Electrostatically Self-Assembled Magnetic Nanoparticles for High-Temperature Resistant and Friction-Controlled Lubrication System.

Magnetic-responsive surfactants are considered promising smart lubricating materials due to their significant stimulation response to applied magnetic fields. In this study, four magneto-responsive surfactants are successfully fabricated and encapsulated on the surface of molybdenum disulfide nanosheets (MoS2@C18H37N+(CH3)3[XCl3Br]-, X = Fe, Ce, Gd, and Ho) as base-oil components using electrostatic self-assembly, thereby constructing a multi-functional magnetic lubrication system (MoS2@STAX). Magnetorheological measurements confirm the remarkable responsiveness of MoS2@STACe lubricants at high shear rates and applied magnetic fields, which is further corroborated by the constant proximity of the magnet. The formation of dense carbon and tribo-chemical films between the friction interfaces at elevated temperatures is the primary factor contributing to the significant reduction in frictional wear. Notably, the magnetic lubricant demonstrates a pronounced response behavior when subjected to an applied magnetic field in the ceramic tribopair, even at lower magnetic fields. This work presents concepts for the development of high-temperature resistant and tunable lubrication additives by designing the material structure and controlling the magnetic stimulation.

Synthesis of C-Alkyl Glycosides from Alkyl Bromides and Glycosyl Carboxylic Acids via Ni/Photoredox Dual Catalysis.

C-Alkyl glycosides, an important class of C-glycosides, are widely found in various drugs and natural products. The synthesis of C-alkyl glycosides has attracted considerable attention. Herein, we developed a Ni/photoredox catalyzed decarboxylative C(sp3)-C(sp3) coupling reaction of stable glycosylcarboxylic acids with simple aliphatic bromides to generate C-alkyl glycosides. The method successfully linked several functional molecular fragments (natural products or drugs) to a sugar moiety, showing the extensive application prospects of this transformation. Controlled experiments and DFT calculations demonstrated that the reaction pathway contains a free radical process, and a possible mechanism is proposed.

Palladium-Catalyzed Three-Component Cascade Carbonylation Reaction to Construct Benzofuran Derivatives.

A novel three-component cyclization carbonylation reaction of iodoarene-tethered propargyl ethers with amine and CO is reported. This palladium-catalyzed cascade reaction undergoes a sequence of oxidative addition, unsaturated bond migration, carbonyl insertion, and nucleophilic attack to deliver the benzofuran skeleton. Both aromatic amines and aliphatic amines could proceed smoothly in this transformation under one atm of CO.

Palladium-Catalyzed Cyclization and Direct Arylation of 1-[2-(2,2-Dibromoethenyl)phenyl]-1H-pyrrole with Allenes.

A novel and efficient palladium-catalyzed highly regioselective reaction of 1-[2-(2,2-dibromoethenyl)phenyl]-1H-pyrrole with allenes was realized to synthesize pyrrolo[1,2-a]quinolones. The tandem process involves intermolecular cyclization and intramolecular direct arylation, leading to the formation three new C-C bonds and two new rings. Notably, this transformation exhibits broad substrate scope and high functional group tolerance.

Synthesis of C-Aryl Glycosides by C-H Functionalization.

In recent years, the synthesis of C-aryl glycosides hrough C-H functionalization has attracted extensive attention of organic synthesis chemists due to its steps and atomic economy. In this concept, we systematically summarizes the synthesis of C-aryl glycosides with diverse regioselectivity and diastereoselectivity from the perspective of C-H arylation of glycosides and C-H glycosylation of arenes. It can be found that a series of recently developed C-H glycosylation reactions have higher site-selectivity and diastereomeric selectivity than Friedel-Crafts glycosylation reaction. The reaction conditions are milder, which can be compatible with acid-sensitive protective groups, such as acetals or ketals, and the deprotection is more convenient. It can be seen that there are few reports on remote C-H glycosylation of aromatic hydrocarbons, which is a new field and needs further research. In addition, C-H glycosylation has a lot of shortcomings, which need to be further explored: a) the precise regulation of stereoselectivity in the reaction process also needs further optimization; b) the research on the reaction mechanism is almost limited to DFT calculation, and there is no exact experimental evidence. For key parts, such as the specific reaction mechanism between cyclo-metal intermediates and glycosyl donors in ortho-CAr -H glycosylation is still unclear; c) due to the fact that aryl glycoside compounds contain bare hydroxyl groups in practical applications, it is an urgent problem to realize the compatibility of glycoside substrates containing naked hydroxyl groups or to remove the protective groups on hydroxyl groups by a mild and efficient method after the reaction; d) In this rapidly developing field, we need to study a greener, more economical and more practical C-H glycosylation of arenes in the future, which will be conducive to the synthesis of C-aryl glycosides with more biological application significance.

