is well suited for late-stage functionalization of complex bioactive molecules. The elucidation of the underlying mechanism was achieved through a comprehensive combination of several control experiments, kinetic studies, isotopic labeling experiments, and the isolation of the HFIP-allenamide intermediate adduct.

Bro̷nsted Acid-Catalyzed Reduction of Furans

Bioderived furans play a pivotal role in advancing defossilized chemical pathways. The complete reduction of furans currently relies on impractical metal-catalyzed hydrogenations at high pressures and temperatures. In addition, the Birch reduction of unbiased furans to 2,5-dihydrofurans remains an unsolved synthetic challenge. Herein, we report a mild Bro̷nsted acid-catalyzed reduction of furans to 2,5-dihydro- and/or tetrahydrofuran derivatives using silanes as reducing agents. In particular, the first formal Birch reduction of furan itself is achieved. Mechanistic investigations reveal an intricate behavior of HFIP as the crucial solvent, preventing the intrinsic polymerization behavior of furans under acidic conditions and introducing additional driving force by specific product binding.

Nitrene-mediated glycosylation with thioglycoside donors under metal catalysis

Glycosylation chemistry plays a pivotal role in glycoscience. Recent substantial developments have poised the field to address emerging challenges related to sustainability, cost efficiency, and robust applicability in complex substrate settings. The transition from stoichiometric activation to metal-catalyzed methods promises enhanced chemoselectivity and greater precision in controlling glycosidic bond breakage and formation, key to overcoming existing obstacles. Here, we report a nitrene-mediated glycosylation strategy using regular aryl sulfide glycosyl donors and easily accessible 3-methyl dioxazolone as an activator under the catalysis of iron or ruthenium. The iron-catalyzed system demonstrates exceptional catalytic reactivity, requiring as little as 0.1 mole % of catalyst at room temperature, and works well for complex peptide substrates. The ruthenium-catalyzed system can accommodate acid-sensitive functional groups and challenging low-reactivity acceptors. Mechanistic investigations have unveiled unusual multistep pathways involving sulfur imidation of sulfide donors via nitrene transfer and sulfur-to-oxygen rearrangement of N-acyl sulfilimines for the nitrene-mediated activation of sulfide donors.

Access to N-α-deuterated amino acids and DNA conjugates via Ca(II)-HFIP-mediated reductive deutero-amination of α-oxo-carbonyl compounds

The development of practical and selective strategies for deuterium incorporation to construct deuterated molecules, particularly deuterium-labeled amino acids, has become as a growing focus of basic research, yet it remains a formidable challenge. Herein, we present a bioinspired calcium-HFIP-mediated site-selective reductive deutero-amination of α-oxo-carbonyl compounds with amines. Utilizing d2-Hantzsch ester as the deuterium source, this reaction attains remarkable deuteration efficiency (> 99% deuteration). It enables the synthesis of N-α-deuterated amino acid motifs with a wide range of functionality, as evidenced by over 130 examples. The method exhibits compatibility with diverse substrates, such as amino acids, peptides, drug molecules, and natural products bearing different substituents. Moreover, the application of this strategy in the synthesis of DNA-tagged N-α-deuterated amino acids/peptides has been demonstrated. This work offers an efficient and innovative solution for deuterated amino acid chemistry and holds substantial application potential in organic synthesis, medicinal chemistry, and chemical biology.

HFIP-mediated cascade aminomethylation and intramolecular cyclization of allenamides with N,O-acetals to access tetrahydro-β-carboline derivatives

The construction of complex molecules under metal-free conditions via multiple bond-forming steps in a cascade manner is highly desirable. Herein, we have developed an HFIP-alone promoted aminomethylation and intramolecular cyclization of allenamides, providing biologically relevant tetrahydro-β-carboline derivatives embedded with an allylic amine functionality. The metal-free protocol provided the desired tetrahydro-β-carboline derivatives under mild conditions. The potential of the protocol is further highlighted by the gram-scale reaction and synthesizing derivatives of biologically important molecules.

