Synthesis of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4-b]pyridines

The synthesis and characterization of a number of 3-aryl-6H-isoxazolo[3,4-d]pyrazolo[3,4-b]pyridines and 3-aryl-6H-isoxazolo[5,4-d]pyrazolo[3,4–6]pyridines from common precursors, 5-benzoyl-4-chloro-1H-pyrazolo-[3,4-b]pyridines, has been described. The structures were determined by unambiguous chemical synthesis and by isolation and ¹³C nmr analysis of some key, isolated, intermediates. The ability of these compounds to displace [3H]flunitrazepam from CNS binding sites was also observed.     

Pyrazolo[3,4-b]pyridines. I. Xanthine and isoguanine analogs derived from 1-methylpyrazolo[3,4-b]pyridine

The synthesis of 4,6-dihydroxy-l-methylpyrazolo[3,4-b Jpyridine ( 2 ) and 4-amino-6-hydroxy-1-methylpyrazolo[3,4-b] pyridine ( 3 ) as analogs of xanthine and isoguanine has been accomplished from ethyl 5-amino-1-methylpyrazole-4-carboxylate ( 4 ) and 5-amino-1-methylpyrazole-4-carbo-nitrile ( 6 ), respectively.     

5α-androstano [3,2-b]pyridines, 5α-androstano[17,16-b]pyridines and androst-4 and 5-eno[17,16-b]pyridines

A new synthesis of 5α-androstano[3,2-b]pyridin-17β-ol acetate (VIa) and 17-methyl-5α-androstano[3,2-b]pyridin-17β-ol (VIb), first reported by Shimizu, Ohta, Ueno, and Takegoshi, was achieved. The analogous 5α - androstano[17,16-b]pyridin-3β-ol (XII), 5α-androstano[17,16-b]pyridin-3-one (XIVa), and androst-4-eno[17,16-b]pyridin-3-one (XIVb) were also prepared. An illustration of the method follows. Condensation of 3β-hydroxy-5α-androstan-17-one (VIIa) with 3-(2-furyl)acrolein afforded 16-[3-(2-furyl)-2-propenylidene]-3β-hydroxy-5α-androstan-17-one (VIIIa), the oxime (IXa) of which was thermally cyclized to 5α-androstano[17,16-b]-6′-(2-furyl)pyridin-3β-ol (Xa). 3β-Hydroxy-5α-androstano[17,16-b]pyridine-6′-carboxylic acid (XI) was obtained by ozonolysis of Xa. Thermal decarboxylation of XI gave XII. Cinnamaldehyde was used in place of 3-(2-furyl)acrolein to give the corresponding phenylpyridines.     

A Facile Synthesis of Pyrazolo[3,4-b]pyridines

Pyrazolo[3,4-b]pyridines (4) and (5) have been obtained by the condensation of 3-(alkyl/aryl)-5-amino-1-phenyl-1H-pyrazole-4-carboxaldehydes (3) with active methylene compounds viz: diethyl malonate and malononitrile.     

Chemistry of thienopyridines. XV. Syntheses of thieno [3,4-b] - and thieno[3,4-c] pyridines

Thieno [3,4-b] pyridine (5) was synthesized by means of the successive steps of (a) photochlorination of 2,3-dimethylpyridine to the bis(chloromethyl) compound, (b) condensation with sodium sulfide, (c) oxidation to the sulfoxide, and (d) catalytic dehydration by means of alumina. Thieno[3,4-c]pyridine (6) was obtained in an analogous manner. Spectral properties indicate that 5 and 6 have aromatic character.     

Mass spectra of isomeric thieno [2,3-b]- and thieno[3,2-b]pyridines

The mass spectra of six isomeric thieno- and thionaphthenopyridines were studied for the first time, and the pathways of fragmentation of the molecular ions, which made it possible to isolate the peaks of the fragment ions that characterize the destruction of the pyridine and thiophene rings, were traced. It is shown that the character and type of conjugation of the heterorings can be distinguished by analyzing the mass-spectral data. The relationship between the intensity of the peak of the doubly charged molecular ion and the number of electrons in the system and the -donor character of the heteroring was illustrated by means of the literature data on the mass spectrometry of heteroaromatic systems with one heteroatom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 758–761, June, 1982.     

Catalyst free synthesis of fused pyrido[2,3-d]pyrimidines and pyrazolo[3,4-b]pyridines in water

A one-pot,three-component condensation reaction of an aldehyde,benzoyl acetonitrile(3-oxo-3-phenylpropane nitrile) and 6- amino-1,3-dimethylpyrimidine-2,4(1H,3H)-dione or 3-methyl-1-phenyl-1H-pyrazol-5-amine in water to give fused pyrido[2,3- d]pyrimidines and pyrazolo[3,4-b]pyridines in high yields without any catalyst,is described.     

Methods for the synthesis of 4-pyrazolyl- and 4pyridyl-5-oxo-1, 4,5,7-tetrahydrofuro[3,4-b]pyridines

The most suitable method for the synthesis of 4-pyrazolyl- or 4-pyridyl-5-oxo-1, 4, 5, 7-tetrahydrofuro[3, 4b]pyridines uses 4-chloro- or 4-acetoxyacetoacetic esters in various versions of the Hantsch synthesis with closure of a lactone ring during the reaction. Some of the intermediate products (2-chloromethyl- and 2acetoxymethyl-1,4-dihydropyridines) were isolated. Cyclization with the formation of lactones does not occur in N-substituted 1, 4-dihydropyridines.Latvian Institute of Organic Synthesis, Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 966–972, July, 1995. Original article submitted May 24, 1995.     

