Derivatives of condensed pyrimidine,pyrazine, and pyridine systems

4-Amino-, 4-methylamino-, and 4-dimethylamino-6-aminopyrimido[4,5-b]-1,4-thiazines were obtained. Some of the properties and transformations of 6-aminopyrimido[4,5-b]-1,4-thiazines — their behavior with respect to acids, reductive desulfuration under the influence of Raney nickel, and reaction with hydrazine — were studied.     

Derivatives of condensed pyrimidine,pyrazine, and pyridine systems

Pyrazinothiazines and the corresponding 3-hydroxy-3,4-dihydroquinoxalinothiazines, which are dehydrated to quinoxalinothiazines under the influence of acidic agents, are formed in the reaction of 2-mercapto-3-amino-5,6-dimethylpyrazine and 2-mercapto-3-aminoquinoxalines with - or -chloroacetoacetic esters in the presence of an equimolar amount of alkali. The IR, UV, and PMR spectra are presented.See [1] for communication XXXIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 695–697, May, 1977.     

Derivatives of condensed pyrimidine,pyrazine, and pyridine systems

It is shown by means of IR, UV, and PMR spectroscopy that 5-amino-6-thio-1,6-dihydropyrimidines exist primarily in the thione form both in the crystalline state and in solution.See [1] for communication XXXIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 398–401, March, 1977.     

Derivatives of condensed systems based on pyrimidine,pyrazine, and pyridine

Pyrimido[4,5-b]-1,4-thiazin-6-one and pyrimido[4,5-b]-1,5-thiazepin-6-one derivatives were obtained by reaction of 5-amino-6-chloropyrimidines with thioglycolic acid and 5-amino-6-mercaptopyrimidines with -bromopropionyl chloride. The IR spectra of the compounds are presented.See [1] for communication XXXV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1332–1335, October, 1977.     

Investigation of condensed pyrimidine,pyrazine, and pyridine systems

The reaction of 5-hydroxy-6-aminopyrimidines with chloromalonic ester in alcohol or with bromomalonic ester in dimethylformamide leads to 6-carbethoxypyrimido-7-oxazinones, whereas a mixture of 6-carbethoxypyrimido-7-oxazinones and 6,6-spirodipyrimido-7-oxazinones is formed in the reaction with bromomalonic ester in alcohol. The latter oxazinones were obtained by reaction of 5-hydroxy-6-aminopyrimidines with dibromomalonic ester. Some of the properties of the synthesized compounds were studied.See [1] for communication XXV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 391–396, March, 1978.     

Study of condensed pyrimidine,pyrazine, and pyridine systems

A new method was developed for the synthesis of pyrimido [5, 4-b][l, 4] oxazin-7-ones by O-alkylation of 5-hydroxy-6-aminopyrimidines with -halo carboxylic acids and subsequent cyclization of the resulting pyrimdyloxyacetic acids in acetic anhydride. The reaction of chloropyrimidooxazinones with hydrazine gives the corresponding hydrazinopyrimidooxazinones, from which the azides were obtained. Unsubstituted pyrimido [5, 4-b][l, 4] oxazin-7-one was synthesized.See [1] for communication XXXIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 681–685, May, 1976.     

Condensed pyrimidine,pyrazine, and pyridine systems.

A simple method was develeped for the synthesis of n₁- and N₃-alkyl- and N₁,N₃-dialkyl(aryl, alkyl)-5-chloroacetyl-6-aminouracil by reaction of 6-aminouracils with chloroacetyl chloride in monochloroacetic acid. 2,4,5-Trioxopyrrole[2,3-d]pyrimidines were obtained by the action of aqueous alkali on N₁alkyl-5-chloroacetyl-6-aminouracils and by the action of sodium ethoxide on N₃-alkyl- and N₁,N₃-dialkyl(aryl, alkyl)-5-chloroacetyl-6-aminouracils. When there is an alkyl substituent attached to the 3-N atom in 2,4,5-trioxopyrrolo[2,3-d]pyrimidines, the pyrrole ring readily opens up under the influence of alkali to give 5-hydroxyacetyl-6-amino uracils.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 537–540, April, 1978.     

