A benzimidazole-based Cu(II) complex catalyzed site-selective C-H sulfenylation of imidazo-[1,2-a]pyridines using CS2 as a sulfur source

A new benzimidazole-based Cu(II) complex catalyzed site-selective sulfenylation of imidazo[1,2-a]pyridines with benzyl/alkyl/allyl bromides and CS2 at 100 °C in DMF : H2O is reported. The present methodology has been developed for the synthesis of 3-sulfenyl imidazo[1,2-a]pyridines in good yields with a broad substrate scope. In this protocol, CS2, commonly known as a non-polar small molecule bioregulator (SMB), is converted to valuable sulfenylated imidazo[1,2-a]pyridine derivatives. In addition, theoretical investigations along with experimental evidence unfold the insights into the probable mechanistic pathway of site-selective sulfenylation from S,S-dibenzyltrithiocarbonate, which is particularly formed as an intermediate during the reaction.

Synthesis and site selective C-H functionalization of imidazo-[1,2-a]pyridines

Imidazo[1,2-a]pyridine has attracted much interest in drug development because of its potent medicinal properties, therefore the discovery of novel methods for its synthesis and functionalization continues to be an exciting area of research. Although transition metal catalysis has fuelled the most significant developments, extremely beneficial metal-free approaches have also been identified. Even though pertinent reviews focused on imidazo[1,2-a]pyridine synthesis, properties (physicochemical and medicinal), and functionalization at the C3 position have been published, none of these reviews has focused on the outcomes obtained in the field of global ring functionalization. We wish here to describe a brief synthesis and an overview of all the functionalization reactions at each carbon atom, viz, C2, C3, C5, C6, C7 and C8 of this scaffold, divided into sections based on site-selectivity and the type of functionalization methods used.

Regioselective C3-H Alkylation of Imidazopyridines with Donor-Acceptor Cyclopropanes

Alkylated imidazopyridines are crucial structures for medicinal chemistry. Here, an efficient method for the C3-H alkylation of imidazopyridines was devised. Under Lewis acid-catalyzed conditions, reactions of imidazopyridines with different donor-acceptor cyclopropanes were carried out. Finally, 1,3-bisfunctionalizaton of donor-acceptor cyclopropanes was performed. In addition, synthesized C3-alkylated imidazopyridines are amenable for diverse synthetic applications.

Copper-catalyzed three-component reaction to synthesize polysubstituted imidazo[1,2-a]pyridines

An efficient three-component one-pot and operationally simple cascade of 2-aminopyridines with sulfonyl azides and terminal ynones is reported, providing a variety of polysubstituted imidazo[1,2-a]pyridine derivatives in moderate to excellent yields. In particular, the reaction goes a through CuAAC/ring-cleavage process and forms a highly active intermediate α-acyl-N-sulfonyl ketenimine with base free.

Three-component one-pot synthesis of polysubstituted imidazo[1,2-a]pyridine derivatives through a base free CuAAC/ring-cleavage process.

CDATA[Recent Advances in the Development of 1,2,3-Triazole-containing Derivatives as Potential Antifungal Agents and Inhibitors of Lanoster ol 14α-Demethylase

1,2,3-Triazole, a five-membered heterocyclic nucleus, is widely recognized as a key chromophore of great value in medicinal chemistry for delivering compounds possessing innumerable biological activities, including antimicrobial, antitubercular, antidiabetic, antiviral, antitumor, antioxidants, and anti-inflammatory activities. Mainly, in the past years, diverse conjugates carrying this biologically valuable core have been reported due to their attractive fungicidal potential and potent effects on various infective targets. Hence, hybridization of 1,2,3-triazole with other antimicrobial pharmacophores appears to be a judicious strategy to develop new effective anti-fungal candidates to combat the emergence of drug-sensitive and drug-resistant infectious diseases. Thus, the current review highlights the recent advances of this promising category of 1,2,3-triazole-containing hybrids incorporating diverse varieties of bioactive heterocycles such as conozole, coumarin, imidazole, benzimidazole, pyrazole, indole, oxindole, chromene, pyrane, quinazoline, chalcone, isoflavone, carbohydrates, and amides. It underlies their inhibition behavior against a wide array of infectious fungal species during 2015-2020.

Metal-free oxidative decarbonylative halogenation of fused imidazoles

An efficient strategy has been developed for the deformylative halogenation of carbaldehyde imidazo-fused heterocycles in the presence of TBHP controlled by temperature.

2-Isoxazolines: A Synthetic and Medicinal Overview

Isoxazolines are nitrogen- and oxygen-containing five-membered heterocyclic scaffolds with extensive biological activities. This framework can be readily obtained in good to excellent yields through 1,3-dipolar cycloaddition between nitrones with alkynes or allenes, aryl/alkyl halides, alkynes, and oxaziridines under mild conditions. This scaffold has been an emerging area of interest for many researchers given their wide range of bioactivities. Herein we review synthetic strategies toward isoxazolines and the role these efforts have had in enhancing the biological activity of natural products and synthetic compounds such as antitubercular agents, COX-1 inhibitors, COX-2 inhibitors (e. g., valdecoxib), nicotinic receptor modulators, and MIF inhibitors. With a focus on efforts from 2010 onward, this review provides in-depth coverage of the design and biological evaluation of isoxazoline systems and their impact on various pathologies.

