A solvent-free interaction between 5-cyano-1.2.4-triazines and 5-methylsulfanyl-4H-1,2,4-triazol-3-amines has been studied. The structure of the product of ipso-substitution of cyano-group with the corresponding heterocyclic amine residue has been proven by 1Н NMR and ESI-MS data. Thus, in the 1Н NMR spectra a three-proton singlet at 2.61 ppm is present, which can be interpreted as the signal of the methylsulfanyl group protons. Subsequent transformation of 1,2,4-triazine scaffold of the resulting product into a pyridine one has been successfully per-formed under autoclave conditions. It has been found that methylsulfanyl group undergoes no transformations in both stages of synthesis. This fact is also proven by X-Ray crystallography data of the obtained functionalised bypyridines. According to the X-Ray crystallography data, compound 4 crystallizes as two crystallographically independent molecules in non-centrosymmetric space group P-1 with triclinic system. The crystal structure is formed by numerous intermolecular N∙∙∙H contacts between two crystallographically independent molecules of triazolylpyridine-2-amine. The 1Н NMR spectra of compound 4 contain two doublets of the new pyridine cycle at 7.37 and 7.61 ppm. Thus, properties of 5-methysulfanyl-4H-1,2,4-triazol-3-amine are different from these of its analogue with mercaptogroup at C5 position. Namely, in accordance to our previous results ipso-substitution of C5-cyanogroup of 1,2,4-triazine with moiety of the latter amine is accompanied by desulfurization reaction.

A facile synthetic approach is reported toward ligands based on 2-(2-pyridyl)quinazoline, which are suitable for the preparation of both water-soluble and liposoluble chelate complexes with lanthanide(iii) cations. The ligands contain an additional rigid chelating moiety, such as the carboxyl group or the diethylenetriaminetetraacetic acid residue. The luminescence properties of the new cationic EuIII and TbIII complexes were studied.

New 5-[4(3)-R-phenyl]-2,2′-bipyridines bearing the 1,1,7,7-tetrakis(tert-butoxycarbonylmethyl)-1,4,7-triazaheptane (DTTA) moiety at the C(6) position (R = Cl, Br, CF3) and their water-soluble EuIII complexes were synthesized. The photophysical properties of the synthesized complexes were investigated. More efficient sensitization of Eu3+ cation luminescence was demonstrated for a number of halogen-containing ligands. Some chelates exhibited moderate cell-staining ability. The synthesized compounds did not show significant photodynamic activity, which may be due to the inhibition of the in situ generation of reactive oxygen species via the supposed interaction with the methylene moiety of DTTA-appended 2,2′-bipyridine ligands.

The reaction of C6-unsubstituted 5-aryl-3-(2-pyridyl)-1,2,4-triazine with generated in situ difluoroaryne intermediate (4,5-difluoro-1,2-dehydrobenzene), previously unused for this aim, was studied. New transformations of the 1,2,4-triazine nucleus were discovered, which lead, along with the domino transformation product (10-(1,2,3-triazole-3-yl)pyrido[1,2-a]indole) natural for this transformation, to the formation of unexpected products, namely 1,3,5-tris-substituted 1,6-dihydro-1,2,4-triazin-6-ol and 1H-1,2,4-triazole. The structure of the products was confirmed by physicochemical methods, including X-ray diffraction analysis.

Five representatives of 4,5-diaryl-substitted 3-hydroxy-2,2′-bipyridine-6-carbonitriles were studied by single-crystal X-ray diffraction. The specific features of the molecular structures of these compounds and the effect of substituents on the crystal packing are discussed. The results of this study may be of interest in terms of the possible biological activity of this series of compounds and their use as polydentate N,N- or N,O-type ligands.

A new transformation of 3,6-diphenyl-1,2,4,5-tetrazine was discovered during the solvent-free reaction with 2-amino-4-aryloxazoles, leading to the formation of 2,5,7-triaryl[1,2,4]triazolo[1,5-a]pyrimidines. Stucture of products was also confirmed by single crystal X-ray diffraction data. A possible mechanism for this reaction was proposed.

