Dimetalation of pyrazines. a one-pot synthesis of multisubstituted pyrazine C-nucleosides.

As a part of our efforts to pursue direct, convergent, and concise methodologies for the synthesis of pyrazine C-nucleosides, we have successfully established a sequential dilithiation-addition method, which allows one to introduce two different functional groups to a pyrazine ring in a one-pot fashion. 2,6-Dichloropyrazine was dilithiated at -100 degrees C and then allowed to react with an electrophile, such as bromine, iodine, or disulfides, followed by a reaction with a protected ribonolactone to afford C-nucleosides. After reduction and deprotection, tetrasubstituted pyrazine C-nucleosides, including 2,6-dichloro-3-iodo-5-(beta-D-ribofuranosyl)pyrazine and 2-bromo-3,5-dichloro-6-(beta-D-ribofuranosyl)pyrazine, were obtained. A tandem reaction sequence occurred when disulfides were used, resulting in the formation of 5,6-bis-methylthio-2-chloro-3-(beta-D-ribofuranosyl)pyrazine and 6-(beta-D-ribofuranosyl)-2,3,5-tris-phenylthiopyrazine.     

红收获蚁信息素的鉴定

利用色谱－质谱联机技术，在红收获蚁P.barbatus和P.maricopa的毒腺体样品中检测到召引信息素甲基吡嗪（MP）、2，5－二吡嗪（DMP）、3－乙基－2，5－二甲基吡嗪（EDMP）、和三甲基吡嗪（TMP）。利用特征离子色谱技术，在P.barbatus样品中还检测到了含6个碳原子侧链烃基的吡嗪X。根据吡嗪X的质谱图推测其结构为3－仲丁基－2，5－二甲基吡嗪（BDMP）。P.barbatus中DMP，TMP和EDMP的平均相对百分比分别为60.71、26.49、12.80；标准偏差分别为6.91、4.92、5.11;P.maricopa中平均相对百分比和标准偏差分别为47.48、20.35、32.17和15.05、4.05、15.44。     

Action du phényllithium en série pyrazine: Piégeage des intermédiaires réactionnels par le benzoate de méthyle

The action of phenyllithium on pyrazine, 2-methyl pyrazine and acetonyl pyrazine gave mono- or di-addition products with azomethines bonds of pyrazine. The adducts can be condensed with methyl benzoate to give C or N condensed derivatives. No product with initial metalation of methyl or acetonyl groups was observed.     

Synthesis of pyrazine acetals by the biased reaction of symmetric 2,5-bis(chloromethyl) or 2,3,5,6-tetrakis(chloromethyl) substituents on pyrazine ring with sodium alkoxides

2,5-Bis(chloromethyl)pyrazine reacted with sodium alkoxide to give unexpected 2-dialkoxymethyl-5-methylpyrazine along with normal substitution product, 2,5-bis(alkoxymethyl)pyrazine. The reaction of 2,3,5,6-tetrakis(chloromethyl)pyrazine with sodium alkoxide afforded similar results to yield 2,6-bis(dialkoxymethyl)-3,5-dimethylpyrazine along with other alkoxymethylpyrazines. The ratio of products depended on the solvent and alkoxide used. A general discussion of the mechanism of such a pyrazine acetal synthesis in the basic conditions is given.     

Synthesis and transformation of N-oxides of some imidazo[4,5-b]pyrazine derivatives

The Böckelheide reaction was accomplished with a number of imidazo[4,5-b]pyrazine N-oxides, and the N-oxidation of the resulting acetoxy(hydroxy)methyl derivatives of imidazo[4,5-b]pyrazine and 6-bromo-1-methylimidazo[4,5-b]pyrazine was studied. The hydrolytic cleavage of 6-bromo-1-methylimidazo[4,5-b]pyrazine and its 4-N-oxide was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 690–693, May, 1975.     