Hexafluorophosphate-Triggered Hydrogen Isotope Exchange (HIE) in Fluorinated Environments: A Platform for the Deuteration of Aromatic Compounds via Strong Bond Activation

There is a perpetual need for efficient and mild methods to integrate deuterium atoms into carbon frameworks through late-stage modifications. We have developed a simple and highly effective synthetic route for hydrogen isotope exchange (HIE) in aromatic compounds under ambient conditions. This method utilizes catalytic amounts of hexafluorophosphate (PF6 -) in deuterated 1,1,1,3,3,3-hexafluoroisopropanol (HFIP-d1) and D2O. Phenols, anilines, anisoles, and heterocyclic compounds were converted with high yields and excellent deuterium incorporations, which allows for the synthesis of a wide range of deuterated aromatic compounds. Spectroscopic and theoretical studies show that an interactive H-bonding network triggered by HFIP-d1 activates the typically inert P-F bond in PF6 - for D2O addition. The thus in situ formed DPO2F2 then triggers HIE, offering a new way to deuterated building blocks, drugs, and natural-product derivatives with high deuterium incorporation via the activation of strong bonds.

Triflic Acid-Catalyzed Dehydrative Amination of 2-Arylethanols with Weak N-Nucleophiles in Hexafluoroisopropanol

The catalytic deoxyamination of readily available 2-arylethanols offers an appealing, simple, and straightforward means of accessing β-(hetero)arylethylamines of biological interest. Yet, it currently represents a great challenge to synthetic chemistry. In most cases, the alcohol has to be either pre-activated in situ or converted into a reactive carbonyl intermediate, limiting the substrate scope for some methods. Examples of direct dehydrative amination of 2-arylethanols are thus still scarce. Here, we describe a catalytic protocol based on the synergy of triflic acid and hexafluoroisopropanol, which enables the direct and stereospecific amination of a broad array of 2-arylethanols, and does not require any pre-activation of the alcohol. This approach yields high value-added products incorporating sulfonamide, amide, urea, and aniline functionalities. In addition, this approach was applied to the sulfidation of 2-arylethanols. Mechanistic experiments and DFT computations indicate the formation of phenonium ions as key intermediates in the reaction.

Photoinduced Regiodivergent and Enantioselective Cross-Coupling of Glycine Derivatives with Hydrocarbon Feedstocks

Regiodivergent asymmetric synthesis represents a transformative strategy for the efficient generation of structurally diverse chiral products from a single set of starting materials, significantly enriching their enantiomeric composition. However, the design of radical-mediated regiodivergent and enantioselective reactions that can accommodate a wide range of functional groups and substrates has posed significant challenges. The obstacles primarily lie in switching the regioselectivity and achieving high enantiodiscrimination, especially when dealing with high-energy intermediates. To address these issues, we have developed a new catalytic system that integrates photoinduced hydrogen atom transfer (HAT) and chiral copper catalysis, involving the fine-tuning of chiral ligands, additives, and other reaction parameters. The strategy facilitates regiodivergent and enantioselective cross-couplings between N-aryl glycine ester/amide derivatives and abundant hydrocarbon feedstocks through strong C(sp3)-H bond activation. This approach allows for the controlled and stereoselective formation of C(sp3)-C(sp3) and C(sp3)-N bonds, yielding a rich variety of C- or N-alkylated glycine esters and amides with commendable yields (up to 92% yield), exclusive regioselectivities (typically >20:1 rr), and high enantioselectivities (up to 96% ee). Our methodology not only provides a promising avenue for the stereoselective incorporation of alkyl functionalities onto specific sites of biologically significant molecules but also offers a practical approach for regioselectivity switching while simultaneously achieving high asymmetric induction within photochemical reactions.

Control of Nanoparticle Size of Intrinsically Fluorescent PET (Polyethylene Terephthalate) Particles Produced Through Nanoprecipitation

Plastics are widely produced due to their stability and ease of manufacturing, but many of them quickly become a waste, breaking down into microplastics and nanoplastics. While methods for the identification and characterization of plastic particles are well consolidated, the small size of nanoplastics presents challenges for their detection and analysis. Furthermore, due to the difficulty of identifying nanoplastics, analytical studies concerning their effect on cells and a comprehensive spectroscopic characterization are still lacking. In this paper, we overcome this obstacle by synthesizing and characterizing, for the first time, PET nanoparticles with specific, stable dimensions through a top-down approach. Using hexafluoroisopropanol-chloroform as a solvent, we prepared PET solutions at various concentrations and analyzed their spectral properties over time. Our results show that PET aggregates into nanoparticles, the quantity of which increases with concentration. These findings provide crucial insights for the detection of nanoplastics in environmental samples through fluorescence measurements and can potentially be used to produce stable PET nanoparticles to evaluate their cytotoxicity.

