Clues from an ionic cocrystal structure: from catalysis to mechanochemistry

A crystal structure is no longer conceived as a static entity; rather, it often mirrors crystallization pathways, linking crystal structures with a solution scenario. In this study, taking a clue from a previously reported ionic cocrystal structure, an in situ acetic acid-based catalytic protocol is developed for the N-acylation of amines using ester sources. In addition to better catalytic efficiency, this in situ approach was extended further to a mechanochemistry protocol in the context of a multicomponent reaction. This points towards a broader applicability of crystal structures that goes beyond the domain of structural chemistry and delves into catalysis and mechanosynthesis.

Organoboron catalysis for direct amide/peptide bond formation

Amides and peptides are ubiquitous functional groups found in several natural and artificial materials, and they are essential for the advancement of life and material sciences. In particular, their relevance in clinical medicine and drug discovery has increased in recent years. Dehydrative condensation of readily available carboxylic acids with amines is the most "direct" method for amide synthesis; however, this methodology generally requires a stoichiometric amount of condensation agent (coupling reagent). Catalytic direct dehydrative amidation has become an "ideal" methodology for synthesizing amides from the perspective of green chemistry, with water as the only byproduct in principle, high atom efficiency, environmentally friendly, energy saving, and safety. Conversely, organoboron compounds, such as boronic acids, which are widely used in various industries as coupling reagents for Suzuki-Miyaura cross-coupling reactions or pharmaceutical structures, are environmentally friendly molecules that have low toxicity and are easy to handle. Based on the chemical properties of organoboron compounds, they have potential Lewis acidity and the ability to form reversible covalent bonds with dehydration, making them attractive as catalysts. This review explores studies on the development of direct dehydrative amide/peptide bond formation reactions from carboxylic acids using organoboron catalysis, classifying them based on chemical bonding and catalysis over approximately 25 years, from the early developmental days to 2023.

Phenalenyl-ruthenium synergism for effectual catalytic transformations of primary amines to amides

The synthesis of amides holds great promise owing to their impeccable contributions as building blocks for highly valued functional derivatives. Herein, we disclose the design, synthesis and crystal structure of a mixed-ligand ruthenium(II) complex, [Ru(η6-Cym)(O,O-PLY)Cl], (1) where Cym = 1-isopropyl-4-methyl-benzene and O,O-PLY = deprotonated form of 9-hydroxy phenalenone (HO,O-PLY). The complex catalyzes the aerobic oxidation of various primary amines (RCH2NH2) to value-added amides (RCONH2) with excellent selectivity and efficiency under relatively mild conditions with common organic functional group tolerance. Structural, electrochemical, spectroscopic, and computational studies substantiate that the synergism between the redox-active ruthenium and π-Lewis acidic PLY moieties facilitate the catalytic oxidation of amines to amides. Additionally, the isolation and characterization of key intermediates during catalysis confirm two successive dehydrogenation steps leading to nitrile, which subsequently transform to the desired amide through hydration. The present synthetic approach is also extended to substitution-dependent tuning at PLY to tune the electronic nature of 1 and to assess substituent-mediated catalytic performance. The effect of substitution at the PLY moiety (5th position) leads to structural isomers, which were further evaluated for the catalytic transformations of amine to amides under similar reaction conditions.

Competing Reaction Mechanisms of Peptide Bond Formation in Water Revealed by Deep Potential Molecular Dynamics and Path Sampling

The formation of an amide bond is an essential step in the synthesis of materials and drugs, and in the assembly of amino acids to form peptides. The mechanism of this reaction has been studied extensively, in particular to understand how it can be catalyzed, but a representation capable of explaining all the experimental data is still lacking. Numerical simulation should provide the necessary molecular description, but the solvent involvement poses a number of challenges. Here, we combine the efficiency and accuracy of neural network potential-based reactive molecular dynamics with the extensive and unbiased exploration of reaction pathways provided by transition path sampling. Using microsecond-scale simulations at the density functional theory level, we show that this method reveals the presence of two competing distinct mechanisms for peptide bond formation between alanine esters in aqueous solution. We describe how both reaction pathways, via a general base catalysis mechanism and via direct cleavage of the tetrahedral intermediate respectively, change with pH. This result contrasts with the conventional mechanism involving a single pathway in which only the barrier heights are affected by pH. We show that this new proposal involving two competing mechanisms is consistent with the experimental data, and we discuss the implications for peptide bond formation under prebiotic conditions and in the ribosome. Our work shows that integrating deep potential molecular dynamics with path sampling provides a powerful approach for exploring complex chemical mechanisms.