Liquid crystal properties of some substituted pyrazines

A number of biphenyl, terphenyl analogues and ethynes which contain a pyrazine ring have been made and their liquid crystal transition temperatures, together with examples of birefringence measurements, are reported. All the 2,5-disubstituted pyrazine systems are liquid crystalline showing high birefringence values for the biphenyl and terphenyl analogues, whereas the 1,5-disubstituted systems are not liquid crystalline. The pyrazine ethyne systems exhibit very high birefringence values. X-ray diffraction has been used to identify the liquid crystal phases of 2-n-nonyloxy-5-(4'-propylbiphenyl-4-yl)pyrazine.     

Indium(III) one-dimensional polymers with pyrazine and pyrazine, 2-carboxylic acid as the spacer molecules

The reactions of indium(III) chloride tetrahydrate with pyrazine (C₄H₄N₂) and pyrazine, 2-carboxylic acid afford two polymeric frameworks, the structures of which were characterized in the solid state by single crystal analysis. The former is a one-dimensional infinite structure interlinked by the pyrazine spacer, while the latter is a one-dimensional ‘zigzag’ polymeric structure. A dimeric indium(III) pyrazine complex is also reported.     

Orientation change of adsorbed pyrazine on roughened rhodium electrodes as probed by surface-enhanced Raman spectroscopy

A surface-enhanced Raman spectroscopic (SERS) study of pyrazine adsorbed on roughened Rh electrodes was performed. Potential and concentration effects on the adsorption behavior of pyrazine were investigated. The SER spectra display four pairs of overlapping bands with the relative intensity of each pair being highly potential dependent, which has not been observed on other metals. The orientation change of the adsorbed pyrazine from the end-on to N/pi bonded edge-on configuration is proposed to account for this potential-dependent relative intensity change. This hypothesis is further supported by the SERS results obtained at different pyrazine concentrations. In conjunction with the orientation effect, the interaction of Rh with hydrogen and oxygen generated at different potentials has a great influence on the adsorption configuration of pyrazine.     

Thermal and chemical decomposition of di(pyrazine)silver(II) peroxydisulfate and unusual crystal structure of a Ag(I) by-product

High purity samples of a [Ag(pyrazine)(2)]S(2)O(8) complex were obtained using modified synthetic pathways. Di(pyrazine)silver(II) peroxydisulfate is sensitive to moisture forming [Ag(pyrazine)(2)](S(2)O(8))(H(2)O) hydrate which degrades over time yielding HSO(4)(-) derivatives and releasing oxygen. One polymorphic form of pyrazinium hydrogensulfate, β-(pyrazineH(+))(HSO(4)(-)), is found among the products of chemical decomposition together with unique [Ag(i)(pyrazine)](5)(H(2)O)(2)(HSO(4))(2)[H(SO(4))(2)]. Chemical degradation of [Ag(pyrazine)(2)]S(2)O(8) in the presence of trace amounts of moisture can explain the very low yield of wet synthesis (11-15%). Attempts have failed to obtain a mixed valence Ag(II)/Ag(I) pyrazine complex via partial chemical reduction of the [Ag(pyrazine)(2)]S(2)O(8) precursor with a variety of inorganic and organic reducing agents, or via controlled thermal decomposition. Thermal degradation of [Ag(pyrazine)(2)]S(2)O(8) containing occluded water proceeds at T > 90 °C via evolution of O(2); simultaneous release of pyrazine and SO(3) is observed during the next stages of thermal decomposition (120-285 °C), while Ag(2)SO(4) and Ag are obtained upon heating to 400-450 °C.     

