Search

[Figure not available: see fulltext.] An azo coupling reaction of α-nitro ketones with 5-diazoazoles was used to obtain 4-alkyl-3-nitro-1,4-dihydroazolo[5,1-с][1,2,4]triazines, which were characterized with respect to their antiviral activity against influenza and Coxsackie B3 viruses. © 2021, Springer Science+Business Media, LLC, part of Springer Nature. This study was funded by the Russian Science Foundation (project No. 20-13-00142).

4-Ethoxycarbonyl(cyano)-1,3-dimethyl-β-carbolines were synthesized via thermolysis of 4-aryl-3(5)-azidopyridines and their optical and hypoglycemic properties were studied. For the first time, the accessible Hantzsch nitropyridines were used as the starting materials. Diazotization of 3-aminopyridines having a trimethoxyaryl substituent at the C-4 position of the pyridine ring by intramolecular azo coupling afforded 7,8,9-trimethoxy-2,4-dimethylpyrido[3,4-c]cinnolines. When evaluating the hypoglycemic properties of the four obtained β-carbolines, it was found that ethyl 7-fluoro-1,3-dimethyl-9H-pyrido[3,4-b]indole-4-carboxylate, the structure of which contains the fluorine atom, has the highest glucose-lowering action.

Herein, a greener approach to the eosin Y-Na2 catalyzed, C(sp2 )-H bond azo coupling of imidazoheteroarene with aryl diazonium salts is described, under acid free conditions. This direct photoredox process resulted in the corresponding azo products in good to excellent yields. Besides, this new approach could also be applicable to anilines, which is a poorly reactive substrate by other methods. The main features of this reaction are that it provides high yields and is gram-scalable and applicable to biologically relevant imidazoheteroarenes and -anilines.

Aim. Expanding the synthetic potential of 4-arylimino-thiazolidin-2-ones; a study of reactivity; and primary screening for antioxidant activity of synthesized compounds. Materials and Methods. All chemicals were of analytical grade and commercially available. When performing the synthetic part of the work, reagents manufactured by Merck (Germany) and Sigma-Aldrich (USA) were used. All the reagents and solvents were used without further purification and drying. Methods of organic synthesis, physical and physical-chemical methods of analysis of organic compounds (NMR spectroscopy, elemental analysis) were used in the study. Results and Discussions. The peculiar pharmacological activities of 4-iminothiazolidin-2-ones prompted us to synthesize certain С5 substituted 4-arylimino-thiazolidin-2-ones and test them for antioxidant activity. The specified scaffold represents a convenient intermediate in order to afford С5 substituteds 4-arylimino-thiazolidin-2-ones. The active methylene group presence in C5 position of the basic scaffold provides an entry for its utilization in azo coupling and aldol condensation reactions leading to appropriate 5-aryl-hydrazono and 5-arylidene derivatives of 4-arylimino-thiazolidin-2-one generation. The structures of the obtained compounds were confirmed by 1H NMR spectroscopy and elemental analysis. The spectroscopic data of all compounds correspond to the proposed structures. The antioxidant activity of the synthesized compounds was measured in vitro by the method of scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals. DPPH radical found many applications due to its high stability in a methanolic solution and intense purple color. In its oxidized form, the DPPH radical has an absorbance maximum at a wavelength of 517 nm. For the first time, antioxidant activity was identified among С5 substituted 4-arylimino-thiazolidin-2-ones. Conclusions. Based on azo coupling and aldol condensation reactions, structural modification of the C5 position of certain 4-arylimino-thiazolidin-2-ones was conducted. For all synthesized compounds, primary pharmacological screening for antioxidant activity was performed. Three highly active compounds with a pronounced antioxidant effect have been identified, which approach or exceed ascorbic acid in terms of activity. Key words: organic synthesis, 4-arylimino-thiazolidin-2-ones, 2,2-diphenyl-1-picrylhydrazyl, antioxidant activity

In this study, a continuous-flow synthesis of the azo pigment Yellow 14 protocol has been developed using a three-stream micromixing process. This method controlled the pH of the azo coupling react...