Supramolecular intermediates in thermo-mechanochemical direct amidations

We present a solvent-free thermo-mechanochemical approach for the direct coupling of carboxylic acids and amines, which avoids activators and additives. Detailed analysis of the reactions by ex situ and in situ monitoring methods led to the observation, isolation, and characterisation of multicomponent crystalline intermediates that precede the formation of amides. We applied our methodology for the quantitative synthesis of the active pharmaceutical ingredient moclobemide.

Lewis Acid Catalyzed Amide Bond Formation in Covalent Graphene-MOF Hybrids

Covalent hybrids of graphene and metal-organic frameworks (MOFs) hold immense potential in various technologies, particularly catalysis and energy applications, due to the advantageous combination of conductivity and porosity. The formation of an amide bond between carboxylate-functionalized graphene acid (GA) and amine-functionalized UiO-66-NH2 MOF (Zr6O4(OH)4(NH2-bdc)6, with NH2-bdc2- = 2-amino-1,4-benzenedicarboxylate and UiO = Universitetet i Oslo) is a highly efficient strategy for creating such covalent hybrids. Previous experimental studies have demonstrated exceptional properties of these conductive networks, including significant surface area and functionalized hierarchical pores, showing promise as a chemiresistive CO2 sensor and electrode materials for asymmetric supercapacitors. However, the molecular-level origin of the covalent linkages between pristine MOF and GA layers remains unclear. In this study, density functional theory (DFT) calculations were conducted to elucidate the mechanism of amide bond formation between GA and UiO-66-NH2. The theoretical calculations emphasize the crucial role of zirconium within UiO-66, which acts as a catalyst in the reaction cycle. Both commonly observed hexa-coordinated and less common hepta-coordinated zirconium complexes are considered as intermediates. By gaining detailed insights into the binding interactions between graphene derivatives and MOFs, strategies for tailored syntheses of such nanocomposite materials can be developed.

Development of fluorous boronic acid catalysts integrated with sulfur for enhanced amidation efficiency

A thermally stable, fluorous sulfur-containing boronic acid catalyst has been developed and was shown to efficiently promote dehydrative condensation between carboxylic acids and amines under environmentally friendly conditions. The methodology can be applied to aliphatic, aromatic and heteroaromatic acids as well as primary and secondary amines. N-Boc protected amino acids were also successfully coupled in good yields with very little racemization. The catalyst could be reused four times with no significant loss of activity.

Heterocyclic Boron Acid Catalyzed Dehydrative Amidation of Aliphatic/Aromatic Carboxylic Acids with Amines

A commercially available and versatile dehydrative amidation catalyst, featuring a thianthrene boron acid structure, has been developed. The catalyst shows high catalytic activity to both aliphatic and less reactive aromatic carboxylic acid substrates, including several bioactive or clinical molecules with a carboxylic acid group.

Volatile Organic Compound Sensing Array and Optoelectronic Filter System using Ion-Pairing Dyes with a Wide Visible Spectrum

An ideal dye-based sensing array has essential design requirements, including facile preparation methodology, tolerance to water vapor, a broad range of color-responsive changes, and a simple readout system. Here, a brief synthetic route is developed for ion-pairing dyes exhibiting unusual chromatic changes across the entire visible spectrum. It requires only mixing and precipitation under mild conditions. The dyes are applied to a sensing array containing 12 sensing elements with different initial states. Owing to the numerous color variations of the dyes, the color map generated by the array is highly simple yet sufficiently accurate to distinguish among the different functional groups (such as amines, aldehydes, and carboxylic acids) as well as carbon chain lengths. Principle component analysis (PCA) demonstrates that volatile organic compounds (VOCs) can be well classified according to the color changes of the sensing array. The ion-pairing dyes are embedded into 3D stacked nanofibers via electrospinning, and function as effective harmful-gas (e.g., formaldehyde) sensors with sub-ppm theoretical detection limits (0.15 ppm). Finally, the 3D stacked nanofibers can be employed in an optoelectronic filter system that automatically checks for formaldehyde in the surroundings and also confirms the effective removal of the detected formaldehyde by the gas filter cartridge.

