The reaction of β-lactam carbenes with 3,6-dipyridyltetrazines: switch of reaction pathways by 2-pyridyl and 4-pyridyl substituents of tetrazines

The reactions of β-lactam carbenes with both 3,6-di(2-pyridyl)tetrazine and 3,6-di(4-pyridyl)tetrazine were studied. It was found that β-lactam carbenes reacted with 3,6-di(2-pyridyl)tetrazine to produce 5-triazolo[1,5-a]pyridylpyrrol-2-ones in good yields, while with 3,6-di(4-pyridyl)tetrazine, they afforded pyrido[c]cyclopenta[b]pyrrol-2-ones in moderate yields. Both reactions were proposed to follow cascade mechanisms containing a 3,6a-dipyridylpyrrolo[3,2-c]pyrazol-5-one intermediate. The different pathways of the transformation of pyrrolo[3,2-c]pyrazol-5-ones were switched by the 2- and 4-pyridyl substituents. This work not only provided a simple and efficient strategy for the construction of novel triazolo[1,5-a]pyridine and pyrido[c]cyclopenta[b]pyrrole derivatives, respectively, but also revealed two different thermal transformation patterns of 3H-pyrazole compounds.     

Simultaneous determination of palladium and rhodium using on-line column enrichment and electrothermal atomic absorption spectrometric detection

Flow injection on-line micro-column pre-concentration was coupled with electrothermal atomic absorption spectrometry (ETAAS) for the simultaneous determination of Rh and Pd in environmental samples. The micro-column contained 1,5-Bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex 1 × 8–200). The sorbent was tested in a micro-column, placed in the auto-sampler arm, at the flow rate 3.1 mL/min. Elution was performed with 2 M HNO₃ and the system was optimised with a 60 s pre-concentration time.     

Automated on-line separation preconcentration system for palladium determination by graphite furnace atomic absorption spectrometry and its application to palladium determination in environmental and food samples

A flow injection (FI) system was used to develop an efficient on-line sorbent extraction preconcentration system for palladium by graphite furnace atomic absorption spectrometry (GFAAS). The investigated metal was preconcentrated on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel). The palladium is eluted with 40 μl of HCl 4 M and directly introduced into the graphite furnace. The detection limit for palladium under the optimum conditions was 0.4 ng ml⁻¹. This procedure was employed to determine palladium in different samples.     

Novel synthesis of 2,4-bis(2-pyridyl)-5-(pyridyl)imidazoles and formation of N-(3-(pyridyl)imidazo[1,5-a]pyridine)picolinamidines: nitrogen-rich ligands

Heating a neat 1:2 mixture of 2-picolylamine and 2-cyanopyridine followed by treatment of the resultant red gummy substance with aqueous KOH resulted in the isolation of 2,4,5-tris(2-pyridyl)imidazole (1a) as the major product and N-(3-(2-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2a) in small amounts. Similarly, by using 3-picolylamine, 2,4,-bis(2-pyridyl)-5-(3-pyridyl)imidazole (1b) and N-(3-(3-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2b) were isolated, and by using 4-picolylamine, 2,4,-bis(2-pyridyl)-5-(4-pyridyl)imidazole (1c) and N-(3-(4-pyridyl)imidazo[1,5-a]pyridine)picolinamidine (2c) were isolated. The plausible mechanism of the formation of 1a-c and 2a-c is delineated.     

Synthesis of some 1,3-disubstituted imidazo[1,5-a]pyridines using 2-cyanopyridine

Heating 2-cyanopyridine and hydrazine hydrate at 100 °C and reheating the resultant liquid with pyridine-2-carboxaldehyde yielded a red semi-solid. On adding aqueous KOH, a mixture of 1-(3,5-bis(2-pyridyl)-1,2,4-triazolyl)-3-(2-pyridyl)imidazo[1,5-a]pyridine (2a) and 1-((2-pyridyl)methanimine)-3-(2-pyridyl)imidazo[1,5-a]pyridine (2b) precipitated and from the filtrate 3,5-bis(2-pyridyl)-1,2,4-triazole (1) was isolated. Similar compounds were obtained from two other pyridinecarboxaldehydes.     

On-line preconcentration of palladium(II) using a microcolumn packed with a chelating resin, and its subsequent determination by graphite furnace atomic absorption spectrometry

Palladium(II) is preconcentrated on a chelating resin microcolumn [1,5-Bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide immobilized on an anion-exchange resin (Dowex 1 X8-200)] placed in the autosampler arm, followed by the elution of the Pd-chelate with nitric acid and subsequent determination of Pd from the eluate by graphite furnace atomic absorption spectrometry. The method was applied to the recovery of Pd(II) ions from different samples.     

