微波照射下膦酰基/硫甲基烯酮硫代缩醛和N-取代膦酰 基/硫甲基硫代碳酸酯的 合成

在微波照射下方便、高收率地合成了新奇的膦酰基杂环的合成子-膦酰基/硫甲基烯酮硫代缩醛和N-取代膦酰基/硫甲基硫代碳酸酯,实验表明微波照射大大加快了反应速率和提高了反应产率。     

An efficient catalytic method for the Friedländer annulation mediated by peptide coupling agent propylphosphonic anhydride (T3P®)

We have demonstrated the utilization of T3P, a mild and low toxic peptide coupling agent, as a promoter and water scavenger in the Friedländer annulation, and thus introduced a highly efficient catalytic process to access carbocyclic and heterocyclic fused quinolines under microwave irradiation or a conventional heating technique. The reaction conditions are sufficiently mild to tolerate the acid and base sensitive functional groups that can serve as levers for further extension of the quinoline products.     

Trifluoroacetic Acid in 2,2,2‐Trifluoroethanol Facilitates SNAr Reactions of Heterocycles with Arylamines

Small‐molecule drug discovery requires reliable synthetic methods for attaching amino compounds to heterocyclic scaffolds. Trifluoroacetic acid‐2,2,2‐trifluoroethanol (TFA‐TFE) is as an effective combination for achieving S_NAr reactions between anilines and heterocycles (e.g., purines and pyrimidines) substituted with a leaving group (fluoro‐, chloro‐, bromo‐ or alkylsulfonyl). This method provides a variety of compounds containing a “kinase‐privileged fragment” associated with potent inhibition of kinases. TFE is an advantageous solvent because of its low nucleophilicity, ease of removal and ability to solubilise polar substrates. Furthermore, TFE may assist the breakdown of the Meisenheimer–Jackson intermediate by solvating the leaving group. TFA is a necessary and effective acidic catalyst, which activates the heterocycle by N‐protonation without deactivating the aniline by conversion into an anilinium species. The TFA‐TFE methodology is compatible with a variety of functional groups and complements organometallic alternatives, which are often disadvantageous because of the expense of reagents, the frequent need to explore diverse sets of reaction conditions, and problems with product purification. In contrast, product isolation from TFA‐TFE reactions is straightforward: evaporation of the reaction mixture, basification and chromatography affords analytically pure material. A total of 45 examples are described with seven discrete heterocyclic scaffolds and 2‐, 3‐ and 4‐substituted anilines giving product yields that are normally in the range 50–90 %. Reactions can be performed with either conventional heating or microwave irradiation, with the latter often giving improved yields.     

Acyl Radicals from Aromatic Carboxylic Acids by Means of Visible‐Light Photoredox Catalysis

Simple and abundant carboxylic acids have been used as acyl radical precursor by means of visible‐light photoredox catalysis. By the transient generation of a reactive anhydride intermediate, this redox‐neutral approach offers a mild and rapid entry to high‐value heterocyclic compounds without the need of UV irradiation, high temperature, high CO pressure, tin reagents, or peroxides.     

Synthesis of 2‐cyanoacrylates containing pyridinyl moiety under ultrasound irradiation

Reaction of ethyl cyanoacetate with carbon disulfide and dimethyl sulfate in the presence of sodium methoxide in anhydrous methanol yields ethyl 2‐cyano‐3,3‐dimethyl‐ thioacrylate, followed by the nucle‐ophilic substitution with 2‐amino‐3‐chloro‐4‐ methylpyridine under ultrasonic irradiation affording the key intermediate, ethyl 3‐(2‐chloro‐4‐methylpyridin‐3‐ylamino)‐2‐cyano‐3‐methylthioacrylate. The title compounds were then obtained through the reaction of the key intermediate with the aliphatic amine under reflux condition. All the new structures were verified by elemental analysis, IR, ¹H NMR and mass spectra. In the MTT test, these new compounds were found to possess moderate antitumor activities against PC3 and A431 cells.     

Mechanism of PtIV Sonochemical Reduction in Formic Acid Media and Pure Water

Sonochemical synthesis of platinum nanoparticles (Pt NPs) in formic acid solutions and pure water was investigated using a 20 kHz ultrasonic irradiation. The obtained results gave new insights on the underneath Pt^IV reduction mechanism in formic acid media under argon and in pure water under Ar/CO atmosphere. It was shown that in pure water sonochemical reduction of platinum ions occurs by hydrogen issued from homolytic water molecule split. Pt^IV ion reduction appears to be a very slow process under argon atmosphere in pure water due to formation of oxidizing species like OH radicals and H₂O₂ leading to reoxidation of intermediate Pt^II ions. Sonochemical reduction is accelerated manifold in the presence of formic acid or Ar/CO gas mixture. Solution and gas‐phase analyses reveal that both CO and HCOOH act as OH^. radical scavenger and reducing agent under ultrasonic irradiation. Their ability to reduce platinum ions at room temperature is enhanced due to the local heating in the liquid shell surround the cavitation bubble. An innovative synthesis route for monodispersed Pt NPs in pure water without any templates or capping agents in the presence of Ar/CO gas mixture is then proposed. Obtained Pt NPs within the range of 2–3 nm exhibited a strong stability towards sedimentation in water. Since Ar/CO atmosphere is the only restriction of the process, this procedure can be applied in various media and is also compatible with a large array of experimental conditions.     