Bioinspired Synthesis of Phelligridin Analogues via Ru-Catalyzed C-H Activation/[4 + 2] Annulation of Aryl Imidates with Heteroaromatic Iodonium Ylides

The first Ru(II)-catalyzed C-H activation/[4 + 2] annulation of aryl imidates with heteroaromatic iodonium ylides is reported. Our approach features the utilization of a commercially available ruthenium catalyst, providing a one-step construction of phelligridin analogues from easily available and nonpreactivated starting materials. The developed methodology is successfully employed for the total synthesis of phelligridin A, significantly streamlining previous multistep synthesis. The potential of this approach is further demonstrated through a modular synthesis of the core structure of phelligridin C/D.

Multicomponent reactions (MCRs) yielding medicinally relevant rings: a recent update and chemical space analysis of the scaffolds

In this review we have compiled multicomponent reactions (MCRs) that produce cyclic structures. We have covered articles reported since 2019 to showcase the recent advances in this area. In contrast to other available reviews on this topic, we focus specifically on MCRs with strong prospects in medicinal chemistry. Consequently, the reactions operating in a single-pot and yielding novel rings or new substitution patterns under mild conditions are highlighted. Moreover, MCRs that do not require special reagents or catalysts and yield diverse products from commercially available building blocks are reviewed. The synthetic schemes, substrate scope, and other key aspects such as regio- and stereoselectivity are discussed for each MCR. Using cheminformatic tools, we have also attempted to characterize the chemical space of the scaffolds obtained from these MCRs. We show that the MCR scaffolds are novel, more complex, and globular in shape compared to the approved drugs and clinical candidates. Thus, our review represents a step towards identifying and characterizing the novel ring space that can be accessed efficiently through MCRs in a short timeframe.

Enantioselective Synthesis of Chiral β2-Amino Phosphorus Derivatives via Nickel-Catalyzed Asymmetric Hydrogenation

Compared with chiral β3-amino phosphorus compounds, which can be easily derived from natural optically pure α-amino acids, obtaining chiral β2-amino phosphorus derivatives remains a challenge. These derivatives, which cannot be derived from chiral natural amino acids, possess unique biological activities or potential catalytic activities. Herein, highly enantioselective hydrogenation for the preparation of chiral β2-amino phosphorus derivatives from E-β-enamido phosphorus compounds is reported by using a green and low-cost earth-abundant metal nickel catalyst (13 examples of 99% ee). In particular, this catalytic system provides the same enantiomer product from the E- and Z-alkene substrates, and the E/Z-substrate mixtures provide good results (up to 96% ee). The products can be diversely derivatized, and the derivatives exhibit good catalytic activities as novel chiral β2-aminophosphine ligands. Density functional theory calculations reveal that the weak attractive interactions between the nickel catalyst and the substrate are crucial for achieving perfect enantioselectivities. In addition, the different coordination modes between the E- or Z-substrates and the catalyst may result in the formation of the same enantiomer product.

Hot shape transformation: the role of PSar dehydration in stomatocyte morphogenesis

Polysarcosine emerges as a promising alternative to polyethylene glycol (PEG) in biomedical applications, boasting advantages in biocompatibility and degradability. While the self-assembly behavior of block copolymers containing polysarcosine-containing polymers has been reported, their potential for shape transformation remains largely untapped, limiting their versatility across various applications. In this study, we present a comprehensive methodology for synthesizing, self-assembling, and transforming polysarcosine-poly(benzyl glutamate) block copolymers, resulting in the formation of bowl-shaped vesicles, disks, and stomatocytes. Under ambient conditions, the shape transformation is restricted to bowl-shaped vesicles due to the membrane's flexibility and permeability. However, dehydration of the polysarcosine broadens the possibilities for shape transformation. These novel structures exhibit asymmetry and possess the capability to encapsulate smaller structures, thereby broadening their potential applications in drug delivery and nanotechnology. Our findings shed light on the unique capabilities of polysarcosine-based polymers, paving the way for further exploration and harnessing of their distinctive properties in biomedical research.