Transformations of the various 6-[4-(methylthio)phenyl]-3-(2-pyridyl)-1,2,4-triazines in their reactions with an aryne intermediate were investigated. It was shown that the interaction of a 5-unsubstituted triazine with the aryne led to an S-arylation product, whereas there were no any transformations of the pyridyltriazine system. Introduction of the pentafluorophenyl substituent at the C(6) position of the triazine changed the pathway in this reaction with the aryne, which proceeded simultaneously at two reaction centers. In particular, there were a rearrangement of the 3-(2-pyridyl)-1,2,4-triazine into the 10-(1H-1,2,3-triazol-1-yl)pyrido[1,2-a]indole system as well as S-arylation. The product of dual functionalization, 10-5-perfluorophenyl-4-[4-(phenylthio)phenyl]-1H-1,2,3-triazol-1-ylpyrido[1,2-a]indole, exhibited a blue emission at λem = 395 nm and a fluorescence quantum yield comparable to the analogs obtained previously.

The reactions of 3-aminopyridine with 9,10-phenanthrenequinone and 1,2-naphthoquinone under various conditions was studied. The formation of the monoimine was observed in the presence of an additional aromatic ring in the structure of the starting dione. The product of the nucleophilic attack of the amino group at position C4 of the aromatic ring was obtained in the absence of this additional ring. One of the products obtained is a derivative of lawsone, a natural dye with a wide range of bioactivity, including antitumor one. Its structure was additionally confirmed by single crystal X-ray diffraction analysis.

New samarium complex of 5-phenyl-2,2'-bipyridine with the diethylenetriaminotetraacetic acid (DTTA) residue in the C6 position, [(L2)Sm2Na5(H2О)9(C2O4)]n (I), is synthesized. The structure of complex I is studied by XRD (CIF file CCDC no. 2217968). The complex in the crystal is found to be a one-dimensional coordination polymer, and the 2,2'-bipyridine fragments do not chelate the Sm3+ cation. The complex is characterized by a luminescence response to the addition of an excess of zinc cations.

The solvent-free reaction of 1,2,4-triazine-5-carbonitriles with newly synthesized 5-[(2-hydroxyethyl)sulfanyl]- and 5-{[2-(2-hydroxyethoxy)ethyl]sulfanyl}-3-amino-1,2,4-triazoles under heating was studied. It was shown that in the case when the C 5 atom of the 1,2,4-triazole ring bears hydroxy(ethoxy)ethylsulfanyl substituents, 5-amino-1,2,4-triazines are formed as the main reaction products, while the ipso -substitution products of the C 5 -cyano group of the substituted 1,2,4-triazole ring were isolated only as by-products. With a 1,2,4-triazole with a monoethylene glycol fragment at the C 5 position, a complex mixture of products was formed.

The solvent-free interaction of 1,2,4-triazine-5-carbonitriles with first synthesized 5-hydroxyethylsulfanyland 5-hydroxyethoxyethylsulfanyl-3-amino-1,2,4-triazoles at heating has been studied. It was shown that the presence of these substituents at the C5 position of 1,2,4-triazole changes the direction of the reaction, and 5-amino-1,2,4-triazines are formed as the main products, while the products of the ipso -substitution of the C5-cyano group containing the moiety of the substituted 1,2,4-triazole were isolated only as by-products. In the case of using 1,2,4-triazole with a fragment of monoethylene glycol at C5 position of triazine, the formation of a complex mixture of products occurred.

Recently we described the solvent-free interaction of 5-aryl-3-(2-pyridyl)-1,2,4-triazine-5-carbonitriles and 2-amino-4-aryloxazoles to form 4,5-diaryl-3-hydroxy-2,2'-bipyridine-6-carbonitriles. It turned out that under absolute (anhydrous) conditions this reaction resulted in the formation of two products, namely, the previously described 4,5-diaryl-3-hydroxy-2,2'-bipyridine-6-carbonitriles (yields up to 44%) and 4,5-diaryl-2,2'-bipyridine-6-carbonitriles (yields up to 32%).

