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.     

Chloral as a formylating agent for some bridge heterosystems

The interaction of condensed nitrogen-containing bridge systems with chloral has been studied and the high sensitivity of the reaction to the -excess of the initial heteroaromatic system has been established. It has been shown that chloral is a convenient formylating agent for systems with a moderate -excess —imidazo[l,2-a]imidazole, 9H-imidazo[1,2-a]benzimidazole, imidazo[1,2-a]pyridine, imidazo[1,2-a]naphtho[2,3-d]imidazole. Heterocycles with a high -excess (indolizine, pyrrolo[1,2-a]benzimidazole) form cyanine dyes under the action of chloral. Systems with a lowered -excess (1H-imidazo[1,2-a]benzimidazole, imidazo[1,2-a]quinoline, imidazo[2,1-a]isoquinoline, imidazo[1,2-a]perimidine, imidazo[5,1-b]benzoxazole, imidazo[1,2-a]benzothiazole, and imidazo[1,2-a]pyrimidine) do not react with chloral in a neutral medium. However, in a number of cases their foraylation can be carried out in an acid medium.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 528–537, April, 1980.     

Regiospecific synthesis of 3-substituted imidazo[1,2-a]pyridines,imidazo[1,2-a]pyrimidines,and imidazo[1,2-c]pyrimidine

3-Substituted imidazo[1,2-a]pyridines, imidazo[1,2-a]pyrimidines, and imidazo[1,2-c]pyrimidine were obtained regiospecifically in yields of 35-92% in one pot by reaction of 2-aminopyridines or 2-(or 4-)aminopyrimidines, respectively, with 1,2-bis(benzotriazolyl)-1,2-(dialkylamino)ethanes.     

Studies of imidazo[1,2-a]benzimidazole derivatives. 21. Synthesis of haloketones in the imidazo[1,2-a] benzimidazole series

Methods for the synthesis of imidazo[1,2-a]benzimidazole haloketone derivatives have been investigated. It has been found that -bromoketone derivatives of this heterocycle can be prepared either by bromination of 3-acylimidazo[1,2-a]benz-imidazoles with bromine in glacial acetic acid or by acylation of 3-unsubstituted imidazo[1,2-a]benzimidazoles with haloanhydride derivatives of -bromoalkanoic acids. Treatment of imidazo[1,2-a]benzimidazoles with 3-chloropropionyl chloride results in the formation of imidazo[1,2-a]benzimidazolyl-3-propionyl chloride and bis(imidazo[1,2-a]benzimidazolyl)propan-3-one derivatives as side products. Reaction of 2-phenylimidazo[1,2-a]benzimidazoles with 3-bromopropionic acid in polyphosphoric acid gives benzocyclohepten[5,6:4,5]imidazo[1,2-a]benzimidazole derivatives.For Communication 20, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 339–345, March, 1986.     

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.     

Fluorescent property of 3-hydroxymethyl imidazo[1,2-a]pyridine and pyrimidine derivatives

ABSTRACT: BACKGROUND: Imidazo[1,2-a]pyridines and pyrimidines are important organic fluorophores which have been investigated as biomarkers and photochemical sensors. The effect on the luminescent property by substituents in the heterocycle and phenyl rings, have been studied as well. In this investigation, series of 3-hydroxymethyl imidazo[1,2-a]pyridines and pyrimidines were synthesized and evaluated in relation to fluorescence emission, based upon the hypothesis that the hydroxymethyl group may act as an enhancer of fluorescence intensity. RESULTS: Compounds of both series emitted light in organic solvents dilutions as well as in acidic and alkaline media. Quantitative fluorescence spectroscopy determined that both fused heterocycles fluoresced more intensely than the parent unsubstituted imidazo[1,2-a]azine fluorophore. In particular, 3-hydroxymethyl imidazo[1,2-a]pyridines fluoresced more intensely than 3-hydroxymethyl imidazo[1,2-a]pyrimidines, the latter emitting blue light at longer wavelengths, whereas the former emitted purple light. CONCLUSION: It was concluded that in most cases the hydroxymethyl moiety did act as an enhancer of the fluorescence intensity, however, a comparison made with the fluorescence emitted by 2-aryl imidazo[1,2-a]azines revealed that in some cases the hydroxymethyl substituent decreased the fluorescence intensity.     

Efficient Pd(0)-mediated microwave-assisted arylation of 2-substituted imidazo[1,2-a]pyrimidines

A short and practical synthesis of 2,3-substituted imidazo[1,2-a]pyrimidines, based on microwave-assisted Heck-type arylation of 2-substituted imidazo[1,2-a]pyrimidines, was developed. A 45-membered library of 2,3-substituted imidazo[1,2-a]pyrimidines was obtained with good yields and purities using this optimized protocol.     

