Synthesis of indolo[2,3-c]coumarins and indolo[2,3-c]quinolinones via microwave-assisted base-free intramolecular cross dehydrogenative coupling

A microwave-assisted base-free intramolecular cross dehydrogenative coupling (CDC) of 3-aniline substituted coumarins and quinolinones have been developed. A broad range of indolo[2,3-c]coumarins and indolo[2,3-c]quinolinones can be easily afforded in good to high yields (up to 93%) under palladium catalysis. The method is among the most straightforward and convenient ways to access these fused polyheterocycles.     

New method for preparation of coumarins and quinolinones via Pd-catalyzed intramolecular hydroarylation of C-C triple bonds

A new and general method has been developed for preparation of coumarins and quinolinones by intramolecular hydroarylation of alkynes. Various aryl alkynoates and alkynanilides undergo fast intramolecular reaction at room temperature in the presence of a catalytic amount of Pd(OAc)(2) in a mixed solvent containing trifluoroacetic acid (TFA), affording coumarins and quinolinones in moderate to excellent yields with more than 1000 turnover numbers (TON) to Pd. The methodology proved to tolerate a number of functional groups such as Br and CHO. On the basis of isotope experiments, a possible mechanism involving ethynyl chelation-assisted electrophilic metalation of aromatic C-H bonds by in-situ generated cationic Pd(II) species has been discussed. Also the involvement of vinylcationic species has been suggested.     

Catalytic Activity Towards Hydrogen Evolution Dependent of the Degree of Conjugation and Absorption of Six Organic Chromophores

Conjugated materials can, in many cases, absorb visible light because of their delocalized π electron system. Such materials have been widely used as a photoactive layers in organic photovoltaic devices and as photosensitizers in dye-sensitized solar cells. Additionally, these materials have been reported for applications in solar fuel production, working as photocatalysts for the hydrogen evolution reaction (HER). The synthesis of three flexible vinyl groups-containing chromophores is reported. The catalytic activity towards hydrogen evolution of these chromophores has been investigated and compared to their non-vinyl-containing analogues. The catalytic effect was confirmed using two different approaches: electrochemical, using the chromophores to modify a working electrode, and photocatalytic, using the chromophores combined with platinum nanoparticles. A relationship between the degree of conjugation and the catalytic activity of the chromophores has been observed with the electrochemical method, while a relationship between the UV absorption in the solid state and the photocatalytic effect with platinum nanoparticles was observed.     

Developments in visible-light-mediated copper photocatalysis

The scope, applications, and understanding of photoinduced, copper-catalysis have advanced considerably in recent times. Many of these transformations exploit the distinctive properties of photoactive copper species to establish original synthetic methodology and reveal novel reactivity. In this regard, the bifunctionality of copper photocatalysts has often allowed these species to direct and influence synthetic processes in new, interesting, and exciting ways. This article summarizes recent advances in the development of copper photoredox catalysts and provides an overview of the emerging applications of these, and related systems, in organic synthesis.     

A practical strategy for the characterization of coumarins in Radix Glehniae by liquid chromatography coupled with triple quadrupole-linear ion trap mass spectrometry

The aim of the present study was to develop a practical method for the characterization of coumarins in Radix Glehniae by liquid chromatography–mass spectrometry (LC–MS). First, 10 coumarin standards (including two pairs of isomers) were studied, and mass spectrometry fragmentation patterns and elution time rules for the coumarins were found. Then, an extract of Radix Glehniae was analyzed by the combination of two scan modes, i.e., multiple ion monitoring-information-dependent acquisition-enhanced product ion mode (MIM-IDA-EPI) and precursor scan information-dependent acquisition-enhanced product ion mode (PREC-IDA-EPI) on a hybrid triple quadrupole-linear ion trap mass spectrometer. A total of 41 coumarins were identified on the basis of their mass spectrometry fragmentation patterns. This is the first time that these two scan modes have been combined to characterize chemical constituents in traditional Chinese medicine. This new method allowed the identification of coumarins in Radix Glehniae in trace amounts. The methodology proposed in this study could be valuable for the structural characterization of coumarins from complex natural and synthetic sources.     

