Search Results (18)

This paper presents the expected and unexpected, but typically substituent-dependent, ferrocene-catalyzed DDQ-mediated oxidative transformations of a series of 5,8-bis(methylthio)-1-aryl-1,2-dihydropyridazino[4,5-d]pyridazines and 8-(3,5-dimethyl-1H-pyrazol-1-yl)-5-(methylthio)-1-aryl-1,2-dihydropyridazino[4,5-d]pyridazines. Under noncatalytic conditions the reactions were sluggish, mainly producing a substantial amount of undefined tarry materials; nevertheless, the ferrocene-catalyzed reactions of the 5,8-bis(methylthio)-substituted precursors gave the aromatic products the expected aromatic products in low yields. Their formation was accompanied by ring transformations proceeding via aryne-generating fragmentation/Diels–Alder (DA)/N₂-releasing retro Diels–Alder (rDA) sequence to construct arene-fused phthalazines. On the other hand, neither the noncatalytic nor the catalytic reactions of the 8-pyrazolyl-5-methylthio-substituted dihydroaromatics yielded the expected aromatic products. Instead, depending on their substitution pattern, the catalytic reactions of these pyrazolyl-substituted precursors also led to the formation of dearylated arene-fused phthalazines competing with an unprecedented multistep fragmentation sequence terminated by the hydrolysis of cationic intermediates to give 4-(methylthio)pyridazino[4,5-d]pyridazin-1(2H)-one and the corresponding 3,5-dimethyl-1-aryl-1H-pyrazole. When 0.6 equivalents of DDQ were applied in freshly absolutized THF, a representative pyrazolyl-substituted model underwent an oxidative coupling to give a dimer formed by the interaction of the cationic intermediate, and a part of the N-nucleophilic precursor remained intact. A systematic computational study was conducted on these intriguing reactions to support their complex mechanisms proposed on the basis of the structures of the isolated products. Full article

A series of novel fluorescent donor–acceptor–donor (D-A-D) dyes containing [1,2,5]oxadiazolo[3,4-d]pyridazine and its 1-oxide as electron-withdrawing groups has been synthesized and thoroughly investigated using X-ray diffraction and molecular spectroscopy methods. This study showed that the introduction of N-oxide into the 1,2,5-oxadiazole ring in the acceptor fragment leads to a significant decrease in the luminescence intensity and quantum yield of the dyes. A comprehensive comparison of the photophysical properties of the obtained compounds containing the 1,2,5-oxadiazole ring with the previously studied [1,2,5]thia- and 1,2,5-selenadiazolo[3,4-d]pyridazine analogs showed that the oxygen substitution in the acceptor fragment shifts the phosphorescence maximum from the NIR region of 980–1100 nm to the red region of 690–770 nm. In contrast, for oxygen- and sulfur-containing dyes, purely red fluorescence with a maximum in the spectral range of 620–900 nm is observed. The crystal structures of furoxan-containing 3d·½CHCl₃ and furazan-containing 4d exhibit a non-planar [1,2,5]oxadiazolo[3,4-d]pyridazine fragment. We have found that short non-covalent interactions of the furoxan system with a lattice chloroform molecule in 3d lead to luminescence quenching. Meanwhile, in the 4d dye, the intermolecular π-π interactions of pyridazine nitrogen atoms with the N-carbazolyl group of the adjacent molecule should facilitate intermolecular charge transfer (ICT) emission. Thus, the luminescence maxima for these dyes can be tuned across a broad range of 700–1100 nm by varying the number of chalcogen atoms, highlighting the potential for tailoring optical properties in optoelectronic applications. Full article

As a result of drug resistance, many antimicrobial medicines become ineffective, making the infections more difficult to treat. Therefore, there is a need to develop new compounds with antibacterial activity. This role may be played, for example, by metal complexes with carboxylic acids. This study reports the formation and characterization of ruthenium complexes with pyridazine-3-carboxylic acid (pdz-3-COOH)—([(η⁶-p-cym)Ru^IICl(pdz-3-COO)] (1), [Ru^IIICl₂(pdz-3-COO)₂Na(H₂O)]_n(H₂O)_0.11 (2) and [Ru^IIICl₂(pdz-3-COO)₂Na(H₂O)₂]_n (3). The synthesized compounds were analyzed using various spectroscopic and electrochemical techniques, with structure confirmation via SC-XRD analysis. Experimental data showed the ligand binds to metal ions bidentately through the nitrogen donor of the pyridazine ring and one carboxylate oxygen. To visualize intermolecular interactions, Hirshfeld surface analysis and 2D fingerprint plots were conducted. Furthermore, the impact of ruthenium compounds (1 and 2) on the planktonic growth of selected bacterial strains and the formation of Pseudomonas aeruginosa PAO1 biofilm was examined. Both complexes demonstrated comparable anti-biofilm activity and outperformed the free ligand. The effect of the complexes on selected virulence factors of P. aeruginosa PAO1 was also investigated. Compounds 1 and 2 show high suppressive activity in pyoverdine production, indicating that the virulence of the strain has been reduced. This inhibitory effect is similar to the inhibitory effect of ciprofloxacin. Within this context, the complexes exhibit promising antibacterial activities. Importantly, the compounds showed no cytotoxic effects on normal CHO-K1 cells. Additionally, a molecular docking approach and fluorescence spectroscopy were used to determine the interactions of ruthenium complexes with human serum albumin. Full article