Robust Janus Superwetting Textile with Large Pore Sizes for Oil-in-Water Emulsion Separation.

Developing advanced oil-water separation technology is significant for environmental conservation. According to the synergetic effects of the size-sieving mechanism, superwetting materials with small pore sizes have been designed to realize high-efficiency separation for oil-water emulsions. However, the separation flux limited by the pore size and the weakness of the superwetting material impede its practical application severely. Herein, we construct a robust Janus superwetting textile with large pore sizes for oil-in-water emulsion separation. The pristine textile is coated by the as-prepared CuO nanoparticles as the bottom layer with superhydrophilicity and then grafted by 1-octadecanethiol as the top layer with superhydrophobicity to construct the Janus textile. When used as a filter, the superhydrophobic layer acts as the nucleation site to coalesce the small oil droplets facilely. Then, the coalesced oil fills the pores of the superhydrophobic layer and selectively permeates it but is blocked by the superhydrophilic layer with large pore sizes. Utilizing the unique separation mechanism, the Janus textile realizes efficient and rapid separation. Even after multicycle separation, hot liquid immersion for 24 h, tribological test for 60 min, and sandpaper abrasion for 500 cycles, the Janus textile still retains the superwettability and excellent separation performance, manifesting outstanding stability to resist severe damage. This separation strategy provides a novel guideline for high-efficiency and high-flux emulsion separation and practical application.

Lewis Acid Catalyzed [4 + 2] Annulation of Propargylic Alcohols with 2-Vinylanilines.

An elegant Lewis acid catalyzed, protection-free, and straightforward synthetic strategy for the assembly of a series of sophisticated polycyclic quinoline skeletons employing propargylic alcohols and 2-vinylanilines as the substrates in the presence of Yb(OTf)3 (10 mol %) and AgOTf (10 mol %) in tetrahydrofuran has been described. This annulation protocol, which proceeds through a sequential Meyer-Schuster rearrangement/nucleophilic substitution/deprotonation sequence, provides a versatile, practical, and atom-economical approach for accessing quinoline derivatives in moderate-to-good yields.

Synthesis of C4-Aminated Carbazoles and Their Derivatives via Pd/NBE Chemistry.

Carbazole, as one of the most important organic frameworks, has been used in optoelectronic materials and biochemistry. However, the synthesis of C4-substituted carbazole has always been an unsolved problem. This report describes the one-step synthesis of C4-aminated carbazoles and their derivatives through the series reaction of C-H amination and arylation. The substrate scope is wide. C4-Amino carbazoles substituted by C2, C6, C7, and C8 methyl groups, especially carbazole derivatives of fused rings, pyridine, and dibenzofuran, can be synthesized.

Nickel-Catalyzed Three-Component Tandem Radical Cyclization 1,5-Difunctionalization of 1,3-Enynes and Alkyl Bromide.

A nickel-catalyzed three-component tandem radical cyclization reaction of aryl bromides with 1,3-enynes and aryl boric acids to construct γ-lactam-substituted allene derivatives has been described. This protocol provides lactam alkyl radicals through the free radical cyclization process, which can be effectively used to participate in the subsequent multicomponent coupling reaction so that 1,3-enynes could directly convert into corresponding poly-substituted allene compounds. In addition, this efficient method enjoys a broad substrate scope and provides a series of 1,5-difunctionalized allenes in a one-pot reaction.

Template Synthesis to Solve the Unreachable Ortho C-H Functionalization Reaction of Aryl Iodide.

This report describes the use of a simple Pd/NBE catalytic system to achieve ortho C-H oxylation and phosphonylation and other functionalizations of aryl iodide through templated conversion reactions. Dimethylamine is introduced in the ortho-site of aryl iodide through C-H amination, and aryl dimethylamine is quickly converted to methyl quaternary ammonium salt precipitation. Methyl quaternary ammonium salt avoids Hofmann elimination in subsequent functionalization. This method solves various ortho functionalization reactions of aryl iodide that have not been achieved for a long time in the field of Pd/NBE chemistry indirectly.

New synthetic approaches toward OCF3-containing compounds.