On-line preconcentration of rhodium on an anion-exchange resin loaded with 1,5-bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide and its determination in environmental samples

A method for the determination of rhodium in different samples at trace levels is presented. The investigated metal is preconcentrated on a chelating resin microcolumn (1,5-bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex 1×8-200)) placed in the autosampler arm. The modification of the autosampler in the tubing line and circuit allowed either the flow of the sample through the column or the operation of the autosampler in the normal mode, where microlitres of 4 M HNO₃, which acts as the elution agent, pass through the microcolumn eluting Rh(III), which is directly deposited in the graphite tube as drop of a precisely defined volume. The detection limit is 0.3 ng ml⁻¹. Linearity is maintained in the concentration range 0-50 ng ml⁻¹ for rhodium, with correlation factor of 0.999 and relative standard deviation of 1.8% for 10 ng ml⁻¹ of Rh. The effects of various parameters such as pH, concentration and volume of eluent, sample loading time, sample flow rate and interference of a large number of metal ions and anions on the determination of this metal was studied in detail to optimize the conditions for their determination in various samples. The method is found to be highly selective, fairly sensitive, simple, rapid and economical and may be safely applied to their determination in different complex materials such as environmental samples and catalysts.     

Thermolysis of the reaction products from 2-pyridylacetohydrazide and nitrous acid

2,3-Dihydroimidazo[1,5-α]pyridin-3-one (IV) was obtained by thermolysis of 2-pyridylacetyl azide (II) which was prepared from 2-pyridylacetohydrazide (I) on treatment with an equivalent mole of nitrous acid. Treatment of I with excess nitrous acid yielded α-oximino-α:-(2-pyridyl)-acetylazide (V). Thermal decomposition of V gave 3-(2-pyridyl)-1,2,4-4H-oxadiazolin-5-one (VII). 2-Cyanopyridine (IX) was obtained from V by the action of alkali. 2,3-Dihydroimidazo-[1,5-α ]pyridin-3-one (IV) was rearranged to VII upon treatment with nitrous acid. J. Chem. Soc., 14, 993 (1977)     

暴露于环境烟气中的大鼠尿样代谢物分析

4-(甲基亚硝胺基)-1-(3-吡啶基)-1-丁醇(NNAL)是烟草特有亚硝胺4-(甲基亚硝胺基)-1-(3-吡啶)-1-丁酮(NNK)在生物体内的一种代谢标记物,分析暴露于烟气中的生物体内NNAL的含量是研究卷烟烟气对生物体健康影响的有效手段.基于人体的个体差异性很大,本文以饲养的大鼠为研究对象,采用LC-MS/MS...     

Discrete half-sandwich Ir, Rh-based organometallic molecular boxes: synthesis, characterization, and their properties

The treatment of binuclear complexes [Cp*(2)M(2)(μ-QA)Cl(2)] (M = Ir, 2a; M = Rh, 2b) (H(2)QA = 1,4-dihydroxyanthraquinone) with pyrazine or bifuncational pyridyl-based ligands (4,4'-dipyridine (bpy), E-1,2-bis(4-pyridyl)ethene (bpe), 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (bpo), and 2,5-bis(4-pyridyl)-1,3,4-thiadiazol (bpt)) in the presence of AgOTf (OTf = CF(3)SO(3)) in CH(3)OH, gave the corresponding tetra-nuclear complexes, with a general formula of [Cp*(4)M(4)(μ-QA)(2)(μ-L)(2)](OTf)(4) (M = Ir, 3a-7a; M = Rh, 3b-7b), respectively. The molecular structure of [Cp*(4)Ir(4)(μ-QA)(2)(μ-pyrazine)(2)](OTf)(4) (3a) has been determined by single-crystal X-ray analysis, revealing that the metal centers were connected by pyrazine and bis-bidentate QA(2-) ligands to construct a rectangular cavity with the dimension of 7.30 × 8.41 × 6.92 ?. Complexes 3a and 3b were found to exhibit selective trapping of halocarbons properties.     

Benzazoles and naphthazoles

Thiazolo[4,5-b]-2-pyridylhydrazine, which like 2-benzothiazolylhydrazine, undergoes autooxidation in ethanol solution to give a symmetrical 1,5-bis(thiazolo[4,5-b]-2-pyridyl)-3-methylformazan, was synthesized. Asymmetrical 1,5-dihetarylformazans were obtained by autooxidative coupling of 2-hydrazinobenzothiazole with acetaldehyde thiazolo[4,5-b]-2-pyridylhydrazone and 5-nitro-2-pyridyl hydrazone. Formazans containing a thiazolopyridine ring have more acidic character than benzothiazolylformazans.See [1] for communication XXXVIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 925–927, July, 1975.     

