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The possibility of preparing 1,2,5-oxa-, -thia-, and -selenadiazole N-oxides from polyfunctional nitroso-and isonitrosopyrimidines and -pyridine was examined.We found previously that the reactions of 6-amino-5-nitrosouracils with sulfur or selenium monochloride yield 1,2,5-chalcogenadiazolo [3,4-d]pyrimidines [1,2]. In this study we examined the applicability of this reaction to o-amino nitroso compounds containing additional reaction centers such as hydroxy and amino groups. As starting compounds we used 5-nitroso derivatives of 1-hydroxyethyl-6-aminouracil (Ia) [3], 4,6-diamino-1,2-dihydropyrimidin-2-one (Ib) [4], and 2,4,6-triaminopyrimidine (Ic) [4], and also 3-nitroso-2,6-diaminopyridine Id [5]. Treatment of Ia3Id with sulfur or selenium monochloride under the conditions similar to those described in [1] resulted in formation of 1,2,5-chalcogenadiazole N-oxides IIa3IIh in good yields (Scheme 1).The reactive functional groups present in the starting amino nitroso compounds, at equimolar ratio of the reactants, exert no appreciable effect on the course of cyclization with the formation of 1,2,5-thiadiazole N-oxides and their selenium analogs.An alternative route to 1,2,5-oxa-, -thia-, and selenadiazoles, based on transformations of aliphatic and aromatic 1,2-dioximes [6 38], is limited by difficult availability of heterocyclic 1,2-dioximes.With 6-amino-5-nitrosouracil Ie as example, we showed that the amino group in an acidic medium is readily replaced by hydroxylamine; the reaction product isomerizes into uracil 5,6-dioxime IIIa existing, according to single crystal X-ray diffraction data, in the form of the (4Z,5E) isomer [9]. The reactions between Ib3Id and excess hydroxylamine taken as a mixture of acetate and hydrochloride resulted in replacement of all the amino groups with the formation of tri-and tetraoxime derivatives of pyrimidine (IIIb, IIIc) and pyridine (IIId) (Scheme 2). The reactivity is apparently influenced by the steric factors: 1-Substituted 6-amino-5-nitrosouracils do not react with hydroxylamine under the similar conditions. Scheme 1.

The hydrogen-bonding networks for seven new binary compounds of dithiooxamide, (NH2CS)2 (dtox) and dithiobiurea (NH2CSNH)2 (dtur) with crown ethers, 18-crown-6 (18C6), 15-crown-5 (15C5), 12-crown-4 (12C4), cis-syn-cis-(DCHA), and cis-anti-cis-(DCHB) isomers of dicyclohexyl-18 -crown-6 are discussed. (15C5.dtox), (18C6.dtur) and (DCHB.dtur) afford one-dimensional hydrogen-bonded polymeric arrays where the components alternate. In (DCHA.2dtox) and (DCHB.2dtox) the similar hydrogen-bonded chains are further interlinked via dtox molecules to generate layered motifs. In (15C5.2dtur) the dtur molecules are self-assembled into layers via N-H...S hydrogen bonds. 15C5 spacers link adjacent layers into a three-dimensional network. In (12C4.dtur) the dtur molecules are arranged in chains. These chains alternate with the crown molecules attached to them through N-H...O hydrogen bonds in such a way that each 12C4 appears to be linked with four dtur molecules and vice versa thus providing a three-dimensional grid.

Two novel pyrimidine derivatives, 2-(2-methylphenyl)-2H-[1,2,3]triazolo[4,5-d ]pyrimidine-5,7(4H,6H)-dione 3-oxide (H-PD) and 6-amino-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-ylsulfamic acid (H-PS), were synthesized and investigated as suitable ligands for co-crystallization with 1,10-diaza-18-crown-6 (DA18C6). Two solid compounds formulated as [(H 2 DA18C6)(PD) 2 (H 2 O) 4 ] (1) and [(H 2 DA18C6)(PS) 2 (H 2 O) 2 ] (2) have been shown by single-crystal structural analysis to be 2D and 3D networks, respectively, through extensive H-bonding intermolecular interactions. Both 1 and 2 incorporate the diaza-18-crown-6 units in the form of macrocyclic cations. In 1 the (PD) 2 anions deprotonated in the fourth position of the pyrimidine ring and water molecules are combined into 2D anionic sheets, the macrocyclic cations occupying the cavities in these sheets. In 2 the ensemble of donor and acceptor binding sites available in the 6-amino-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-ylsulfamate anions (PS) 2 facilitates their self-assembly into a double layer via diverse hydrogen bonds. Water molecules and H 2 -1,10-diazonia-18-crown-6 cations bridge the neighboring layers thus providing the final 3D supramolecular architecture.

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