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.     

3-Substituted imidazo[1,5-a]pyridines

Cyclization of amides of 2-aminomethylpyridine gave imidazo[1,5-a]pyridines. In several examples the literature preparation (phosphorus oxychloride) gave extensive tar formation. The use of phosphorus trichloride-triethylamine (?20°) gave the desired imidazo[1,5-a]pyridines.     

Macrocycles,derivatives of nitrogen-containing heterocycles 2. Synthesis and electrochemical properties of diindolizinadiquinoxalinacyclooxaalkaphanes

Phenylindolizinylquinoxalinomonopodands, obtained by the reaction of 1-(phenylindolizin-2-yl)quinoxalin-2(1H)-one with corresponding dibromotrioxa- and dibromopentaoxaalkanes, undergo oxidative dehydrocyclization assisted by molecular iodine to yield new redox-active diindolizinadiquinoxalinacyclooxaalkaphanes. Using CVA, the indolizine fragments of the heterocyclophanes in acetonitrile are found to undergo three-step oxidation with transfer of one electron in each step. The first and the third steps are reversible, whereas the second is irreversible. The oxidation at potentials of the first peak leads to the stable radical cations registered by ESR (g = 2.0024, a _2N = 0.26 mT).     

Synthesis of nitrogen-containing heterocycles. 5. A new route to 5-amino-[1,2,4]triazolo[1,5-a][1,3,5]triazine derivatives

Treatment of certain diaminomethylenehydrazones 1 of aromatic carbonyl compounds with ethyl N-cyanoimidate ( 2 ) in acetonitrile in the presence of a tertiary amine at room temperature gives the corresponding amino(N-cyanoiminomethyl)aminomethylenehydrazones 3 in high yields. The intermediate 3 can readily be cyclized to the corresponding 5-amino-2,3-dihydro[1,2,4]triazolo[1,5-a][1,3,5]triazines 4 in moderate to good yields by brief heating in acetonitrile. When the reaction of diaminomethylenehydrazones 1 with ethyl N-cyanoimidate ( 2 ) is performed at reflux temperature in the presence of a tertiary amine, 5-amino-2,3-dihydro[1,2,4]triazolo[1,5-a]1,3,5]triazines 4 can be directly obtained in moderate yields. The yields of triazolotriazine produced by the one-step synthesis are generally comparable or even higher than the overall yields from the two-step procedure.     

Synthese von imidazo[1,5-a]- und pyrazino[1,2-a]benzimidazolen

1,2-Dihydro-3H-imidazo[1,5-a]benzimidazoles (6), 1-oxo-1,2-dihydro-3H-imidazo[ 1,5-a] benzimidazoles (8), 3H-imidazo[1,5-a]benzimidazoles (7), 3-oxo-1,2,3,4-tetrahydro-pyrazino[1,2-a] benzimidazoles (12), and 3,4-dioxo-1,2,3,4-tetrahydro-pyrazino[1,2-a]benzinudazoles (13) were synthesized from 2-α-aminobenzyl (benzhydryl)-benzimidazoles (2).     

Fused heterocycles: synthesis of some new imidazo[1,2-a]- pyridine derivatives

Some new thiazolidines and spirothiazolidines derived from hydrazones of 2-methylimidazo[1,2-a]pyridine-3-carboxylic acid hydrazide, a bioisosteric derivative of isoniazid, were synthesized and characterized by analytical, IR, (1)H- and (13)C-NMR and mass spectral data. Some of the newly synthesized compounds were screened for their antimycobacterial activities. None of the tested compounds showed significant in vitro antituberculous activity at 6.25 mirog/mL (MIC rifampin 0.031 microg/mL).     

Synthesis of imidazo[1,5-c]pyrimidine derivatives

Two complementary procedures, each starting from 6-aminomethyluracil ( 2 ), have been used to prepare imidazo[1,5-c]pyrimidines with a variety of substituents at positions 3, 5, 6, and 7. The starting material, 2 , can be readily prepared from commercially available 6-chloromethyluracil by reaction with anhydrous ammonia. In the first procedure, 2 is acylated and then cyclodehydrated by reaction with phosphorus oxychloride to give a separable mixture of a 3-substituted 5,7-dichloroimidazo[1,5-c]pyrimidine and a 3-substituted 7-chloroimidazo[1,5-c]pyrimidin-5(6H)-one. The relative product distribution is subject to some control by the choice of the acyl substituent on the starting uracil. The resulting dichloro compounds were derivatized by reaction at the 5-position with various nucleophiles, although the 7-chloro substituent is unreactive. An alternative synthetic method proceeds from 2 in six efficient steps (protection as the phthalimide, chlorination, nucleophilic substitution, deprotection, acylation, and cyclodehydration) to 3-substituted-5,7-bis(methylthio)imidazo[1,5-c]pyrimidines. These compounds may also be derivatized by nucleophilic substitution at the 5-position.     