Photochemical Activities of N‐Nitroso Carboxamides and Sulfoximides and Their Application to DNA Cleavage

N‐Nitroso compounds containing benzene, fluorene or fluorenone rings were synthesized. Photolysis of these compounds with 312‐nm UV light provided the NO ^. species, the presence of which was corroborated by use of an EPR method and of 2‐phenyl‐4,4,5,5‐tetramethylimidazolin‐1‐oxyl 3‐oxide (PTIO) as a trapping agent. During irradiation of N‐methyl‐N‐nitroso‐9‐fluorenone carboxamide ( 14 c ) in the absence of PTIO, it underwent decomposition followed by recombination to give the heterocyclic nitric oxide radical 15 . Incorporation of intercalating moieties endowed the N‐nitroso compounds with DNA‐cleaving ability through single‐strand scission upon UV irradiation in a phosphate buffer (pH 5.0–8.0) under aerobic conditions.     

Microwave-assisted synthesis of benzoxazinediones under solvent-free conditions

Benzoxazinediones exhibit potential as versatile synthons in the synthesis of wide variety of heterocyclic compounds with biological activity. In this work, an efficient and eco-friendly one-step synthesis of benzoxazine-2,4-diones from phthalic anhydrides derivatives and trimethylsilyl azide using the microwave technique was developed and compared with conventional heating. Microwave irradiation plays a critical role in driving the reaction and providing access to products and/or regioisomers not available from conventional heating. Thus, the regioselectivity of the reaction may be modulated by the irradiation time. Depending on the method employed the benzoxazinediones were isolated with yields in the range of 30–90%.     

N‐Heterocyclic Carbene Catalyzed Photoenolization/Diels–Alder Reaction of Acid Fluorides

The combination of light activation and N‐heterocyclic carbene (NHC) organocatalysis has enabled the use of acid fluorides as substrates in a UVA‐light‐mediated photochemical transformation previously observed only with aromatic aldehydes and ketones. Stoichiometric studies and TD‐DFT calculations support a mechanism involving the photoactivation of an ortho‐toluoyl azolium intermediate, which exhibits “ketone‐like” photochemical reactivity under UVA irradiation. Using this photo‐NHC catalysis approach, a novel photoenolization/Diels–Alder (PEDA) process was developed that leads to diverse isochroman‐1‐one derivatives.     

Static and Ultrasonic‐assisted Aging Effects on the Synthesis of Analcime Zeolite

The synthesis of zeolite ANA under static hydrothermal conditions was performed accompanied by an additional static and ultrasonic‐assisted aging of the reaction mixture prior to crystallization. The aging process was compared with stirring‐assisted aging, microwave‐assisted aging and syntheses without any aging. The influence of aging time on the crystallization time of zeolite ANA was investigated. The static and ultrasonic‐assisted aging can shorten the crystallization time of the ANA phase. Moreover, ultrasonic‐assisted aging leads to altered morphologies of the particles. The products were characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM).     

Microwave-assisted reactions in heterocyclic compounds with applications in medicinal and supramolecular chemistry

Microwave irradiation has been successfully applied in organic chemistry. Spectacular accelerations, higher yields under milder reaction conditions and higher product purities have all been reported. Indeed, a number of authors have described success in reactions that do not occur under conventional heating and modifications in selectivity (chemo-, regio- and stereoselectivity) have even been reported. Recent advances in microwave-assisted combinatorial chemistry include high-speed solid-phase and polymer-supported organic synthesis, rapid parallel synthesis of compound libraries, and library generation by automated sequential microwave irradiation. In addition, new instrumentation for high-throughput microwave-assisted synthesis continues to be developed at a steady pace. The impressive speed combined with the unmatched control over reaction parameters justifies the growing interest in this application of microwave heating. In this review we highlight our recent advances in this area, with a particular emphasis on cycloaddition reactions of heterocyclic compounds both with and without supports, applications in supramolecular chemistry and the reproducibility and scalability of organic reactions involving the use of microwave irradiation techniques.     

