Pyrazolo[5,4-h]quinazolines

The reaction of 1-phenyl- and 4-chloro-5-formyl-3-methyl-1-(2-pyridyl)-6,7-dihydroindazoles with carbamidinopyrrolidine, 4-carbamidinomorpholine, creatine, 2-carbamidinopyrazine, and 2-carbamidino-5-trifluoromethylpyridine gives the corresponding 3,8-substituted 1-methyl-4,5-dihydropyrazolo-[5,4-h]quinazolines and with 2-aminobenzimidazole gives 3-phenyl- and 3-(2-pyridyl)-1-methyl-4,5-dihydrobenzo[b]indazolo[4,5-e]imidazolo[1,2-a]pyrimidines.Riga Technical University, Riga LV-1658, Latvia; e-mail; marina@osi.lv . Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 962–965, July, 2000.     

Synthesis and reactions of 1-(4-chloro-, 3-chloro-, 2-chloro-, 2,4-dichloro-, and 2,4-difluorophenyl)-6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles

Reaction of the potassium salt of 2-formyldimedone with hydrochlorides of 4-chloro-, 3-chloro-, 2-chloro-, 2,4-dichloro-, and 2,4-difluorophenylhydrazines gave the corresponding 2-arylhydrazinomethylene-dimedones which cyclized in acid media to 1-substituted 6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles. Oxidation of the latter with selenious acid gave the corresponding 4,5-dioxo-4,5,6,7-tetrahydroindazoles which were further converted into 3-aryl-5,5-dimethyl-4,5-dihydro-3H-pyrazolo[4,3-a]phenazines and 2,6-diaryl-4,4-dimethyl-4,5-dihydro-1H(3H)-indazolo[4,5-g]imidazoles.Riga Technical University, Riga LV-1658, Latvia; e-mail: marina@osi.lv. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, 533–539, April, 2000.     

Reactions of 2-cyano-3-ethoxy-5,5-dimethyl-2-cyclohexen-1-one with 2-amino- and 2-hydrazionobenzimidazoles

The reactions of 2-cyano-3-ethoxy-5,5-dimethyl-2-cyclohexen-1-one with 2-amino- and 2-hydrazinobenzimidazoles gave 1-oxo-3,3-dimethyl-11-amino-1,2,3,4-tetrahydroquinazolino[3,2-a]benzimidazole and 2-(2-benzimidazolyl)-3-amino-4-oxo-6,6-dimethyl-4,5,6,7-tetrahydroindazole, respectively.Riga Technical University, Riga LV-1658. Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 235–240, Feburary, 1997.     

Synthesis of 2-oxooxazolo[5,4-b]pyridines and their reactions with amines

Riga Technical University, Riga, LV-1658. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 271–272, February, 1995. Original article submitted December 29, 1994.     

2-Oxooxazolopyridines. 1. Synthesis of alkyl N-(2-oxo-3-pyridyl)carbamates

A convenient method is proposed for the synthesis of new derivatives of the pyridine series, alkyl N-(2-oxo-3-pyridyl)carbamates (IIa-i, IVa-j), in the reaction of 7-trifluoromethyl-5-phenyl-2-oxooxazolo[5,4-b]pyridines (I, IIIa-j) with alcohols.Riga Technical University, Riga LV-1048. Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 241–249, February, 1997.     

Oxazoles based on 2-amino-3-hydroxyphenalenone

2-Phenyl-and 2-(p-nitrophenyl)-4H-phenaleno[1,2-d]oxazol-4-ones were synthesized from 2-amino-3-hydroxyphenalenone.Riga Technical University, Riga LV-1048, Latvia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1065–1067, August, 1998.     

Synthesis of 2,3-dihydroimidazo[1,2-a]-pyridines and their salts. (review)

In the present review the published data on the nomenclature, structure, and synthesis of 2,3-dihydroimidazo[1,2-a]pyridines up to 1998 are reviewed. Riga Technical University, Riga, Latvia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1299–1321, October, 1999.     

Catalytic intermolecular hydrogen transfer in the hydrogenation of heterocyclic aldehydes and ketones. A review

Literature data and the investigation results of the present authors on the reduction of heterocyclic aldehydes and ketones using catalytic hydrogen transfer have been analyzed.Riga Institute of Organic Synthesis, Riga LV-1006, Latvia. Translated from Khimiya Geterotskilicheskikh Soedinenii, No. 4, pp. 435–449, April, 1994. Original articla submitted November 29, 1993.     

Synthesis and investigation of 4,5-dimethyl-1,3-dithiolylidene-(4-dimethylaminophenyl)acetonitrile

A method was developed for the synthesis of unsymmetrical strong electron donors. 4,5-Dimethyl-1,3-dithiolylidene(4-dimethylaminophenyl)acetonitrile was obtained, and its properties were investigated by electrochemica, spectroscopic, and quantum-chemical methods.Riga Technical University, Riga, Latvia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 22–25, January, 2000.     

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.     

Synthesis and properties of 2-oxooxazolopyridines (review)

Published data on the synthesis and properties of 2(3H)-oxooxazolo[4,5-b]-, 2(1H)-oxooxazolo[5,4-b]-, and 2(3H)-oxooxazolo[4,5-c]pyridines up to 1997 are reviewed.Riga Technical University, Riga, Latvia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 168–183, February, 1999.     

