Quasi-tautomerism of 5-hydroxy-5-phenyl-5H-pyrido[2,3-b]chromenes in sulfuric acid

The existence of a quasi-tautomeric equilibrium in solutions of 5-hydroxy-5-phenyl-5H-pyrido[2,3-b]chromenes in sulfuric acid, which was confirmed by a linear dependence of the logarithms of the indicator ratios on acidity function H_R — H_O with a slope close to unity, was established. The pK values of this equilibrium correlate with the _p ^o and _R. ^o substituent constants.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 753–755, June, 1984.     

Synthesis and acid-base transformations of 8-substituted 10-phenyl-10-hydroxy-10H- pyrido [2,3-b ]chromenes

The corresponding 2-(p-substituted phenoxy)-3-aroylpyridines were obtained by the reaction of 2-(p-substituted phenoxy)nicotinonitriles with phenylmagnesium bromide. It is shown that they are readily cyclized to 8-substituted 10-phenyl-10-hydroxy-10H-pyrido[2,3-b]chromenes by the action of concentrated sulfuric acid in glacial acetic acid. The pK_R+ values of the cyclization products, which range from–7.70 to –10.83 and correlate with the _p ⁰ substituent constants, were determined by spectrophotometry.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 614–616, May, 1982.     

Synthesis of substituted thieno[2,3-b]pyrroles

A relatively simple route for synthesis of substituted thieno[2,3-b]pyrroles from readily available starting material and data for structural assignment are reported.     

Synthesis and properties of chromono[2,3-b]pyridines

Chromono[2,3-b]pyridines were synthesized by cyclization of 2-phenoxynicotinic acids. Their UV spectra are due to - ^* transitions and, in contrast to the spectrum of xanthone, are of high intensity. In concentrated sulfuric acid the chromono[2,3-b]pyridines form a doubly charged pyridinium-pyrylium ion, and the reaction is accompanied by an increase in the intensity of the long-wave bands (330–340 nm) in the UV spectrum. The spectrophotometrically determined pK_a values of 8-R-chromono[2,3-b]pyridines range from –8.62 to –9.81, depending on the substituent in the 8 position, and correlate with Hammett _p constants.Translated from Khimiya Geterotsiklicheskikh Soedinenii No. 9, pp. 1235–1238, September, 1976.     

新型六氢吡啶-2,3-并吲哚化合物的合成及其抗肿瘤活性

以3-取代氧化吲哚与丙烯酸酯为原料,经Michael加成反应制得中间体--3-丙酸酯取代氧化吲哚（3a~3d）; 3a~3d与甲胺发生酰胺化反应制得3 丙酰胺取代氧化吲哚（4a~4d）; 4a~4d用氢化铝锂还原-环化,合成了4个六氢吡啶-2,3-并吲哚化合物(5a~5d）; 5a和5b用氢化铝锂还原合成了2个六氢吡啶-2,3-并吲哚化合物（6a和6b）, 5a～5d, 6a和6b均为新化合物,总产率42%～61%,其结构经¹H NMR, ¹³C NMR和HR-ESI-MS表征。采用MTT法研究了5a～5d, 6a和6b对人肺癌细胞（A549）,人前列腺（PC-3）和人白血病细胞（K562）的体外抗肿瘤活性。结果表明：5b对A549, PC 3和K562的抑制活性均较好,其IC₅₀分别为27.2μmol·L^-1, 37.5 μmol·L^-1和21.7 μmol·L^-1。     

3-Phenacylidene-3,4-dihydro-1H-pyrido[2,3-b]pyrazin-2-ones and 2-Phenacylidene-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-ones

Condensation of 2,3-diaminopyridine ( 1 ) with ethyl o-, m- and p-substituted benzoylpyruvates 2–9 gave two isomeric products. The preferential formation of one or the other isomer has been achieved by different reaction conditions. All the products appear to exist in the enamine form as evidenced by their ¹H nmr and ir spectra.     

Synthesis and some properties of 2,3-dihydrofuro[2,3-b]quinol-4-one

The reaction of O-ethylbutyrolactonium tetrafluoroborate with ethyl anthranilate gave the corresponding imido ester, which undergoes cyclization to a furo[2,3-b]-quinol-4-one derivative when it is heated in a solution of sodium butoxide. When the latter product is heated in diphenyl oxide, it is converted to a furo[3,2-c]-quinol-2-one derivative.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 65–67, January, 1982.     

Synthesis of substituted 1-benzyl-2,4,6-triphenyl-2,3-dihydro-pyrazolo [3,4-b] [1,4]diazepines

The acid catalyzed condensation of 4,5-diaminopyrazoles and chalcones gave the hitherto unknown 1-benzyl-2,4,6-triphenyl-2,3-dihydropyrazolo[3,4-b][1,4]diazepines derivatives. The structure of all products was supported by ir, ¹H and ¹³C-nmr and mass spectra.     

