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Synthetic approaches for 2,4,6-trisubstituted-1,3,5-triazine systems are analyzed, and their properties attractive to practical applications in fluorescent materials are reviewed.

In this review article, the currently available synthetic approaches to 1,2,4-triazolo[5,1-c][1,2,4]triazin-7-ones have been discussed. This moiety is considered as a basic heterocyclic structure of the antiviral drug Riamilovir (“Triazavirin®”).

1-Butane sulfonic acid-3-methylimidazolium tosylate, [BSMIM]OTs, is a remarkable catalyst for the cascade synthesis of coumarin-functionalized indole derivatives via a tandem cyclization reaction of aniline and phenylglyoxal monohydrate.

A green protocol has been developed for the synthesis of simple coumarins and linear pyrano[2,3-f] and [3,2-f]indoles by the reaction of phenol derivatives with β-ketoesters under ball milling at ambient temperature in the presence of methanesulfonic acid.

This review discusses the synthetic routes for 2,7-diazapyrene derivatives and highlights the opportunities for application of 2,7-diazapyrenes, including their remarkable photophysical and supramolecular properties, in sensors and related areas.

Push-pull fluorophores exhibiting pronounced intramolecular charge transfer have a low fluorescence quantum yield. Here we report a new series of D-π-A push-pull fluorophores containing a unified 2,2'-bipyridine domain acceptor with...

Azapyrenes are the nitrogen isosteres of pyrene. Based on theoretical and experimental studies, electron–acceptor azapyrene domains may be considered as convenient scaffolds for constructing a large variety of “push–pull” π-conjugated chromophores with pronounced ICT properties. Over the past decade, due to the unrelenting interest in functional materials and modern methodologies such as cross-coupling, peri-annulation, direct C–H-functionalization, etc., methods for the synthesis of aryl(alkyl) K-functionalized azapyrenes and other derivatives have been developed, and their photophysical and electrochemical properties have been studied. This short review aims at critical analysis of the best known/modern methods for the preparation of functionalized azapyrene derivatives, as well as an assessment of their photophysical/electrochemical properties in comparison with the structural and electronic properties of the parent pyrene.

Computer vision (CV) algorithms are widely utilized in imaging processing for medical and personal electronics applications. In sensorics CV can provide a great potential to quantitate chemosensors' signals. Here we wish to describe a method for the CV-assisted spectrofluorometer-free detection of common nitro-explosive components, e.g. 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), by using polyaromatic hydrocarbon (PAH, PAH = 1-pyrenyl or 9-anthracenyl) – based bola-type chemosensors. The PAH components of these chemical bolas are able to form stable, bright emissive in a visual wavelength region excimers, which allows their use as extended matrices of the RGB colors after imaging and digital processing. In non-polar solvents, the excimers have poor chemosensing properties, while in aqueous solutions, due to the possible micellar formation, these excimers provide “turn-off” fluorescence detection of DNT and TNT in the sub-nanomolar concentrations. A combination of these PAH-based fluorescent chemosensors with the proposed CV-assisted algorithm offers a fast and convenient approach for on-site, real-time, multi-thread analyte detection without the use of fluorometers. Although we focus on the analysis of nitro-explosives, the presented method is a conceptual work describing a general use of CV for quantitative fluorescence detection of various analytes as a simpler alternative to spectrofluorometer-assisted methods.

We have observed that a reagent combination of NaIO4 and NH2OH·HCl reacts with α,β-unsaturated ketones followed by the nucleophile ethylene glycol allowing the synthesis of 2,3-disubstituted 1,4-dioxanes using cesium carbonate as a base under Williamson ether synthesis. This reaction is useful for the synthesis of functionalized 1,4-dioxane having a carbonyl functionality. A variety of 2,3-disubstituted 1,4-dioxanes have been synthesized using these reaction conditions. A probable reaction mechanism has also been proposed.

Extensive research on the synthesis and application of tetrazine derivatives for electronic devices, luminescent elements, photoelectric conversion elements, and image sensors has been published recently. This review covers reported data on the modern trends in the design of functionalized tetrazines obtained within the period 2010–2020. Aryl(heteroaryl) and arylvinyl derivatives of tetrazines and their photoluminescence and application for fluorogenic probes are discussed. Examples of photosensitive oligomers and polymer 3,6-dithienyltetrazines are reviewed.