2-Substituted 5-oxo-5,6,7,8-tetrahydroquinazolines

Twenty novel 2-substituted 5-oxo-5,6,7,8-tetrahydroquinazolines in reactions of 2-formyl-1,3-cyclohexanedione and its 5,5-dimethyl- and 5-phenyl derivatives with 4-chloro- and 4-carbonylaminobenzamidines, 3- and 4-carbamidinopyridines, 2-carbamidinopyrazine, 2-carbamidino-5-trifluoromethylpyridine, 1-carbamidinopyrrolidine, 4-carbamidinomorpholine, and 1-carbamidino-3,5-dimethylpyrazole have been obtained.Riga Technical University, Riga LV-1658, Latvia; e-mail: marina@osi.lv. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 212–26, February, 2000.     

Preparation of two stereoisomers of the macrocyclic electron donor tetramethoxycarbonyl[5.5]-tetrathiafulvalenophane with bridges containing two sulfur atoms

Isomers of a macrocycle containing two tetrathiafulvalene structural units joined by propylenedithio bridges are prepared. The electrochemical oxidation potentials are determined. Possible conformations of tetramethoxycarbonyl[5.5] tetrathiafulvalenophane are analyzed using the AM1 method.Riga Technical University, Riga LV-1048, Latvia. Department of Chemistry, Ben Gurion University of Negev, 84105 Israel. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 910–913, July, 1999.     

Synthesis of n-alkyl 4,5-dithionaphthalimides

Riga Technical University, Riga LV-1048. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, p. 420, March, 1995. Original Article submitted February 12, 1995.     

Study of Arrhenius activation energy on the thermo-bioconvection nanofluid flow over a Riga plate

Journal of Thermal Analysis and Calorimetry - This article deals with a study of Arrhenius activation energy on thermo-bioconvection nanofluid propagates through a Riga plate. The Riga plate is...     

1- and 2-(4-Hydroxycarbonylphenyl)-4-oxo-4,5,6,7-tetrahydroindazoles

Reactions of 4-hydrazinobenzoic acid with 2-formyl- and 2-acetyldimedones were utilized to synthesize 6,6-dimethyl- and 3,6,6-trimethyl-1-(4-hydroxycarbonylphenyl)-4-oxo-4,5,6,7-tetrahydroindazoles corre-spondingly, and the reaction with 2-cyano-3-ethoxy-5,5-dimethylcyclohex-2-en-1-one gave 2-(4-hydroxy-carbonylphenyl)-3-amino-4-oxo-6,6-dimethyl-4,5,6,7-tetrahydroindazole. Riga Technical University, Riga LV-1658. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 516–519, April, 1997.     

Synthesis and reactions of 1-(2-pyridyl)-3-methyl-4-chloro-5-formyl-6,7-dihydroindazoles

The Vilsmeier formylation of 1-(2-pyridyl)-3-methyl-4-oxo-4,5,6,7-tetrahydroindazole and its 6-phenyl derivative gives 1-(2-pyridyl)-3-methyl-4-chloro-5-formyl-6,7-dihydroindazoles. Reactions of these derivatives with different N- and C-nucleophilic agents, including bisnucleophiles, were studied as a means of obtaining new 4- and 5-functional derivatives of indazole and its condensed systems.Riga Technical University, Riga LV-1658, Latvia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 768–773, June, 1998.     

Synthesis of 2,5-bis(2-aminothiazol-5-yl)-3,6-dichloro-1,4-benzoquinones

A series of 2-(2-aminothiazol-5-yl)-3,6-dichloro-5-diethylaminoethenyl-1,4-benzoquinones was synthesized from 2-(2-aminothiazol-5-yl)-3,5,6-trichloro-1,4-benzoquinones using acetaldehyde and diethylamine in toluene solution. Refluxing these compounds with substituted thioureas in acetonitrile in the presence of hydrochloric acid gives the corresponding 2,5-bis(2-aminothiazol-5-yl)-3,6-dichlorohydroquinones which can be oxidized to the target products with ferric chloride in aqueous DMF.Riga Technical University, Riga LV-1048, LatviaTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 835–839, June, 2000     

Synthesis and reactions of 1-(4-bromo-, 4-fluoro-, and 4-trifluoromethylphenyl)-6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles

From 2-formyldimedone and 4-bromo-, 4-fluoro-, and 4-trifluoromethylphenylhydrazines we have obtained the corresponding 2-arylhydrazinomethylenedimedones, which in acid medium undergo ring closure to form 1-substituted 6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles. Oxidation of the latter by selenous acid leads to the corresponding 4,5-dioxo-4,5,6,7-tetrahydroindazoles, which then were converted to derivatives of 4,5-dihydro-3H-pyrazolo[4,3-a]phenazine and 4,5-dihydro-1H(3H)-indazolo[4,5-d]imidazole.Riga Technical University, Riga LV-1658. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1669–1675, December, 1997.     

Reaction of acetyltetramic acid witho-phenylenediamine

Acetyltetramic acid forms 3-[-(2-aminophenylamino)ethylidene]-2,4-pyrrolidinedione (Ia) witho-phenylenediamine. NMR spectroscopy showed that compound Ia in solutions of CDCl₃ and DMSO exists as an equilibrium mixture of two rotational isomers caused by hindered rotation around an exocyclic double bond. The analysis of the¹³C NMR spectra of compounds of type I and the results of quantum chemical calculations indicate preferred chelation of amide carbonyl and predominance of the corresponding rotamer. The reaction of a Ia with hydrochloric acid yields 10-methyl-1H-benzo[b]pyrrolo[3,4-f]-1,4-diazepin-1-one.Riga Technical University, Riga LV-1658; Latvian Institute of Organic Synthesis, Riga LV-1006; Institute of Bioorganic Chemistry, Academy of Sciences of Belarus' Minsk 220141. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp336–342, March, 1995. Original article submitted December 29, 1994.