Transition-metal-free synthesis of benzimidazoles mediated by KOH/DMSO

Electrochemical Cyclization of o-Aminyl Azobenzenes: Roles of Aldehydes in N-N Bond Cleavage

Direct functionalization of azobenzenes provides an approach to obtaining valuable molecules in synthetic chemistry. However, an efficient method for the cleavage of the N═N bond of azobenzenes, which is a key process for this transformation, is still lacking. We herein disclose an electrochemical reduction-induced cyclization of azobenzenes with aldehydes via N═N bond cleavage. This electrochemical cyclization of azobenzenes proceeds well in the absence of any transition metals or external chemical oxidants, leading to the formation of N-protected benzimidazoles in moderate to good yields.

Copper-Catalyzed Coupling between ortho-Haloanilines and Lactams/Amides: Synthesis of Benzimidazoles and Telmisartan

An efficient copper-catalyzed synthesis of (annelated) benzimidazoles is reported. This transformation is based on a simple and straightforward one-pot sequence involving a copper-catalyzed cross coupling between o-haloanilines and lactams/amides followed by a subsequent cyclization under acidic conditions. A variety of (annelated) benzimidazoles could be easily obtained in high yields from readily available starting materials, and this procedure could be further applied to the synthesis of the antihypertensive blockbuster drug telmisartan.

Synthesis, Optical Properties, and Applications of Luminescent Benzothiazole: Base Promoted Intramolecular C-S Bond Formation

A novel base-catalyzed method for the synthesis of luminescent benzothiazole derivatives had been developed under metal-free conditions via C-S bond formation, which provided an efficient, convenient, and mild alternative method for constructing substituted benzothiazoles. As-prepared benzothiazole derivatives thus produced emissions in solution with quantum yield up to 85%. In addition, they still exhibited fairly strong fluorescence in the solid state. Furthermore, the compounds were used as a facile "On-Off" fluorescence probe to create handy test strips for detecting NaClO by naked eyes.

Metal-Free Synthesis of Heteroaryl Amines or Their Hydrochlorides via an External-Base-Free and Solvent-Free C-N Coupling Protocol

Herein, a metal-free and solvent-free protocol was developed for the C-N coupling of heteroaryl halides and amines, which afforded numerous heteroaryl amines or their hydrochlorides without any external base. Further investigations elucidated that the basicity of amines and specific interactions derived from the X-ray crystallography analysis of 3j'·HCl played pivotal roles in the reactions. Moreover, this protocol was scalable to gram scales and applicable to drug molecules, which demonstrated its practical value for further applications.

Advances in the Synthesis of Ring-Fused Benzimidazoles and Imidazobenzimidazoles

This review article provides a perspective on the synthesis of alicyclic and heterocyclic ring-fused benzimidazoles, imidazo[4,5-f]benzimidazoles, and imidazo[5,4-f]benzimidazoles. These heterocycles have a plethora of biological activities with the iminoquinone and quinone derivatives displaying potent bioreductive antitumor activity. Synthesis is categorized according to the cyclization reaction and mechanisms are detailed. Nitrobenzene reduction, cyclization of aryl amidines, lactams and isothiocyanates are described. Protocols include condensation, cross-dehydrogenative coupling with transition metal catalysis, annulation onto benzimidazole, often using CuI-catalysis, and radical cyclization with homolytic aromatic substitution. Many oxidative transformations are under metal-free conditions, including using thermal, photochemical, and electrochemical methods. Syntheses of diazole analogues of mitomycin C derivatives are described. Traditional oxidations of o-(cycloamino)anilines using peroxides in acid via the t-amino effect remain popular.

Enantioselective C2-Allylation of Benzimidazoles Using 1,3-Diene Pronucleophiles

Although substituted benzimidazoles are common substructures in bioactive small molecules, synthetic methods for their derivatization are still limited. Previously, several enantioselective allylation reactions of benzimidazoles were reported that functionalize the nucleophilic nitrogen atom. Herein we describe a reversal of this inherent selectivity toward N-allylation by using electrophilic N-OPiv benzimidazoles with readily available 1,3-dienes as nucleophile precursors. This CuH-catalyzed approach utilizes mild reaction conditions, exhibits broad functional-group compatibility, and exclusively forms the C2-allylated product with excellent stereoselectivity.