Different supramolecular motifs are formed by the crystallisation of amino-substituted derivatives of quinoxaline, pyrimidine and pyridazine. These were made from the corresponding mono- or dichlorinated heterocycles by a nucleophilic displacement reaction. The pyridine-type nitrogen atoms activate the chlorine atoms because they can stabilise a negative charge, which forms when the amine attacks the ring. One amino group can be attached under mild conditions in hot ethanol or acetonitrile, but the first then deactivates the ring so the second requires more forceful conditions using a pressure vessel at 150 °C. Butylamine is frequently used because it reduces the polarity of the product, making it easier to purify and isolate. The extended structure of the quinoxaline derivatives 16–18 show a common ‘pincer’ hydrogen-bond motif, with a quinoxaline nitrogen atom accepting two N–H···N hydrogen bonds, giving a spiral or helical axis. The chain symmetries are 4₁, 2₁ and 3₁, respectively, depending on the substituents. A stereoview of each is shown. The pyrimidine derivatives 19, 12, 20, 14 and 21 form hydrogen-bonded tapes and compound 20 forms inversion dimers. Full article

1,2,5-Chalcogenadiazoles fused with electron-withdrawing heterocycles have been actively investigated for the preparation of organic photovoltaic materials. [1,2,5]Oxadiazolo[3,4-d]pyridazines are much less studied than other chalcogenadiazolopyridazines due to their low availability. In this communication, we report our study showing that 5,6-dihydro-[1,2,5]oxadiazolo[3,4-d]pyridazine-4,7-dione, a key precursor for the synthesis of 4,7-dihalo-[1,2,5]oxadiazolo[3,4-d]pyridazines, is formed via the cyclization of 1,2,5-oxadiazole-3,4-dicarbohydrazide in hydrochloric acid. The structure of the newly synthesized compound was established by means of elemental analysis; high-resolution mass spectrometry; ¹H and ¹³C NMR; IR spectroscopy, and mass spectrometry. Full article

In this work, O- and N-N-bridging complexes of technetium (V), previously known only for rhenium, were obtained for the first time. Tc(V) complexes with pyridazine (pyd), 1,2,4-triazole (trz), 3,5-dimethylpyrazole (dmpz) and pyrimidine (pyr) were obtained. In three complexes [{TcOCl₂}₂(μ-O)(μ-pyd)₂], [{TcOCl₂}₂(μ-O)(μ-trz)₂]·Htrz·Cl and [{TcO(dmpz)₄}(μ-O)(TcOCl₄)] two technetium atoms are linked by a Tc-O-Tc bond, and in the first two, Tc atoms are additionally linked by a Tc-N-N-Tc bond through the nitrogen atoms of the aromatic rings. We determined the role of nitrogen atom position in the aromatic ring and the presence of substituents on the formation of such complexes. For the first time, a reaction mechanism for the formation of such complexes was proposed. This article details the crystal structures of four new compounds. The work describes in detail the coordination of Tc atoms in the obtained structures and the regularities of the formation of crystal packings. The spectroscopic properties of the obtained compounds and their mother solutions were studied. The decomposition temperatures of the described complexes were determined. An assumption was made about the oligomerization of three-bridged complexes based on the results of mass spectrometry. Through the analysis of non-valent interactions in the structures, π-stacking, halogen-π and CH-π interactions were found. An analysis of the Hirshfeld surface for [{TcOCl₂}₂(μ-O)(μ-pyd)₂], [{TcOCl2}2(μ-O)(μ-trz)₂] and their rhenium analogues showed that the main contribution to the crystalline packing is made by interactions of the type Hal···H/H···Hal (45.4–48.9%), H···H (10.2–15.8%), and O···H/H···O (9.4–16.5%). Full article