Pyrazine control of the solid-state supramolecular chemistry of zinc phthalocyanine

Crystals of monoaxially coordinated T-shaped and H-shaped supramolecular zinc(II) phthalocyaninato complexes with pyrazine are obtained. In both types of molecules the central Zn atom of ZnPc complexes with pyrazine exhibits 4 + 1 coordination. The Zn atom is equatorially coordinated by four isoindole N atoms of Pc macrocycle and axially by N atom of pyrazine molecule. The interaction of the central Zn atom of ZnPc with the axial N atom of pyrazine leads to a deviation of Zn from the centre of cavity by 0.371(2) Å in the T-shaped complex and by 0.296(2) Å in the H-shaped complex. Thermogravimetric analysis of the crystals exhibits three slopes down, corresponding to the loss in succession of solvated pyrazine molecules, than the loss of ligated pyrazine molecules from the T-shaped complex and the finally the loss of the bridged pyrazine molecule from the H-shaped complex. Finally the thermal processing leads to the β-ZnPc as residue. The UV–Vis spectrum taken in solution shows the batochromic shift in the polar solvent like α-chloronaphthalene in relation to the spectrum in non-polar solvent like benzene.     

A comparison of surface-enhanced infrared and surface-enhanced Raman spectra of pyrazine adsorbed on polycrystalline gold electrodes

The adsorption of pyrazine at a polycrystalline Au film electrode has been investigated using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), chronocoulometry, and ac impedance. Combining the SEIRA data and the thermodynamic data (the surface charge density of the electrode and the relative Gibbs surface excess of pyrazine), pyrazine was found to adsorb on the surface with a vertical end-on configuration via one N atom. The SEIRA spectra were compared with published surface-enhanced Raman (SER) spectra of pyrazine in order to clarify the reason for the breakdown of the Raman selection rule in the SER spectra. The activation of originally Raman-forbidden modes in the SER spectra is well explained by a photo-driven charge-transfer mechanism. The charge-transfer is deduced to be from filled metal states near the Fermi level to the first and second excited states of pyrazine. It is emphasized that the comparative SEIRA and SER studies are important for a better understanding of the electrochemical interface.     

2,6-Bis(porphyrin)-substituted pyrazine: a new class of supramolecular synthon binding to a transition-metal ion and fullerene (C60)

2,6-Disubstituted-3,5-dimethylpyrazines have been synthesized via biased acetal synthesis from symmetric 2,3,5,6-tetrakis(chloromethyl)pyrazine. The pyrazine ligands coordinated to trans-dichloropalladium(II) at the nitrogen whose neighboring carbons were connected to less hindered methyl groups. 2,6-Bis(porphyrin)-substituted pyrazine bound C₆₀ to yield 1:1 inclusion complex. The binding of C₆₀ with the pyrazine ligand and its zinc complex was determined by ESI-MS, NMR, and fluorescence spectroscopic analyses.     

Structural effects on the electronic properties of extended fused-ring thieno[3,4-b]pyrazine analogues

The synthesis and characterization of the extended thieno[3,4-b]pyrazine analogues acenaphtho[1,2-b]thieno[3,4-e]pyrazine (3a), 3,4-dibromoacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3b), 3-octylacenaphtho[1,2-b]thieno[3,4-e]pyrazine (3c), dibenzo[f,h]thieno[3,4-b]quinoxaline (4), and thieno[3',4':5,6]pyrazino[2,3-f][1,10]phenanthroline (5) are reported. Comparison of structural, electrochemical, and photophysical properties to those of simple thieno[3,4-b]pyrazines are provided in order to provide structure-function relationships within this series of compounds.     

Syntheses,Structures, and Thermal Reactivity of New ZnII and CdII Thio‐ and Selenocyanato Coordination Compounds

