Visible light-mediated photocatalytic bromination of 2-arylimidazo[1,2-a]pyridines using CBr4 as bromine source

Abstract

The photocatalytic bromination of 2-arylimidazo[1,2-a]pyridines is described in this paper. This reaction uses the readily accessible and shelf-stable CBr₄ as a bromine source. This photocatalytic system is shown to serve as a convenient and practical synthetic protocol for the preparation of 2-aryl-3-bromoimidazo[1,2-a]pyridines.     

Triarylimidazo[1,2-a]pyridine-8-carbonitriles: solvent-free synthesis and their anti-cancer evaluation

In this study, we have presented the synthesis of novel 2,5,7-triarylimidazo[1,2-a]pyridine-8-carbonitriles from 2-amino-4,6-diarlypyridine-3-carbonitrile and nitrostyrene using FeCl₃ (20?mol%) as Lewis acid under solvent-free conditions. A library of compounds with diverse substitutions have also been synthesized and screened for in-vitro anti-cancer activity against various cell lines such as A549 (Lung), HCT-116 (Colon), SW-620 (Colon), and MIAPACA (Pancreas).     

Microwave-prompted rapid and efficient synthesis of 3-alkyl substituted imidazo[1,5-a]pyridines

Under regular heating and microwave irradiation, 3-alkyl substituted imidazo[1,5-a] pyridines were synthesized from 2,2＇- pyridil, di-2-pyridyl ketone and aliphatic aldehydes in the presence of ammonium acetate and acetic acid. Compared to the traditional heating condition, the reaction time under microwave irradiation was shorter and 3-alkyl imidazo[1,5-a]pyddines were given in higher yield.     

Xanthate-based microwave-assisted CH radical functionalization of caffeine, 1,3-dimethyluracil,and imidazo[1,2-a]pyridines

Xanthate-based radical chemistry was used for the regioselective direct alkylation of caffeine, uracil, and imidazo[1,2-a]pyridine systems, using dilauroyl peroxide as initiator and oxidant, under microwave irradiation. Under these conditions, several electrophilic radicals (located alpha to a carbonyl function such as esters, amides, ketones, malonates and cyano groups) were added to the title heterocyclic systems. The methodology allows the intermolecular regioselective construction of a sp²-sp³ CC bond via a CH functionalization in an aromatic substitution, from readily available starting materials.     

Synthesis of imidazo[1,2a]pyridines via three-component reaction of 2-aminopyridines, aldehydes and alkynes

A novel three-component reaction towards the synthesis of imidazo[1,2a]pyridines was independently developed based on 2-aminopyridines, aldehydes and alkynes, and thereby imidazo[1,2a]pyridines were obtained in acceptable yields by the CuSO4/TsOH catalyzed three-component reaction.     

Synthesis and Neurotropic Activity of New Heterocyclic Systems: Pyridofuro[3,2-d]pyrrolo[1,2-a]pyrimidines,Pyridofuro[3,2-d]pyrido[1,2-a]pyrimidines and Pyridofuro[3′,2′:4,5]pyrimido[1,2-a]azepines

Background: Neurotic disturbances, anxiety, neurosis-like disorders, and stress situations are widespread. Benzodiazepine tranquillizers have been found to be among the most effective antianxiety drugs. The pharmacological action of benzodiazepines is due to their interaction with the supra-molecular membrane GABA-a-benzodiazepine receptor complex, linked to the Cl-ionophore. Benzodiazepines enhance GABA-ergic transmission and this has led to a study of the role of GABA in anxiety. The search for anxiolytics and anticonvulsive agents has involved glutamate-ergic, 5HT-ergic substances and neuropeptides. However, each of these well-known anxiolytics, anticonvulsants and cognition enhancers (nootropics) has repeatedly been reported to have many adverse side effects, therefore there is an urgent need to search for new drugs able to restore damaged cognitive functions without causing significant adverse reactions. Objective: Considering the relevance of epilepsy diffusion in the world, we have addressed our attention to the discovery of new drugs in this field Thus our aim is the synthesis and study of new compounds with antiepileptic (anticonvulsant) and not only, activity. Methods: For the synthesis of compounds classical organic methods were used and developed. For the evaluation of biological activity some anticonvulsant and psychotropic methods were used. Results: As a result of multistep reactions 26 new, five-membered heterocyclic systems were obtained. PASS prediction of anticonvulsant activity was performed for the whole set of the designed molecules and probability to be active Pa values were ranging from 0.275 to 0.43. The studied compounds exhibit protection against pentylenetetrazole (PTZ) seizures, anti-thiosemicarbazides effect as well as some psychotropic effect. The biological assays evidenced that some of the studied compounds showed a high anticonvulsant activity by antagonism with pentylenetetrazole. The toxicity of compounds is low and they do not induce muscle relaxation in the studied doses. According to the study of psychotropic activity it was found that the selected compounds have an activating behavior and anxiolytic effects on the models of “open field” and “elevated plus maze” (EPM). The data obtained indicate the anxiolytic (anti-anxiety) activity of the derivatives of pyrimidines, especially pronounced in compounds 6n, 6b, and 7c. The studied compounds increase the latent time of first immobilization on the model of “forced swimming” (FST) and exhibit some antidepressant effect similarly to diazepam. Docking studies revealed that compound 6k bound tightly in the active site of GABA_A receptor with a value of the scoring function that estimates free energy of binding (ΔG) at −7.95 kcal/mol, while compound 6n showed the best docking score and seems to be dual inhibitor of SERT transporter as well as 5-HT_1A receptor. Conclusions: Тhe selected compounds have an anticonvulsant, activating behavior and anxiolytic effects, at the same time exhibit some antidepressant effect.     