Vectorial property dependence in bis {4'-(n-pyridyl)-2,2':6',2"-terpyridine}iron(II) and ruthenium(II) complexes with n = 2, 3 and 4

A comparative structural and spectroscopic investigation of the complexes [M(1)2]2+, [M(2)2]2+ and [M(3)2]2+ in which M = Fe or Ru, and ligands 1, 2 and 3 are 4'-(2-pyridyl)-, 4'-(3-pyridyl)- and 4'-(4-pyridyl)-2,2':6',2"-terpyridine, respectively, is reported. The complexes [Ru(1)2]2+, [Ru(2)2]2+ and [Ru(3)2]2+ undergo mono- and bis-N-methylation. The consequences of methylation on the absorption spectra and electrochemical properties are discussed; the solid-state structure of the bis(N-methylated) derivative of [Ru(2)2][PF6]2 is presented.     

Synthesis of an mRNA fragment of alanyl-tRNA synthetase gene in Escherichia coli using the 6-methyl-3-pyridyl group for protection of the imide functions of uridine and guanosine

The synthesis of 5'-GpGpUpGpU-3' is reported to demonstrate the synthetic use of the 6-methyl-3-pyridyl group for the protection of the O-4 and O-6 imide functions of uridine and guanosine, respectively. The 2'- and 5'-hydroxyl functions of the key intermediates were protected with two acid-labile groups: 3-methoxy-1,5-dicarbomethoxypentane-3-yl (MDMP) and 9-(4-octadecyloxyphenyl)xanthen-9-yl (C18Px), respectively. The internucleotide phosphotriesters were protected with 2-chlorophenyl and the 9-fluorenylmethyl group was employed for 3'-terminal phosphate protection.     

Pyrazolo [1,5-a]indole. 10. Mitteilung über metallogranische reaktionen und folgeprodukte

Pyrazolo[1,5- a ]indoles Treatment of 1-(2-heteroaroyl or aroyl-phenyl)-pyrazoles ( 3 ) with potassium hydroxide in 95% ethanol or with sodium ethanolate in ethanol produces a novel ring closure to new 4-hydroxy-4-(4-heteroaryl or aryl)-4H-pyrazolo [1,5-a]indoles 5 and 6 (Table 1). A 2, 3, or 4-pyridyl at position 4 is easily reduced yielding the 4-(2, 3, or 4-piperidyl)-derivatives 7 and 8 (Table 2). Water is split off from these piperidyl-derivatives 7 or 8 to give the piperidylidene derivatives 9 or 10 (Table 3) which may be considered as heterocyclic analogues to known tricyclic psychopharmaceuticals with antidepressant or neuroleptic activities.     

Nonlinear optically active polymeric coordination networks based on metal m-pyridylphosphonates

A family of polymeric coordination networks based on meta-pyridylphosphonate bridging ligands has been synthesized and characterized by single-crystal X-ray crystallography. Compounds [M(2)(L-Et)(4)(mu-H(2)O)] (M = Mn, 1; Co, 2; Ni, 3; L-Et = ethyl-4-[2-(3-pyridyl)ethenyl]phenylphosphonate) were obtained by hydro(solvo)thermal reactions between diethyl-4-[2-(3-pyridyl)ethenyl]phenylphosphonate (L-Et(2)) and corresponding metal salts, while [Cd(L-H)(2)], 4 (L-H is monoprotonated 4-[2-(3-pyridyl)ethenyl]phenylphosphonate), was obtained by a hydro(solvo)thermal reaction between (L-H(2)).HBr and Cd(CF(3)SO(3))(2).6H(2)O. Compounds 1-3 are isostructural and crystallize in noncentrosymmetric space group Fdd2, and they adopt a complicated 3D framework structure composed of [M(2)(L-Et)(4)(mu-H(2)O)] building units, while compound 4 adopts a centrosymmetric 3D network structure resulted from linking 1D sinusoidal cadmium phosphate chains with L-H bridging ligands. Consistent with their polar structures, compounds 1-3 exhibit powder second harmonic generation signals larger than that of potassium dihydrogen phosphate.     

