Three-Component Reaction of Triphenylphosphine,Dimethyl Acetylenedicarboxylate,and Aldehyde Benzoylhydrazones: An Efficient One-Pot Synthesis of Stable Phosphorus Ylides

Protonation of the reactive 1:1 intermediate produced in the reaction between dimethyl acetylenedicarboxylate and triphenylphosphine by benzoylhydrazones leads to vinylphosphonium salts, which undergo Michael addition with the conjugate base of the NH acid to produce highly fanctionalized, salt-free phosphorus ylides in excellent yields.     

Photochemical Activation of Aromatic Aldehydes: Synthesis of Amides,Hydroxamic Acids and Esters

A cheap, facile and metal-free photochemical protocol for the activation of aromatic aldehydes has been developed. Utilizing thioxanthen-9-one as the photocatalyst and cheap household lamps as the light source, a variety of aromatic aldehydes have been activated and subsequently converted in a one-pot reaction into amides, hydroxamic acids and esters in good to high yields. The applicability of this method was highlighted in the synthesis of Moclobemide, a drug against depression and social anxiety. Extended and detailed mechanistic studies have been conducted, in order to determine a plausible mechanism for the reaction.     

Azomethine Ylides from Nitrones: Using Catalytic nBuLi for the Totally Stereoselective Synthesis of trans‐2‐Alkyl‐3‐oxazolines

The cycloaddition of azomethine ylide N‐oxides (nitrone ylides) with aldehydes provides 3‐oxazolines in a completely stereoselective manner in the presence of a catalytic amount of n‐butyllithium. The process involves an initial nucleophilic attack on the aldehyde, followed by intramolecular oxygen addition to the nitrone moiety and lithium‐assisted elimination of water, regenerating the catalytic species. Various Li‐based catalytic systems are possible and the in situ generated water is required for continuing the catalytic cycle. The best results are observed with 20 mol % of n‐butyllithium, whereas the use of stoichiometric amounts inhibit the rate of catalysis. Experimental, spectroscopic, and computational mechanistic studies have provided evidence of lithium‐ion catalysis and rationalized several competing catalytic pathways     

Multicomponent reactions involving zwitterionic intermediates for the construction of heterocyclic systems: one pot synthesis of aminofurans and iminolactones

The reaction of 1:1 zwitterionic intermediate generated in situ from dimethyl acetylenedicarboxylate (DMAD) and cyclohexyl isocyanide with aldehydes and quinones is described. The reaction of stoichiometric amounts of DMAD, isocyanide and aldehydes afforded 2-aminofurans in good yields, while the reaction with quinones gave iminolactones.     

A Facile Method for the Synthesis of Hydrazine‐4‐oxothiazolidine and Imino‐5‐oxothiadiazine Derivatives from 1,4‐Disubstituted Thiosemicarbazides

1,4‐Disubstituted thiosemicarbazides reacted with dimethyl acetylenedicarboxylate with formation of (2‐hydrazono‐4‐oxothiazolidin‐5‐ylidene)acetates and, in one case, a (2‐imino‐1,3,4‐thiadiazin‐5‐on‐6‐ylidene)acetate. Several mechanistic options involving nucleophilic interaction are presented. The structures of all newly synthesized compounds were identified by ¹H NMR, ¹³C NMR, COSY, HMQC and HMBC spectral data.     

Environmentally Friendly Techniques and Their Comparison in the Extraction of Natural Antioxidants from Green Tea,Rosemary, Clove,and Oregano

Many current food and health trends demand the use of more ecological, sustainable, and environmentally friendly techniques for the extraction of bioactive compounds, including antioxidants. However, extraction yields and final antioxidant activities vary between sources and are highly influenced by the given extraction method and nature and ratio of the employed solvent, especially for total polyphenols, flavonoids, and anthocyanins, which are well recognized as natural antioxidants with food applications. This review focused on the most common extraction techniques and potential antioxidant activity in the food industry for various natural antioxidant sources, such as green tea, rosemary, clove, and oregano. Green extraction techniques have been proven to be far more efficient, environmentally friendly, and economical. In general, these techniques include the use of microwaves, ultrasound, high hydrostatic pressure, pulsed electric fields, enzymes, and deep eutectic solvents, among others. These extraction methods are described here, including their advantages, disadvantages, and applications.     