New Approaches for the Synthesis of Heterocyclic Compounds Corporating Benzo[d]imidazole as Anticancer Agents, Tyrosine, Pim-1 Kinases Inhibitions and their PAINS Evaluations

BACKGROUND

Benzo[d]imidazoles are highly biologically active, in addition, they are considered as a class of heterocyclic compounds with many pharmaceutical applications.

OBJECTIVE

We are aiming in this work to synthesize target molecules that possess not only anti-tumor activities but also kinase inhibitors. The target molecules were obtained starting from the benzo[d]imidazole derivatives followed by their heterocyclization reactions to produce anticancer target molecules.

METHODS

The 1-(1H-benzo[d]imidazol-2-yl)propan-2-one (3) and the ethyl 2-(1H-benzo[d]imidazol-2- yl)acetate (16) were used as the key starting material which reacted with salicylaldehyde to give the corresponding benzo[4,5]imidazo[1,2-a]quinoline derivatives. On the other hand, both of them were reacted with different reagents to give thiophene, pyran and benzo[4,5]imidazo[1,2-c]pyrimidine derivatives. The synthesized compounds were evaluated against the six cancer cell lines A549, HT-29, MKN-45, U87MG, SMMC-7721, and H460 together with inhibitions toward tyrosine kinases, c-Met kinase and prostate cancer cell line PC-3 using the standard MTT assay in vitro, with foretinib as the positive control.

RESULTS

Most of the synthesized compounds exhibited high inhibitions toward the tested cancer cell lines. In addition, tyrosine and Pim-1 kinases inhibitions were performed for the most active compounds where the variation of substituent through the aryl ring and heterocyclic ring afforded compounds with high activities. Our analysis showed that there is a strong correlation between the structure of the compound and the substituents of target molecules.

CONCLUSION

Our present research proved that the synthesized heterocyclic compounds with varieties of substituents have a strong impact on the activity of compounds. The evaluations through different cell lines and tyrosine kinases indicated that the compounds were the excellent candidates as anticancer agents. This could encourage doing further research within this field for the building of compounds with high inhibitions.

The selective synthesis of N-arylbenzene-1,2-diamines or 1-arylbenzimidazoles by irradiating 4-methoxy-4'-substituted-azobenzenes in different solvents

The solvent-controllable photoreaction of 4-methoxyazobenzenes to afford 1-aryl-1H-benzimidazoles or N-arylbenzene-1,2-diamines has been studied. The irradiation of 4-methoxyazobenzenes in DMF containing 0.5 M hydrochloric acid provided N²-aryl-4-methoxybenzene-1,2-diamines as the major product, while irradiation in acetal containing 0.16 M hydrochloric acid led to 1-aryl-6-methoxy-2-methyl-1H-benzimidazoles as the major product. A possible reaction mechanism explaining the selectivity was also discussed.

A solvent-controllable photoreaction involving 4-methoxyazobenzenes has been developed to synthesize 1-aryl-1H-benzimidazoles or N-arylbenzene-1,2-diamines in moderate to good yields.

Generation of aryl radicals by redox processes. Recent progress in the arylation methodology

Arylation methods based on the generation and use of aryl radicals have been a rapidly growing field of research in recent years and currently represent a powerful strategy for carbon – carbon and carbon – heteroatom bond formation. The progress in this field is related to advances in the methods for generation of aryl radicals. The currently used aryl radical precursors include aryl halides, aryldiazonium and diaryliodonium salts, arylcarboxylic acids and their derivatives, arylboronic acids, arylhydrazines, organosulfur(II, VI) compounds and some other compounds. Aryl radicals are generated under mild conditions by single electron reduction or oxidation of precursors induced by conventional reagents, visible light or electric current. A crucial role in the development of the radical arylation methodology belongs to photoredox processes either catalyzed by transition metal complexes or organic dyes or proceeding without catalysts. Unlike the conventional transition metal-catalyzed arylation methods, radical arylation reactions proceed very often at room temperature and have high functional group tolerance. Without claiming to be exhaustive, this review covers the most important advances of the current decade in the generation and synthetic applications of (het)aryl radicals. Examples of reactions are given and mechanistic insights are highlighted.

