Search

An approach was developed for the synthesis of polyfunctionalized pyrimidines based on analogs of 1,2,4-triketones. Acetal-substituted β-diketones are involved in the condensation with amidines in the presence of an excess of (EtO)3B/Et3N in acetonitrile. The conditions of the acid hydrolysis of acetal-containing pyrimidines were found to depend on the nature of substituents in diazine. The use of 1,2,4-triketone in the condensation with amidine allows the synthesis of acetylpyrimidine in one step. [ABSTRACT FROM AUTHOR]

A new method for regioselective zincations of challenging N‐heterocyclic substrates such as pyrimidines and pyridazine was reported using bimetallic bases TMPZnX⋅LiX (TMP=2,2,6,6‐tetramethylpiperidyl; X=Cl, Br). Reactions occurred under mild conditions (25–70 °C, using 1.75 equivalents of base without additives), furnishing 2‐zincated pyrimidines and 3‐zincated pyridazine, which were then trapped with a variety of electrophiles. Contrasting with other s‐block metalating systems, which lack selectivity in their reactions even when operating at low temperatures, these mixed Li/Zn bases enabled unprecedented regioselectivities that cannot be replicated by either LiTMP nor Zn(TMP)2 on their own. Spectroscopic and structural interrogations of organometallic intermediates involved in these reactions have shed light on the complex constitution of reaction mixtures and the origins of their special reactivities. [ABSTRACT FROM AUTHOR]

Crystal structures of two salts of (E)-2-(3,4-dimethoxystyryl)pyrimidinium (HDmsPy+) are studied: (HDmsPy)Cl·H2O and (HDmsPy)Cl·0.5С6H4(OH)2. (E)-2-(3,4-dimethoxystyryl)pyrimidinium chloride is photoinert. Upon UV irradiation, the (E)-2-(3,4-dimethoxystyryl)pyrimidinium cocrystal with catechol as well as pure (E)-2-(3,4-dimethoxystyryl)pyrimidine (DmsPy) are involved in the [2+2]-photocycloaddition reaction with crystal destruction. Structures of solid phase reaction products and a similar photocycloaddition reaction in the solution are analyzed by 1H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

In this contribution, a series of seven new push–pull systems has been designed by combining a protonable diazine heterocycle (pyrimidine/pyrazine) with a deprotonable phenol unit through various π-conjugated linkers (phenylene, thienylene, thienylenevinylene, and phenylenevinylene). The (de)protonation in solution resulted in a systematic bathochromic shift both in the absorption and emission maxima compared to the neutral forms. Extensive Density Functional Theory (DFT) and its Time Dependent counterpart (TD-DFT) calculations were performed to rationalize this behavior and understand the impact of (de)protonation on the different optical transitions. These computations showed that (de)protonation affects both the energy and the nature of the vertical transitions, with a significant increase in the Intramolecular Charge Transfer (ICT) character of the (de)excitations. Some of the compounds remained moderately luminescent after (de)protonation, giving a mixture of complementary emitting species that were used to obtain white light emission. [ABSTRACT FROM AUTHOR]

We present a comprehensive ab-initio study of electron collisions with pyrazine, pyrimidine, and pyridazine. The emphasis is placed on the identification and characterization of electron resonances in these systems. We use the R-matrix method and show that analysing the time-delay reveals resonances whose signature is not visible in the eigenphase sums. In addition to the well known π* resonances below 5 eV, we find three core-excited shape resonances in the energy range 5.5-8.5 eV and a few Feshbach resonances in the dipolar molecules. Additionally, 11 resonances with little effect on the elastic scattering from ground state diazines (but significant effect in elastic collisions with the molecules in an excited state) are found and characterized. We correlate these resonances across the three molecules and discuss their possible correspondence to resonances described in earlier studies on uracil. [ABSTRACT FROM AUTHOR]

A series of 7-azinyl-substituted triazolopyridines and 3-(6-azinyl- substituted 2-pyridyl)triazolopyridines were synthesized by addition of the corresponding 3-substituted 7-lithiotriazolopyridine to pyrimidine, pyrazine, pyridazine, and 1,3,5-triazine respectively, followed by hydrolysis and oxidation. [ABSTRACT FROM AUTHOR]

A new series of 3-methyl-6-[1-(pyrimidin-4-yl)ethyl]-5H-pyrimido[5,4-e][1,2,4]triazolo[3,4-b][1,3,4]thiadiazine derivatives was synthesised through the condensation reaction of 5-bromo-4-[1-(5-bromo-2,6-dichloropyrimidin-4-yl)ethyl]-2-chloro-6-methylpyrimidine and 4-amino-5-methyl-4H-1,2,4-triazole-3-thiol. [ABSTRACT FROM AUTHOR]