Fluorinated organic compounds are an important class of organic molecules and play a key role in both academic and industrial communities due to the unique nature of fluorine. Among the fluorine-containing functional groups, the OCF3 group is of vital importance because of its favorable physicochemical properties, so it frequently acts as the pivotal skeletal motif in a broad spectrum of pharmaceutical molecules, agrochemicals, natural products, and materials. Over the past few decades, a wider range of strategies for the efficient, versatile, and practical synthesis of trifluoromethoxylated compounds have been the focus of a number of research initiatives. These synthesis approaches are especially fascinating in the context of the design of agrochemicals and new drugs as established pathways for installing the OCF3 moiety. In this review, the state of the art of the synthesis of OCF3-containing compounds is summarized. It can be segmented into six categories: (1) de novo formation of the OCF3 group; (2) construction of trifluoromethoxylated compounds via trifluoromethylation of the corresponding alcohol or phenol; (3) construction of trifluoromethoxylated compounds via installing the entire OCF3 group straightaway onto a complex molecule; (4) visible-light-induced trifluoromethoxylation; (5) transition metal-catalyzed trifluoromethoxylation; and (6) construction of the trifluoromethoxylated compounds via rearrangement reactions.

Aryl-to-Vinyl 1,4-Nickel Migration/Reductive Cross-Coupling Reaction for the Stereoselective Synthesis of Multisubstituted Olefins.

The aryl-to-vinyl nickel 1,4-migration (1,4-Ni migration) reaction has been reported for the first time. The generated alkenyl Ni species undergo a reductive coupling reaction with unactivated brominated alkanes affording a series of trisubstituted olefins. This tandem reaction exhibits mild conditions, a broad substrate scope, high regioselectivity, and excellent Z/E stereoselectivity. A series of controlled experiments have shown that the critical 1,4-Ni migration process is reversible. In addition, the alkenyl nickel intermediates obtained after migration are highly Z/E stereoselective and do not undergo Z/E isomerization. The obtained trace isomerization products are caused by the instability of the product.

Bioinspired Polysaccharide Derivative with Efficient and Stable Lubrication for Silicon-Based Devices.

It is becoming increasingly important to synthesize efficient biomacromolecule lubricants suitable for medical devices. Even though the development of biomimetic lubricants has made great progress, the current system suitable for hydrophobic silicone-based medical devices is highly limited. In this work, we synthesize one kind of novel polysaccharide-derived macromolecule lubricant of chitosan (CS) grafted polyethylene glycol (PEG) chains and catechol groups (CT) (CS-g-PEG-g-CT). CS-g-PEG-g-CT shows good adsorption ability by applying quantitative analysis of quartz crystal microbalance (QCM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and confocal fluorescence imaging technique, as well as the typical shear-thinning feature. CS-g-PEG-g-CT exhibits low and stable coefficients of friction (COFs) (0.01-0.02) on polydimethylsiloxane (PDMS) surfaces at a wide range of mass concentrations in diverse media including pure water, physiological saline, and PBS buffer solution and is even tolerant to various normal loads and sliding frequencies for complex pressurizing or shearing environments. Subsequently, systematic surface characterizations are used to verify the dynamic attachment ability of the CS-g-PEG-g-CT lubricant on the loading/shearing process. The lubrication mechanism of CS-g-PEG-g-CT can be attributed to the synergy of strong adsorption from catechol groups to form a uniform assembly layer, excellent hydration effect from PEG chains, and typical shear-thinning feature to dissipate viscous resistance. Surprisingly, CS-g-PEG-g-CT exhibits efficient lubricity on silicone-based commercial contact lenses and catheters. The current macromolecule lubricant demonstrates great real application potential in the fields of medical devices and disease treatments.

Palladium-Catalyzed Intramolecular Heck Dearomative Alkenylation of Indoles with N-Tosylhydrazones.

An elegant Pd-catalyzed intramolecular Heck dearomative alkenylation of aryl iodides with functionalized N-tosylhydrazones proceeded through a sequential dearomative carbopalladation, migratory insertion, and ß-hydride elimination in the presence of Pd(CF3COO)2 (10 mol %), PPh3 (30 mol %), and Cs2CO3 (2.0 equiv) in 1,4-dioxane (2.0 mL) at 120 °C for 14 h under an argon atmosphere. This cascade cycloaddition protocol provided a reliable and versatile approach to a sequence of structurally diverse indolines in moderate to good yields with good functional group compatibility. In addition, the synthetic robustness of the methodology is highlighted by a scaled-up experiment and derivatization of products via epoxidation and reduction reactions.