Derivatives of condensed pyrimidine,pyrazine, and pyridine systems. 39. Synthesis and structures of 9-oxo-5H-6,7,8,9-tetrahydropyrimido[4,5-b][1,4]thiazines

A number of 9-oxo-5H-6,7,8,9-tetrahydropyrimido[4,5-b][1,4]benzothiazines were synthesized by the reaction of 5-amino-6-mercaptopyrimidines with 2-halo-substituted cyclohexane-1,3-diones. It is demonstrated by means of the IR and UV spectra that these compounds exist primarily in the enamino ketone form. See [1] for communication 38. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 755–760, June, 1980.     

Ultrafast resonance-enhanced multiphoton ionization in the azabenzenes: pyridine, pyridazine, pyrimidine, and pyrazine

We report on the ultrafast photoionization of pyridine, pyridazine, pyrimidine, and pyrazine. These four molecules represent a systematic series of perturbations into the structure of a benzene ring which explores the substitution of a C-H entity with a nitrogen atom, creating a heterocyclic structure. Data are recorded under intense-field, single-molecule conditions. The pulses (50 fs, 800 nm) are focused into the molecular vapor, and ion mass spectra are recorded for intensities of ~10(13) W/cm(2) to ~10(15) W/cm(2). We measure ion yields in the absence of the focal volume effect without the need for deconvolution of the data. For all targets, stable singly- and doubly-charged parent ions (C(6-n)H(6-n)N(n)(+(+))) are observed with features suggesting resonance-enhanced ionization. From the intensity dependence of the ion yield, we infer that excitation occurs both through (1)ππ* transitions (remnants of the benzene structure) and through (1)nπ* transitions, the latter being a result of Rydberg-like excitations of the lone pair electrons of the nitrogen atoms. Stability against intense-field fragmentation is also discussed.     

Synthesis of condensed pyrimidine systems based on 2,4,6-triphenylpyrylium perchlorate

1,3-Diphenylpyrimido[1,2-a]benzimidazolium perchlorates were obtained by reaction of 2,4,6-triphenylpyrylium perchlorate with 2-aminobenzimidazoles.     

Lithium-mediated zincation of pyrazine, pyridazine, pyrimidine, and quinoxaline

Deprotonation of pyrazine, pyridazine, pyrimidine, and quinoxaline using an in situ mixture of ZnCl2.TMEDA (0.5 equiv) and LiTMP (1.5 equiv) was studied. Pyrazine and pyrimidine were deprotonated in THF at room temperature, a result evidenced by trapping with I2. The competitive formation of dimer observed in net hexane was reduced by using cosolvents (TMEDA or THF). Starting from quinoxaline, the dimer formation took place in THF also, and mixtures of mono- and diiodides were obtained whatever the solvent and conditions used. A similar competitive formation of a diiodide was noted with pyridazine; the use of THF at reflux temperature nevertheless afforded the 3-iodo derivative in good yield.     

Selective catalytic hydrogenation of the pyridine ring in arylpyridines and condensed pyridine systems (review)

Data are summarized concerning selective hydrogenation of the pyridine ring in arylpyridines, including those containing silicon, and in annelated pyridines. An effective catalyst, rhenium heptasulfide, has been found, which makes it possible to reduce the pyridine ring without affecting the benzene rings.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1443–1450, November, 1992.     

Electrophoretic determination of thioamides, pyridine and pyrimidine derivatives

We have optimized the conditions for the separation and quantification of a mixture of heteroaromatic thioamides, potential thyreostatics: pyridine-2-thione (I), 5-trifluoromethylpyridine-2-thione (II), pyrimidine-2-thiol (III), 4-trifluoromethylpyrimidine-2-thiol (IV) by capillary zone electrophoresis using a 60 cm × 75 μm capillary (effective length of 50 cm), 15-kV voltage, and borate buffer solution (pH 9.18) as the running electrolyte. The procedure provides the estimation of analyte concentrations in the range from 6.7 × 10^?6 to 1.0 × 10^?4 M with the detection limits (by electrophoretic peak areas) 0.72 (I), 0.47 (II), 0.43 (III), and 0.76 (IV) μg/mL.     

