Diversity-Oriented Synthesis of [2.2]Paracyclophane-derived Fused Imidazo[1,2-a]heterocycles by Groebke-Blackburn-Bienaymé Reaction: Accessing Cyclophanyl Imidazole Ligands Library

This report describes the synthesis of a [2.2]paracyclophane-derived annulated 3-amino-imidazole ligand library through a Groebke-Blackburn-Bienaymé three-component reaction (GBB-3CR) approach employing formyl-cyclophanes in combination with diverse aliphatic and aromatic isocyanides and heteroaromatic amidines. The GBB-3CR process gives access to skeletally-diverse cyclophanyl imidazole ligands, namely 3-amino-imidazo[1,2-a]pyridines and imidazo[1,2-a]pyrazines. Additionally, a one-pot protocol for the GBB-3CR by an in situ generation of cyclophanyl isocyanide is demonstrated. The products were analyzed by detailed spectroscopic techniques, and the cyclophanyl imidazo[1,2-a]pyridine was confirmed unambiguously by single-crystal X-Ray crystallography. The cyclophanyl imidazole ligands can be readily transformed to showcase their useful utility in preparing N,C-palladacycles through regioselective ortho-palladation.     

Heterocyclic amino acids as synthons. Reactions with dicarbonyl compounds

From some alkyl heteroarylglycinates and dicarbonyl compounds various heterocyclic systems are easily accessible. Transformations are described which lead to imidazo[1,5-α]pyridines, heteroaryl-substituted pyrroles, pyrido[1,2-α]pyrazines, pyrido[1,2-α]pyrimidines or quinolizin-4-ones.     

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.     

Aza-2-dienes-1,3. Partie 5. Préparation de N-aminoimidazoles, 3H-pyrroles,triazolo[1,2,4][1,5-a]pyrazines et imidazo[1,2-a]pyrazines

2-Aza-1,3-dienes. Access to N-Aminoimidazoles, 3H-Pyrroles, [1,2,4]Triazolo[1,5-a]pyrazines, or Imidazo[1,2-a]pyrazines Nucleophilic attack of 5-(dialkylamino)-2-aza-1,3-diene-1,1-dicarbonitriles (or their 1-methoxycarbonyl analogous) by hydrazines or hydrazdes gives substituted N-aminoimidazoles, [1,2,4]triazolo-[1,5-a]pyrazines, or α-dihydrazino derivatives. With α-amino esters (or analogous), imidazo[1,2-a]pyrazines are produced. Addtion of cyanide anions occurs also with formation of substituted 3H-pyrroles. Structures and rationalisation of this nucleophilic attack are discussed.     

Aza and deaza analogs of purine nucleosides (review)

Methods for the preparation of aza and deaza analogs of purine nucleosides, viz., nucleosides of imidazo[4,5-d]-v-triazines, imidazo[4,5-b]pyridines, and imidazo[4,5-c]pyridines, and their properties are described. References to the synthesis of nucleosides of imidazo[4,5-d]pyridazines, imidazo[4,5-c]pyridazines, and imidazo[4,5-b]pyrazines are also given.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 147–161, February, 1981.     

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.     

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.     

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.     

Reaction of 1-amino-, 2-amino-, and 1,2-diaminoimidazoles with β-diketones

1,2-Diamino-4-phenylimidazolium perchlorate condenses with 2 mole of β-diketones to give pyrimido[2′,1′:2,3]imidazo[1,5-b]pyridazinium derivatives, while, like 1-amino-2-mercapto-4-phenylimidazole, to give imidazo[1,5-b]pyridazine derivatives. Salts of 1-benzylideneamino- and 1-(2-thiazolyl)-2-aminoimidazoles react with β-diketones to give substituted imidazo[1,2-a]pyrimidinium derivatives.     

Novel synthesis of bicycles with fused pyrrole, indole, oxazole, and imidazole rings

Reactions of benzotriazol-1-yl(1H-pyrrol-2-yl)methanone 10 and benzotriazol-1-yl(1H-indol-2-yl)methanone 11 with diverse ketones, isocyanates, and isothiocyanates in the presence of base afforded pyrrolo[1,2-c]oxazol-1-ones 1, oxazolo[3,4-a]indol-1-ones 2, pyrrolo[1,2-c]imidazoles 3, and imidazo[1,5-a]indoles 4 by a simple one-step procedure.     

Reaction of Imidazo[1,2‐a]pyridines with Aliphatic Aldehydes: A Simple and Efficient Method for the Preparation of Novel C‐3 Vinylic Derivativesof Imidazo[1,2‐a]pyridines

A simple and efficient method for the preparation of novel C‐3 vinylic derivatives of imidazo[1,2‐a]pyridines has been developed by the reaction of imidazo [1,2‐a]pyridines with appropriate aliphatic aldehydes in acetic acid in a sealed tube.     