1,2,3,9a-Tetrahydro-9H-imidazo[1,2-a]indoles

When derivatives of 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-one or 1-carbamoylmethyl-2-methylene-2,3-dihydroindole are reacted with lithium aluminum hydride, derivatives of 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indole are formed. Under the same conditions 1-(N-phenylcarbamoylmethyl)-2-methylene-2,3-dihydroindole is not cyclized to an imidazo[1,2-a]indole. WHen treated with proton acids imidazo[1,2-a]indoles are converted to 3H-indolium salts. Opening of the imidazolidine ring is also found when imidazo[1,2-a]indole is acylated with benzoyl chloride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 227–230, February, 1987.     

a -Oxo Ketene Dithioacetals Chemistry-A Facile Route to the Synthesis of Fused Heterocyclic Compounds

The fused heterocyclic compounds 2 : imidazo [1,2-a] pyridine 2a-c and pyrido [1,2-a] pyrimidine 2d were obtained from the reaction of a -cinnamoyl ketene dibenzylthio acetals 1 with diamine. When a -cinnamoyl -a '-benzoyl ketene N, N-acetals 3a-b were treated by t-BuONa/t-BuOH solution, 8- benzoyl-pyrido[1,2-a] pyrimidine 4 was produced.     

Solid-phase synthesis of imidazo[1,2-a]pyridine using sodium benzenesulfinate as a traceless linker

[formula: see text] The preparation of the first library of imidazo[1,2-a]pyridine derivatives on a solid support is described. A sulfone linker strategy was applied in the synthesis. Key steps involved in the solid-phase synthetic procedure include (i) alpha-haloketone resin formation by sulfinate-->sulfone alkylation, (ii) imidazo[1,2-a]pyridine ring formation by treatment with 2-aminopyridine, (iii) sulfone anion alkylation, and (iv) traceless product release by oxidation-elimination. A library of 12 imidazo[1,2-a]pyridines was synthesized.     

Synthesis of heterocyclic compounds on the basis of carboxylic acid arylamides

The exchange and cyclization of phenyliminooxalyl chloride with ammonium thiocyanate, sodium azide, aniline, amidoximes, and diphenylthiourea, and with 2-aminopyridine, 2-aminobenzothiazole, and 2-amino- and 2-mercaptobenzimidazole were studied. The cyclization products are derivatives of thiazolidine, imidazo[1,2-a]pyridine, imidazo[2,1-b]benzothiazole, imidazo[1,2-a]benzimidazole, and thiazolo[3,2-a]benzimidazole. A trimer of 1-phenyltetrazole-5-carboxylic acid was obtained when an attempt was made to convert its azide to the corresponding isocyanate.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 471–474, April, 1971.     

Direct arylation of imidazo[1,2-a]pyridine at C-3 with aryl iodides, bromides, and triflates via copper(I)-catalyzed C-H bond functionalization

A convenient method for the copper(I)-catalyzed arylation of substituted imidazo[1,2-a]pyridine has been developed. This method is applicable to a variety of aryl electrophiles, including bromides, iodides, and triflates. It represents the first general process for C-3 arylation of substituted imidazo[1,2-a]pyridine by Cu(I) catalysis to construct various functionalized imidazo[1,2-a]pyridine core π-systems.     

Imidazo[1,2-a]quinoxaline and its transformations. I

The transformations that occur during the reduction of 1-(o-nitrophenyl)-2-formylimidazole with sodium hydrosulfite in the presence of ammonia were studied. The 4-amino derivatives of imidazo[1,2-a]quinoxaline and the bisulfite derivatives of 1-(o-aminophenyl)-2-formylimidazole are formed along with the previously described imidazo[1,2-a]quinoxaline. 4-Aminoimidazo[1,2-a]quinoxaline was also obtained by alternative synthesis by amination of imidazo-[1,2-a]quinoxaline with sodium amide in dimethylaniline. The major product of the transformation is 4,4-bisimidazo[1,2-a]quinoxalyl when the reaction is carried out in xylene.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 416–418, March, 1972.     

Reaction of β-lactam carbenes with 2-pyridyl isonitriles: a one-pot synthesis of 2-carbonyl-3-(pyridylamino)imidazo[1,2-a]pyridines useful as fluorescent probes for mercury ion

The one-pot reaction of β-lactam carbenes with 2-pyridyl isonitriles followed by an acidic hydrolysis was reported, which produced 2-carbonyl-3-(pyridylamino)imidazo[1,2-a]pyridines in moderate to good yields. Among the resulting novel imidazo[1,2-a]pyridine derivatives, 1-(6-chloro-3-(5-chloropyridin-2-ylamino)imidazo[1,2-a]pyridin-2-yl)-2-ethylbutan-1-one was demonstrated to be an efficient fluorescent probe for mercury ion both in acetonitrile and in buffered aqueous solution.     