Research on imidazo[1,2-a]benzimidazole derivatives. 22. Synthesis of 2,3-dihydroimidazo[1,2-a]benzimidazoles starting from 2-imino-3-(2-hydroxyethyl)benzimidazolines

A -elimination reaction with the formation of 2-imino-3-vinylbenzimidazolines occurs simultaneously with intramolecular alkylation and the formation of an imidazoline ring in the action of alcoholic alkali on 2-imino-3-(2-chloroethyl) benzimidazolines. The thermolysis of 3-chlorethyl-substituted imines without a solvent or in an inert solvent leads exclusively to 2,3-dihydroimidazo[1,2-a] benzimidazoles. An attempt to obtain the latter directly from 2-imino-3-(2-hydroxyethyl) benzimidazolines by the action of a mixture of thionyl chloride and acetic anhydride on them also leads to ambiguous results.See [1] for communication 21.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 918–925, July, 1986.     

Research on imidazo[1,2-a]benzimidazole derivatives XII. 3-Acyl-substituted imidazo[1,2-a]benzimidazoles

Stable 3-acetyl derivatives of imidazo[1,2-a]benzimidazole were synthesized by the action of acetic anhydride on 2,9-disubstituted imidazo[1,2-a]benzimidazole. The former were also obtained by cyclization of 1-alkyl (aralkyl) -3-acylmethyl-2-iminobenzimidazoline hydrobromides in acetic anhydride in the presence of anhydrous sodium acetate. 3-Benzoyl-substituted imidazo[1,2-a]benzimidazoles, which are unstable in acidic media, were synthesized by the action of benzoyl chloride in the presence of pyridine or excess starting imidazo [1,2-a] benzimidazole.See [1] for communication XI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 121– 125, January, 1976.     

One-pot synthesis of imidazo[1,2-b]pyrazole,imidazo[1,2-b]-1,2,4-triazole,imidazo[1,2-a]pyridine,imidazo[1,2-a]pyrimidine,imidazo[1,2-a]benzimidazole,and 1,2,4-triazolo[4,3-a]benzimidazole derivatives

Hydrazonoyl bromides 1a-c react with 5-amino-3-phenyl-1H-pyrazole, 5-amino-1H-1,2,4-triazole, 2-aminopyridine, and 2-aminobenzimidazole to afford the corresponding imidazol[1,2-b]pyrazoles 10, imidazo[1,2-b]-1,2,4-triazoles 11, imidazo[1,2-a]pyridines 16, imidazo[1,2-a]pyrimidines 17, and imidazo[1,2-a]benzimidazoles 20, respectively. Compounds 1a-c reacted also with 2-methylthiobenzimidazole to give 1,2,4-triazolo[4,3-a]benzimidazole derivatives 21. © 1997 John Wiley & Sons, Inc.     

Heterocycles from amino acids. A novel synthetic approach for imidazo[1,5-a]pyridines and imidazo[1,5-a]quinolines

From the corresponding heterocyclic amino acids 2 and 9a the heterocyclic systems imidazo[1,5-a]pyridine ( 3 ) and imidazo[1,5-a]quinoline ( 10 ) are easily accessible. From compound 7 the tricyclic system 11 was prepared and from compound 17a a pyridyl-1,2,4-triazinone ( 18 ) could be obtained.     

Synthesis of Functionalized 2-(2-Pyrrolyl)pyrazolo[1,5-a]pyrimidines

Reactions of 5-amino-3-(2-pyrrolyl)pyrazoles with -dicarbonyl compounds (acetylacetone and ethyl acetoacetate) lead to formation of up to 90% of polysubstituted pyrazolo[1,5-a]pyrimidines.     

Polyfused nitrogen heterocycles: XIX. Oxidative imidazo-fusion of 3-benzoylquinoxalin-2-ones with benzylamines in the synthesis of bis(imidazo[1,5-a]quinoxalin-1- and -5-yl) derivatives

Oxidative cyclocondensation of bis(3-benzoylquinoxalin-1-yl)alkanes and oxaalkanes with benzylamine and 3-benzoylquinoxalinones with m-xylylenediamine proceeded with the formation of bis-(imidazo[1,5-a]quinoxalinyl) derivatives where the hetaryl fragments were linked by a spacer both through the imidazole and quinoxaline fragments