Zirconium-Based Catalysts in Organic Synthesis

Zirconium is a silvery-white malleable and ductile metal at room temperature with a crustal abundance of 162 ppm. Its compounds, showing Lewis acidic behavior and high catalytic performance, have been recognized as a relatively cheap, low-toxicity, stable, green, and efficient catalysts for various important organic transformations. Commercially available inorganic zirconium chloride was widely applied as a catalyst to accelerate amination, Michael addition, and oxidation reactions. Well-designed zirconocene perfluorosulfonates can be applied in allylation, acylation, esterification, etc. N-Chelating oganozirconium complexes accelerate polymerization, hydroaminoalkylation, and CO₂ fixation efficiently. In this review, the applications of both commercially available and synthesized zirconium catalysts in organic reactions in the last 5 years are highlighted. Firstly, the properties and application of zirconium and its compounds are simply introduced. After presenting the superiority of zirconium compounds, their applications as catalysts to accelerate organic transformations are classified and presented in detail. On the basis of different kinds of zirconium catalysts, organic reactions accelerated by inorganic zirconium catalysts, zirconium catalysts bearing Cp, and organozirconium catalysts without Cp are summarized, and the plausible reaction mechanisms are presented if available.

Mechanochemical Nucleophilic Substitution of Alcohols via Isouronium Intermediates

An expansion of the solvent-free synthetic toolbox is essential for advances in the sustainable chemical industry. Mechanochemical reactions offer a superior safety profile and reduced amount of waste compared to conventional solvent-based synthesis. Herein a new mechanochemical method was developed for nucleophilic substitution of alcohols using fluoro-N,N,N',N'-tetramethylformamidinium hexafluorophosphate (TFFH) and K₂ HPO₄ as an alcohol-activating reagent and a base, respectively. Alcohol activation and reaction with a nucleophile were performed in one milling jar via reactive isouronium intermediates. Nucleophilic substitution with amines afforded alkylated amines in 31-91 % yields. The complete stereoinversion occurred for the S_N 2 reaction of (R)- and (S)-ethyl lactates. Substitution with halide anions (F^- , Br^- , I^- ) and oxygen-centered (CH₃ OH, PhO^- ) nucleophiles was also tested. Application of the method to the synthesis of active pharmaceutical ingredients has been demonstrated.

Methyltrimethoxysilane (MTM) as a Reagent for Direct Amidation of Carboxylic Acids

Methyltrimethoxysilane [MTM, CH₃Si(OMe)₃] has been demonstrated to be an effective, inexpensive, and safe reagent for the direct amidation of carboxylic acids with amines. Two simple workup procedures that provide the pure amide product without the need for further purification have been developed. The first employs an aqueous base-mediated annihilation of MTM. The second involves simple product crystallization from the reaction mixture providing a low process mass intensity direct amidation protocol.

UV-Light-Induced Dehydrogenative N-Acylation of Amines with 2-Nitrobenzaldehydes To Give 2-Aminobenzamides

A simple, mild, green, and efficient method for the synthesis of 2-aminobenzamides is highly desirable. Herein, we report the development of an efficient, one-pot strategy starting from 2-aminobenzaldehydes and amines with acetic acid in ethyl acetate/acetone using irradiation with UV light for the synthesis of 2-aminobenzamides in high yields; 32 examples proceeded successfully by this photo-induced protocol in up to 92% yield. The reaction was also readily achieved on a gram scale. The utility of the 2-aminobenzamide building block in organic synthesis was shown by their use in the preparation of quinazolinone derivatives. The method was applied to amino acid derivatives as the amine component, which smoothly gave N-(2-aminobenzoyl)acetate derivatives at room temperature. Finally, a plausible mechanism is proposed.