The azo coupling of arenediazonium chlorides with (Z)-2-(3,3-dimethyl-3,4-dihydroisoquinolin-1(2H)-ylidene)-N-(4-methylphenyl)acetamide afforded (Z)-2-(2-arylhydrazinylidene)-2-(3,3-dimethyl-3,4-dihydroisoquinolin-1-yl)-N-(4-methylphenyl)acetamides whose structure was confirmed by 1H NMR and X-ray diffraction data. The azo coupling products containing no p-tolyl substituent on the amide nitrogen atom exist in solution as mixtures of azo and hydrazone tautomers. Electronic absorption spectra of the synthesized compounds were studied.

An azo coupling-based derivatization method is reported for high-sensitivity liquid chromatography–tandem mass spectrometry (LC–MS/MS) quantitation of tetrahydrocannabinol (THC) and other aromatic compounds, i.e. phenols and amines. Through the azo coupling of a diazonium to an analyte, it produces a derivatized analyte which has enhanced ionization efficiency and results in high-response fragments in tandem mass spectrometry. The derivatization method was applied to six typical aromatic compounds using three different diazonium salts as derivatization reagents, demonstrating its applicability to a variety of analytes and reagents. The derivatization reaction can be directly carried out in neat samples, and after derivatization the samples can be immediately sent to the LC–MS/MS instrument for analysis. These advantages facilitate a one-step sample preparation procedure that can be completed in less than one hour, allowing for a “derivatize & shoot” lab workflow. The derivatization method was applied to establish an LC–MS/MS assay for the quantitation of THC in human breath samples. The derivatization conditions were studied in this application, including the effects of acidity, organic solvent, and diazonium concentration in the reaction. The THC derivatization assay was validated and achieved a limit of quantitation (LOQ) of 0.50 pg/ml using either of the two regio-isomers of the azo-derivative of THC (THC-DRV). To prove that the derivatization method has compatibility with complex-matrix samples, a THC derivatization assay for serum samples was established, in which the azo coupling reaction was directly carried out in crude protein-precipitated supernatants. An LOQ of 5.0 pg/ml was achieved. In addition, excellent correlation between THC derivatization and non-derivatization assays was found in the analysis of whole blood samples.

The well-known azo coupling reaction was utilized to yield a new group of triptycene-derived azo polymers (TAPs) bearing phloroglucinol units. TAPs have hierarchical porosity (presence of micropores and mesopores) and are thermally stable. TAPs have moderate surface area (SABET up to 772 m2 g–1) but demonstrate rather high CO2 uptake (up to 150 mg g–1). Azo functional group is reportedly N2-phobic and hence porous organic polymers (POPs) with azo (−N═N−) units show high CO2/N2 selectivity. TAPs register CO2/N2 selectivity (273 K) that is higher than most azo-POPs reported until date. This favorable property of TAPs is attributed to the simultaneous coexistence of triptycenes (aromatic and three-dimensional rigid with high internal free volume), phenolic-OH (polar and CO2-philic), and azo (CO2-philic and N2-phobic) functional groups in the polymeric framework.

The 3-(4-(methoxycarbonyl)phenyl)triazapentalene is a highly fluorescent small molecule which is readily accessible via a two-step synthesis. In the search for postfunctionalization methods, a radical CH-arylation with diazonium salts was attempted. However, azo coupling resulted in a ring-degenerate rearrangement toward a 2-aryl-4-azotriazapentalene, which was confirmed via crystallographic analysis. A mechanism involving the generation of a nitrilimine is proposed. In addition, reduction of the azo group led to cleavage of the triazapentalene core. The present results further demonstrate the sensitivity of the triazapentalene fluorophore. ispartof: The Journal of Organic Chemistry vol:84 issue:14 pages:9434-9439 ispartof: location:United States status: Published online

A comparative analysis of physicochemical properties and reactivity of 3-aryl-1H-pyrazole-5-diazonium tetrafluoroborates and 5-aryl-3-diazo-3H-pyrazoles in azo coupling reactions is presented. It is shown that diazonium salts have higher reactivity compared to the respective 3-diazopyrazoles, which is in agreement with their physicochemical properties. Heterocyclization of the synthesized azo compounds provided 2-arylpyrazolo[5,1-c][1,2,4]benzotriazines, which were screened for antitumor activity against human uterine endothelium cancer cells (HeLa cell line) and human skin fibroblasts using the MTT assay and flow cytometry. It was found that all of the tested compounds exhibited moderate to high cytotoxic activity. The best results were obtained with 6,8-dimethoxy-2-phenylpyrazolo-[5,1-c][1,2,4]benzotriazine.