NiFe2O4@SiO2 nPr@glucose catalyzed synthesis of novel 5-pyrazolin-1,2,4- triazazolidine-3-ones (thiones)

INTRODUCTION

NiFe2O4@SiO2nPr@glucose catalyzed synthesis of novel 5-pyrazolin-1,2,4-triazazolidine-3- ones (thiones).

MATERIALS AND METHODS

Amino glucose- functionalized silica- coated NiFe2O4 nanoparticles (NiFe2O4@SiO2 nPr@glucose amine or NiFe2O4@SiP@GA) were synthesized and characterized by X-ray powder diffraction (XRD), X-ray spectroscopy (EDX), transmission electron microscope (TEM), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometry (VSM) and fourier transform infrared spectroscopy (FT-IR).

RESULTS AND DISCUSSION

NiFe2O4@SiP@GA supply an eco-friendly procedure for the synthesis of some novel 5- pyrazolin-1,2,4-triazazolidine-3-ones or thiones through one-pot reaction of thiosemicarbazide (hydrazinecarbothioamide) and synthetized pyrazole carbaldehydes. These compounds were obtained in high yields in short reaction times. The catalyst could be easily recovered and reused for six cycles with almost consistent activity. The structures of the synthesized 5-pyrazolin-1,2,4-triazazolidine-3-ones or thiones were confirmed by 1H NMR, 13C NMR and FTIR spectral data and elemental analyses.

CONCLUSION

In conclusion, we have investigated NiFe2O4@SiO2nPr@amino glucose as a new, eco-friendly, inexpensive, mild and reusable catalyst for the synthesis of 5-pyrazolin-1,2,4-triazazolidine-3-ones or thiones. High yield, a simple work- up procedure, adherence to the basics of green chemistry, environmental friendly and based on natural ingredients, ease of separation and recyclability of the magnetic catalyst and waste reduction are some advantages of this method.

Synthesis, Characterization and Antimicrobial Activities of 1,4- Disubstituted 1,2,3-Triazole Compounds

BACKGROUND

1,2,3-triazoles are five-membered heterocyclic scaffold; their broad-spectrum biological activities are known. Researchers around the world are increasingly being interested in this emerging area, owing to its immense pharmacological scope.

OBJECTIVE

This work summarizes the synthesis of 1,2,3-triazoles and the significance of this pattern as a lead structure for new drug molecules discovery.

METHODS

1,2,3-triazoles can be obtained on a multigram scale through "click chemistry" under ambient conditions.

RESULTS

Sixteen compounds were synthesized and evaluated on five microbial strains E. coli, E. faecalis, P. aeruginosa, S. aureus and C. albicans. NMR, MS and IR were used to characterize all compounds. They were evaluated with their Minimum Inhibitory Concentrations (MICs) and interesting results were obtained with compounds 12a, 12b, 3, 2a and 2c, with MIC 0.14 μM (P. aeruginosa), 1.08 μM (E. coli), 1.20 μM (E. faecalis and C. albicans), 3.5 μM (E. faecalis) and 4.24 μM (C. albicans), respectively. P. aeruginosa and C. albicans were the most sensitive among all the strains.

CONCLUSION

The synthesized compounds were found as potential antimicrobial agents against Gram (+), Gram (-) strains and fungi.

La(OTf)3-catalysed one-pot synthesis of pyrazole tethered imidazo[1,2-a]azine derivatives and evaluation of their light emitting properties

La(OTf)₃catalysed one-pot facile protocol has been unfolded towards diversity-oriented synthesis of highly fluorescent pyrazole C-3(5) tethered imidazo[1,2-a]azines.

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

A comprehensive account of recent advances in the synthesis of imidazopyridines, assisted through transition-metal-catalyzed multicomponent reactions, C-H activation/functionalization and coupling reactions are highlighted in this review article. The basic illustration of this review comprises of schemes with concise account of explanatory text. The schemes depict the reaction conditions along with a quick look into the mechanism involved to render a deep understanding of the catalytic role. At some instances optimizations of certain features have been illustrated through tables, i.e., selectivity of catalyst, loading of the catalyst and percentage yield with different substrates. Each of the reported examples has been rigorously analyzed for reacting substrates, reaction conditions and transition metals used as the catalyst. This review will be helpful to the chemists in understanding the challenges associated with the reported methods as well as the future possibilities, both in the choice of substrates and catalysts. This review would be quite appealing to a wider range of organic chemists in academia and industrial R&D sectors working in the field of heterocyclic syntheses. In a nutshell, this review will be a guiding torch to envisage: (i) the role of various transition metals in the domain dedicated towards method development and (ii) for the modifications needed thereof in the R&D sector.