Amide bond formation in aqueous solution: direct coupling of metal carboxylate salts with ammonium salts at room temperature

Herein, we report a green, expeditious, and practically simple protocol for direct coupling of carboxylate salts and ammonium salts under ACN/H₂O conditions at room temperature without the addition of tertiary amine bases. The water-soluble coupling reagent EDC·HCl is a key component in the reaction. The reaction runs smoothly with unsubstituted/substituted ammonium salts and provides a clean product without column chromatography. Our reaction tolerates both carboxylate (which are unstable in other forms) and amine salts (which are unstable/volatile when present in free form). We believe that the reported method could be used as an alternative and suitable method at the laboratory and industrial scales.

UV-Light-Induced N-Acylation of Amines with α-Diketones

Herein, we develop a mild method for N-acylation of primary and secondary amines with α-diketones induced by ultraviolet (UV) light. Forty-six examples with various functional groups are explored at room temperature with irradiation by three 26 W UV lamps (350-380 nm). The yield reaches 97%. The gram scale experiment product yield is 76%. Moreover, this system can be applied to the synthesis of several amino acid derivatives. Mechanistic studies show that benzoin is generated in situ from benzil under UV irradiation.

Key advances of carboxymethyl cellulose in tissue engineering & 3D bioprinting applications

Carboxymethyl cellulose (CMC) is a water-soluble derivative of cellulose and a major type of cellulose ether prepared by the chemical attack of alkylating reagents on the activated non-crystalline regions of cellulose. It is the first FDA approved cellulose derivative which can be targeted for desired chemical modifications. In this review, the properties along with current advances in the physical and chemical modifications of CMC are discussed. Further, CMC and modified CMC could be engineered to fabricate scaffolds for tissue engineering applications. In recent times, CMC and its derivatives have been developed as smart bioinks for 3D bioprinting applications. From these perspectives, the applications of CMC in tissue engineering and current knowledge on peculiar features of CMC in 3D and 4D bioprinting applications are elaborated in detail. Lastly, future perspectives of CMC for wider applications in tissue engineering and 3D/4D bioprinting are highlighted.

Microwave-assisted green synthesis of bile acid derivatives and evaluation of glucocorticoid receptor binding

Herein, we present microwave-assisted AlCl3 catalyzed oxidation of bile acid hydroxyl groups in the presence of Oxone® in water media. Significant rate enhancements were observed for Wolff-Kishner reduction of synthesized bile acids oxo derivatives to the 5β-cholanic acid. Reaction of amidation of the simplest bile acid and aminolysis of the deoxycholic acid was accomplished in the absence of solvent and catalysts under sealed vessel microwave conditions. Because 5β-cholanic acid reportedly modulates glucocorticoid receptor signaling in cell models of Parkinson's disease, we tested the affinity of 5β-cholanic acid and deoxycholic acid derivatives for the glucocorticoid receptor in vitro using a yeast-based fluorescent screen. Treatment of GR-expressing yeast with prednisolone resulted in a dose-dependent increase in fluorescence; whereas 5β-cholanic acid binds to the glucocorticoid receptor with more moderate affinity. Similarly, molecular docking also suggests that 5β-cholanic acid can bind to the glucocorticoid receptor, with similar geometry to known GR ligands.

Direct Amide Synthesis over Composite Magnetic Catalysts in a Continuous Flow Reactor

Composite magnetic catalysts containing different amounts of sulfated titania (33–50 wt %) have been prepared by means of high energy ball-milling between TiO2 and NiFe2O4. The catalysts have been characterized with N2 adsorption/desorption isotherms, XRD, temperature programmed oxidation (TPO) and vibrating sample magnetometer (VSM). The catalytic activity was measured in the reaction of aniline and 4-phenylbutyric acid in the continuous mode under conventional and inductive heating. The effect of catalyst loading in the reactor on reaction and deactivation has been studied, indicating the catalyst containing 50 wt % titania gave the highest reaction rate and least deactivation. The operation in a flow reactor under inductive heating increased the amide yield by 25% as compared to conventional heating. The initial reaction rate decreased by 30% after a period of 15 h on stream. The catalyst activity was fully restored after a treatment with an air flow at 400 °C.