Reaction of Zn^II and Cd^II thiocyanate or selenocyanate with pyrazine leads to the formation of new Zn^II and Cd^II coordination compounds. The structures of [Zn(NCSe)₂(pyrazine)₂]_n ( 1A ), [Cd(NCS)₂(pyrazine)₂]_n ( 2A ) and [Cd(NCSe)₂(pyrazine)₂]_n ( 3A ) consist of octahedrally coordinated metal cations which are surrounded by two terminal N‐bonded anions and two μ₂‐bridging pyrazine molecules. The metal cations are connected via the pyrazine ligands into layers, which are further linked by weak intermolecular S···S respectively Se···Se interactions. Investigations on the thermal degradation behavior of 1A , 2A , and 3A using simultaneous differential thermoanalysis and thermogravimetry as well as X‐ray powder diffraction, IR‐ and Raman spectroscopy prove that on heating, the pyrazine‐rich compound 1A decomposes in one step into zinc selenocyanate without the formation of a pyrazine‐deficient intermediate. In contrast, for compounds 2A and 3A a stepwise decomposition is observed, leading to the formation of the pyrazine‐deficient compounds [Cd(NCS)₂(pyrazine)]_n ( 2B‐I and 2B‐II ) and [Cd(NCSe)₂(pyrazine)]_n ( 3B ) as intermediates. The structures and the thermal reactivity are discussed and compared with that of related transition metal thiocyanates and selenocyanates with pyridine as N‐donor ligand.     

Monomeric ruthenium carbonyls containing 2-substituted pyrazines: From synthesis to catalytic activity in 1-hexene hydroformylation

Synthesis and catalytic properties of a series of ruthenium carbonyl complexes with 2-substituted pyrazine ligands (pz–R; R = Cl, OMe, SMe, CN, NH₂) have been studied. Reactions between the [Ru(CO)₃Cl₂]₂ and the pyrazines led mainly to mononuclear compounds of the type [Ru(CO)₃Cl₂(R–pz)]. All of these ruthenium pyrazine compounds showed activity in 1-hexene hydroformylation. With an exception of NH₂, addition of the substituent to the pyrazine ring was found to improve the catalytic activity compared to the unsubstituted pyrazine. The catalytic cycle was studied by computational DFT methods. The results suggest that the key step in the formation of the active species involves release of one of the carbonyl in the cis position with respect to the pyrazine ring.     

Synthesis and structure of Zn7(mu4-O)2(OAc)10(Pz)2(OAc = acetate; Pz = pyrazine)

Reaction of Zn(OAc)(2).2H(2)O with pyrazine in refluxing ethanol gives the unusual heptanuclear complex Zn7(mu4-O)(2)(OAc)(10)(Pz)(2) (1) (OAc = acetate, Pz = pyrazine) in 46% yield. A single-crystal X-ray diffraction study of revealed a central Zn(7) core in which two pseudo-tetrahedral Zn(4) units are joined at a common vertex. The two pyrazine molecules are bound as terminal (eta1) ligands.     

Multidynamic Crystalline Molecular Rotors Comprising an N-Heterocyclic Carbene Binuclear Au(I) Complex Bearing Multiple Rotators

We report multidynamic molecular rotations in crystals using a concave-shape N-heterocyclic carbene (NHC) binuclear Au(I) complex rotor bearing pyrazine and tetrahydrofuran (THF) molecules as multicomponent rotators. Single-crystal X-ray diffraction (XRD) measurements revealed that two THF molecules are located near the central pyrazine encapsulated by two bulky NHC ligands. From ²H solid-state NMR analysis, it was observed that the pyrazine rotated in a 2-fold site exchange with a 180° rotational angle and a 31 kJ mol⁻¹ energy barrier, while the THF molecules showed a 23°-38° libration with a lower energy barrier (14 kJ mol⁻¹). Interestingly, the pyrazine rotation was accelerated when the THF molecules rotated in fast site exchange with a large angle of libration, suggesting that the rotators exhibit multidynamics in a correlated manner.     

Hydrogen bond formations between pyrazine and formic acid and between pyrazine and trichloroacetic acid

The hydrogen bond formations between pyrazine and formic acids and between pyrazine and trichloroacetic acids were studied through observation of the Raman and infrared spectra for mixture of pyrazine and formic acid and also mixture of pyrazine and trichloroacetic acid at 77 K. It was observed that the mutual exclusion principle held for the Raman and infrared spectra of both mixtures, even for the spectra of the samples whose mixing mole ratio of acids was very low. This fact clearly indicates that the hydrogen bonded molecule does not exist in the form of formic acid-pyrazine or trichloroacetic acid-pyrazine whose geometry belongs to the Cs point group, but exists in the form of formic acid-pyrazine-formic acid or trichloroacetic acid-pyrazine-trichloroacetic acid belonging to the C(i) point group.     