Cyclization of 4,5‐Diamino Pyrazole Derivatives and Their Antibacterial Activities

A convenient synthesis of intermediate 4,5‐diamino‐3‐aryl‐1‐phenylpyrazoles 4a – 4c was reported. The different cyclization reactions were carried out with chalcone, 2‐mercaptoacetic acid and p‐anisialdehyde, ethyl chloroformate, glyoxal and thiourea to afford different N and S containing heterocycles. The reaction conditions were compared by conventional heating and microwave irradiation. The structures of the cyclization products were determined by analytical and spectroscopic data. All the synthesized compounds were screened for antibacterial activities in vitro.     

External‐Photocatalyst‐Free Visible‐Light‐Mediated Synthesis of Indolizines

A visible‐light‐mediated synthesis of valuable polycyclic indolizine heterocycles from easily accessed brominated pyridine and enol carbamate derivatives has been developed. This process, which operates at room temperature under irradiation from readily available light sources, does not require the addition of an external photocatalyst. Instead, an investigation into the reaction mechanism indicates that the indolizine products themselves may be in some way involved in mediating and accelerating their own formation. Preliminary studies also show that these simple heterocyclic compounds may be capable of facilitating other visible‐light‐mediated transformations.     

Synthesis of Some Substituted Pyrazolopyrimidine Derivatives: An Environmentally Benign Approach

Pyrazolopyrimidines constitute a medicinally important class of heterocyclic compounds. Herein, we report an efficient and environmentally benign method for the synthesis of pyrazolo[3,4‐d]pyrimidin‐3‐ones from 2,4‐dinitrophenylhydrazine and diethyl malonate under microwave irradiation in 1,3‐dibutylimidazolium bromide ionic liquid. The synthesized compounds were analyzed by elemental analysis and standard spectroscopic techniques. The compounds were screened for their antibacterial and antifungal activities.     

Ultrasound-assisted green synthesis of five-membered O- and S-heterocycles

This review gives an overview of utilization of ultrasound for the synthesis of various heterocyclic compounds. Ultrasonic irradiation has been considered as an efficient methodology in many organic syntheses. With ultrasonic assistance short reaction times, good selectivity and high yields are reported. The use of ultrasound irradiation in organic reactions has been increasing rapidly in recent years.     

Synthesis of six- and seven-membered heterocycles under ultrasound irradiation

This review gives an overview of utilization of ultrasound for the synthesis of various heterocyclic compounds. Ultrasonic irradiation has been considered as an efficient methodology in many organic syntheses. With ultrasonic assistance short reaction times, good selectivity and high yields are reported. The use of ultrasound irradiation in organic reactions has been increasing rapidly in recent years.     

Synthesis and spectroscopic characterization of two tetrasubstituted cationic porphyrin derivatives

An imidazolium tetrasubstituted cationic porphyrin derivative (the free base and its Zn(II) complex) with five-membered heterocyclic groups in the meso-positions were synthesized using microwave irradiation, and the compounds obtained characterized by (1)H-NMR and mass spectrometry. We observed that under microwave irradiation the yield is similar to when the synthesis is performed under conventional heating, however, the time required to prepare the porphyrins decreases enormously. In order to investigate the electronic state of these compounds, we employed UV-Vis and fluorescence spectroscopy combined with quantum chemical calculations. The results reveal the presence, in both compounds, of a large number of electronic states involving the association between the Soret and a blue-shifted band. The Soret band in both compounds also shows a considerable solvent dependence. As for emission, these compounds present low quantum yield at room temperature and no solvent influence on the fluorescence spectra was observed.     

Synthesis and Antifungal Activity of Novel 1,2,4‐Triazole Derivatives Containing 1,2,3‐Thiadiazole Moiety

Starting from carbonic acid diethyl ester, a series of 1,2,4‐triazole derivatives containing 1,2,3‐thiadiazole were synthesized. Reactions were performed by microwave irradiation or ultrasonic irradiation as well as by conventional heating. The structure of title compounds was characterized by ¹H‐NMR, MS, and elemental analyses. The fungicidal activities of these compounds were tested in vivo. Most of title compounds exhibited good antifungal activity against Pseudoperonospora cubensis. Some of title compounds displayed moderate antifungal activities against Fusarium oxysporum, Pseudoperonospora cubensis, Sphaerotheca fuligenea, Corynespora cassiicola, and Xanthomonas axonopodis.     

A New Application of Hexamethylenetetramine‐Bromine Supported onto Wet Alumina as an Efficient Reagent for Cleavage of Phenylhydrazones under Classical Heating and Microwave Irradiation

2,4‐Dinitrophenylhydrazones were converted to their parent carbonyl compounds using hexamethylenetetramine‐bromine complex supported onto wet alumina under classical heating and microwave irradiation.     

A Fast and Solvent-Free Conversion of Thioamides into Thioesters

Summary. Solvent-free irradiation of thiomorpholides with two kinds of methylating agents under microwave or ultrasonic conditions gave the corresponding thioesters in high yield. The method is simple and avoids prolonged heating with solvents.