Synthesis of 3-aryl-2-phosphinoimidazo[1,2-a]pyridine ligands for use in palladium-catalyzed cross-coupling reactions

3-Aryl-2-phosphinoimidazo[1,2-a]pyridine ligands were synthesized from 2-aminopyridine via two complementary routes. The first synthetic route involves the copper-catalyzed iodine-mediated cyclizations of 2-aminopyridine with arylacetylenes followed by palladium-catalyzed cross-coupling reactions with phosphines. The second synthetic route requires the preparation of 2,3-diiodoimidazo[1,2-a]pyridine or 2-iodo-3-bromoimidazo[1,2-a]pyridine from 2-aminopyridine followed by palladium-catalyzed Suzuki/phosphination or a phosphination/Suzuki cross-coupling reactions sequence, respectively. Preliminary model studies on the Suzuki synthesis of sterically-hindered biaryl and Buchwald-Hartwig amination compounds are presented with these ligands.

BCl3-Mediated C-N, C-S, and C-O Bond Formation of Imidazo[1,2-a]pyridine Benzylic Ethers

An efficient BCl3-mediated reaction of imidazo[1,2-a]pyridines has been developed for the C-N, C-S, and C-O bond formation. The salient features of this method correspond to the substitution of different nucleophiles via in situ unconventional debenzylation. The developed process is applicable for the synthesis of a wide variety of ((3-amino/thio/alkoxy)-methyl)-imidazo[1,2-a]pyridines.

Chemodivergent synthesis of N-(pyridin-2-yl)amides and 3-bromoimidazo[1,2-a]pyridines from α-bromoketones and 2-aminopyridines

N-(Pyridin-2-yl)amides and 3-bromoimidazo[1,2-a]pyridines were synthesized respectively from α-bromoketones and 2-aminopyridine under different reaction conditions.

Chloroform as a carbon monoxide source in palladium-catalyzed synthesis of 2-amidoimidazo[1,2-a]pyridines

A palladium-catalyzed aminocarbonylation strategy exploiting chloroform as a CO source has been developed for the synthesis of biologically potent 2-amidoimidazopyridine scaffolds. The aminocarbonylation reaction was found to be general with a range of amines and substituted imidazopyridines. Preliminary biological evaluation of cytotoxicity on selected examples provides scope for future investigations.

A Cu(ii)-promoted tandem decarboxylative halogenation and oxidative diamination reaction of 2-aminopyridines with alkynoic acids for the synthesis of 2-haloimidazo[1,2-a]pyridines

A copper-promoted cascade decarboxylative halogenation and oxidative diamination reaction sequence of 2-aminopyridines with alkynoic acids has been developed for the synthesis of 2-haloimidazo[1,2-a]pyridines. In this reaction, two C-N bonds and one C-halogen bond are formed in one pot, generating the desired products in good yields. This is the first report on the synthesis of 2-haloimidazo[1,2-a]pyridine derivatives from alkynoic acids.

Synthesis of Imidazopyridines via Copper-Catalyzed, Formal Aza-[3 + 2] Cycloaddition Reaction of Pyridine Derivatives with α-Diazo Oxime Ethers

The Cu-catalyzed, formal aza-[3 + 2] cycloaddition reaction of pyridine derivatives with α-diazo oxime ethers in trifluoroethanol was used to synthesize imidazopyridines via the release of molecular nitrogen and elimination of alcohol. These methods enabled modular synthesis of a wide range of N-heterobicyclic compounds such as imidazopyridazines, imidazopyrimidines, and imidazopyrazines with an α-imino Cu-carbenoid generated from the α-diazo oxime ethers and copper.

Medicinal attributes of 1,2,3-triazoles: Current developments

1,2,3-Triazoles are important five-membered heterocyclic scaffold due to their extensive biological activities. This framework can be readily obtained in good to excellent yields on the multigram scale through click chemistry via reaction of aryl/alkyl halides, alkynes and NaN₃ under ambient conditions. It has been an emerging area of interest for many researchers throughout the globe owing to its immense pharmacological scope. The present work aims to summarize the current approaches adopted for the synthesis of the 1,2,3-triazole and medicinal significance of these architectures as a lead structure for the discovery of drug molecules such as COX-1/COX-2 inhibitors (celecoxib, pyrazofurin), HIV protease inhibitors, CB1 cannabinoid receptor antagonist and much more which are in the pipeline of clinical trials. The emphasis has been given on the major advancements in the medicinal prospectus of this pharmacophore for the period during 2008-2016.

Indium-based metal–organic frameworks as catalysts: synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines via oxidative amination under air using MIL-68(In) as an effective heterogeneous catalyst

The metal–organic framework MIL-68(In) has emerged as a productive heterogeneous catalyst for the synthesis of 2-nitro-3-arylimidazo[1,2-a]pyridines via oxidative amination between 2-aminopyridines and nitroalkenes using air as an oxidation agent.

Regiocontrolled functionalization of 2,3-dihalogenoimidazo[1,2-a]pyridines by Suzuki–Miyaura and Sonogashira cross-coupling reactions

An efficient method for regiocontrolled functionalization of 2,3-dihalogenoimidazo[1,2-a]pyridine was developed.

In(OTf)3 assisted synthesis of β-carboline C-3 tethered imidazo[1,2-a]azine derivatives

Synthesis of β-carboline based natural products and synthetic derivatives is one of the frontier areas of research owing to their medicinal properties.