In this paper, two simple methods of introducing an azodye into a siloxane matrix using hydrosilylation and azo coupling reactions are presented by the example of the model heptamethyltrisiloxane. It has been shown that the introduction of the bisazoevgenol fragment into the heptamethyltrisiloxane molecule results in the crystallization of the siloxane derivative. The obtained compound was studied by nuclear magnetic resonance (NMR) spectroscopy methods, polarization optical microscopy (POM) and differential scanning calorimetry (DSC).

Anthrone tautomerized predominantly, under the reaction conditions, into anthrol and involved in the azo coupling reaction with aryl diazonium chloride to give the corresponding azo dye. UV-Vis experiments have supported the tautomerization of anthrone and the presence of the azo dye products in the hydrazone form. Aryl amines with broad biological applications have been involved to increase the utility of the obtained products. Preliminary antibacterial activity resulted in compounds 7a,d which showed the lowest MIC values of 0.2 and 0.1 × 10−3 µg/mL against Enterococcus feacalis and Escherichia coli, respectively. Furthermore, the insecticidal activity of the nominated compounds 7a,b against the adults of vine mealybug, Planococcusficus (Signoret), showed LC50 values of 152.22 and 216.12 mg/mL, respectively.

New 1,3-dihydroxyacridine-9-carboxylic acids were obtained by Pfitzinger reaction from 2,4,6-trihydroxytoluene (methylphloroglucinol). Their bromination and azo-coupling reactions were studied. Computer simulation was used to determine potential pharmacokinetic and toxic properties of the synthesized compounds.

This communication reported azo coupling reaction induced macromolecular self-assembly in aqueous solution. Diblock copolymer (PEG-b-PSNHBoc) consisting of a hydrophilic PEG block, and a hydrophobic N-Boc protected poly(p-vinylaniline) block was synthesized by RAFT polymerization. Then double hydrophilic diblock copolymer (PEG-b-PSN2+) composed of PEG and PS based macromolecular diazonium salts was prepared by the diazotization of PEG-b-PSNH2, which was obtained by deprotection of PEG-b-PSNHBoc. As N,N-dimethylaniline was gradually added into the freshly prepared PEG-b-PSN2+ aqueous solution, the azo coupling reaction between N,N-dimethylaniline and diazonium salts took place, which would lead to the generation of azobenzene pendants. Due to the poor solubility of azobenzene pendants in water, the formed hydrophobic polymeric chains aggregated to form the self-assembly colloidal particles. By incorporating a fluorescent group into the aniline, the aggregates formed through azo coupling reaction induced ma...

In this research investigation, novel isoxazolone-thiazole based azo dyes (Io1-Io4) were synthesized by a conventional azo coupling reaction at 0-5°C. The structure elucidation was precisely assessed using various spectroscopic techniques like FT-IR, NMR and HRMS. Through computational study, molecular geometry, mulliken atomic charges and global reactive descriptors were investigated to get a better insight into the molecular properties. Molecular electrostatic potential (MEP) and reduced density gradient analysis (RDG) were also examined. The solvatochromic UV-Vis absorption study was performed using different solvents. A diffuse reflectance study was carried out to determine the optical band gap of the synthesized novel dyes (Io1-Io4). Biological efficacy towards antimycobacterial and anti-inflammatory activity was examined and the results revealed that, the compounds showed very good antimycobacterial and anti-inflammatory activity.

Azo compounds are important class of compounds and have verstile applications in various fields of life. Because of their broad range of applications, it is necessary to have versatile methods of synthesis to have new azo derivatives in good yields. This review covers the synthetic methodology with emphasis on the classical and versatile ones. The overall feasible methods for azo compounds synthesis mentioned in this review includes, diazotization/azo coupling, solvent free-silica supported boron trifluoride, methyl nitrite-active iron based-Japp-Kalingemann, Novartis/Ciba-Geigy-Cupric chloride catalyzed-Mild one-pot two step-nitroamatics and anilines-deoxygenation of nitrobenzene-decomposition of N,N, Ortho para benzoquinonediimines dioxide dehydrogenation, arylhydrazines dimerization reaction of diazonium salts-metal catalyzed coupling, Opening of benzotriazoles-Oxidation of anilines-arylcalcium and nitrous oxide-quinone acetals and arylhydrazines-quinones, reduction of azoxybenzenes and azo-MOFs, etc, which yield azo compounds in good to moderate yields . The most widely used methods to synthesize azo compounds are by Mills reaction and azo coupling which are important in industrial point of view and are extensively used worldwide. Though there are various reported methods to get azo compounds but they have limitations as well. Therefore there is still a need to have latest and efficient methods keeping in view the advantages and disadvantages of above mentioned methods in order to have innovative and more efficient method for synthesis of azo compounds.