The bibliography includes 341 references.

Metal-Free Synthesis of Benzimidazoles via Oxidative Cyclization of d-Glucose with o-Phenylenediamines in Water

d-Glucose has been identified as an efficient C1 synthon in the synthesis of benzimidazoles from o-phenylenediamines via an oxidative cyclization strategy. Isotopic studies with ¹³C₆-d-glucose and D₂O unambiguously confirmed the source of methine. The notable features of this method include the following: broad functional group tolerance, a biorenewable methine source, excellent reaction yields, a short reaction time, water as an environmentally benign solvent, and the synthesis of vitamin B₁₂ component on the gram scale.

Organophosphorus chemistry based on elemental phosphorus: advances and horizons

The results of studies on the application of elemental phosphorus for the synthesis of important organophosphorus compounds are surveyed and summarized. Currently, this trend represents a synthetically, environmentally and technologically attractive alternative to classical organophosphorus chemistry based on toxic and corrosive phosphorus chlorides. Direct phosphination and phosphinylation of organic compounds with elemental phosphorus (discussed in the first part of the review) basically extend the range of available phosphines, phosphine chalcogenides and phosphinic acids and provides further development of their synthetic potential (discussed in the second part of the review). It is shown that the breakthrough in this area is largely due to the discovery of reactions of elemental phosphorus (white and red) with various electrophiles in superbasic suspensions and emulsions derived from alkali metal hydroxides and to the development of electrochemical, electrocatalytic and catalytic activation of white phosphorus.

The bibliography includes 299 references.

Triflic anhydride mediated synthesis of 3,4-dihydroquinazolines: a three-component one-pot tandem procedure

A one-pot three-component tandem reaction involving a key Pictet-Spengler-like annulation step has been developed, providing an efficient method for the synthesis of 3,4-dihydroquinazolines in moderate to good yields from amides, aldehydes, and amines. The multicomponent triflic anhydride mediated reaction tolerates the installation of numerous functional groups, affording extensive diversity about the heterocyclic scaffold.

An improved synthesis of telmisartan via the copper-catalyzed cyclization of o-haloarylamidines

A concise synthetic route was designed for making telmisartan. The key bis-benzimidazole structure was constructed via the copper-catalyzed cyclization of o-haloarylamidines. By adopting this approach, telmisartan was obtained in a 7-step overall yield of 54% starting from commercially available 3-methyl-4-nitrobenzoic acid, and the use of HNO₃/H₂SO₄ for nitration and polyphosphoric acid (PPA) for cyclization in the reported literatures were avoided.

A concise synthetic route of telmisartan was developed via the copper-catalyzed cyclization of o-haloarylamidines, avoiding the use of HNO₃/H₂SO₄ and polyphosphoric acid (PPA).

Quinazolinone Synthesis through Base-Promoted SNAr Reaction of ortho-Fluorobenzamides with Amides Followed by Cyclization

A transition-metal-free synthesis of quinazolin-4-ones by Cs2CO3-promoted SNAr reaction of ortho-fluorobenzamides with amides followed by cyclization in dimethyl sulfoxide has been developed. The present procedure can provide efficient synthetic methods for the formation of both 2-substituted and 2,3-disubstituted quinazolin-4-one rings depending on the use of easily available starting materials and an efficient, one-pot protocol for the synthesis of the marketed drug product of methaqualone.