Fast Collective Hydrogen-Bond Dynamics in Hexafluoroisopropanol Related to its Chemical Activity

Using fluorinated mono-alcohols, in particular hexafluoro-isopropanol (HFIP), as a solvent can enhance chemical reaction rates in a spectacular manner. Previous work has shown evidence that this enhancement is related to the hydrogen-bond structure of these liquids. Here, we investigate the hydrogen-bond dynamics of HFIP and compare it to that of its non-fluorinated analog, isopropanol. Ultrafast infrared spectroscopy experiments show that the dynamics of individual hydrogen-bonds is about twice as slow in HFIP as in isopropanol. Surprisingly, from dielectric spectroscopy we find the opposite behavior for the dynamics of hydrogen-bonded clusters: collective rearrangements are 3 times faster in HFIP than in isopropanol. This difference indicates that the hydrogen-bonded clusters in HFIP are smaller than in isopropanol. The differences in cluster size can be traced to changes in the hydrogen-bond donor and acceptor strengths upon fluorination. The smaller cluster size can boost reaction rates in HFIP by increasing the concentration of reactive, terminal OH-groups of the clusters, whereas the fast collective dynamics can increase the rate of formation of hydrogen-bonds with the reactants. The longer lifetime of the individual hydrogen-bonds in HFIP can enhance the stability of the hydrogen-bonded clusters, and so increase the probability of reactant-solvent hydrogen-bonding.

Influence of Solvent Dielectric Constant on the Complex Coacervation Phase Behavior of Polymerized Ionic Liquids

Complex coacervation is an associative phase separation process of oppositely charged polyelectrolyte solutions, resulting in a coacervate phase enriched with charged polymers and a polymer-lean phase. To date, studies on the phase behavior of complex coacervation have been largely restricted to aqueous systems with relatively high dielectric constants due to the limited solubility of most polyelectrolytes, hindering the exploration of the effects of electrostatic interactions from differences in solvent permittivity. Herein, we prepare two symmetric but oppositely charged polymerized ionic liquids (PILs), consisting of poly[1-[2-acryloyloxyethyl]-3-butylimidazolium bis(trifluoromethane)sulfonimide] (PAT) and poly[1-ethyl-3-methylimidazolium 3-[[[(trifluoromethyl)sulfonyl]amino]sulfonyl]propyl acrylate] (PEA). Due to the delocalized ionic charges and their chemical structure similarity, both PAT and PEA are soluble in various organic solvents with a wide range of dielectric constants, ranging from 16.7 (hexafluoro-2-propanol (HFIP)) to 66.1 (propylene carbonate (PC)). Notably, no significant correlation is observed between the solvent dielectric constant and the phase diagram of the complex coacervation of PILs. Most organic solvents lead to similar phase diagrams and salt resistances regardless of their dielectric constants, except two protic solvents (HFIP and 2,2,2-trifluoroethanol (TFE)) showing significantly low salt resistances compared to the others. The low salt resistance in these protic solvents primarily arises from strong hydrogen bonding between PILs and solvents as evidenced by 1H NMR and small-angle neutron scattering (SANS) experiments. Our finding suggests that for the coacervation of PILs, particularly those with delocalized and weak charge interactions, entropy from the counterion release and polymer-solvent interaction χ parameter play a more important role than the electrostatic interactions of charged molecules, rendered by the dielectric constant of the solvent medium.

Remote Alkynylation of Aliphatic Amines

Advancements in transition metal catalyzed C-H activation/functionalization cascades have allowed the synthetic chemist's toolbox to be significantly expanded. Despite this, protocols for the remote alkynylation of linear aliphatic amines still remain limited. Herein, a palladium-catalyzed directing-group approach to alkynylation of aliphatic amines is disclosed. The synthetic utility was demonstrated with a gram-scale reaction and a functional group compatibility test.

Gold-catalyzed hydrofluorination of terminal alkynes using potassium bifluoride (KHF2)

A gold-catalyzed hydrofluorination of terminal alkynes is reported. The salient features of this study showcase the use of potassium bifluoride, KHF2, as the fluorinating agent in conjunction with a fluorinated solvent, hexafluoroisopropanol. The reaction is mediated by a well-defined precursor, [Au(IPr)(OH)] with an acid activator. A wide range of functionalized terminal alkynes can be converted to the corresponding monofluoroalkenes in up to 97% yield.

Acid-Solvent Cluster-Promoted General and Regioselective Friedel-Crafts Acylation with Carboxylic Acids

Carboxylic acids are considered to be the most ideal acylating reagents for Friedel-Crafts acylation. However, the low electrophilicity of carboxylic acids and the ability of their byproduct water to deactivate Lewis and Brønsted acids greatly limit their application in this reaction. In this work, we developed a general and regioselective Friedel-Crafts acylation with carboxylic acids, wherein unactivated/activated arenes and various aromatic and aliphatic carboxylic acids were viable starting materials. Key to this accomplishment is the use of trifluoromethanesulfonic acid-hexafluoroisopropanol clusters.