Access to 2-pyridinylamide and imidazopyridine from 2-fluoropyridine and amidine hydrochloride

Under catalyst-free conditions, an efficient method to synthesize 2-pyridinylamides has been developed, and the protocol uses inexpensive and readily available 2-fluoropyridine and amidine derivatives as the starting materials. Simultaneously, the copper-catalysed approach to imidazopyridine derivatives has been established with high chemoselectivity and regiospecificity. The results suggest that the nitrogen-heterocycles containing iodide substituents can also be compatible for the reaction via the cascade Ullmann-type coupling, and the nucleophilic substitution reaction provides the target products in a one-pot manner.

Amine-boranes as Dual-Purpose Reagents for Direct Amidation of Carboxylic Acids

Amine-boranes serve as dual-purpose reagents for direct amidation, activating aliphatic and aromatic carboxylic acids and, subsequently, delivering amines to provide the corresponding amides in up to 99% yields. Delivery of gaseous or low-boiling amines as their borane complexes provides a major advantage over existing methodologies. Utilizing amine-boranes containing borane incompatible functionalities allows for the preparation of functionalized amides. An intermolecular mechanism proceeding through a triacyloxyborane-amine complex is proposed.

Pyridine-Enabled C-N Bond Activation for the Rapid Construction of Amides and 4-Pyridylglyoxamides by Cooperative Palladium/Copper Catalysis

A pyridine-enabled C-N bond activation of peptidomimetics employing cooperative palladium/copper catalysis in water is developed. Diverse amides and 4-pyridylglyoxamides are simultaneously synthesized through two steps from commercially available materials in a rapid, environmentally friendly, and high atom-economical manner.

Microwave-Assisted Catalytic Method for a Green Synthesis of Amides Directly from Amines and Carboxylic Acids

Amide bonds are among the most interesting and abundant molecules of life and products of the chemical pharmaceutical industry. In this work, we describe a method of the direct synthesis of amides from carboxylic acids and amines under solvent-free conditions using minute quantities of ceric ammonium nitrate (CAN) as a catalyst. The reactions are carried out in an open microwave reactor and allow the corresponding amides to be obtained in a fast and effective manner when compared to other procedures of the direct synthesis of amides from acids and amines reported so far in the literature. The amide product isolation procedure is simple, environmentally friendly, and is performed with no need for chromatographic purification of secondary amides due to high yields. In this report, primary amines were used in most examples. However, the developed procedure seems to be applicable for secondary amines as well. The methodology produces a limited amount of wastes, and a catalyst can be easily separated. This highly efficient, robust, rapid, solvent-free, and additional reagent-free method provides a major advancement in the development of an ideal green protocol for amide bond formation.

Study of glycation process of human carbonic anhydrase II as well as investigation concerning inhibitory influence of 3-beta-hydroxybutyrate on it

Glycation is a non-enzymatic reaction between carbonyl groups in sugar and free amino groups in proteins. This reaction leads to changes in structure and functions of proteins in which the advanced glycation end products (AGEs) are the final outcome and cause many complications in diabetic patients. We herein examined the effect of fasting on the glycation process of human Carbonic anhydrase II under physiological conditions (37 °C and pH 7.4) employing various techniques, including Ultraviolet-visible spectroscopy, fluorescence spectroscopy and CD Spectroscopy. We found an increased 3-beta-hydroxybutyrate upon fasting. We studied various samples of control carbonic anhydrase (without glucose and 3-beta-hydroxybutyrate), carbonic anhydrase with glucose, carbonic anhydrase treated with 3-beta-hydroxybutyrate (BHB) and carbonic anhydrase along with glucose and 3-beta-hydroxybutyrate. The samples were incubated for 35 days under physiological conditions. Our results indicated that 3-beta-hydroxybutyrate inhibited the glycation process, decreased glucose binding to the protein, prevented the formation of AGEs, and modified the enzyme activity. Our findings would open new windows toward the enzymatic procedure which would have profound implication in understanding the diabetes mechanisms.