Solvent Moisture-Controlled Self-Assembly of Fused Benzoimidazopyrrolopyrazines with Different Ring’s Interposition

This article shows that two extremely important families of fused heterocyclic assemblies, namely 6-methylbenzo[4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazine and 5a-methyl-5a,6-dihydro-5H,12H-benzo[4,5]imidazo[1,2-a]pyrrolo[1,2-d]pyrazine, can be synthesized from only two available building blocks (N-allenylpyrrole-2-carbaldehyde and o-phenylenediamine) by controlling only one reaction parameter (water content of the medium). It should be emphasized that the latter class of compounds (with an a/d arrangement) is previously unknown. If the allene group is introduced not into the starting compound, but during the reaction (in superbase media), a heterocyclic ensemble, 5-methylbenzo[4,5]imidazo[1,2-a]pyrrolo[2,1-c]pyrazines, with a different position of the methyl group is formed.     

One-pot synthesis of 6H-2,2a1,3-triazaaceanthrylen-6-ones and 6H-2,2a1,4-triazaaceanthrylen-6-ones via tandem cyclization strategies

Two operationally simple one-pot protocols have been developed for the synthesis of 6H-2,2a¹,3-triazaaceanthrylen-6-ones and 6H-2,2a¹,4-triazaaceanthrylen-6-ones. The first Pd-catalyzed tandem cyclization of imidazo[1,2-a]pyrimidines/imidazo[1,2-a]pyrazines with 2-chlorobenzaldehydes could proceed in aqueous medium under air, affording the desired products in moderate to good yields. The molecular structures of products 3i and 5b were confirmed by X-ray crystallographic analysis.     

Synthesis of 1-functionalized imidazo[1,5-а]pyrazolo[5,1-с]pyrazines

Chemistry of Heterocyclic Compounds - 4-Chloropyrazolo[1,5-a]pyrazines react with ethyl isocyanoacetate to form ethyl imidazo[1,5-a]pyrazolo[5,1-c]pyrazine-1-carboxylates, hydrolysis of which...     

Dealkylation of quaternary 1-alkylazolo[a]pyridinium salts

A convenient method is proposed for the preparation of new derivatives of free heterocyclic bases of imidazo[1,2-a]pyridine, pyrido[1,2-a]benzimidazole, and [1,2,4]triazolo[4,3-a]pyridine series. This method entails the dealkylation of N-(2-cyanoethyl)- or N-benzylazolopyridinium quaternary salts in the presence of bases and reaction with ammonium formate in the presence of Pd/C, respectively.     

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.     

1-(Trifluoromethyl)-3,4-dihydropyrrolo-[1,2-<Emphasis Type="Italic">a</Emphasis>] pyrazines: synthesis and reactions with O- and N-nucleophiles

The method of synthesis has been developed and reactions of 1-(trifluoromethyl)-3,4-dihydro-pyrrolo[1,2-a]pyrazines with O- and N-nucleophiles have been studied. It was found that reactions of nucleophiles with 1-(trifluoro-methyl)pyrrolo[1,2-a]pyrazines transforms the trifluoromethyl group to amide and amidine groups together with aromatization of the pyrrolo[1,2-a]pyrazine system as a result of the formal elimination of a molecule of hydrogen fluoride.     

Green procedure for highly efficient,rapid synthesis of imidazo[1,2-a]pyridine and its late stage functionalization

We unfold a rapid synthetic protocol for the preparation of imidazo[1,2-a]pyridine in cyclohexane. This methodology includes several advantages like shorter reaction time, catalyst free, broader substrate scope, and good yields of the desired products. Late stage functionalization of imidazo[1,2-a]pyridine has also been performed through C–H bond activation and C–C cross-coupling reactions.     

Cyclization of N-alkylammonium cations with bifunctional nucleophiles. 17. Annelation of imidazole and 1,2,4-triazine rings with pyrazines via the reactions of thiosemicarbazides with pyrazinium salts

1- and 4-mono- as well as 1,4-disubstituted thiosemicarbazies undergo cyclization reactions upon treatment with N-alkylpyrazinium and quinoxalinium salts to give N-aminosubstituted imidazo[4,5-b]pyrazines and imidazo[4,5-b]quinoxalines, respectively. Thiosemicarbazides containing substituents in the 2-position react with N-alkylquinoxaline salts to give 1,2,4-triazino[5,6-b]quinoxalines after cyclization.For communication No, 16, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 960–966, July, 1985.     

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.