Pyrroloquinolines,a New Platform for Developing Organic Photosensitizers: When Synthetic Methodology Meets Photophysics†

New molecular architectures with triplet sensitization properties can have a big impact on photochemistry and photobiology. In their recent work, de Bonfils et al. have tackled this challenge in a very systematic way using a powerful synthetic strategy. This consists of an elegant yet practical organocatalyzed cyclization/oxidation rearrangement sequence which they now apply to the synthesis of pyrroloquinolines, a new scaffold for photosensitizers. However, beyond this new class of compounds, the strategy has potential to produce a myriad of compact organic chromophores with promising photoinduced intersystem crossing properties. The study therefore provides interesting clues to serve the rational design of biocompatible molecular photosensitizers but also raises puzzling questions on the intriguing excited state reactivity of these molecular architectures.     

2,3-位稠杂环喹唑啉酮类化合物的合成研究进展

2,3-位稠环喹唑啉酮类化合物由于具有多种优良的生物和生理活性而广泛应用于药物领域,其合成方法是目前药物研究的热点领域之一.本文主要介绍了包括以2-氨基苯甲酸类化合物、2-氨基苯甲酸甲酯类化合物、靛红酸酐类化合物、喹唑啉酮类化合物等为原料合成2,3-位稠环喹唑啉酮类化合物的方法,并对这些方法进行了简单的评述.     

Covalent Organic Frameworks for Photocatalytic Organic Transformation

Photocatalytic organic transformation is an efficient, energysaving and environmentally friendly strategy for organic synthesis. The key to developing a green and economical route for photocatalytic organic synthesis lies in the construction of optimal photocatalysts. Covalent organic frameworks(COFs), a kind of porous crystalline materials with characteristics of high surface area, excellent porosity, and superior thermo-chemical stability, have driven people to explore their potential as photocatalysts in photocatalytic organic transformations by virtue of their structural versatility and designability. Furthermore, the insolubility of COFs makes it possible to recycle the catalysts by simple technical means. In recent years, researchers have made great efforts to develop both the design strategies of COFs as heterogeneous photocatalysts and the reaction types of photocatalytic organic transformations. In this review, we focus on the design of COF-based photocatalytic materials and analyze the influence factors of photocatalytic performance. Moreover, we summarize the application of COFbased photocatalysts in photocatalytic organic conversion. Finally, the perspectives on new opportunities and challenges in the field are discussed.     

Ligand‐Controlled Palladium(II)‐Catalyzed Regiodivergent Carbonylation of Alkynes: Syntheses of Indolo[3,2‐c]coumarins and Benzofuro[3,2‐c]quinolinones

Regiodivergent syntheses of indolo[3,2‐c]coumarins and benzofuro[3,2‐c]quinolinones through a controllable palladium(II)‐catalyzed carbonylative cyclization are established. The chemo‐ and regioselectivity are exclusively tuned by the ligand on the palladium catalyst. The rigid framework of the electron‐deficient ligand promotes the O‐attack/N‐carbonylation cyclization leading to benzofuro[3,2‐c]quinolinones, while a sterically bulky and electron‐rich ligand facilitates N‐attack/O‐carbonylation cyclization to generate indolo[3,2‐c]coumarins. Furthermore, various other nucleophiles are applicable for delivering a variety of indoloquinolinones, pyranoquinolones, and chromeno[3,4‐c]quinolinones in one step, and serves as a method for creating compound libraries for drug discovery.     

Recent advances in the microwave- and ultrasound-assisted green synthesis of coumarin-heterocycles

Given the importance of the highly reactive nature and attractiveness of coumarins as a precursor of natural products and pharmacological agents, tremendous efforts have been dedicated to their synthesis in the last decades. Starting from the Knoevenagel, Perkin, Kostanecki-Robinson, Pechmann, Reformansky, Baylis Hillman reactions to several new one-pot multicomponent, sequential tandem reactions have been devised. After the emergence of non-conventional energy sources like microwaves (MW) and ultrasound irradiation, the field of organic synthesis has reached an outstanding level in this century in terms of synthetic efficiency as well as green chemistry viewpoint. Enlightened by this, a great deal of attention has been paid to the synthesis of bioactive coumarin-heterocycles by employing the non-conventional approach and a vast array of synthetic procedures has been established. Therefore, a time to time investigation is required for the synthesis and biological aspects of these hybrid molecules. The present review aims to highlight the current progress achieved in the synthesis of coumarins either linked or fused with diverse bioactive five- and six-membered heterocycles by making the utilization of microwaves and ultrasound-assisted strategies from 2014 to date. Besides highlighting the development achieved in this field, we have attempted to point out the drawbacks and challenges associated with the reaction discovery, which would hopefully provide the impetus for future exploration.     