Mechanistic Insights into La-Catalyzed Amidation of Aldehyde with Amine

A new mechanism of La-catalyzed amidation of N-methylbenzylamine with p-chlorobenzaldehyde has been computationally proposed, where L₂La[NR₁R₂] (I) rather than previously proposed L₂La[OCHRNR₁R₂] (II) is the catalytically active species. Interestingly, the side-product alcohol acting as a proton relay to reduce reaction energy barrier could participate in the regeneration of I. Besides, DFT calculations suggest that an addition of alcohol additive into the initial reaction system could accelerate the reaction, which has been further verified by experiments.

A metal-free approach for the synthesis of amides/esters with pyridinium salts of phenacyl bromides via oxidative C-C bond cleavage

An efficient, simple, and metal-free synthetic approach for the N- and O-benzoylation of various amines/benzyl alcohols with pyridinium salts of phenacyl bromides is demonstrated to generate the corresponding amides and esters. This protocol facilitates the oxidative cleavage of a C–C bond followed by formation of a new C–N/C–O bond in the presence of K₂CO₃. Various pyridinium salts of phenacyl bromides can be readily transformed into a variety of amides and esters which is an alternative method for the conventional amidation and esterification in organic synthesis. High functional group tolerance, broad substrate scope and operational simplicity are the prominent advantages of the current protocol.

Solvent-Free Synthesis of Amidated Carboxymethyl Cellulose Derivatives: Effect on the Thermal Properties

The present work explores the possibility of chemically modifying carboxymethyl cellulose (CMC), a widely diffused commercial cellulose ether, by grafting of hydrophobic moieties. Amidation of CMC, at high temperature and in heterogeneous conditions, was selected as synthetic tool for grafting on CMC a panel of commercially available amines (bearing long aliphatic chains, alkyl aromatic and heteroaromatic groups, more or less spaced from the cellulose backbone). The reaction was successfully carried out in absence of solvents, catalysts and coupling agents, providing a promising and more sustainable alternative to conventional amidation procedures. Relationships between the chemical structure of the obtained CMC derivatives and their thermal properties were carefully studied, with a particular attention to the thermal behavior. Grafting of aromatic and heteroaromatic alkyl amines, presenting a linear alkyl chain between CMC backbone and a terminal bulky moiety, allowed for efficiently separating the polysaccharide chains, improving their mobility and resulting in a consequent lowering of the glass transition temperature (T_g). The T_g values obtained (90-147 °C) were found to be closely dependent on both the size of the aliphatic spacer, the structure of the aromatic ring and the extent of amidation.

Diboronic Acid Anhydrides as Effective Catalysts for the Hydroxy-Directed Dehydrative Amidation of Carboxylic Acids

The direct catalytic dehydrative amidation of β-hydroxycarboxylic acids with amines is described. A biphenyl-based diboronic acid anhydride with a B-O-B skeleton is shown to be an exceptionally effective catalyst for the reaction, providing β-hydroxycarboxylic amides in high to excellent yields with a low catalyst loading (minimum of 0.01 mol %, TON up to 7,500). This hydroxy-directed amidation shows excellent chemoselectivity and is applicable to gram-scale drug synthesis.

Prevention of haemoglobin glycation by acetylsalicylic acid (ASA): A new view on old mechanism

Diabetic hyperglycemia provokes glycation of haemoglobin (Hb), an abundant protein in red blood cells (RBCs), by increasing its exposure to carbohydrates. Acetylsalicylic acid (ASA; Aspirin) is one of the first agents, which its antiglycation effect was witnessed. Although the precise molecular mechanism of action of ASA on protein glycation is not indisputably perceived, acetylation as its main molecular mechanism has been proposed. This report aims to unravel the meticulous mechanism of action of ASA by using two ASA analogues; benzoic acid (BA) and para-nitrobenzoic acid (NBA), despite their lack of acetyl group. In this regard, the inhibitory effect of these two chemicals in comparison with ASA on Hb fructation is reported. UV-visible spectroscopy, intrinsic advanced glycation end products (AGE) fluorescence spectroscopy, extrinsic thioflavin T (ThT) binding fluorescence spectroscopy, 2,4,6-trinitrobenzenesulfonic acid (TNBSA) assay, and single cell gel electrophoresis (SCGE) were used to explore the effects of BA and NBA in comparison with aforementioned chemicals in the context of protein glycation. In spite of the lack of acetyl substitution, NBA is reported as a novel agent with prominent inhibitory efficacy than ASA on the protein glycation. This fact brings up a possible new mechanism of action of ASA and reconsiders acetylation as the sole mechanism of inhibition of protein glycation.