In this study, a novel phthalonitrile monomer containing a pyridazine ring, 3,6-bis[3-(3,4-dicyanophenoxy)phenoxy]pyridazine (BCPD) with a low melting point (74 °C) and wide processing window (178 °C), was prepared by a nucleophilic substitution reaction. The molecular structure of the BCPD monomer was identified by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). Poly(BCPD) resins were derived from the formulations by curing at 350 and 370 °C. The thermoset that was post-cured at 370 °C demonstrated outstanding high heat-resistant (glass transition temperature (T_g) > 400 °C, 5% weight loss temperature (T_5%) = 501 °C, Y_c at 900 °C > 74%) and was flame-retardant (limiting oxygen index (LOI) = 48)). Further, the poly(BCPD) resin simultaneously exhibited a superior storage modulus, which could reach up to 3.8 Gpa at room temperature. Excellent processability and heat resistance were found for phthalonitrile thermosets containing the pyridazine ring, indicating poly(BCPD) resin could be potentially applied as high-temperature structural composite matrices. Full article

Pyrazines and pyridazines fused to 1,2,3-triazoles comprise a set of heterocycles obtained through a variety of synthetic routes. Two typical modes of constructing these heterocyclic ring systems are cyclizing a heterocyclic diamine with a nitrite or reacting hydrazine hydrate with dicarbonyl 1,2,3-triazoles. Several unique methods are known, particularly for the synthesis of 1,2,3-triazolo[1,5-a]pyrazines and their benzo-fused quinoxaline and quinoxalinone-containing analogs. Recent applications detail the use of these heterocycles in medicinal chemistry (c-Met inhibition or GABA_A modulating activity) as fluorescent probes and as structural units of polymers. Full article

Cyclic 6-membered aromatic compounds such as benzene and azabenzenes (pyridine, pyridazine, and pyrazine) are known to be light-sensitive, affording, in particular, the Dewar benzene type of intermediates. Pyridine is known to provide the only Dewar pyridine intermediate that undergoes reversible ring-opening. We found that irradiation of photosensitive gels prepared from poly(4-vinyl pyridine) and pyridine at 254 or 312 nm leads to pyridine ring-opening and subsequent formation of 5-amino-2,4-pentadienals. We show that this light-induced process is only partially reversible, and that the photogenerated aminoaldehyde and aminoaldehyde-pending groups undergo self-condensation to produce cross-linked, conjugated oligomers that absorb light in the visible spectrum up to the near-infrared range. Such a sequence of chemical reactions results in the formation of gel with two distinct morphologies: spheres and fiber-like matrices. To gain deeper insight into this process, we prepared poly(4-vinyl pyridine) with low molecular weight (about 2000 g/mol) and monitored the respective changes in absorption, fluorescence, ¹H-NMR spectra, and electrical conductivity. The conductivity of the polymer gel upon irradiation changes from ionic to electronic, indicative of a conjugated molecular wire behavior. Quantum mechanical calculations confirmed the feasibility of the proposed polycondensation process. This new polyacetylene analog has potential in thermal energy-harvesting and sensor applications. Full article

New heterocyclic systems containing 1,2,5-chalcogenadiazoles are of great interest for the creation of organic photovoltaic materials and biologically active compounds. In this communication, 3,6-dibromopyridazine-4,5-diamine was investigated in reaction with selenium dioxide in order to obtain 4,7-dibromo-[1,2,5]selenadiazolo[3,4-d]pyridazine. We found that 7-bromo-[1,2,5]selenadiazolo[3,4-d]pyridazin-4(5H)-one, the first representative of the new heterocyclic system, was isolated as a hydrolysis product of the corresponding 4,7-dibromoderivative. The structure of the newly synthesized compound was established by means of elemental analysis, high-resolution mass spectrometry, ¹H, ¹³C NMR, IR and UV spectroscopy, and mass spectrometry. Full article

In orderto synthesize new pyridazine derivatives anellated with different nitrogen heterocyclic moieties, spiro[cycloalkane]pyridazinones were transformed into the corresponding thioxo derivatives via a reaction with phosphorus pentasulfide. The reaction of the formed 2,3-diazaspiro[5.5] undec-3-ene-1-thiones with hydrazine provided the corresponding 1-hydrazono-2,3-diazaspiro[5.5] undec-3-ene, whose diazotization led to the desired spiro[cyclohexane-1,8${}^{\prime }$-tetrazolo[1,5-b]pyridazines. The reaction of dihydropyridazinethiones with benzhydrazide afforded the corresponding 7H-spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,1${}^{\prime }$-cyclohexanes]. As a result of our work, seven new pyridazinethione intermediates were prepared, which served as starting materials for the synthesis of two kinds of new ring systems: tetrazolo-pyridazines and triazolo-pyridazines. The six new annulated derivatives were characterized by physicochemical parameters. The new N-heterocycles are valuable members of the large family of pyridazines. Full article