Superbase-promoted selective carbon-carbon bond cleavage driven by aromatization

A novel selective carbon-carbon single bond cleavage has been disclosed through the copper-catalyzed reaction of 1-alkyl-3-alkylindolin-2-imine hydrochlorides with substituted 1-(bromomethyl)-2-iodobenzenes leading to fused N-heterocycles. Mechanistic studies showed that the intrinsic drive of aromatization and the action of the superbase derived from sodium tert-butoxide and dimethylsulfoxide were the key factors leading to the carbon-carbon single bond cleavage. Furthermore, the obtained N-heterocycles are indoloquinoline derivatives with wide biological activities.

Base-Promoted SNAr Reactions of Fluoro- and Chloroarenes as a Route to N-Aryl Indoles and Carbazoles

KOH/DMSO-promoted C-N bond formation via nucleophilic aromatic substitution (S_NAr) between chloroarenes or fluoroarenes with indoles and carbazole under transition metal-free conditions affording the corresponding N-arylated indoles and carbazoles has been developed.

Developments towards synthesis of N-heterocycles from amidines via C–N/C–C bond formation

This review focuses on the synthesis of N-heterocycles using amidines as starting materials, with an emphasis on the mechanisms of these reactions via C–N/C–C bond formation.

Harnessing the reactivity of ortho-formyl-arylketones: base-promoted regiospecific synthesis of functionalized isoquinolines

An efficient and base-mediated one-pot regiospecific synthesis of structurally diversified isoquinolines and benzo[h] isoquinolines from easily accessible ortho-formyl-arylketones and aryl/(het)arylmethanamines has been described.

Synthesis of Indoles via Electron-Catalyzed Intramolecular C-N Bond Formation

A new protocol for the preparation of N-substituted indole-3-carboxylates has been developed. The key C-N bond formation occurs under transition-metal-free conditions employing a t-BuOK/DMF system without special initiators or additives. Across a number of substrates, indoles were afforded in yields higher or comparable to those obtained under transition-metal-catalyzed conditions. While demonstrating high functional group tolerance, new conditions are particularly attractive for manufacturing halogenated indoles that cannot be made in a pure form using other metal-based catalytic methods.

Construction of Druglike 2-Amido Benzo[ d]imidazole Analogues via Desulfurative Cyclization of Thiourea Intermediate Resin on Solid-Phase

A 2-amido benzo[ d]imidazole library has been constructed by solid-phase synthesis. The key step of this solid-phase synthesis involves the preparation of polymer-bound 2-amino benzo[ d]imidazole resin through desulfurative cyclization of thiourea resin using 2-chloro-1,3-dimethylimidazolinium chloride and N, N-diisopropylethylamine in dichloromethane (DCM), and the resin is then functionalized by acylation at the 2-amine position to afford 2-amidobenzo[ d]imidazole resin. In the case of 2-amidobenzo[ d]imidazole resin having a p-I or m-NO₂, the resin was further functionalized by Suzuki/Sonogashira-coupling ( p-I) and reduction to the primary amine ( m-NO₂) followed by acylation. Finally, the functionalized 2-amido-benzo[ d]imidazole resin was cleaved from the polymer support by treatment with a cocktail of trifluoroacetic acid and DCM. As a result, we obtained 2-amidobenzo[ d]imidazole analogues in high yield and good purities.

Synthesis of Novel Thiophene, Thiazole and Coumarin Derivatives Based on Benzimidazole Nucleus and Their Cytotoxicity and Toxicity Evaluations