In this study, we report on a general synthetic approach to both symmetrical and asymmetrical 3-cyano-1,5-diarylformazan dyes. The reaction of enaminonitrile with aromatic diazonium salts in slightly acidic medium affords arylhydrazonals as stable intermediate that are readily converted into asymmetrical formazans via second azo-coupling in a weak alkaline medium. Symmetrical formazan dyestuffs are synthesized directly via double azo-coupling of the key intermediate 3-piperidinylacrylonitrile with the corresponding diazonium salts in weak alkaline medium using sodium acetate as a weak base. The structures of the prepared dyestuffs and intermediates are demonstrated by elemental analysis (C, H, N), 1H and 13C NMR, FTIR and GC-MS spectroscopic techniques. The prepared formazan disperse colorants are applied to dye polyester fabric to give satisfactory fastness properties to wash, perspiration, rubbing and light.

Intramolecular hydrogen bonds (IMHBs) in 5-azopyrimidines are investigated by NMR spectroscopy and DFT computations that involve nuclear quantum effects. A series of substituted 5-phenylazopyrimidines with one or two hydrogen bond donors able to form IMHBs with the azo group is prepared by azo coupling. The barrier of interconversion between two rotamers of the compounds with two possible IMHBs is determined by variable temperature NMR spectroscopy and it is demonstrated that the barrier is significantly affected by intramolecular charge transfer. Through-hydrogen-bond scalar coupling is investigated in 15N labeled compounds and the stability of the IMHBs is correlated with experimental NMR parameters and rationalized by path integral molecular dynamics simulations that involve nuclear quantum effects. Detailed information on the hydrogen bond geometry upon hydrogen-to-deuterium isotope exchange is obtained from a comparison of experimental and calculated NMR data.

The radical arylation of anilines and pyrroles can be achieved under transition-metal- and catalyst-free conditions by using aryldiazotates in strongly alkaline aqueous solutions. The aryldiazotates act as protected diazonium ions, which do not undergo azo coupling with electron-rich aromatic substrates, but can still serve as an aryl radical source at slightly elevated temperatures. Based on an improved preparation of aryldiazotates in aqueous solution, homolytic aromatic substitutions of anilines and pyrroles were conducted with good overall yields and high regioselectivity. Moreover, DFT calculations provided further mechanistic insights.

Using atom transfer radical polymerization (ATRP) and macromolecular azo coupling reaction, both o-nitrobenzyl (ONB) group and azobenzene group were efficiently incorporated into the center of the amphiphilic diblock copolymer chain. The prepared diblock copolymer was well characterized by UV–vis, 1H NMR, and GPC methods. Self-assembly of the amphiphilic copolymer in selected solvents can result in uniform self-assembly aggregates. In the presence of external stimuli [upconversion nanoparticles (UCNPs)/NIR light or enzyme], the amphiphilic diblock copolymer chain could be broken by the cleavage of ONB or azobenzene group, which would lead to the disruption of the self-assembly aggregates. This photo- and enzyme-triggered disruption process was proved by using transmission electron microscopy (TEM) and GPC method. Fluorescence emission spectra measurements indicated that the release of Nile red, a hydrophobic dye, encapsulated by the self-assembly aggregates, could be successfully realized under the NIR light and enzyme stimuli. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2450–2457

Azo compounds were synthesized in a multi-step catalyst-free reaction by using tert-butyl nitrite as a diazotization reagent and a mixture of bis(trifluoromethane)-sulfonimide (CF3SO2)2NH, (TFSI-H) and glacial acetic acid as a mild acidic agent in ethanol/water mixed solvent followed by azo coupling reaction with 4-hydroxybenzaldehyde was investigated. The stable arenediazonium bis(trifluoromethane)-sulfonimide salts were stored for long periods of time and then were used without any loss of activity and ascertained threads. The current method has the advantages such as reduce waste by avoiding solvent for the purification of products in diazotization step; no nitrous acid was produced during the diazotization; save energy, time and cost; simple experimental procedure, environmentally benign conditions, and good yield of the products with potential use as azo-dyes, pigments and therapeutic agents.