Herein, we report the successful syntheses of scarcely represented indole-based heterocycles which have a structural connection with biologically active natural-like molecules. The selective oxidation of indoline nucleus to indole, hydrolysis of ester and carbamoyl residues followed by decarboxylation with concomitant aromatization of the pyridazine ring starting from tetrahydro-1H-pyridazino[3,4-b]indole derivatives lead to fused indole-pyridazine compounds. On the other hand, non-fused indole-pyrazol-5-one scaffolds are easily prepared by subjecting the same C2,C3-fused indoline tetrahydropyridazines to treatment with trifluoroacetic acid (TFA). These methods feature mild conditions, easy operation, high yields in most cases avoiding the chromatographic purification, and broad substrate scope. Interestingly, the formation of indole linked pyrazol-5-one system serves as a good example of the application of the umpolung strategy in the synthesis of C3-alkylated indoles. Full article

A new series of nitrogen and sulfur heterocyclic systems were efficiently synthesized by linking the following four rings: indole; 1,2,4-triazole; pyridazine; and quinoxaline hybrids. The strength of the acid that catalyzes the condensation of 4-amino-5-(1H-indol-2-yl)-2,4-dihydro-3H-1,2,4-triazole-3-thione 1 with aromatic aldehydes controlled the final product. Reflux in glacial acetic acid yielded Schiff bases 2–6, whereas concentrated HCl in ethanol resulted in a cyclization product at C-3 of the indole ring to create indolo-triazolo-pyridazinethiones 7–16. This fascinating cyclization approach was applicable with a wide range of aromatic aldehydes to create the target cyclized compounds in excellent yield. Additionally, the coupling of the new indolo-triazolo-pyridazinethiones 7–13 with 2,3-bis(bromomethyl)quinoxaline, as a linker in acetone and K₂CO₃, yielded 2,3-bis((5,6-dihydro-14H-indolo[2,3-d]-6-aryl-[1,2,4-triazolo][4,3-b]pyridazin-3 ylsulfanyl)methyl)quinoxalines 19–25 in a high yield. The formation of this new class of heterocyclic compounds in high yields warrants their use for further research. The new compounds were characterized using nuclear magnetic resonance (NMR) and mass spectral analysis. Compound 6 was further confirmed by the single crystal X-ray diffraction technique. Full article

Dihalogenated derivatives of 1,2,5-chalcogenadiazoles fused with benzene or heterocyclic rings are of interest as starting compounds for photovoltaic materials. The 1,2,5-chalcogenadiazole ring in these heterocycles was most commonly prepared from the corresponding ortho-diamine moiety. In this communication, 3,6-dibromopyridazine-4,5-diamine was prepared via the reaction of 4,7-dibromo[1,2,5]thiadiazolo[3,4-d]pyridazine with sodium methoxide in THF by heating at reflux for four hours. The structure of the newly synthesized compound was established by means of high resolution mass-spectrometry, ¹H, ¹³C-NMR and IR spectroscopy, and mass-spectrometry. Full article

The arylmethylidene derivatives of furan-2(3H)-ones are important building blocks for the synthesis of various heterocyclic compounds containing pyrimidine and pyridazine structural fragments, analogues of nitrogen-containing bases of pyrimidine series. In order to continue the development of constructing of molecules containing pyridine and pyridazine fragments, this article is devoted to the synthesis of new biologically active compounds with these moieties. The introduction of a heterocyclic chromenone fragment changes the previously observed 5-R-3-arylmethylidenefuran-2(3H)-ones route of reaction with guanidine carbonate and leads to 3-[(2-amino-4-(2-hydroxyphenyl)pyrimidin-5-yl)methylene]-5-phenylfuran-2(3H)-ones (2a–d). The structure of the reaction products depends on the nature of the aromatic substituent at the C-3 position of the furanone ring. The interaction of 5-aryl-3-arylmethylidenefuran-2(3H)-ones (1e–h) with thiourea in the basic medium leads to the isolation of 5-(2-oxo-2-phenylethyl)-6-aryl-2-thioxotetrahydropyrimidine-4(1H)-ones (3a–d), demonstrating pronounced plant-growth regulatory activity. Optimal conditions for all discussed processes were developed. Full article