Highly Regioselective C–N Bond Formation through C–H Azolation of Indoles Promoted by Iodine in Aqueous Media

I2-Cs2CO3 Mediated Intramolecular C2-Amination and Oxidative Rearrangement Cascade of C-3 Phenylthio Indoles: A Route to Synthesize Thiosulfonate-Embedded 2-Iminoindolin-3-ones

An efficient, transition-metal-free protocol employing I2/Cs2CO3 for the synthesis of thiosulfonate containing 2-iminoindolin-3-ones motifs has been developed from C-3 phenylthio indoles. The reaction proceeded through intramolecular cyclization involving C-N bond formation, leading to the formation of indole-fused benzothiazines as a key intermediate. Remarkably, Cs2CO3 played a crucial role in the reaction as an oxygen source, enabling oxidative rearrangement with [1,4]-sulfonyl migration to furnish the final products with the formation of multiple functional groups such as C═O, C═N, and S-SO2.

Aryliodonium Salt-Induced Regioselective Access to meta-Substituted Anilines by Arylation of Azoles

A highly efficient aryliodonium salt-induced regioselective access to meta-substituted anilines by arylation of azoles has been developed under catalyst-free conditions. This efficient transformation provides a facile and scalable approach to a wide range of biologically active N-arylazoles with moderate to high yields. According to the control experiments, two plausible pathways, including a Michael pathway and a free radical coupling pathway, for the reaction were proposed.

Iodine-Mediated C2,3-H Aminoheteroarylation of Indoles

A metal-free one-pot oxidative cross-dehydrogenation coupling reaction for the formation of C-N/C-C bonds at the C2,3-positions of indoles with azoles and quinoxalinones has been developed. The proposed method has several notable features, including metal-free catalysis, the use of N-H free indoles as substrates, ease of operation, mild reaction conditions, and compatibility with a wide range of substrates.

Selective modification of tryptophan in polypeptides via C-N coupling with azoles using in situ-generated iodine-based oxidants in aqueous media

This study demonstrates the C-N coupling of tryptophan with azoles, promoted by an in situ-generated iodine-based oxidant. The protocol was successfully applied to the selective modification of tryptophan in nonprotected polypeptide bearing oxidatively sensitive residues in acidic aqueous media. The present method allows the attachment of reactive handles to polypeptides and the peptide stapling.

Preclinical Evaluation of an Imidazole-Linked Heterocycle for Alzheimer's Disease

Humanity is facing a vast prevalence of neurodegenerative diseases, with Alzheimer's disease (AD) being the most dominant, without efficacious drugs, and with only a few therapeutic targets identified. In this scenario, we aim to find molecular entities that modulate imidazoline I2 receptors (I2-IRs) that have been pointed out as relevant targets in AD. In this work, we explored structural modifications of well-established I2-IR ligands, giving access to derivatives with an imidazole-linked heterocycle as a common key feature. We report the synthesis, the affinity in human I2-IRs, the brain penetration capabilities, the in silico ADMET studies, and the three-dimensional quantitative structure-activity relationship (3D-QSAR) studies of this new bunch of I2-IR ligands. Selected compounds showed neuroprotective properties and beneficial effects in an in vitro model of Parkinson's disease, rescued the human dopaminergic cell line SH-SY5Y from death after treatment with 6-hydroxydopamine, and showed crucial anti-inflammatory effects in a cellular model of neuroinflammation. After a preliminary pharmacokinetic study, we explored the action of our representative 2-(benzo[b]thiophen-2-yl)-1H-imidazole LSL33 in a mouse model of AD (5xFAD). Oral administration of LSL33 at 2 mg/Kg for 4 weeks ameliorated 5XFAD cognitive impairment and synaptic plasticity, as well as reduced neuroinflammation markers. In summary, this new I2-IR ligand that promoted beneficial effects in a well-established AD mouse model should be considered a promising therapeutic strategy for neurodegeneration.

Indolyl-Derived 4H-Imidazoles: PASE Synthesis, Molecular Docking and In Vitro Cytotoxicity Assay

The strategy of the nucleophilic substitution of hydrogen (SNH) was first applied for the metal-free C-H/C-H coupling reactions of 4H-imidazole 3-oxides with indoles. As a result, a series of novel bifunctional azaheterocyclic derivatives were obtained in yields up to 95%. In silico experiments on the molecular docking were performed to evaluate the binding possibility of the synthesized small azaheterocyclic molecules to the selected biotargets (BACE1, BChE, CK1δ, AChE) associated with the pathogenesis of neurodegenerative diseases. To assess the cytotoxicity for the synthesized compounds, a series of in vitro experiments were also carried out on healthy human embryo kidney cells (HEK-293). The leading compound bearing both 5-phenyl-4H-imidazole and 1-methyl-1H-indole moieties was defined as the prospective molecule possessing the lowest cytotoxicity (IC50 > 300 µM on HEK-293) and the highest binding energy in the protein–ligand complex (AChE, −13.57 kcal/mol). The developed compounds could be of particular interest in medicinal chemistry, particularly in the targeted design of small-molecule candidates for the treatment of neurodegenerative disorders.