The ester group in ethyl 7-amino-3-tert-butyl-4-oxo-4,6-dihydropyrazolo[5,1-c][1,2,4]triazine-8-carboxylate was converted for the first time to methyl by the action of lithium tetrahydridoborate in the presence of boron trifluoride–diethyl ether complex. This reaction has almost no analogies among other classes of organic compounds. New difficultly accessible 7-chloro and 7-azido derivatives were synthesized via diazotization of the reduction product, and treatment of the latter with acetic anhydride afforded the exhaustively acetylated derivative. Diazotization of ethyl 7-amino-3-tert-butyl-4-oxo-4,6-dihydropyrazolo-[5,1-c][1,2,4]triazine-8-carboxylate, followed by reaction with sodium azide, gave the corresponding azide, and the product of azo coupling with ethyl acetoacetate failed to undergo intramolecular cyclization to tricyclic pyrazolo[3,2-c: 5,1-c′]bis[1,2,4]triazine system.

Magnetic titanium dioxide core-shell nanoparticles(Fe3O4@TiO2 NPs) were synthesized as particles with appropriate size for intravenous injection. They subsequently were functionalized with p-aminothiophenol(PATP) to facilitate the covalent attachment of target drugs through azo coupling reaction, which can be universally observed in a variety of drugs containing phenols, anilines, and imidazoles. The proposed drug nanocarrier was designed to possess the ability to release drugs upon UV irradiation because of the photocatalytic property of the TiO2 shells. All the results indicate the potential application of the Fe3O4@TiO2 NPs in targeted drug delivery with greater chemical sta-bility and universality.

A method for the preparation of pharmacologically active conjugates of interferon α-2b with poly(ethylene glycol)s that absorbed in the visible spectral range was proposed. New covalent conjugates of linear poly(ethylene glycol)s with interferon α-2b were prepared via diazotization of 4-aminobenzoic acid poly(ethylene glycol) esters followed by azo coupling of the obtained diazonium salts with histidine imidazoles and tyrosine phenols of the protein amino-acid chain. The synthesized conjugates retained a high degree of interferon α-2b antiviral activity in vitro and had longer blood circulation times than a foreign analog and very low acute toxicity and immunogenicity.

The azo coupling reaction between 4-nitrobenzenediazonium tetrafluoroborate and a series of benzene derivatives bearing as electron donating substituents at least one hydroxy or methoxy group has been carried out. Depending on the nucleophile and its relative ratio with the diazonium salt it was possible to obtain mono-, di-, and, only in the case of phloroglucinol, evidence of trisubstitution products. The reaction between 3,5-diaminoanisole- or 3,5-diaminophenol- derivatives and two equivalents of diazonium salt gave, in the first case, the product derived from a mono attack, and a diadduct in the second case; their X-ray diffraction analysis showed an highly symmetric structure for the latter. The different behavior of hydroxy- with respect to the methoxy-substituted compounds was particularly evident for phloroglucinol and 1,3,5-trimethoxybenzene and it may be rationalized on the basis of the different electronic effect of the substituents. The propensity to undergo H/D exchange reaction on the aromatic ring was investigated on a series of substrates and the comparison of the results obtained provided new insights on this kind of phenomenon and permitted a better explanation of the findings reported here, by introducing a new particular interaction which competes with the -complex formation between proton and phloroglucinol

Base-promoted decarboxylative azo couplings of carboranyl carboxylic acids with diazo salts have been developed to provide trans-azocarboranes in high yields (up to 94%). This approach is simple, efficient, and compatible with various functional groups. Mechanistically, the coupling has been proven to proceed in a nonradical pathway, which is distinct from those classical decarboxylative couplings.

A novel one-pot cascade method for the assembly of valuable NO-donor azasydnone scaffold has been developed. The construction strategy involves a diazotization/azo coupling/elimination/double rearrangement cascade sequence of readily available amines. The current protocol enables the generation of a diverse array of azasydnones, including previously hardly accessible heteroaryl substituted azasydnones (25 examples, 70-97 % yield) with a good functional group tolerance under very mild conditions. Preliminary NO-releasing studies revealed an ability of azasydnones to produce NO in a wide range of concentrations. This method provides a new approach to nitrogen-oxygen heterocycles with potential applications in medicine and material science.