A Re‐Examination of the Reaction of 3,4‐Diamino[1,2,5]oxadiazole with Glyoxal

Reaction coordinate mapping was used to study the reaction of 3,4‐diamino[1,2,5]oxadiazole (3,4‐diaminofurazan) and 3,4‐diamino[1,2,5]thiadiazole with glyoxal. The thiadiazole was known to give a good yield of [1,2,5]thiadiazolo[3,4‐b]pyrazine, whereas the oxadiazole had not yielded, until now, [1,2,5]oxadiazolo[3,4‐b]pyrazine (or furazano[2,3‐b]pyrazine). The calculations suggested that the diols, 5,6‐dihydroxy‐4,5,6,7‐tetrahydro[1,2,5]oxadiazolo[3,4‐b]pyrazine and 5,6‐dihydroxy‐4,5,6,7‐tetrahydro[1,2,5]thiadiazolo[3,4‐b]pyrazine should be stable intermediates, and once formed, should provide a pathway to the target compounds via two dehydration steps, under forcing conditions. With this information in mind, the reactions of 3,4‐diamino[1,2,5]oxadiazole with glyoxal and pyruvic aldehyde were re‐examined. The reaction of 3,4‐diamino[1,2,5]oxadiazole with glyoxal and pyruvic aldehyde produced, under slightly basic conditions, a near quantitative yield of the expected initial products, 5,6‐dihydroxy‐4,5,6,7‐tetrahydro[1,2,5]oxadiazolo[3,4‐b]pyrazine and the 5‐methyl analog, respectively. The diols were easily isolated by lyophilizing the aqueous reaction mixture. The diols were pyrolized on silica gel at 160°C to give the desired [1,2,5]oxadiazolo[3,4‐b]pyrazine and the 5‐methyl analog. Both compounds were easily reduced to the corresponding 4,5,6,7‐tetrahydro‐derivative using sodium borohydride in THF/methanol. The [1,2,5]oxadiazolo[3,4‐b]pyrazine also displayed other interesting chemistry.     

Recurrence of carboxylic acid-pyridine supramolecular synthon in the crystal structures of some pyrazinecarboxylic acids.

X-ray crystal structures of pyrazinic acid 1 and isomeric methylpyrazine carboxylic acids 2-4 are analyzed to examine the occurrence of carboxylic acid-pyridine supramolecular synthon V in these heterocyclic acids. Synthon V, assembled by (carboxyl)O-H...N(pyridine) and (pyridine)C-H...O(carbonyl) hydrogen bonds, controls self-assembly in the crystal structures of pyridine and pyrazine monocarboxylic acids. The recurrence of acid-pyridine heterodimer V compared to the more common acid-acid homodimer I in the crystal structures of pyridine and pyrazine monocarboxylic acids is explained by energy computations in the RHF 6-31G* basis set. Both the O-H.N and the C-H...O hydrogen bonds in synthon V result from activated acidic donor and basic acceptor atoms in 1-4. Pyrazine 2,3- and 2,5-dicarboxylic acids 10 and 11 crystallize as dihydrates with a (carboxyl)O-H...O(water) hydrogen bond in synthon VII, a recurring pattern in the diacid structures. In summary, the carboxylic acid group forms an O-H...N hydrogen bond in pyrazine monocarboxylic acids and an O-H...O hydrogen bond in pyrazine dicarboxylic acids. This structural analysis correlates molecular features with supramolecular synthons in pyridine and pyrazine carboxylic acids for future crystal engineering strategies.