NaClO-Mediated Cross Installation of Indoles and Azoles Benefits Anticancer Hit Discovery

Innovations in synthetic chemistry have a profound impact on the drug discovery process, and will always be a necessary driver of drug development. As a result, it is of significance to develop novel simple and effective synthetic installation of medicinal modules to promote drug discovery. Herein, we have developed a NaClO-mediated cross installation of indoles and azoles, both of which are frequently encountered in drugs and natural products. This effective toolbox provides a convenient synthetic route to access a library of N-linked 2-(azol-1-yl) indole derivatives, and can be used for late-stage modification of drugs, natural products and peptides. Moreover, biological screening of the library has revealed that several adducts showed promising anticancer activities against A549 and NCI-H1975 cells, which give us a hit for anticancer drug discovery.

Hypoiodite-Catalyzed Oxidative Umpolung of Indoles for Enantioselective Dearomatization

Here we report the oxidative umpolung of 2,3-disubstituted indoles toward enantioselective dearomative aza-spirocyclization to give the corresponding spiroindolenines using chiral quaternary ammonium hypoiodite catalysis. Mechanistic studies revealed the umpolung reactivity of C3 of indoles by iodination of the indole nitrogen atom. Moreover, the introduction of pyrazole as an electron-withdrawing auxiliary group at C2 suppressed a competitive dissociative racemic pathway, and enantioselective spirocyclization proceeded to give not only spiropyrrolidines but also four-membered spiroazetidines that are otherwise difficult to access.

Copper-iodine Co-catalyzed C−H Aminoalkenylation of Indoles via Temperature-controlled Selectivity Switch: Facile Synthesis of 2-Azolyl-3-alkenylindoles

An efficient copper-iodine co-catalyzed 2,3-difunctionalization of indoles with azoles and phenols via temperature-controlled selectivity switch has been developed for the green synthesis of 2-azolyl-3-alkenylindoles. The strategy involves the simultaneous establishment...

Dehydrogenative Azolation of Arenes in a Microflow Electrochemical Reactor

The electrochemical synthesis of aryl azoles was performed for the first time in a microflow reactor. The reaction relies on the anodic oxidation of the arene partners making these substrates susceptible for C–H functionalization with azoles, thus requiring no homogeneous transition-metal-based catalysts. The synthetic protocol benefits from the implementation of a microflow setup, leading to shorter residence times (10 min), compared to previously reported batch systems. Various azolated compounds (22 examples) are obtained in good to excellent yields.

Electro-Oxidative C-N Bond Formation through Azolation of Indole Derivatives: An Access to 3-Substituent-2-(Azol-1-yl)indoles

A practical protocol to synthesize 3-substituent-2-(azol-1-yl)indole derivatives has been developed via an electrochemical oxidative cross coupling process under mild conditions. This electro-oxidative C-N bond formation strategy tolerates a range of functional groups and is amenable to gram scale synthesis. Moreover, this method was applied to the late-stage functionalization of bioactive molecules.

Aerobic Oxidative C-H Azolation of Indoles and One-Pot Synthesis of Azolyl Thioindoles by Flavin-Iodine-Coupled Organocatalysis

The aerobic oxidative cross-coupling of indoles with azoles driven by flavin-iodine-coupled organocatalysis has been developed for the green synthesis of 2-(azol-1-yl)indoles. The coupled organocatalytic system enabled the one-pot three-component synthesis of 2-azolyl-3-thioindoles from indoles, azoles, and thiols in an atom-economical manner by utilizing molecular oxygen as the only sacrificial reagent.

Electrochemical Iodoamination of Indoles Using Unactivated Amines

An environmentally friendly electrochemical approach for iodoamination of various indole derivatives with a series of unactivated amines, amino acid derivatives, and benzotriazoles (more than 80 examples) has been developed. This strategy was further applied in late-stage functionalization of natural products and pharmaceuticals and gram-scale synthesis and radiosynthesis of ¹³¹I-labeled compounds. Fundamental insights into the mechanism of the reaction based on control experiments, density functional theory calculation, and cyclic voltammetry are provided.