Base-Promoted Coupling of HFIP in Cu-Catalyzed Asymmetric Ring Opening of Cyclic Diaryliodoniums

We report a Cu-catalyzed asymmetric ring-opening reaction of cyclic diaryliodoniums with 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), enabling the construction of axially chiral biaryl compounds containing HFIP ether. HFIP is highly polar and exceptionally stable; thus, it is commonly used as a solvent due to its poor nucleophilicity. However, its use as a nucleophilic reagent has been rare. In this study, we successfully employed HFIP as a nucleophilic coupling partner in a Cu-catalyzed asymmetric ring-opening experiment of cyclic diaryliodoniums.

Enantioselective synthesis of inherently chiral sulfur-containing calix[4]arenes via chiral sulfide catalyzed desymmetrizing aromatic sulfenylation

Inherently chiral calixarenes hold great potential for applications in chiral recognition, sensing, and asymmetric catalysis due to their unique structures. However, due to their special structures and relatively large sizes, the catalytic asymmetric synthesis of inherently chiral calixarenes is challenging with very limited examples available. Here, we present an efficient method for the enantioselective synthesis of inherently chiral sulfur-containing calix[4]arenes through the desymmetrizing electrophilic sulfenylation of calix[4]arenes. This catalytic asymmetric reaction is enabled by a chiral 1,1'-binaphthyl-2,2'-diamine-derived sulfide catalyst and hexafluoroisopropanol. Various inherently chiral sulfur-containing calix[4]arenes are obtained in moderate to excellent yields with high enantioselectivities. Control experiments indicate that the thermodynamically favored C-SAr product is formed from the kinetically favored N-SAr product and the combination of the chiral sulfide catalyst and hexafluoroisopropanol is crucially important for both enantioselectivity and reactivity.

Correspondence on "Organo-Mediator Enabled Electrochemical Deuteration of Styrenes"

The recently reported electrochemical, organo-mediator enabled deuteration of styrenes, a reaction referred to as "electrochemical deuterium atom transfer", differs mechanistically from reported direct electrochemical hydrogenations/deuterations only by a mediated, homogeneous SET to the substrates. By comparing direct vs. mediated processes in general and for styrene reduction, we display that Qiu's work does not change the concept of this chemistry. Experiments with mediators and the direct reduction of examples from the reported scope show that even electron-rich substrates can be reduced when our direct protocol, published six months before Qiu's work, is applied.

Cobalt-catalyzed dithiolation of unactivated alkenes with thiols: facile access to diverse vicinal dithioethers

Direct dithiolation of alkenes with thiols has been rarely reported. Herein, a simple cobalt-catalyzed aerobic approach has been developed to realize this transformation. With the aid of HFIP, diverse vicinal dithioethers including symmetric and unsymmetric ones could be obtained from readily available substrates. Gram-scale synthesis and late-stage modification of complex molecules highlight the practicability of this approach.

Iron(II)-Catalyzed 1,2-Diamination of Styrenes Installing a Terminal NH2 Group Alongside Unprotected Amines

1,2-Diamination of alkenes represents an attractive way to generate differentiated vicinal diamines, which are prevalent motifs in biologically active compounds and catalysts. However, existing methods are usually limited in scope and produce diamines where one or both nitrogens are protected, adding synthetic steps for deprotection and further N-functionalization to reach a desired target. Furthermore, the range of amino groups that can be introduced at the internal position is fairly limited. Here we describe a 1,2-diamination of styrenes that directly installs a free amino group at the terminal position and a wide variety of unprotected nitrogen nucleophiles (primary or secondary alkyl or aromatic amines, sulfoximines, N-heterocycles, and ammonia surrogate) at the internal position. Two complementary sets of conditions encompass electronically activated and deactivated styrenes with diverse substitution patterns and functional groups. Moreover, this strategy can be extended to the 1,2-aminothiolation of styrenes.

Electron Donor-Acceptor Complex-Enabled Autoinductive Conversion of Acylnitromethanes to Acylnitrile Oxides in a Photochemical Machetti-De Sarlo Reaction: Synthesis of 5-Substituted 3-Acylisoxazoles

A photochemical Machetti-De Sarlo reaction has been developed for preparing 5-substituted 3-acylisoxazoles from acylnitromethanes and terminal alkynes. This photochemical protocol utilizes an innovative electron donor-acceptor complex, generated in situ from acylnitromethanes, catalytic LiOtBu, and 1,1,1,3,3,3-hexafluoro-2-propanol, as a photosensitizer to promote rapid conversion with a broad substrate scope in up to 80% efficiency. A sigmoidal autoinductive kinetic profile is revealed, demonstrating the novel and unique dual catalysis in the first photochemical approach of this reaction.