Chelating sorbents based on silica gel and their application in atomic spectrometry

This mini-review covers chelating sorbents anchored to silica gel and their analytical applications for the preconcentration, separation and determination of trace metal ions, focussing mainly on the last 20 years. The article summarizes also the experience gathered by our research group in the synthesis and characterization of new modified silica gels via silanization, and their affinity toward selective extraction and separation of trace elements. The introduction of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide silica gel (DPTH-gel) and methylthiosalicylate silica gel (TS-gel) chelating sorbents in trace and ultratrace analysis provide vital breakthroughs in preconcentration methods. These home-made materials allow certain analytes to be selectively extracted from complex matrices without matrix interference and good detection limits. The advantages of these new chelating sorbents in comparison with 8-hydroxyquinoline chelating sorbent immobilized on silica gel are discussed.     

Ligand effects on the structures and magnetic properties of tricyanomethanide-containing copper(II) complexes

The preparation, crystal structure and magnetic properties of four heteroleptic copper(II) complexes with the tricyanomethanide (tcm(-)) and the heterocyclic nitrogen donors 3,6-bis(2-pyridyl)pyridazine (dppn), 2,5-bis(2-pyridyl)pyrazine (2,5-dpp), 2,3-bis(2-pyridyl)pyrazine (2,3-dpp) and 2,3-bis(2-pyridyl)quinoxaline (2,3-dpq) are reported, {[Cu(2)(dppn)(OH)(tcm)(2)] x tcm}(n) (1), {[Cu(2,5-dpp)(tcm)] x tcm}(n) (2), {[Cu(2)(2,3-dpp)(2)(tcm)(3)(H(2)O)(0.5)] x tcm x 0.5H(2)O}(n) (3) and [Cu(2,3-dpq)(tcm)(2)](n) (4). 1 has a ladder-like structure with single mu-1,5-tcm ligands forming the sides and a bis-bidentate dppn and a single mu-hydroxo providing the rung. Each copper atom in 1 exhibits a distorted square pyramidal CuN(4)O surrounding: the basal plane is built by the hydroxo-oxygen, a nitrile-nitrogen atom from a tcm group and one pyrazine and a pyridyl nitrogen atoms from the dppn whereas the apical position is filled by a nitrile-nitrogen atom from a symmetry-related tcm ligand. The structures of 2-4 consists of zig-zag (2 and 3)/linear (4) chains of copper(II) ions which are bridged by either bis-bidentate 2,5-dpp (2) and 2,3-dpp (3) molecules or single mu-1,5-tcm (4) groups. The copper atoms in 2 and 4 are five coordinated with distorted trigonal bipyramidal (2) and square pyramidal (4) CuN(5) surroundings. The axial positions in 2 are occupied by two pyridyl-nitrogen atoms from two 2,5-dpp ligands whereas the trigonal plane is built by a nitrile-nitrogen from a terminally bound tcm group and two pyrazine nitrogen atoms from two 2,5-dpp molecules. The basal plane in 4 is defined by a pyridyl and a pyrazine nitrogen atoms from the bidentate 2,3-dpq ligand and two nitrile nitrogen atoms from two tcm groups (one terminal and the other bridging) whereas the apical position is filled by a nitrile nitrogen from another tcm ligand. The crystallographically independent copper atoms in 3 [Cu(1) and Cu(2)] exhibit elongated octahedral geometries being defined by four nitrogen atoms from two 2,3-dpp groups [Cu(1) and Cu(2)] either two terminally bound tcm ligands [Cu(1)] or a water molecule and a monodentate tcm ligand [Cu(2)] in cis positions. Magnetic susceptibility measurements for 1-4 in the temperature range 1.9-295 K reveal the occurrence of strong [J ca.-1000 cm(-1) (1); H = -JS(A) x S(B)] and weak [J = -0.13 (2), -0.67 (3) and -0.18 cm(-1) (4); H = -J Sigma(I)S(i) x S(i+1)] antiferromagnetic interactions in agreement with the different nature of the exchange pathways involved, diazine and single mu-hydroxo (1) and the extended 2,5-dpp (2), 2,3-dpp (3) and single mu-1,5-tcm (4) bridges with copper-copper separations of 3.363(8) (1), 7.111(1) (2), 6.823(1) and 7.056(1) (3) and 7.446(1) A (4).     

3-(2-Pyridyl)-[1,2,3]triazolo[1,5-a]pyridines. An experimental and theoretical (DFT) study of the ring-chain isomerization

An experimental ((1)H NMR) and theoretical (DFT) study of the ring-chain-ring isomerization of 3-(2-pyridyl)-[1,2,3]triazolo[1,5-a]pyrid-7-yl derivatives (A) into 6-{[1,2,3]triazolo[1,5-a]pyrid-3-yl}-2-pyridyl derivatives (B) has been carried out. Based on the calculations, a mechanism of several steps will be proposed. The experimental results as well as the calculations lead to the conclusion that the A-B ratio depends on the electronic properties of the substituents.     