Polyethylene glycol-promoted synthesis of pyrimido[1,2-a]benzimidazole and pyrano[2,3-c]pyrazole derivatives in water

Synthesis of pyrimido[1,2-a]benzimidazole and pyrano[2,3-c]pyrazole derivatives were achieved using polyethylene glycol (PEG-400) as promoting reaction medium in water under catalyst-free conditions at reflux and room temperature, respectively. The structure of pyrimido[1,2-a]benzimidazole was confirmed using ¹H NMR, ¹³C NMR, DEPT, and HMBC experiments. The promising points for the present methodology are efficiency, generality, high yield, short reaction time, cleaner reaction profile, ease of product isolation, simplicity, potential of recycling reaction medium, and finally agreement with green chemistry protocols.     

Hypervalent Iodine in Synthesis. 94. A Facile Synthesis of 2-Substituted-imidazo[1,2-a]pyridines by Cyclocondensation of Alkynyl(phenyl) iodonium Salts and 2-Aminopyridine

Abstract

A facile method for the synthesis of 2-substituted-imidazo[1,2-a]pyridines is achieved by cyclocondensation of alkynyl(phenyl)iodonium salts with 2-aminopyridine.     

Studies on the Synthesis of New 3-(3,5-Diamino-1-substituted-pyrazol-4-yl)azo-thieno[2,3-b]pyridines and 3-(2-Amino-5,7-disubstituted-pyrazolo[1,5-a]pyrimidine-3-yl)azothieno[2,3-b]pyridines

Coupling the diazonium salt of 3-amino-2-cyano-4,6-dimethylthieno[2,3-b]pyridine 1 with malononitrile 2 gave 2-cyano-3-(hydrazonomalononitrile)-4,6-dimethylthieno[2,3-b]pyridine 3 which then reacted with hydrazine compounds 4a-4h to yield corresponding 2-cyano-3-(3,5-diamino-1-substituted-pyrazol-4-yl)azo-4,6-dimethylthieno[2,3-b]pyridines 5a-5h. The 2-cyano-3-(2-amino-5,7-disubstituted-pyrazolo-[1,5-a]pyrimidine-3-yl)azo-4,6-dimethylthieno[2,3-b]pyridines 7a-7f were obtained in good yield by the cyclocondensation reaction of 2-cyano-3-(3,5-diamino-pyrazol-4-yl)azo-4,6-dimethylthieno[2,3-b]pyridine 5a with the appropriate 1,3-diketones 6a-6f under acidic condition.     

Visible Light-Induced C-5 Selective C—H Radical Borylation of Imidazo[1,2-a]pyridines with NHC-Boranes

A visible-light-induced C-5 selective C—H borylation of imidazo[1,2-a]pyridines with NHC-BH₃ via Minisci-type radical borylation reaction has been developed for the first time. The present sustainable protocol provides a new family of regioselectively C5-borylated imidazopyridines that would otherwise be difficult to prepare. It is a supplement to site-selective borylation of azines (nitrogen-containing aromatic heterocycles) and the assembly of sp² carbon-boron bond.      

p-Toluenesulfonic acid-catalyzed one-pot synthesis of 2-amino-4-substituted-1,4-dihydrobenzo[4,5]imidazolo[1,2-a]pyrimidine-3-carbonitriles under neat conditions

A simple, efficient, and green procedure for the preparation of 2-amino-4-substituted-1,4-dihydrobenzolo[4,5]imidazolo[1,2-a]pyrimidine-3-carbonitriles has been developed by multi-component condensation of 2-aminobenzimidazole with aldehydes and malononitrile in the presence of a catalytic amount of p-toluenesulfonic acid, affording excellent yields under neat conditions. The protocol avoids the use of expensive catalysts, toxic solvents, and chromatographic separation. We believe that this new environmentally metal-free procedure, combined to a solvent-free reaction, would be of importance in the search of green laboratory-scale synthesis.     