Imine-based covalent organic framework as photocatalyst for visible-light-induced atom transfer radical polymerization

Photoinduced atom transfer radical polymerization (ATRP) is an economical and environment-friendly method for synthesizing polymers with pre-designable structures and precise molecular weight. Although significant progress for copper-mediated photoinduced ATRP has been achieved, several drawbacks still remain, such as poor electron transfer capability and absorption bands of photocatalysts near UV region. Herein, imine-based covalent organic framework, TAPPy-TPA-COF , has been synthesized as potential heterogeneous photocatalyst for photoinduced ATRP. The “living” feature of polymerizations of methyl methacrylate (MMA) can be well controlled by efficiency maintain the balance between activation and inactivation of Cu^I and Cu^II. The chain extension experiments have further demonstrated the chain-end fidelity of polymers. Meanwhile, the catalyst recycle experiments have revealed stability of TAPPy-TPA-COF toward ATRP processes. These results support the feasibility of using COFs as heterogeneous photocatalysts for copper-mediated ATRP under visible light irradiation.     

An artificial [FeFe]-hydrogenase mimic with organic chromophore-linked thiolate bridges for the photochemical production of hydrogen

An artificial [FeFe]-hydrogenase ([FeFe]-H₂ase) mimic 3II, consisting of dual organic chromophores covalently assembled to the [Fe₂S₂] active site, was constructed for light-driven hydrogen evolution. The structural conformation of synthetic photocatalyst was characterized crystallographically and spectroscopically. The photo-induced intramolecular electron transfer was evidently demonstrated by the combination of electrochemical, steady-state, and transient absorption spectroscopic studies. Finally, a remarkable activity was obtained in the present photocatalytic system, indicating the covalent incorporation of photosensitizer and catalytic center as a promising strategy to construct inexpensive, easily accessible [FeFe]-H₂ase model photocatalysts.     

Photocatalysis in Supramolecular Fluorescent Metallacycles and Metallacages

The utilization of photocatalytic techniques for achieving light-to-fuel conversion is a promising way to ease the shortage of energy and degradation of the ecological environment. Fluorescent metallacycles and metallacages have drawn considerable attention and have been used in widespread fields due to easy preparation and their abundant functionality including photocatalysis. This review covers recent advances in photocatalysis in discrete supramolecular fluorescent metallacycles and metallacages. The developments in the utilization of the metallacycles skeletons and the effect of fluorescence-resonance energy transfer for photocatalysis are discussed. Furthermore, the use of the ligands decorated by organic chromophores or redox metal sites in metallacages as photocatalysts and their ability to encapsulate appropriate catalytic cofactors for photocatalysis are summarized. For the sake of brevity, macrocycles and cages with inorganic coordination complexes such as ruthenium complexes and iridium complexes are not included in this minireview.     

Metal-facilitated Photocatalytic Nanohybrids: Rational Design and Promising Environmental Applications

As a promising technique to potentially address the energy crisis and environmental issues, photocatalysis has been reported widely to exhibit various outstanding behaviors in production of new fuels/chemicals and treatment of contaminants. The photocatalytic performance is extremely dependent on the used photocatalysts, so that the design and preparation of efficient photocatalysts are critically important for significantly improving the photocatalytic activity. Among various strategies, the hybridization of metal with semiconductors has recently been attracting more and more research interest owing to their expended spectral absorption, promoted transferring rate of charge carriers and Plasmon-enhanced effect. In this minireview, the metal-facilitated hybrid photocatalysts are overviewed comprehensively to first reveal unique functions of metals in improvement of photoactivity and summarize the emerging metal-involved hybrid systems. Subsequently, the synthetic methods towards hybrid photocatalysts are introduced and their practical applications are emphasized in environmental remediation including degradation of organic pollutants, conversion of harmful gases, treatment of heavy metal ions and sterilization of bacteria. At the end, the challenges for industrializing these hybrid photocatalysts are discussed carefully and future development is suggested rationally.     