Recent photoemission spectroscopic (X-ray photoemission spectra) study revealed less dramatic chemical changes for pyrimidine (PyM, 1, 3-diazine) with in its ionization potential. Present systematic study using density functional theory calculations shows that PyM is indeed quite different from its diazine isomers (PyD, 1, 2-diazine and PyA, 1, 4-diazine). It is discovered that the most stable isomer PyM is relaxed from C2V to C1 point symmetry with a total electronic energy deduction of −15.86 kcal.mol−1. Although not substantial, PyM has the smallest molecule shape (electronic spatial extent) and the largest HOMO-LUMO energy gap of 5.65 eV; only one absorption band in the region of 200-300 nm of the UV-Vis spectrum but three clusters of chemical shift in the carbon and hydrogen NMR spectra. The energy decomposition analyses revealed that the interaction energy (Δ EInt) of PyM is preferred over PyA by 4.08 kcal.mol−1 and over PyD by 22.32 kcal.mol−1, with the preferred NCN bond revealed by graph theory. [ABSTRACT FROM AUTHOR]

A mild, easy-to-perform, and versatile method for the formation of aminochlorodiazines from reaction of several types of dichlorodiazines (i.e., pyridazines, pyrimidines, and pyrazines) with primary or secondary amines in ethanol in the presence of triethylamine as a base, is described. The methodology is general and efficient despite noticeable difference in reactivity between diazines. While dichloropyridazine and dichloropyrazine require several hours of heating at reflux for the reaction to proceed, dichloropyrimidines reach completion within minutes at room temperature. [ABSTRACT FROM AUTHOR]

This review gives an overview of the application of guanidine and its salts in multicomponent reactions. It can act as a catalyst or solvent for multicomponent reactions or as a reagent for synthesis of substituted diazines, triazines, and macroheterocycles by multicomponent reactions. [ABSTRACT FROM AUTHOR]

Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)2(pyrimidine)2]n (2) which is isotypic to [Co(NCS)2(pyrimidine)2]n (1) reported recently. In the crystal structure, the Ni2+ ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)2(pyrimidine)]n (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni2+ ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two S atoms of μ-1,3 bridged thiocyanato anions, which conntect these chains into layers, within a slightly distorted octahedral geometry. On heating compounds 1 and 2 transform quantitatively into the ligand-deficient 1:1 Ni compound 4 and its isotypic Co compound 3. If nickel and cobalt thiocyanate are reacted with an excess of pyrimidine in a solvent-free reaction, discrete ligand-rich 1:4 complexes of composition [M(NCS)2(pyrimidine)4] (M = Co 5 and Ni 6) are obtained, which could be determined by single crystal structure analysis. In their crystal structure the metal ions are coordinated by four terminal bonded pyrimidine ligands and two terminal N-bonded thiocyanato anions. For the ligand-rich 1:2 and ligand-deficient 1:1 compounds magnetic measurements were performed, which reveal different magnetic properties: The 1:2 compounds show a ferromagnetic and the 1:1 compounds an antiferromagnetic ordering at lower temperatures. Five new thiocyanato metal coordination polymers with pyrimidine as N-donor ligand were prepared and their structural, thermal, and magnetic properties were determined. Upon heating, the ligand-rich 1:2 compounds transform quantitatively into new ligand-deficient 1:1 compounds. Depending on the connection of the thiocyanato anions, different magnetic interactions are observed. [ABSTRACT FROM AUTHOR]

The adsorption of 2-amino pyrimidine (2APM) on sepiolite and montmorillonite has been investigated using FT-IR spectrometry. The intercalation of 2-amino pyrimidine within montmorillonite has been shown by X-ray diffraction to increase the interlayer spacings. 2APM interacted with montmorillonite by direct or indirect coordination (through water molecules) to the exchangeable cations. Adsorption on sepiolite was due to hydrogen bonding with surface Si–OH groups. It is concluded that endocyclic nitrogen is mainly involved in coordination. Moreover, amino group hydrogens may be involved in hydrogen bonding interaction with water molecules (NH…OH2). [Copyright &y& Elsevier]

The reaction of dibenzoylacetylene with triazoles gives the title compounds with excellent yields via a catalyst-free one-pot cyclization at room temperature. [ABSTRACT FROM AUTHOR]

Simple pyridazines are unreactive under the investigated conditions. [ABSTRACT FROM AUTHOR]