A novel and convenient synthesis of thiazolo[3,2-a]pyrimidin-7-ones and pyrido[1,2-a]pyrimidin-2-ones using Vilsmeier reagent

A novel route for the synthesis of thiazolo[3,2-a]pyrimidin-7-ones and pyrido[1,2-a]pyrimidin-2-ones from acetylated 2aminothiazoles and 2-aminopyridines under Vilsmeier conditions has been developed.The plausible mechanism has also been proposed.     

Exploration of versatile reactions on 2-chloro-3-nitroimidazo[1,2-a]pyridine: expanding structural diversity of C2- and C3-functionalized imidazo[1,2-a]pyridines

Alternative strategies for functionalizing 2-chloro-3-nitroimidazo[1,2-a]pyridine have been developed. Suzuki–Miyaura cross-coupling reaction provided easily the corresponding 2-arylated compounds, and herefrom the nitro group was reduced into amine which afforded amides, anilines, and ureas in the 3-position. The amination of the key compound using a metal-catalyzed reaction was reported. This study highlighted the importance of the nitro group to facilitate the chlorine displacement. Other nucleophilic aromatic substitutions open a route to various products derived from imidazo[1,2-a]pyridine.     

One-step synthesis of thiazolo[3,2-a]pyridines by a multicomponent reaction of β-enaminonitriles, α,β-unsaturated aldehydes, and 2-aminothiol hydrochlorides

A wide library of 3,7,8,8a-tetrahydro-2H-thiazolo[3,2-a]pyridines has been prepared by simple heating in acetonitrile of β-enaminonitriles, α,β-unsaturated aldehydes and 2-aminothiol hydrochlorides. Chemical yields depend on the nature, hindrance, and position of the substituents. The scope, limitations, and stereocontrol associated to this three-component reaction have been studied in detail. In general, the diastereoinduction observed in the three new stereogenic centers generated in the pro-chiral α,β-unsaturated aldehyde is low.     

Silica sulfuric acid/ethylene glycol as an efficient catalyst for the synthesis of benzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitrile derivatives

A simple and efficient eco-friendly method was developed for the synthesis of new benzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitrile derivatives in excellent yields. The synthesis was achieved through the reaction of 2-aminobenzimidazole, aldehydes and active nitriles (malononitrle or ethyl cyanoacetae) in the presence of silica sulfuric acid/ethylene glycol. This protocol offers very short reaction times (in some cases, reaction times were reduced to five minutes), high yields and low cost. This method thus provides an improvement over the existing methods.     

Asymmetric synthesis of pyrrolo[1,2-a]indoles via organocatalytic[3 + 2] annulation of substituted 2-vinylindoles with azlactones

The chiral phosphoric acid catalyzed asymmetric[3+2]annulation of substituted 2-vinylindoles with azlactones has been established.This reaction represented a practical approach for the synthesis of structurally diverse pyrrolo[1,2-a]indoles with two vicinal stereocenters including one tetrasubstituted stereocenter in good yields and good stereoselectivities under mild conditions.     

Cu(OTf)2-catalyzed synthesis of imidazo[1,2-a]pyridines from α-diazoketones and 2-aminopyridines

α-Diazoketones undergo smooth coupling with 2-aminopyridines in the presence of 10 mol % of copper(II) triflate to produce the corresponding 2-substituted imidazo[1,2-a]pyridines (IPs) in excellent yields with high selectivity. Rh₂(OAc)₄ is also found to be an equally effective catalyst for this transformation.     

Synthesis of thiazolo[3,2-a]pyridines via an unusual Mannich-type cyclization

The Mannich-type reaction of N-methylmorpholinium 4-aryl-3-cyano-6-oxo-1,4,5,6-tetrahydropyridine-2-thiolates with 3-(1,3-benzodioxol-5-yl)-2-methylpropanal (ocean propanal) and p-toluidine afforded 7-aryl-2-(1,3-benzodioxol-5-ylmethyl)-2-methyl-3-[(4-methylphenyl)amino]-5-oxo-2,3,6,7-tetrahydro-5H-thiazolo[3,2-a]pyridine-8-carbonitriles in modest (25–46%) yields. The structure of the key compound was confirmed by X-ray crystal structure analysis.     

Facile synthesis of novel 3-substituted pyrido[1,2-a]pyrimidinium salts using vinamidinium salts

Pyrido[1,2-a]pyrimidinium salt derivatives 2a–f were prepared in good yields by condensation of 2-aminopyridine with 2-substituted vinamidinium salt derivatives 1a–f. The purity and the structure of the synthetized compounds were ascertained by elemental analysis, mass spectrometry, infrared, and NMR (¹H and ¹³C 400?MHz) spectroscopy.     

An efficient synthesis of 3-amino-2-arylimidazo[1,2-a]pyridines

An efficient synthesis of 3-amino-2-arylimidazo[1,2-a]pyridines is described via a novel multicomponent reaction between 2-aminopyridines, benzaldehydes and imidazoline-2,4,5-trione under solvent-free conditions.