Vibronic coupling by out-of-plane modes in pyridine,pyrazine and quinoxaline

Detailed spectroscopic observations on the first ¹n, π^* states of three different N-heterocycles are successfully modelled through vibronic coupling calculations incorporating a small number of adjusted but non-arbitrary parameters: in pyridine, the “pseudo-planar” potential of the out-of-plane vibration 5b₁(=ν_16b); in pyrazine, the very anharmonic vibration of surprisingly low frequency, 1b_1g(=ν_10a); in quinoxaline, vibronic coupling through more than one frequency.     

New manganese-scaffolded organic triple-deckers based on quinoxaline, pyrazine and pyrimidine cores

The thermolytic coupling of Ph(2)CN(2) and (t-Bu)(Ph)CN(2) with doubly cyclomanganated 2,5-diphenylpyrazine and 4,6-diphenylpyrimidine afforded substantial amounts of new triple decker compounds of either C(i) and C(2) symmetry respectively containing, in both series, two eta(3)-bonded Mn(CO)(3) fragments which intervene as scaffolds sustaining the helical non-conjugated triaryl backbone. The molecular structures of two pyrazine derivatives show a typical non-parallel stacking of the aromatic rings and the encapsulation of the central pyrazyl fragment with interplanar centroid-to-centroid distances of ca. 3.5 A. The stacking of the aromatics in the triple-decker pyrimidine derivatives has been assessed by (1)H NMR experiments at low temperature. All the triple-decker-type compounds are electroactive. Pyrimidine triple-deckers can reversibly be electrochemically reduced to the corresponding anions.     

VUV photoionisation of free azabenzenes: Pyridine, pyrazine, pyrimidine, pyridazine and s-triazine

Photoionisation mass spectrometry was used to obtain the fragmentation pathways of pyridine, pyridazine, pyrimidine, pyrazine and s-triazine molecules upon absorption of 23.0, 15.7 and 13.8 eV synchrotron photons. The ionic fragments observed vary from molecule to molecule, however C₂H₂⁺, HCN⁺and HCNH⁺ are common to all five molecules at the three photon energies. Furthermore, the presence of C₂H₂N₂⁺, C₃H₃N⁺ and C₄H₄⁺ in the spectra of some of the molecules suggests dissociation pathways via loss of HCN moieties. The respective parent cations, m/q=79, 80 and 81 have a greater yield at low photon energies when compared to the most intense fragment peak in each spectra. We recorded two of the fragment cation yields, as well as the parent photoion yield curves of pyridine, pyridazine, and pyrimidine in the 8–30 eV range. The formation of abundant cation fragments show a strong propensity of the molecules for dissociation after the absorption of VUV photons higher than 14 eV. The differences in relative fragment yields from molecule to molecule, and when changing the excitation energy, suggest significant bond rearrangements and nuclear motion during the dissociation time. Thus, bond cleavage is dependent on the photon energy deposited in the molecule and on intramolecular reactivity. With the aid of photoion yield curves and energy estimations we have assigned major peaks in the spectra and discussed their fragmentation pathways.     

Synthesis of New Furo[2,3-b]pyridine and Furo[3,2-d]pyrimidine Derivatives

Russian Journal of Organic Chemistry - New furo[2,3-b]pyridine and pyrido[3′,2′:4,5]furo[3,2-d]pyrimidine derivatives were synthesized from ethyl...     

Free radical chlorination of methyl derivatives of pyridine,pyrazine, and thiazole by N-chlorosuccinimide

When methylazines (2-, 3-, and 4-methylpyridines, methylpyrazine) are treated with N-chlorosuccinimide they undergo successive chlorination of the methyl group to give 2-chloromethylpyridine, 2-dichloromethylpyridine, and dichloromethylpyrazine in preparative yields. 3-Dichloromethylpyridine was synthesized from pyridine-3-aldehyde and PC1₅. The primary chlorination products of 4-methylthiazole are 4-methyl-5-chlorothiazole and 5-chloro-4-chloromethylthiazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 543–546, April, 1989.