We previously reported the solvent-free reaction of 5-aryl-3-(pyridin-2-yl)-1,2,4-triazine-5-carbo­nitriles with 2-amino-4-aryl-1,3-oxazoles, which afforded 4,5-diaryl-3-hydroxy-2,2′-bipyridine-6-carbonitriles. Similar reaction in anhydrous medium led to the formation of two products, previously described 4,5-diaryl-3-hydroxy-2,2′-bipyridine-6-carbonitriles (up to 44%) and 4,5-diaryl-2,2′-bipyridine-6-carbonitriles (up to 32%).

The reactions of 5-(1,2-dicarbadodecaboran-1-yl)-3-(2-pyridyl)-1,2,4-triazines with various dienophiles (2,5-norbornadiene, 1-morpholinocyclopentene, 1,2-dehydrobenzene, and 2-amino-4-phenyloxazole) were studied. It was shown that the presence of a carborane fragment in the 1,2,4-triazine ring causes an atypical reaction with dienophiles without the formation of the expected aza-Diels-Alder reaction products except for the reaction with 2,5-norbornadiene. The reaction of 5-(1,2-dicarbadodecaboran-1-yl)-3-(2-pyridyl)-1,2,4-triazines with 2-amino-4-phenyloxazole unexpectedly led to the formation of the corresponding 4,5-dihydro-1,2,4-triazines. One of the previously described procedures for the direct introduction of a carborane residue into the C-5 position of 1,2,4-triazines was optimized.

An interaction of 6-aryl-1,2,4-triazine-5-carbonitriles with 2‑amino-4-aryl-substituted thiazoles and oxazoles has been studied. The difference in the reactivity of these aminoheterocycles depending on the presence of an oxygen or a sulfur atom in their composition has been demonstrated. Previously, the 4-aryl-3-hydroxy-2,2′-bipyridines were obtained as products of aza-Diels−Alder reaction between 6-aryl-3-(2-pyridyl)-1,2,4-triazine-5-carbonitriles and 2-amino-4-aryloxazoles. It was shown that the reaction of 6-aryl-1,2,4-triazine-5-carbonitriles with 2-aminothiazoles led to the products of ipso-substitution of cyano group. The aza-Diels−Alder reaction of these compounds with 2,5-norbornadiene gave (2,2′-bi)pyridines with the 2-aminothiazolyl at alpha-position.

The efficient synthetic approaches to new 2,2'-bipyridine ligands functionalized with a 3-thienyl moiety have been developed. These compounds are of interest as monomeric units for electropolymerization. The “1,2,4-triazine” methodology was used for the synthesis.

Solvent-free reaction of 3,6-diaryl-1,2,4-triazine-5-carbonitriles with 2-amino-4-aryloxazoles was studied. In this case, the formation of 3- and 4-aryl-substituted pyridines (two isomeric products) in yields up to 20 and 27%, respectively, was found. This result is different from that for the reaction of 3-(2-pyridyl)-1,2,4-triazine-5-carbonitriles with these substrates. Thus, in this case, 2-amino-4-aryloxazoles act as synthetic analogues of arylacetylenes.

The solvent-free reaction of 1,2,4-triazine-5-carbonitriles with newly synthesized 5-[(2-hydroxyethyl)sulfanyl]- and 5-{[2-(2-hydroxyethoxy)ethyl]sulfanyl}-3-amino-1,2,4-triazoles under heating was studied. It was shown that in the case when the C5 atom of the 1,2,4-triazole ring bears hydroxy(ethoxy)ethylsulfanyl substituents, 5-amino-1,2,4-triazines are formed as the main reaction products, while the ipso-substitution products of the C5-cyano group of the substituted 1,2,4-triazole ring were isolated only as by-products. With a 1,2,4-triazole with a monoethylene glycol fragment at the C-5 position, a complex mixture of products was formed.

A convenient method for the preparation of 5-aryl-2,2′-bipyridines with para -arylsulfanyl group in an aromatic substituent was proposed. The synthesis was performed using in situ generated aryne intermediates without the use of complex experimental procedures and expensive reagents/catalysts. The structure of one product was confirmed by XRD data. This approach is a new variant for the preparation of 5-aryl-2,2’-bipyridines with an extended conjugation system.