Combined Photoredox and Carbene Catalysis for the Synthesis of Ketones from Carboxylic Acids**

As a key element in the construction of complex organic scaffolds, the formation of C−C bonds remains a challenge in the field of synthetic organic chemistry. Recent advancements in single-electron chemistry have enabled new methods for the formation of various C−C bonds. Disclosed herein is the development of a novel single-electron reduction of acyl azoliums for the formation of ketones from carboxylic acids. Facile construction of the acyl azolium in situ followed by a radical–radical coupling was made possible merging N-heterocyclic carbene (NHC) and photoredox catalysis. The utility of this protocol in synthesis was showcased in the late-stage functionalization of a variety of pharmaceutical compounds. Preliminary investigations using chiral NHCs demonstrate that enantioselectivity can be achieved, showcasing the advantages of this protocol over alternative methodologies.     

Lewis酸催化下2-(2,3,5-三-O-苯甲酰基-D-呋喃核糖)-1,4-氢醌的合成

在不同Lewis酸催化下, 使用1,4-二苯酚和1-O-乙酰基-2,3,5-三-O-β-D-呋喃核糖进行反应, 以较高产率合成了α和β型芳香呋喃糖苷, 并利用¹H-¹H NOESY谱对2-(2,3,5-三-O-苯甲酰基-D-呋喃核糖)-1,4-氢醌(5)的立体构型进行了表征. 应用无水AlCl₃, ZnCl₂和BF₃•Et₂O等Lewis酸催化剂仅得到β型氧糖苷3, 应用TiCl₄得到β型氧糖苷3以及α和β型碳糖苷的混合物5, 而应用SnCl₄则得到α和β型碳糖苷5.     

PEG‐Supported Sulfonic Acid as an Efficient and Recyclable Catalyst for the Synthesis of 1,1‐Diacetates under Solvent‐Free Conditions

An operationally simple, efficient, and environmentally benign synthesis of 1,1‐diacetates in good yields by reaction of different aldehydes with acetic anhydride in the presence of PEG‐supported sulfonic acid under solvent‐free conditions is described.     

A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

We report herein the use of a dual catalytic system comprising a Lewis base catalyst such as quinuclidin‐3‐ol or 4‐dimethylaminopyridine and a photoredox catalyst to generate carbon radicals from either boronic acids or esters. This system enabled a wide range of alkyl boronic esters and aryl or alkyl boronic acids to react with electron‐deficient olefins via radical addition to efficiently form C−C coupled products in a redox‐neutral fashion. The Lewis base catalyst was shown to form a redox‐active complex with either the boronic esters or the trimeric form of the boronic acids (boroxines) in solution.     

Atom-economy Synthesis of N-Substituted Carbamate from Urea Derivative and Dimethyl Carbonate Catalyzed by La/SiO_2: Characterization and Activity

A series of silica gel immobilized lanthanum catalysts were prepared for the atom‐economy synthesis of N‐substituted carbamates from urea derivatives and dimethyl carbonate. The La/SiO₂ catalysts with lanthanum loadings varied from 1.3 wt% to 8.5 wt% were characterized by AES, BET, XRD, TEM, FT‐IR, XPS and TPD. According to the characterization, lanthanum species with particle sizes of 5–10 nm on the surface of silica gel were formed. The catalysts were all amorphous and the surface areas were 336.5–530.2 m²/g. NH₃‐TPD analysis showed that all samples exhibited similar acid strength with different acid amounts. FT‐IR measurement indicated that the component of lanthanum species on the catalyst surface were La(OH)₃, LaOOH and hydrated La₂O₃. Also, the peak value of the absolute amount of LaOOH was obtained with 4.3 wt% lanthanum loading. The BET surface area decreased dramatically when the lanthanum loading was above 4.3 wt%. In consideration of the results obtained from the catalytic reactions, it could be concluded that LaOOH was the possible active species and high surface area was important for the high catalytic activity.     

Bromamine-B/PdCl2 is an Efficient System for the Synthesis of Anthranilic Acids from Indoles and Indigos

A convenient method has been developed for the conversion of indoles and indigos into anthranilic acids in good to excellent yields using a bromamine-B/PdCl₂ system. The general process utilizes our efficient method for the oxidation of indoles and indigos in alkaline (pH 12) acetonitrile/water (1:1) at 60 °C.     