Synthesis of pyrido[2,1-b]- and thiazolo[2,3-b]purines

Some pyrido[2,1-b]- and thiazolo[2,3-b]purines, tricyclic compounds structurally related to [1,2,4]triazolo[1,5-c]quinazolines 1 have been synthesized with a view to study their possible adenosine and benzodiazepine receptors affinity.     

Synthesis and spectroscopic studies of some new substituted 6H-indolo[2,3-b]quinoxalines

Six substituted 6H-indolo[2,3-b]quinoxalines were synthesized by the interaction o-phenyl-enediamine with substituted isatins. The uv, ir and nmr spectral data for the compounds synthesized are presented and discussed.     

Unambiguously confirmed structure of 2-phenacylidene-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one and 3-phenacylidene-3,4-dihydro-1H-pyrido[2,3-b]pyrazin-2-one

To determine the structures of two isomeric products, 2-phenacylidene-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one (2) and 3-phenacylidene-3,4-dihydro-1H-pyrido[2,3-b]pyrazin-2-one (3) obtained by condensation of 2,3-diaminopyridine (1) with ethyl benzoylpyruvate [1–3], these compounds were hydrolyzed to give 2-methyl-4H-pyrido[2,3-b]pyrazin-3-one (4) and 3-methyl-1H-pyrido[2,3-b]pyrazin-2-one (5) , respectively [4,5]. Both hydrolysates 4 and 5 were hydrogenated to afford 2-methyl-1,2-dihydro-4H-pyrido[2,3-b]pyrazin-3-one (6) and 3-methyl-3,4-dihydro-1H-pyrido[2,3-b]pyrazin-2-one (7) . The latter compound was identical with an unequivocally synthesized compound providing proof for the structures of all these compounds.     

Synthesis of furo[2,3-b]pyridine

Two routes were employed to synthesize unsubstituted furo[2,3-b]pyridine (IV). The first method started with ethyl 5-aminofuro[2,3-b] pyridine-2-carboxylate (1) and involved successive deamination, hydrolysis, and decarboxylation. The second method began with 5-nitrofuro[2,3-b ]-pyridine-2-carboxylic acid (V) and consisted of successive decarboxylation, reduction, and deamination reactions.     

Synthesis of substituted 4H-imidazo[5,1-b]benzimidazoles VI. Some reactions of 3-phenyl-4-methylimidazo[5,1-b]benzimidazole

Several substitution reactions (the Mannich reaction, azo coupling, and bromination) of 3-phenyl-4-methylimidazo[5,1-b]benzimidazole were carried out. The corresponding 1-nitro derivative was obtained from 1-bromo-3-phenyl-4-methylimidazo[5,l-b]benzimidazole.See [1] for communication V.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 396–398, March, 1972.     

Synthesis and structural characterization of substituted thieno[2,3-b]pyridines from o-chloroformyl-1,4-dihydropyridines

Novel 4,7-dihydrothieno[2,3-b]pyridines 10a-d have been prepared in a one step procedure from the readily available o-chloroformyl substituted 1,4-dihydropyridines 9a-d and ethyl mercaptoacetate in good yields. Semiempirical calculations reveal a favoured geometry with a boat conformation in the dihydropyridine system and a planar thieno ring. The calculated charge density values for the olefmic carbons (C5 and C6) are in agreement with the experimental push-pull effect observed in the ¹³C nmr.     

Synthesis of 1H-pyrrolo[2,3-b]phenoxathiin-2,3-dione

The title compound was obtained using the Sandmeyer reaction starting from 2-aminophenoxathiine. A new synthesis of N-methylpyrrolo[2,3-b]phenoxathiin-2,3-dione was also presented. Chemical and spectral data supporting the structure of the newly synthesized compounds were given. The isatin analogue, 1-methylpyrrolo-[2,3-b]phenoxathiin-2,3-dione-10, 10-dioxide, could not be obtained.Faculty of Chemistry, Organic Chemistry Department, University of Bucharest, 90–92 Panduri Road, Romania. Faculty of Pharmacy, Organic Chemistry Department, University of Medicine and Pharmacy Carol Davila, Bucharest, Romania. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 396–399, March, 1998.     

Unexpected formation of a 11H-pyrido[2,1-b]quinazolin-11-one derivative from 5,11-dihydro-6H-pyrido[2,3-b]-1,4-benzodiazepin-6-one

The unexpected formation of 11H-pyrido[2,1-b]quinazolin-11-one derivative 6 from 5,11-dihydro-6H-pyrido[2,3-b]-1,4-benzodiazepin-6-one (2) has been observed. Its structure 6 was determined by X-ray crystallography. Detailed nmr study provided a complete set of proton and carbon-13 nmr parameters of compound 6 in solution.