Herein, a strategy for the selective derivatization of 3-nitrotyrosine-containing proteins using the classic azo coupling reaction as the key step is described. This novel approach featured multiple advantages and was successfully applied to detect picomole levels of protein tyrosine nitration in biological samples.

A new azo compound was prepared via the azo coupling reaction between 4-(ethoxycarbonyl)-3-methyl-1H-pyrazole-5-diazonium chloride and 8-hydroxyquinoline (oxine). The ester functional group of the obtained compound was hydrolyzed and thus a new chemical structure with a carboxylic functional group resulted. The structures of the new compounds were fully characterized by: UV–Vis, FT-IR, 1D and 2D NMR spectroscopy, and HRMS spectrometry.

Low concentrations of nitrogen dioxide, which arises as a side product from a range of industrial processes, can effectively be recycled through the diazotization of anilines. The studies reported herein now demonstrate that the removal of nitrogen dioxide from gas streams is even more effective when hydrophilic anilines are used as starting materials. The diazonium salts, which are obtained in this way in up to quantitative yields, can directly be employed in azo coupling reactions, thus opening up an attractive route to the industrially important group of azo compounds.

Four novel tricyanofuran disperse dyestuffs 3a-d bearing hydrazone moiety were synthesized in order to investigate their possible antibacterial activity. The hydrazone moiety was introduced via azo-coupling of the tricyanofuran with the appropriately functionalized diazonium salt. The optical properties of these compounds showed interesting solvatochromic properties. The absorption peaks are observed in the wavelength range 454-513 nm. It can also be seen that they display different maximum emissions in the wavelength range 528-615 nm. The functional groups attached to the hydrazone moiety influenced both on absorption and emission maxima. The prepared hydrazone-based disperse dyes were applied for dyeing polyester fabrics, affording satisfactory results. Furthermore, compounds 3a and 3c demonstrated a relatively strong antibacterial activity against some selected gram positive Staphylococcus aureus and Bacillus subtilis;and gram negative Escherichia coli and Pseudomonas aeuroginosa employing Ampicillin as standard drug.

We report the first systematic study on the channel size effect in various microreactor systems on the efficiency of phase-transfercatalyzed azo coupling reactions. The optimum scaled-up channel diameter was 0.5 mm, which facilitated the synthesis of diazo compounds in high yields.

Amphiphilic diblock copolymer with an azobenzene linkage has been synthesized by the combination of macromolecular azo coupling reaction and nitroxide-mediated radical polymerization (NMP). In this strategy, an azobenzene linkage would naturally establish at the copolymer junction of the amphiphilic diblock copolymer after the macromolecular azo coupling reaction. Self-assembly of this azobenzene linked copolymer in selected solvents can result uniform self-assembly aggregates. In the presence of enzyme azoreductase and coenzyme NADPH, the amphiphilic diblock copolymer chain will be broken by the cleavage of the azobenzene linkage, which will lead to the disruption of the self-assembly aggregates. UV–vis absorption spectra measurements indicated the release of Nile red, a hydrophobic dye, encapsulated by the self-assembly aggregates. Thus, the amphiphilic diblock copolymer with azobenzene linkage can potentially be applied for the fabrication of nanocarriers for colon-specific delivery purposes applications.

In this paper, a micro-fluidic optimized process for the continuous flow synthesis of azo compounds is presented. The continuous flow synthesis of Sudan II azo dye was used as a model reaction for the study. At found optimal azo coupling reaction temperature and pH an investigation of the optimum flow rates of the reactants for the diazotization and azo coupling reactions in Little Things Factory-MS microreactors was performed. A conversion of 98% was achieved in approximately 2.4 minutes and a small library of azo compounds was thus generated under these reaction conditions from couplers with aminated or hydroxylated aromatic systems. The scaled up synthesis of these compounds in PTFE tubing (i.d. 1.5 mm) was also investigated, where good reaction conversions ranging between 66–91% were attained.