[1,2,3]Triazoloazine/(Diazomethyl)azine Valence Tautomers from 5-Azinyltetrazoles

[1,2,3]Triazoloazines are formed by thermolysis of 5-azinyltetrazoles in the gasphase or in solution. Thus, 5-(2-pyridyl)tetrazole ( 7 ) and 5-(2-pyrazinyl)tetrazole ( 11 ) yield [1,2,3]triazolo[1,5-a]pyridine ( 9 ) and [1,2,3]triazolo[1,5-a]pyrazine ( 13 ), respectively, at 400°/10^?3 - 10^?5 Torr. 5-(2-Phenyl-4-quinazolinyl)tetrazole ( 15 ) gives 5-phenyl[1,2,3]triazolo[1,5-c]quinazoline ( 17 ) in 75% yield by heating under reflux in mesitylene solution. 2-(Diazomethyl)pyridine ( 8 ), a valence tautomer of 9 , can be trapped by fumaronitrile, leading to 3-(2-pyridyl)-1, 2-cyclopropanedicarbonitrile ( 19 ). The [1,2,3]triazoloazines undergo base catalysed H/D-exchange in D₂O solution.     

N- vs O-Coordination in cyclomanganation of 1,5-diaryl-3-(2-pyridyl)pentane-1,5-diones and 3-(2-pyridyl)chalcones; cyclomanganation at saturated carbon and the crystal structure of [1,5-diphenyl-κC-3-(2-pyridyl- κN)pentan-2-yl-κC-1,5-dione-κOκO]tetracarbonylmanganesetricarbonylmanganese

Reaction of 1,5-diphenyl-3-(2-pyridyl)pentane-1,5-dione (5a) with 2.5 moles of benzylpentacarbonylmanganese in petroleum spirit under reflux gives a small amount of the symmetric di-aryl-manganated product [1,5-diphenyl-κC²-3-(2-pyridyl)pentane-1,5-dione-κO¹κO⁵]bis-(tetracarbonylmanganese) (7a), but mostly [1,5-diphenyl-κC²-3-(2-pyridyl-κN)pentan-2-yl- κC²-1,5-dione-κO¹κO⁵]tetracarbonylmanganesetricarbonylmanganese (6a) which is manganated at only one aryl carbon [by Mn(CO)₄] but also [by Mn(CO)₃ with N and O coordination] at the methylene carbon adjacent to the Mn(CO)₄-coordinated ketone carbonyl. The latter is a rare example of direct cyclomanganation at a saturated carbon and the only known case adjacent to a carbonyl group; the X-ray crystal structure of 6a is reported. With 3 moles of benzylpentacarbonylmanganese the yield of 6a remains unchanged but some trimanganation product [1,5-diphenyl-κC^2′κC^2?-3-(2-pyridyl-κN)pentan-2-yl-κC²-1,5-dione-κO¹κO⁵]tris-(tetracarbonylmanganese) (8a) is formed, presumably from 7a. Routes to products are proposed and activating factors considered. 1,5-Di-(2-thienyl)-3-(2-pyridyl)pentane-1,5-dione (5b) and its 3-thienyl isomer (5c) similarly give 6a analogues [1,5-di-(2-thienyl-κC³)-3-(2-pyridyl-κN)pentan-2-yl-κC²-1,5-dione-κO¹κO⁵]tetracarbonylmanganesetricarbonylmanganese (6b) and [1,5-di-(3-thienyl-κC²)-3-(2-pyridyl-κN)pentan-2-yl-κC²-1,5-dione-κO¹κO⁵]tetracarbonylmanganesetricarbonylmanganese (6c).Also reported are the mono-cyclomanganation product [1-(2,6-dimethoxyphenyl)-3-(2-pyridyl-κN)prop-2-en-2-yl-κC²-1-one]tetracarbonylmanganese (16) and dicyclomanganation product [1-(2,5-dimethyl-3-thienyl-κC⁴)-3-(2-pyridyl-κN)prop-2-en-2-yl- κC²-1-one-κO ]bis-(tetracarbonylmanganese) (17) from reaction of the respective (E)-1-aryl-3-(2-pyridyl)prop-2-en-1-ones (3-(2-pyridyl)chalcones), the first reported examples of enone metallation at the α-carbon via N-coordination by a β-2-pyridyl group.