Bio-Inspired Carbon Dots as Malondialdehyde Indicator for Real-Time Visualization of Lipid Peroxidation in Depression

Brain lipidic peroxidation is closely associated with the pathophysiology of various psychiatric diseases including depression. Malondialdehyde (MDA), a reactive aldehyde produced in lipid region, serves as a crucial biomarker for lipid peroxidation. However, techniques enabling real-time detection of MDA are still lacking due to the inherent trade-off between recognition dynamics and robustness. Inspired by the structure of phospholipid bilayers, amphiphilic carbon dots named as CG-CDs targeted to cell membrane are designed for real-time monitoring of MDA fluctuations. The design principle relies on the synergy of dynamic hydrogen bonding recognition and cell membrane targetability. The latter facilitates the insertion of CG-CDs into lipid regions and provides a hydrophobic environment to stabilize the labile hydrogen bonding between CG-CDs and MDA. As a result, recognition robustness and dynamics are simultaneously achieved for CG-CDs/MDA, allowing for in situ visualization of MDA kinetics in cell membrane due to the instant response (<5 s), high sensitivity (9-fold fluorescence enhancement), intrinsic reversibility (fluorescence on/off), and superior selectivity. Subsequently, CG-CDs are explored to visualize nerve cell membrane impairment in depression models of living cells and zebrafish, unveiling the extensive heterogeneity of the lipid peroxidation process and indicating a positive correlation between MDA levels and depression.

HFIP as a versatile solvent in resorcin[n]arene synthesis

Herein, we present 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as an efficient solvent for synthesizing resorcin[n]arenes in the presence of catalytic amounts of HCl at ambient temperature and within minutes. Remarkably, resorcinols with electron-withdrawing groups and halogens, which are reported in the literature as the most challenging precursors in this cyclization, are tolerated. This method leads to a variety of 2-substituted resorcin[n]arenes in a single synthetic step with isolated yields up to 98%.

2,2-Difluoroethylation of Heteroatom Nucleophiles via a Hypervalent Iodine Strategy

The 2,2-difluoroethyl group is an important lipophilic hydrogen bond donor in medicinal chemistry, but its incorporation into small molecules is often challenging. Herein, we demonstrate electrophilic 2,2-difluoroethylation of thiol, amine and alcohol nucleophiles with a hypervalent iodine reagent, (2,2-difluoro-ethyl)(aryl)iodonium triflate, via a proposed ligand coupling mechanism. This transformation offers a complementary strategy to existing 2,2-difluoroethylation methods and allows access to a wide range of 2,2-difluoroethylated nucleophiles, including the drugs Captopril, Normorphine and Mefloquine.

Transition-Metal-Free Direct α-Arylation of Weinreb-type Amides with Arylboronic Acids through Aza-oxyallyl Cation Intermediates

Here, we report an efficient transition-metal-free C(sp2)-C(sp3) Suzuki-Miyaura-type cross-coupling between α-halo Weinreb-type amides and arylboronic acids. The reaction is carried out by capturing active aza-oxyallyl cation (AOAC) with arylboronic acid to form a boron "ate" complex, followed by 1,4-migration to give α-aryl amides with good yields.

Hydrogen-bond activation enables aziridination of unactivated olefins with simple iminoiodinanes

Iminoiodinanes comprise a class of hypervalent iodine reagents that is often encountered in nitrogen-group transfer (NGT) catalysis. In general, transition metal catalysts are required to effect efficient NGT to unactivated olefins because iminoiodinanes are insufficiently electrophilic to engage in direct aziridination chemistry. Here, we demonstrate that 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) activates N-arylsulfonamide-derived iminoiodinanes for the metal-free aziridination of unactivated olefins. 1H NMR and cyclic voltammetry (CV) studies indicate that hydrogen-bonding between HFIP and the iminoiodinane generates an oxidant capable of direct NGT to unactivated olefins. Stereochemical scrambling during aziridination of 1,2-disubstituted olefins is observed and interpreted as evidence that aziridination proceeds via a carbocation intermediate that subsequently cyclizes. These results demonstrate a simple method for activating iminoiodinane reagents, provide analysis of the extent of activation achieved by H-bonding, and indicate the potential for chemical non-innocence of fluorinated alcohol solvents in NGT catalysis.