氨基酸钛螯合物和高分子氨基酸钛螯合物对N-丙烯酰-1，3-噁唑烷-2-酮与环? 於┑腄iels-Alder反应的对映选择性催化作用

用磺酰化的L-缬氨酸、L-苯丙氨酸、L-亮氨酸和L-异亮氨酸的钛螯合物催化N- 丙烯酰-1,3-噁唑烷-2-酮与环戊二烯的对映选择性Diels-Alder（D-A）反应,其 ee值为48.1% ～ 78.2%。将这些磺酰基氨基酸钛螯合物受载于高分子链上,用来催 化同一D-A反应时,反应的对映选择性更好,其ee值为82.8% ～ 84.5%。     

Reaction between tert-butyl isocyanide, dialkyl acetylenedicarboxylates, and aromatic carboxylic acids: an efficient method for the synthesis of dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives

Protonation of the reactive intermediates produced in the reaction between tert-butyl isocyanide and dialkyl acetylenedicarboxylates by aromatic carboxylic acids leads to vinylnitrilium cations, which undergo nucleophilic reaction with conjugate bases of the carboxylic acids to produce dialkyl (E)-2-[(benzoyloxy)(tert-butylimino)methyl]-2-butenedioates and this intermediate rearranges to the dialkyl (E)-2-{[benzoyl(tert-butyl)amino]carbonyl}-2-butenedioate derivatives.     

氟代苯基异羟肟酸钴的合成及其对乙苯氧化的催化性能

以全氟碘丁烷为原料,分别与4-碘硝基苯和4-碘苯甲酸反应合成了4-全氟丁基硝基苯（1）和4-全氟丁基苯甲酸（3）; 1经还原反应,3经酰氯化反应,后再缩合反应制得氟代苯基异羟肟酸（5）; 5经络合反应合成了氟代苯基异羟肟酸钴（6）, 其结构经 UV-Vis, ¹H NMR, FT-IR和HR-MS（EI）表征。在氟两相中考察了其对乙苯氧化的催化性能。结果表明：在全氟己烷中,6 0.04 mmol,于60 ℃反应6 h,乙苯的转化率为49.2%,苯乙酮的选择性为88.3%。6循环使用5次,选择性保持良好。     

A General,Activator‐Free Palladium‐Catalyzed Synthesis of Arylacetic and Benzoic Acids from Formic Acid

A new catalyst for the carboxylative synthesis of arylacetic and benzoic acids using formic acid (HCOOH) as the CO surrogate was developed. In an improvement over previous work, CO is generated in situ without the need for any additional activators. Key to success was the use of a specific system consisting of palladium acetate and 1,2‐bis((tert‐butyl(2‐pyridinyl)phosphinyl)methyl)benzene. The generality of this method is demonstrated by the synthesis of more than 30 carboxylic acids, including non‐steroidal anti‐inflammatory drugs (NSAIDs), under mild conditions in good yields.     

A Catalyst and Solvent Free Route for the Synthesis of N-Substituted Pyrrolidones from Levulinic Acid

An efficient, metal-free, catalyst-free and solvent-free methodology for the reductive amination of levulinic acid with different anilines has been developed using HBpin as the reducing reagent. This protocol offers an excellent method to avoid solvents and added catalysts on the synthesis of different kinds of N-substituted pyrrolidones under metal free conditions. It is also the first report for the synthesis of different pyrrolidones by solvent-free as well as catalyst-free methods. The proposed mechanism for the formation of pyrrolidone has been supported by DFT calculations and control experiments.     

Methanesulfonic Acid/SiO2 as an Efficient Combination for the Synthesis of 2-Substituted Aromatic and Aliphatic Benzothiazoles from Carboxylic Acids

Methanesulfonic acid/SiO₂ (1 mL/0.3 g) was found to be as an expeditious mixture in the synthesis of 2-substituted aromatic and aliphatic benzothiazoles at 140 °C using carboxylic acids. After a simple workup, benzothiazoles were obtained in good yields. Simplicity, use of widely available and diverse carboxylic acids, and easy handling of the reaction conditions are among the benefits of the method.     

Complexes of Fe(III) and Ga(III) Derived from the Cyclic 6- and 7-Membered Hydroxamic Acids Found in Mixed Siderophores

Six- and seven-membered cyclic hydroxamic acids are found as terminal binding units in different families of siderophores, including exochelins and mycobactins. The simplest models of these preorganized chelating ligands were known, but their coordination chemistry with Fe³⁺, the target metal ion of siderophores, had never been reported. Four complexes were synthesized and studied: two Fe³⁺ complexes, one with the six-membered ring hydroxamate PIPO⁻ and one with the seven-membered ring hydroxamate AZEPO⁻, and the two corresponding Ga³⁺ complexes. X-ray diffraction studies showed that the interligand repulsion energies were better minimized in the case of the AZEPO⁻ complexes whatever the metal cation considered, and that the Fe−O bond distances were shorter in [Fe(AZEPO)₃] by comparison with [Fe(PIPO)₃].