Ruthenium-Catalyzed Stereo- and Site-Selective ortho- and meta-C-H Glycosylation and Mechanistic Studies.

C-aryl glycosides are popular basic skeletons in biochemistry and pharmaceutical chemistry. Herein, ruthenium-catalyzed highly stereo- and site-selective ortho- and meta-CAr -H glycosylation is described. A series of C-aryl pyranosides and furanosides were synthesized by this method. The strategy showed good substrate scope, and various N-heterocyclic directing groups were compatible with the reaction system. A mechanistic study suggested that the key pathway of ortho-CAr -H glycosylation might involve oxidative addition/reduction elimination, whereas aryl meta-C-H glycosylation was mediated by σ-activation. Density functional theory calculations also showed that the high stereoselectivity of meta-CAr -H glycosylation was due to steric hindrance.

Experimental and Computational Studies of Palladium-Catalyzed Spirocyclization via a Narasaka-Heck/C(sp3 or sp2)-H Activation Cascade Reaction.

The first synthesis of highly strained spirocyclobutane-pyrrolines via a palladium-catalyzed tandem Narasaka-Heck/C(sp3 or sp2)-H activation reaction is reported here. The key step in this transformation is the activation of a δ-C-H bond via an in situ generated σ-alkyl-Pd(II) species to form a five-membered spiro-palladacycle intermediate. The concerted metalation-deprotonation (CMD) process, rate-determining step, and energy barrier of the entire reaction were explored by density functional theory (DFT) calculations. Moreover, a series of control experiments was conducted to probe the rate-determining step and reversibility of the C(sp3)-H activation step.

Palladium-Catalyzed Asymmetric Intramolecular Dearomative Heck Annulation of Aryl Halides to Furnish Indolines.

An unprecedented Pd-catalyzed asymmetric intramolecular cascade cyclization of aryl halides with readily available arylboronic acids proceeds through a Heck-type dearomative cyclization terminated with arylation in the presence of Pd2(dba)3 (10 mol %), Cu2O (5 mol %), and Cs2CO3 (2.0 equiv) in 1,2-dichloroethane (1.0 mL) at 100 °C for 15 h in air using BINOL-based phosphoramidite as the chiral ligand. This dearomative Heck protocol, which tolerates a broad variety of functional groups, is amenable to the generation of optically active indoline derivatives bearing all-carbon quaternary stereogenic centers in one step in moderate to excellent yields, with excellent diastereoselectivities (>20:1) and enantioselectivities (up to >99% ee). It is worth mentioning that no decrease in the enantiopurity of the indoline derivatives was observed during the synthetic transformations of the products.

Correction: Visible-light-mediated borylation of aryl and alkyl halides with a palladium complex.

Correction for 'Visible-light-mediated borylation of aryl and alkyl halides with a palladium complex' by Jia-Hui Zhao, et al., Org. Biomol. Chem., 2020, 18, 4390-4394, DOI: 10.1039/D0OB00028K.

Visible-Light-Induced Palladium-Catalyzed Carbocyclization of Unactivated Alkyl Bromides with Alkenes Involving C-I or C-B Coupling.

A palladium-catalyzed, photochemical tandem cyclization/dicarbofunctionalization of unactivated alkyl halides containing an alkene moiety offers an appealing route to produce five- or six-membered rings in a redox-neutral fashion. Multisubstituted carbo- and heterocyclic compounds were prepared through the formation of new C-B or C-O bonds, which provides a convenient synthetic route for further transformations. This protocol is characterized by the reaction of alkene regio- and stereoselectivities, good functional group compatibility, wide substrate scope, and mild reaction conditions.

Copper-Catalyzed Three-Component Redox-Neutral Ring Opening of Benzothiazoles to 1-Amino-N-(2-(phenylthio)phenyl)methanimine.

Copper-catalyzed three-component redox-neutral ring opening of benzothiazoles with aryl iodides and O-benzoyl hydroxylamines for the synthesis of 1-amino-N-(2-(phenylthio)phenyl)methanimine has been developed. This one-pot reaction undergoes C-S and N-O bond cleavage and new C-S and C-N bond construction. Several control experiments excluded a free radical procedure and also demonstrated the secondary amine as a possible intermediate, which was vital to the catalytic reaction. Meanwhile, the deuteration experiment got rid of the C-H activation dehydroisomerization of the benzothiazole mechanism.