An Improved Synthesis of 2-Chlorinated Imidazo[1,2-α]-pyridines and the Application of this Procedure for the Synthesis of Several New Polychlorinated Imidazo[1,2-α]Pyridnes.

Polychlorinated imidazo[1,2-α]pyridines were synthesized as analogs of certain chlorinated benzimidazoles. The imidazo[1,2-α]pyridines were obtained by a condensation of ethyl bromoacetate and chlorinated 2-aminopyridines. These condensation products were treated with an ion exchange resin to effect an exchange of hydrobromide salts with hydrochloride salts. These compounds were subsequently treated with POCl₃ to convert the imidazo[1,2-α]pyridin-2-ones into 2-chloroimidazo[1,2-a]pyridines.     

Oxidative bromination of imidazoheterocycle bromohydrates*

The behavior of imidazo[1,2-a]pyridinium, imidazo[1,2-a]pyrimidinium, and imidazo[2,1-b]thiazolium bromides derivatives in oxidative bromination reactions has been studied. It has been established that reaction products structures and their yields depend on the properties of the substituents in the bicycle and the oxidant concentration.     

Studies on antiulcer drugs. III. Synthesis and antiulcer activities of imidazo[1,2-a]pyridinylethylbenzoxazoles and related compounds. A novel class of histamine H2-receptor antagonists.

A series of imidazo[1,2-a]pyridinylalkylbenzoxazole derivatives was synthesized and tested for histamine H2-receptor antagonist, gastric antisecretory and antiulcer activities. Some of 2-amino-6-[2-(imidazo[1,2-a]pyridin-2-yl)ethyl]benzoxazole derivatives were found to have good pharmacological activities. Among them, 2-amino-6-[2-(7-methoxy-3-methylimidazo[1,2-a]pyridin-2-yl)ethyl] benzoxazole (II-11) and 2-acetamido-6-[2-(7-methylimidazo[1,2-a]pyridin-2-yl)ethyl] benzoxazole (II-38) showed potent antisecretory and cytoprotective activity. The structure-activity relationships of these compounds are discussed.     

Cyclocondensation of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyrid-2-ones with heterocyclic N,N-and N,C-1,3-dinucleophiles

[3+3] Cyclocondensation of 5-benzoyl-3-ethoxycarbonyl-6-methylthio-1-R-1,2-dihydropyrid-2-ones with heterocyclic N,N-and N,C-1,3-dinucleophiles proceeds regioselectively to give a series of new tri-and tetracyclic heterosystems, viz. derivatives of 5,6-dihydropyrazolo[1,5-a]pyrido[2,3-d]pyrimidin-6-one, 1,2-dihydropyrido[2,3-d]pyrido[2′,3′: 3,4]pyrazolo[1,5-a]pyrimidin-2-one, 8,9-dihydro-5H-pyrido-[2,3-d]thiazolo[3,2-a]pyrimidin-8-one, 1,2-dihydrobenzo[4,5]imidazo[1,2-a]pyrido[2,3-d]pyrimidin-2-one, and 1,2-dihydrobenzo[4,5]imidazo[1,2-g][1,6]naphthyridin-2-one.     

Formation of bromo-substituted imidazo[1,2-a]pyridines and their aza and thia analogs when the chichibabin reaction is carried out in dimethyl sulfoxide

The reactions of bromomethyl ketones with 2-aminopyridine, 2-aminopyrimidine, 2-aminothiazole, and 2-aminobenzothiazole in dimethyl sulfoxide lead to bromo-substituted (with respect to the position of the imadozole ring) imidazo[1,2-a] pyridines, imidazo[1,2-a]pyrimidines, imidazo[2,1-b]thiazoles, and imidazo[2,1-b]-benzothiazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 258–262, February, 1978.     

One-pot Copper Nanoparticle-catalyzed Synthesis of Imidazo[1,2-α]pyridines Under Solvent-free Conditions

A direct and efficient approach to synthesize imidazo[1,2-α]pyridines through three-component one-pot reaction of 2-aminopyridine,aldehyde and terminal alkyne catalyzed by Cu-nanoparticles under solvent-free conditions has been developed.This method provides a rapid access to substituted imidazo[1,2-α]pyridines with good yields（up to 85％）.