Synthesis and alkylation of pyrazolo[3,4-c]isoquinolines and hexahydrocyclohepta[d]pyrazolo[3,4-b]pyridines

The condensation of 1-acyl-2-(morpholin-4-yl)cycloalkenes with 3-amino-1-phenyl-1H-pyrazol-5(4H)-ones gave the corresponding 2,3,6,7,8,9-hexahydropyrazolo[3,4-c]isoquinoline and 3,6,7,8,9,10-hexahydrocyclohepta[ d]pyrazolo[3,4-b]pyridine derivatives. Alkylation of 2,3,6,7,8,9-hexahydropyrazolo[3,4-c]-isoquinolines with alkyl halides occurred at the nitrogen atom in the 3-position. The structure of 7-methyl-2,5-diphenyl-2,3,6,7,8,9-hexahydro-1H-pyrazolo[3,4-c]isoquinolin-1-one was proved by X-ray analysis.     

ESR spectra of electrochemically generated free anion radicals of hetaryl-substituted trichloro-1,4-benzoquinones

The ESR method was used to confirm the formation of free anion radicals in the source of electrochemical reduction of 5-thiazolul-substituted 1,4-benzoquinones and related compounds, as well as the ability of the unpaired electron to become delocalized over the system of electrons not only of the benzoquinone nucleus but also of the hetaryl substituent added to it.Latvian Institute of Organic Synthesis, Riga, LV-1006. Riga Technical University, Riga, LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 258–261, February, 1995. Original article submitted December 30, 1994.     

Study of the structures of indazoles,pyrazolo [3,4-b] pyridines,and pyrazolo[3,4-b]pyrazine by IR spectroscopy

It is shown on the basis of a study of the IR spectra of indazoles, pyrazolopyridines, and pyrazolopyrazine in the solid state and of their N-deutero-substituted derivatives and hydrochlorides at room temperature and at the temperature of liquid nitrogen that these heterocycles exist in a tautomeric form in which the labile hydrogen atom is localized on the nitrogen atom of the pyrazole ring. It was established that 6-aminopyrazolopyridine exists in the crystalline state in the amino form and that it is protonated at the ring nitrogen atom rather than at the amino group. The applicability of the temperature-shift method for the detection not only of NH bands but also of ND bands is demonstrated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 662–667, May, 1977.     

1H-Pyrazolo[3,4-b]pyridines: Synthesis and Biomedical Applications

Pyrazolo[3,4-b]pyridines are a group of heterocyclic compounds presenting two possible tautomeric forms: the 1H- and 2H-isomers. More than 300,000 1H-pyrazolo[3,4-b]pyridines have been described which are included in more than 5500 references (2400 patents) up to date. This review will cover the analysis of the diversity of the substituents present at positions N1, C3, C4, C5, and C6, the synthetic methods used for their synthesis, starting from both a preformed pyrazole or pyridine, and the biomedical applications of such compounds.     

Chemistry of furazano[3,4-b]pyrazine. 4. 5,6-Dichlorofurazano[3,4-b]pyrazine in cyclization reactions

A method was developed for the production of polycyclic compounds containing the furazano[3,4-b]pyrazine fragment by the reaction of difunctional nucleophiles with 5,6-dichlorofurazano[3,4-b]pyrazine. It was shown that the reaction is affected by the hydrogen chloride acceptor (triethylamine). For Communication 3, see [1]. Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11. pp. 1561–1564, November, 1997.     

Synthesis and nucleophilic dearomatization of highly electrophilic [1,2,5]selenadiazolo[3,4-b]pyridines

Russian Chemical Bulletin - A number of [1,2,5]selenadiazolo[3,4-b]pyridines were synthesized on the basis of readily available 5-R-2,3-diaminopyridines. It was found that these compounds can be...     

Thieno [2,3 -b] pyridines and thieno [ 3,2 -b] pyridines by the method of gould-jacobs

Bis(2-, and 3-thienylammonium) hexachlorostannates were condensed with ethoxymethylene derivatives of active methylene compounds in pyridine. The resulting condensation products IVa-IVc and Va-Vc on heating under reflux in Dowtherm or diphenyl ether provided various 4-hydroxythieno[2,3-b] pyridines (Ia-Ic) and 7-hydroxythieno[3,2-b]pyridines (IIa-IIc). The compound Ic on further transformations gave yet other derivatives If-Ik.     

Chemistry of furazano[3,4-b]pyrazine. 5. 1,2,3-Triazolo[4,5-e]furazano[3,4-b]pyrazine 6-oxides

New representatives of a little-investigated class of compound-1,2,3-triazole 2-oxides — were obtained by a nonphotochemical method. Mononitroamines and dinitroamines are produced during their formation as intermediate products. For Communication 4, see [1]. Latvian Institute of Organic Synthesis Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii. No. 11, pp. 1565–1570. November, 1997.