A high yield synthesis of fluorescent benzo, thieno, and furo [c]-fused methyl 7-aryl-6H-pyrrolo[3,4-c]pyridazine-5-carboxylates, including unprecedented heterocyclic skeletons, was performed by the transformation of methyl 4-aminopyrrole-2-carboxylate into the corresponding diazo compound, followed by intramolecular azo coupling under acid conditions onto a nucleophilic aryl or hetaryl group in the 3-position. Azo coupling is completely regioselective and, according to DFT calculations, a kinetically controlled reaction. N-Methylation of 1,3-disubstituted 2H-pyrrolo[3,4-c]cinnolines occurs selectively at N5 under kinetic control, leading exclusively to 5-methyl-5H-pyrrolo[3,4-c]cinnoline derivatives.

Herein, we illustrate how microreactor technology can be used as a tool for reaction screening and optimization, in addition to improving the reaction chemistry. We report the in-situ generation of azo compounds by reactive quenching of diazonium intermediates in microreactors. This involves an electrophilic aromatic substitution reaction, namely, an azo-coupling reaction performed in continuous-flow systems in the presence of a phase transfer catalyst with great emphasis on compounds that do not easily couple. Capitalizing on the benefits of a large surface area and the short molecular diffusion distances observed in microreactors, in-situ phase transfer catalyzed azo-coupling reaction of diphenylamine to p-nitroaniline was investigated. A rapid and easy optimization protocol was established which yielded a 99%, 22%, and 33% conversion of diphenylamine, carbazole, and triphenylamine, respectively, in approximately 2.4 min.

A general and practical synthetic method for the construction of unsymmetrically substituted diphenyldiazenes based on classical azo coupling reaction has been developed. A key feature of this method is the use of N,N-diallyl protected aniline derivatives as coupling components. The N,N-diallyl moiety of the coupling component warrants sufficient reactivity and allows to avoid formation of constitutional isomers resulting from intermediate triazene formation. Furthermore, subsequent to the coupling reaction, the N,N-diallyl aminofunction, can be replaced by other substituents including hydrogen via diazonium ion intermediates. In general, following this approach target compounds can be obtained in reasonable to good yields.

A tBuONO mediated practical and efficient method for the synthesis of azo imidazoheterocycles with broad functionalities has been achieved by the reaction between imidazoheterocycles and anilines at room temperature in goods yields. Azo indolizines were also prepared by employing this methodology. Mild reaction conditions, tolerance of wide functionalities, operational simplicity and easy purification of the products are the notable advantages of the current protocol.

A [Cp*Rh(iii)]-catalyzed electrophilic amination of arylboronic acids with diethyl azodicarboxylate (DEAD) was developed, and arylhydrazides were produced in excellent yields and selectivity. The analogous amination with the arylazocarboxylates afforded the corresponding N,N-diarylhydrazides. The electrophilic amination of arylboronic acids with azocarboxylates proceeds readily under mild conditions with excellent functional group tolerance. Up to 99% yields were obtained. Preliminary mechanistic studies revealed that prior formation of an arylrhodium(iii) intermediate for the azo coupling reaction can be ruled out.

Chemists often use an amine group as an intermediate in syntheses of imines, amides and ureas; however, in the case of syntheses of p-aminophenol type compounds, several problems might occur. In this article, we prepared p-aminocalix[5]arene-pentaol by reduction of both nitro and azo derivatives, and compared four methods of the amine preparation, focusing mainly on its gramme scale and time-consuming issues.

Chromogenic redox indicators―3,5-diphenyl-2-(4-sulfophenyl)-2Н-tetrazolium betaine and 2-(4-nitrophenyl)-5-phenyl-3-(4-sulfophenyl)-2Н-tetrazolium betaine―were synthesized by the oxidative cyclization of 1,3-diphenyl-5-(4-sulfophenyl)formazan and 5-(4-nitrophenyl)-3-phenyl-1-(4-sulfophenyl)formazan under the action of N-bromosuccinimide. The synthesis of sulfoformazans is accompanied by formation of azo coupling products with substitution of the sulfo group in the hydrazone molecule by the arylazo group. Spectral and voltage–current characteristics of the synthesized compounds were studied.

As a result of the reaction of ethyl 3-amino-4-dimethylamino-benzothiophene-2-carboxylate (1) with 2-thiazolediazonium salt 2, tricyclic ethyl 5-(thiazol-2-yl)-8-(thiazol-2-yldiazenyl)-5H-isothiazolo[3,4,5-d,e]cinnoline-3-carboxylate 4, instead of the expected 7-thiazolylazo derivative 3, is formed. A mechanism in which sulfanyl cations occur as intermediates is proposed.