通过自由基加成环化反应制备香豆素衍生物的研究进展

香豆素衍生物是一类重要的杂环内酯化合物,广泛应用于有机合成、生物医药及荧光材料等领域。开发新型简单高效的功能化香豆素合成策略一直受到人们的关注,通过苯丙炔酸酯与各类自由基前驱体的直接自由基加成环化反应为香豆素衍生物的功能化修饰提供了一条简单、清洁、高效的合成路线。本文综述了近年来基于自由基加成环化历程制备各类功能化香豆素衍生物的新进展。     

Dicyanomethylene-4H-pyran chromophores for OLED emitters, logic gates and optical chemosensors

Dicyanomethylene-4H-pyran (DCM) chromophores are typical donor-π-acceptor (D-π-A) type chromophores with a broad absorption band resulting from an ultra-fast internal charge-transfer (ICT) process. In 1989, Tang et al. firstly introduced a DCM derivative as a highly fluorescent dopant in organic electroluminescent diodes (OLEDs). Integration of ICT chromophore-receptor systems based on DCM chromophores with ion-induced shifts in absorption or emission is a convenient method to perform the logic expression for molecular logic gates. In recent years, various DCM-type derivatives have been explored due to their excellent optical-electronic properties and diverse structural modification. This feature article provides an insight into how the structural modification of DCM chromophores can be utilized for OLED emitters, logic gates and optical chemosensors. In addition, the aggregation-induced-emission (AIE) of DCM derivatives for further optical applications was also introduced.     

Molecular switches controlled by light

The photochemical processes of singlet-singlet energy transfer and photoinduced electron transfer are important not only in natural and artificial photosynthetic energy conversion, but also in a variety of other scientific and technological applications. Controlling these functions at the molecular level using outside stimuli is an interesting scientific challenge. Photochromes, organic molecules that are isomerized by light between two stable forms, can be covalently linked to other chromophores, and changes in their properties resulting from photoisomerization used to switch electron and energy transfer on or off. Simple single- and double-throw molecular switches have been constructed, as well as Boolean logic gates. Such molecules are potentially useful in light-controlled molecular data processing and storage applications.     

Dispirofluorene-indenofluorene derivatives as new building blocks for blue organic electroluminescent devices and electroactive polymers

A series of new dispiro[fluorene-9',6,9',12-indeno[1,2b]fluorenes] (DSF-IFs) has been synthesised. These new building blocks for blue-light-emitting devices and electroactive polymers combine indenofluorene (IF) and spirobifluorene (SBF) properties. We report here our synthetic investigations towards these new structures and their thermal, structural, photophysical and electrochemical properties. These properties have been compared to those of IF and SBF. We also report the anodic oxidation of DSF-IFs that leads to the formation of non-soluble transparent three-dimensional polymers. The structural and electrochemical behaviour of these polymers has been studied. The first application of these building blocks as new blue-light-emitting materials in organic light-emitting diodes (OLED) is also reported.     

Synthesis and structural revision of naturally occurring ayapin derivatives

The synthesis of three highly oxygenated naturally occurring coumarins, 8-methoxy-6,7-methylenedioxycoumarin, 5-methoxy-6,7-methylenedioxycoumarin and 5,8-dimethoxy-6,7-methylenedioxycoumarin is described for the first time, together with a new method for the preparation of ayapin (6,7-methylenedioxycoumarin). Comparison of the spectroscopic data of the synthetic tetraoxygenated coumarin 5,8-dimethoxy-6,7-methylenedioxycoumarin with literature reports resulted in the structural revision of several natural coumarins. Two coumarins, both identified as 5,8-dimethoxy-6,7-methylenedioxycoumarin must have other structures, while the structure of another coumarin, described as the isomeric 7,8-dimethoxy-5,6-methylenedioxycoumarin has to be revised to 5,8-dimethoxy-6,7-methylenedioxycoumarin.