Recent advances in the global ring functionalization of 7-azaindoles

The 7-azaindole building block has attracted considerable interest in the field of drug discovery in the current portfolio. Because of their powerful medicinal properties, the development of synthetic, elegant techniques for the functionalization of 7-azaindoles continues to be an active area of research. Advances in metal-catalyzed chemistry have recently supported the successful development of a number of novel and effective methods for functionalization of the 7-azaindole template. This review reports state-of-the-art functionalization chemistry of 7-azaindoles with an aspiration to highlight the global ring functionalization of 7-azaindoles that are potential as pharmacophores for various therapeutic targets. Other relevant reviews focused on 7-azaindole synthesis, properties and applications have also been reported. However, none of these reviews have been dedicated to the results achieved in the field of metal-catalyzed cross-coupling/C-H bond functionalized reactions. So we wish to discuss and summarize the advances made since 2011 in this field toward 7-azaindole functionalization.

Electrooxidative and Regioselective C-H Azolation of Phenol and Aniline Derivatives

A general and practical protocol was developed for the regioselective C-H azolation of phenol and aniline derivatives by electrooxidative cross-coupling. The reaction occurs under metal-, oxidant-, and reagent-free conditions, allowing access to a wide variety of synthetically useful heteroarene derivatives. The reaction also tolerates a broad range of functional groups and is amenable to gram-scale synthesis. Finally, a preliminary mechanistic study indicated that a radical-radical-combination pathway might be involved in the coupling reaction.

Multi-component synthesis of 3-substituted indoles and their cyclisation to α-carbolines via I2-promoted intramolecular C2 oxidative amination/aromatisation at room temperature

Condensation of indoles, aldehydes and pyrazol-5-amine in the presence of ceric ammonium nitrate gives 3-substituted indoles. These then cyclise to α-carbolines at room temperature through I2-promoted intramolecular C2 amination and aromatisation in open air. A plausible mechanism is proposed based on some controlled experiments.

I2-Mediated transition-metal-free aromatic C–H amination for the synthesis of benzimidazol-2-ones and related heterocycles

A practical I₂-mediated aromatic C–H amination reaction was established for benzimidazol-2-one synthesis under transition-metal-free conditions. The present reaction can be performed directly from disubstituted amines and isocyanates without the purification of the urea intermediates in a scalable fashion.

Direct intramolecular amination of tryptophan esters to prepare pyrrolo[2,3-b]indoles

A metal-free iodine-catalyzed intramolecular amination has been developed for the practical synthesis of pyrrolo[2,3-b]indoles from readily available tryptophan esters. The transformation has been applied to a wide array of substrates and can be performed on gram scale under very mild conditions.

A facile I2-catalyzed synthesis of imidazo[1,2-a]pyridines via sp3 C–H functionalization of azaarenes and evaluation of anticancer activity

A three component synthetic protocol has been developed for the synthesis of medicinally important imidazo[1,2-a]pyridines via the iodine-catalyzed oxidative amination of benzylic C–H bonds of azaarenes. The synthesized compounds were evaluated for their anti-cancer activity.

Regioselective Csp2–H dual functionalization of indoles using hypervalent iodine(iii): bromo-amination via 1,3-migration of imides on indolyl(phenyl)iodonium imides

A regioselective C_sp2–H dual functionalization of indoles, which underlies bromo-amination via the 1,3-migration of imide groups on indolyl(phenyl)iodonium imides, has been developed to provide 2-bis(sulfonyl)amino-3-bromo-indoles under the metal-free conditions.

H-phosphonate-mediated sulfonylation of heteroaromatic N-oxides: a mild and metal-free one-pot synthesis of 2-sulfonyl quinolines/pyridines

A smart H-phosphonate-mediated synthetic strategy for the sulfonylation of heteroaromatic N-oxides has been developed in one pot under metal-free conditions at room temperature.

Palladium-catalyzed oxidative cross-coupling of azole-4-carboxylates with indoles: an approach to the synthesis of pimprinine

A palladium-catalyzed oxidative cross-coupling reaction between azole-4-carboxylates and indoles forming 5-(3-indolyl)azoles with excellent regioselectivity has been developed.

Oxidative regioselective amination of chromones exposes potent inhibitors of the hedgehog signaling pathway

A novel selective coupling of chromones with azoles for the synthesis of biologically active compounds was developed.

Metal-free one-pot synthesis of 1,3-diazaheterocyclic compounds via I2-mediated oxidative C–N bond formation

A variety of 1,3-diazaheterocyclic compounds, including quinazolinones, benzimidazoles, and cyclic amidines, were readily synthesized through this metal-free one-pot annulation reaction.