The reactivity of compounds 2-(1-(2-chloroacetyl)-1H-benzo[d]imidazol-2-yl)acetonitrile 2 and 3-(1-(2-chloroacetyl)-1H-benzo[d]imidazol-2-yl)-2H-chromen-2-one 8 towards different chemical reagents were studied and a series of novel benzimidazole derivatives were obtained (2-6a-d and 8-12a-d). Moreover, in vitro growth inhibitory effect of the newly synthesized compounds were evaluated in term of [IC₅₀ µM] against the six cancer cell lines, human lung carcinoma (A549), lung cancer (H460), human colorectal (HT29), gasteric cancer cell (MKN-45), glioma cell line (U87MG) and cellosaurus cell line (SMMC-7721) where foretinib was used as standard reference. The results showed that compounds 2 (only for A549 cell line), 3a, 4, 6c, 6d, 8, 9a, 9e and 9f were the most active compounds towards the six cancer cell lines. On the other hand, the toxicity of these most potent compounds against shrimp larvae indicated that compounds 3a, 4, 6d, 9e and 9f were non toxic while compounds 6c and 8 were very toxic and compounds 2 and 9a were harmful against the tested organisms.

Cesium carbonate promoted cascade reaction involving DMF as a reactant for the synthesis of dihydropyrrolizino[3,2-b]indol-10-ones

A cesium carbonate promoted cascade reaction for the synthesis of dihydropyrrolizino[3,2-b]indol-10-ones has been developed.

Synthesis of fused benzimidazoles via successive nucleophilic additions of benzimidazole derivatives to arynes under transition metal-free conditions

An expedient and efficient strategy was developed for the synthesis of benzimidazole derivatives from aryne precursors under transition metal-free conditions.

Synthesis of 2-Alkoxy/Thioalkoxy Benzo[d]imidazoles and 2-Thione Benzo[d]imidazoles via a Phase-Based, Chemoselective Reaction

2-Alkoxy/thioalkoxy benzo-[d]-imidazole and 2-thione benzo-[d]-imidazole libraries were constructed in solution phase and on solid phase, respectively. The key step in this work is the phase-based chemoselective reaction of the 2-mercaptobenzo-[d]-imidazole intermediate with benzyl chloride (solution phase) and Merrifield resin (solid phase). In the solution-phase case, benzyl chloride reacted with the thiol group of 2-mercaptobenzo-[d]-imidazole, whereas in the solid-phase case, Merrifield resin was introduced at an internal amine group of benzo-[d]-imidazole. To afford the desired 2-alkoxy/thioalkoxy benzo-[d]-imidazole analogues, we used various alkyl halides, alcohols, and thiols in solution phase, and to obtain 2-thione benzo-[d]-imidazole derivatives on solid phase, we used diverse alkyl halides and boronic acids. Finally, to measure the drug potential to be orally active and the molecular diversity in three-dimensional (3D) space, we calculated physicochemical properties and displayed energy-minimized 3D structures. As a result, the libraries from solution phase and solid phase show distinct features in physicochemical properties and skeletal diversities in 3D space.

Atom-Economical and Metal-Free Synthesis of Multisubstituted Furans from Intramolecular Aziridine Ring Opening

Multisubstituted furans were prepared from dialkyl 2-(aziridin-2-ylmethylene)malonate and/or 1,3-dione through aziridine ring opening by the internal carbonyl oxygen with the assistance of BF3·OEt2, followed by aromatization. This synthetic method is free from any metal and is atom-economical with all of the atoms in the starting material retained in the final product.

Base-Mediated One-Pot Synthesis of Aliphatic Diazirines for Photoaffinity Labeling

Aliphatic diazirines have been widely used as prominent photophores for photoaffinity labeling owing to their relatively small size which can reduce the steric effect on the natural interaction between ligands and proteins. Based on our continuous efforts to develop efficient methods for the synthesis of aliphatic diazirines, we present here a comprehensive study about base-mediated one-pot synthesis of aliphatic diazirines. It was found that potassium hydroxide (KOH) can also promote the construction of aliphatic diazirine with good efficiency. Importantly, KOH is cheaper, highly available, and easily handled and stored compared with the previously used base, potassium tert-butoxide (t-BuOK). Gram-scale study showed that it owned great advantages in being used for the large-scale production of aliphatic diazirines. This protocol is highly neat and the desired products can be easily isolated and purified. As the first comprehensive study of the base-mediated one-pot synthesis of aliphatic diazirines, this work provided good insight into the preparation and utilization of diazirine-based photoaffinity labeling probes.