All Non-Carbon B3 NO2 Exotic Heterocycles: Synthesis, Dynamics, and Catalysis

The B₃ NO₂ six-membered heterocycle (1,3-dioxa-5-aza-2,4,6-triborinane=DATB), comprising three different non-carbon period 2 elements, has been recently demonstrated to be a powerful catalyst for dehydrative condensation of carboxylic acids and amines. The tedious synthesis of DATB, however, has significantly diminished its utility as a catalyst, and thus the inherent chemical properties of the ring system have remained virtually unexplored. Here, a general and facile synthetic strategy that harnesses a pyrimidine-containing scaffold for the reliable installation of boron atoms is disclosed, giving rise to a series of Pym-DATBs from inexpensive materials in a modular fashion. The identification of a soluble Pym-DATB derivative allowed for the investigation of the dynamic nature of the B₃ NO₂ ring system, revealing differential ring-closing and -opening behaviors depending on the medium. Readily accessible Pym-DATBs proved their utility as efficient catalysts for dehydrative amidation with broad substrate scope and functional-group tolerance, offering a general and practical catalytic alternative to reagent-driven amidation.

Organ-specific distribution and non-enzymatic conversions indicate a metabolic network of phenylphenalenones in Xiphidium caeruleum

We investigated the organ-specific phytochemistry of the inflorescences, leaves at different stages of senescence, and roots of Xiphidium caeruleum (Haemodoraceae) and elucidated the structure of six undescribed compounds. Among these, a phenylcarbamoylnaphthoquinone (PCNQ), representing the first member of a class of undescribed phenylphenalenone-derived nitrogenous compounds, was identified and its spontaneous formation elaborated. Starting from phenylbenzoisochromenone glucosides, the reaction cascade proceeds through oxidative decarboxylation and several oxidation steps to an anhydride, which is further converted to a carboxy-phenylnaphthoquinone. In the presence of amino acids, this carboxy-phenylnaphthoquinone readily reacts to PCNQs. Hence, the carboxy-phenylnaphthoquinone was hypothesized to be involved in plant defense because of its reactivity towards amino acids. It was also hypothesized that reduced levels of the corresponding glucosidic phenylbenzoisochromenone precursors in older leaves may foster pathogen-driven senescence.

Diboron-Catalyzed Dehydrative Amidation of Aromatic Carboxylic Acids with Amines

Tetrakis(dimethylamido)diboron and tetrahydroxydiboron are herein reported as new catalysts for the synthesis of aryl amides by catalytic condensation of aromatic carboxylic acids with amines. The developed protocol is both simple and highly efficient over a broad range of substrates. This method thus represents an attractive approach for the use of diboron catalysts in the synthesis of amides without having to resort to stoichiometric or additional dehydrating agents.

An Efficient Protocol to Synthesize N-Acyl-enamides and -Imines by Pd-Catalyzed Carbonylations

For the first time, the bidentate phosphinite ligand 1,2-bis(di-tert-butylphosphinoxy)ethane (tBu₂ POCH₂ CH₂ OPtBu₂ ) was synthesized. In the presence of this ligand, various N-acyl enamides were obtained in good yields and chemoselectivity by Pd-catalyzed carbonylation reaction of imines containing α-H. Meanwhile, imines without α-H could be transformed to N-acyl imines, which form highly hindered amides by straightforward addition of Grignard reagents.

Tetramethyl Orthosilicate (TMOS) as a Reagent for Direct Amidation of Carboxylic Acids

Tetramethyl orthosilicate (TMOS) is shown to be an effective reagent for direct amidation of aliphatic and aromatic carboxylic acids with amines and anilines. The amide products are obtained in good to quantitative yields in pure form directly after workup without the need for any further purification. A silyl ester as the putative activated intermediate is observed by NMR methods. Amidations on a 1 mol scale are demonstrated with a favorable process mass intensity.