Functionalized pyranocoumarins are an important class of oxygen-containing heterocyclic compounds. Fused coumarin systems, in particular pyranocoumarins, are abundant in nature and constitute building blocks for many natural products found across the plant kingdom. Pyranocoumarin derivatives have been found to possess antifungal, insecticidal, anticancer, anti-HIV, anti-inflammatory, antioxidant, and antibacterial activities. Synthesis of this moiety from easily available chemicals is desirable due to its tremendous use in various branches of chemistry. Owing to the broad spectrum of biological properties and natural occurrence, pyrano[3,2-c]coumarins have become attractive synthetic targets from the point of view of medicinal chemistry. This short review discusses the synthesis of this scaffold using different strategies including mechanistic illustrations.

Mechanochemical approaches in an organic synthesis have received increased interest because of their wide applications in green methodologies. Ball milling has been fruitfully utilized in the synthesis of various (elemental) organic scaffolds, including common drugs or drug candidates. However, the utilization of ball milling in asymmetric organic synthesis has not been adequately investigated. Thus, the aim of this review is to highlight the attractive features of the applications of mechanochemistry via ball milling in asymmetric organic syntheses in order to attract the attention of a wider section of the synthesis community.

The visible light promoted cross-dehydrogenative coupling reaction has emerged as an excellent strategy for the direct formation of C–C/C–heteroatom bonds from simple compounds. The use of renewable energy resources without the need for prefunctionalization of the reactant synergistically promote the synthetic pathway towards green synthesis. Although the introduction of the terminology “cross-dehydrogenative coupling (CDC)” was done by Li’s group in 2004, visible light promoted CDC has attracted tremendous attention from synthetic chemists since the first report of Ir-photocatalysis by Stephenson et al. in 2010. The efficiency of different transition-metal salts (Ir-, Ru-, Rh-, Cu-, Pt-, Co-, etc.), organic molecules (eosin Y, eosin B, rose bengal, rhodamine, methylene blue, acridines, etc.), I2, and heterogeneous catalysts as photocatalysts in this transformation has been extensively investigated during this period. A number of methodologies have been also developed under visible light irradiation even in the absence of any photocatalysts. In this review, all the visible light promoted cross-dehydrogenative coupling methodologies developed over the last decade have been disclosed. Furthermore, the applicability and the mechanistic pathways of the methodologies have been also discussed.

A library of substituted quinolines has been synthesized by the reaction of aldehydes, anilines and nitroalkanes using a catalytic amount of Fe(iii) chloride. The reaction is a simple, efficient, one-pot, three-component domino strategy in ambient air which afforded the products in high yields. A probable pathway of the reaction is a sequential aza-Henry reaction/cyclization/denitration. The use of commercially available chemicals as starting materials, an inexpensive metal catalyst, aerobic reaction conditions, tolerance of a wide range of functional groups, and operational simplicity are the notable advantages of this present protocol.

2-Azaanthracene(benzo[g]isoquinoline) is the second most common nitrogenous derivative of anthracene after acridine (2,3-benzoquinoline, 9-azaanthracene). The introduction of the nitrogen atom into the aromatic core of this molecule allowed it to significantly push the boundaries of the application fields of 2-azaanthracene and its derivatives, compared to regular anthracene. This review aims to summarize the common synthetic approaches towards 2-azaanthracenes in chronological order, as well as systematize information on the areas of application of 2-azaanthracenes. In particular, emphasis is placed on the description of the 2-azaanthracene family as unique fluorophores and chromophores for creating modern cell stains, chemosensors, pH-probes, etc. In addition to regular 2-azaanthracene, the common methods for the synthesis of fused 2-azaanthracene as promising OLED components or as ligands for metal cations are reported.

The interactions between substituted 5-R-3-(pyridyl-2)-1,2,4-triazines with in situ generated substituted aryne intermediates have been studied. The reaction afforded either inverse demand (ID) aza-Diels-Alder products or 1,2,4-triazine ring rearrangement (domino) products as major ones depending on the nature of both the substituents at the C5 position of the 1,2,4-triazine core or in the aryne moiety. The structures of the key products were confirmed based on X-ray data. Based on the density functional theoretical (DFT) studies of the Diels-Alder transition state geometries, the influence of the nature of arynes on the direction of the 1,2,4-triazine transformation has been proposed.

1-Butane sulfonic acid-3-methylimidazolium tosylate, [BSMIM]OTs, is found to be a remarkable catalyst for the tandem cyclization of 4-hydroxycoumarin with chalcones for the syntheses of pyrano[3,2-c]coumarins under solvent-free conditions. The developed protocol is applicable for the construction of biologically important pyranocoumarins from easily accessible chalcones having various substituents. This reaction possibly proceeds through Michael addition followed by cyclization. The feasibility of catalyst recycling is also demonstrated. This method produces only water as the byproduct and represents a green synthetic protocol. The catalytic reaction proceeded very smoothly under solvent-free conditions and showed high regioselectivity. Clean reaction, non-chromatographic purification technique, easily accessible reactants, and metal and solvent-free and environmentally friendly reaction conditions are the notable advantages of this procedure. In addition, this method shows lower E-factors.

Particular success has been achieved in the synthesis of new products and in processes since the twelve principles of “green chemistry” were formulated in the 1990s. These products and processes are more compatible with human health, society, and the environment. In this review, a collection of research reports have been documented from the viewpoint of green chemistry. The main theme of this review is neat reactions, which are solvent and catalyst-free reactions. Neat reactions in the absence of any solvent or catalyst with concise summaries of microwave, ball milling, and neat reactions have been described.

An efficient solvent-free procedure for the synthesis of pillar[6]arenes has been developed. The procedure involves the solid-state condensation of finely milled 1,4-dialkoxybenzene and paraformaldehyde by grinding in the presence of a catalytic amount of H2SO4. The use of organic solvents for the extraction of products has also been avoided. Operational simplicity, compatibility with various 1,4-dialkoxybenzenes, non-chromatographic purification technique, high yields and mild reaction conditions are the notable advantages of this procedure. A large scale reaction demonstrated the practical applicability of this methodology.

We have demonstrated a new application of our oxidizing reagent, a combination of NH2OH·HCl and NaIO4, in the first generalized regioselective 1,2-difunctionalization of olefins. It is a general method for the preparation of β-iodo-β′-hydroxy ethers, β-iodo ethers, β-iodohydrin, and β-iodo acetoxy compounds using different reaction media. The reactions are highly regioselective, always affording Markovnikov's type addition products. The methodology is also applicable for the easy access of terminal acetals. Molecular iodine-free synthesis, room temperature reaction conditions, high yields, use of less expensive reagents, mild reaction conditions, broad applicability of nucleophiles, and applicability for gram-scale synthesis are the notable advantages of this present protocol.

An efficient procedure for the synthesis of pillar[6]arenes has been developed. The procedure involves the condensation of 1,4-dialkoxybenzenes and paraformaldehyde in the presence of a catalytic amount of H2SO4 or BF3·OEt2 in polar solvent media (acetonitrile, ethyl alcohol, acetone etc.). In all cases the interaction afforded pillar[6]arenes in high yields.

A green and highly efficient method has been developed for the synthesis of 5-(aryl/alkyl)amino-1,2,4-triazines and α-arylamino-2,2′-bipyridines according to the principles of atom economy. It has been performed by two consecutive solvent-free reaction pathways: the ipso-substitution of a cyano-group in 5-cyano-1,2,4-triazines and the aza-Diels-Alder reaction of the resulting 5-arylamino-1,2,4-triazines with 1-morpholinocyclopentene used as a dienophile. Solvent and catalyst-free conditions, operational simplicity, the compatibility with various functional groups, nonchromatographic purification technique, and high yields are the notable advantages of this procedure. The present methodology possesses a low E-factor.

Fluorescent tripodal anion sensors with a 1,3,5-triethylbenzene core display a turn-on fluorescence response to phosphonate and phosphate anions and may be used as optical sensors. The properties of the receptors and sensors as well as their anion binding behavior were investigated both in solution and in solid state. The turn-on fluorescence response can be leveraged in sensing of phosphate anions and, most importantly, hydrolysis products of the nerve gas sarin, isopropyl methylphosphonate (IMP), and methylphosphonate (MP). The fluorescence signal amplification in the presence of anions allows for application of these molecules in a sensor microarray suitable for high-throughput screening.

8-Hydroxyquinoline-based ligands with extended conjugated fluorophores were designed to provide turn-on and ratiometric signal output optimized for use in fluorescence-based sensor arrays, where the changes in blue and green channels of the RGB signal are used to distinguish between cationic analytes.

A Ru(II) porphyrin rapidly reacts with NO2/N2O4 with the formation of a stable Ru(II) nitrosyl nitrato complex.