Rapid and Cheap Synthesis of Benzimidazoles via Intermittent Microwave Promotion: A Simple and Potential Industrial Application of Air as Oxidant

Using inexpensive KI as the catalyst in the presence of ambient air, benzimidazoles were synthesized from aromatic aldehydes and o-phenylenediamine with excellent yields via intermittent microwave irradiation without reflux equipment. The synthesis process was mild and only needed only a short reaction time (7–10 min). As a simple example of the utilization of molecular oxygen under mild conditions, this method provides a novel way to synthesize benzimidazoles. The industrial synthesis of benzimidazoles may be realized by a cycle of microwave irradiation.     

Microwave‐Assisted Solid‐Phase Synthesis of a 1,2‐Disubstituted Benzimidazole Library by Using a Phosphonium Linker

An efficient and rapid microwave‐assisted solid‐phase method for the synthesis of 5‐methyl‐1,2‐disubstituted benzimidazoles derivatives has been developed. The phosphonium linker, obtained by reaction between polymer‐supported triphenylphosphine and 4‐fluoro‐3‐nitrobenzyl iodide, underwent aromatic substitution with primary amines, followed by one‐pot reaction with aldehydes in the presence of SnCl₂·2H₂O, yielded the benzimidazole system under microwave irradiation. The final products were released from the resin with NaOH under microwave irradiation and were obtained in high purity and good overall yield.     

Light fluorous-tagged traceless one-pot synthesis of benzimidazoles facilitated by microwave irradiation

A novel protocol for rapid assemble of benzimidazole framework has been demonstrated. This method incorporated with light fluorous-tag provides a convenient method for diversification of benzimidazoles and for easy purification via fluorous solid-phase extraction (F-SPE) in a parallel manner. The key transformation of this study involves in situ reduction of aromatic nitro compound, amide formation, cyclization and aromatization promoted by microwave irradiation in a one-pot fashion. The strategy is envisaged to be applied for the establishment of drug-like small molecule libraries for high throughput screening.     

阻燃剂苯并咪唑的微波合成研究进展

苯并咪唑类化合物广泛应用于医药、农药等领域,也在阻燃剂中具有重要应用.因此,利用微波辅助方法快速、高效地合成苯并咪唑类化合物已成为近年来的研究热点,本文对此进行了综述,并从经济与规模化制备苯并咪唑等方面进行了展望.     

Rapid microwave-assisted liquid-phase combinatorial synthesis of 2-(arylamino)benzimidazoles

An efficient, facile, and practical liquid-phase combinatorial synthesis of benzimidazoles under microwave irradiation is described. In the first step of reaction sequence, polymer-bound activated aryl fluoride was condensed with selective primary amines via an ipso-fluoro displacement reaction. Reduction of the polymer-bound nitro group followed by cyclization with isothiocyanates afforded immobilized benzimidazoles. The desired products were obtained in high yield with high purity after detaching from the soluble matrix. All reactions involved (S(N)Ar reaction, reduction, cyclization, and support cleavage) were performed completely within a few minutes under microwave irradiation. The coupling of microwave technology with liquid-phase combinatorial synthesis constitutes a novel and particularly attractive avenue for the rapid generation of structurally diverse libraries.     

A Rapid and Convenient Synthesis of Derivatives of Imidazoles under Microwave Irradiation

An efficient and a quick microwave‐assisted synthesis of benzimidazoles and trisubstituted imidazoles was developed. Three benzimidazoles were obtained as a result of the condensation of 1,2‐phenylenediamine with carboxylic acids and acetoacetic ester without catalyst. A series of trisubstituted imidazoles were synthesized by condensation of benzil, aromatic aldehyde and ammonium acetate in the presence of glacial acetic acid.     

VO(acac)_2 catalyzed condensation of o-phenylenediamine with aromatic carboxylic acids/aldehydes under microwave radiation affording benzimidazoles

Vanadyl acetylacetonate,VO（acac）₂,has been found to be very effective catalyst for synthesis of a variety of benzimidazoles under solvent-free condition.The methodology involves the exposure of a mixture of o-phenylenediamine and a selected aromatic carboxylic acid/aldehyde to microwave radiation without the use of any solvent or supporting agents.The benzimidazoles were obtained in quick time with high yields.     

Microwave‐Assisted Tandem Transformation on an Ionic‐Liquid Support: Efficient Synthesis of Pyrrolo/Pyridobenzimidazolones and Isoindolinone‐Fused Benzimidazoles

A tandem transformation that involves the formation of three bonds and two heterocyclic rings in a one‐pot fashion through amino‐alkylation of an ionic‐liquid‐immobilized diamine with keto acids followed by successive double intramolecular cyclizations to afford a tricyclic framework has been explored. This tandem cyclization has been utilized to develop a rapid and efficient method to synthesize various pyrrolo[1,2‐a]benzimidazolones and pyrido[1,2‐a]benzimidazolones on an ionic‐liquid support by using focused microwave irradiation. The application of this tandem cyclization was further extended to the aromatic keto acids to provide isoindolinone‐fused benzimidazoles, a structurally heterogeneous library with skeletal diversity. The outcome of the cascade reaction was confirmed by the X‐ray crystallographic study of the product directly attached to the ionic‐liquid support. Use of the ionic liquid as a soluble support facilitates purification by simple precipitation along with advantages like high loading capacity, homogeneous reaction conditions, and monitoring of the reaction progress by regular conventional spectroscopic methods, whereas application of microwave irradiation greatly accelerates the rate of the reactions.     

CN bond formation and cyclization: A straightforward and metal-free synthesis of N-1-alkyl-2-unsubstituted benzimidazoles

A straightforward and metal-free synthesis of N-1-alkyl-2-unsubstituted benzimidazoles from the corresponding o-fluoro aryl formamidines and primary amines using microwave irradiation is described. The displacement of -F by the primary amine and cyclization to form the corresponding benzimidazoles took place in one pot.     

Mercury chloride assisted cyclization toward benzimidazoles by focused microwave irradiation

An efficient, microwave-assisted method for the mercury chloride mediated synthesis of 1,2-disubstituted benzimidazoles has been developed. Biologically interesting benzimidazoles were readily assembled utilizing S_NAr reactions, reduction, and followed with mercury(II) mediated cyclization under microwave irradiation. The desired products were then liberated from the soluble matrix in excellent yield and purity after cleavage.     

超声辐射下NH4OAc高效催化合成2-取代苯并咪唑类衍生物（英文）

超声辐射下,以NH4OAc为催化剂,利用芳香醛和邻苯二胺一锅法合成了一系列2-取代苯并咪唑类衍生物,该方法具有反应条件温和、收率高的特点。     

Microwave-assisted synthesis of 1-aryl-3-acetyl-1,4,5,6-tetrahydrobenzimidazo[1,2-d][1,2,4]triazine: first example of a novel ring system

Novel highly functionalized benzimidazoles were synthesized in two steps by microwave irradiation: construction of the benzimidazole ring followed by ring closure to the new tricyclic system.     

Microwave-assisted one step high-throughput synthesis of benzimidazoles

One-pot synthesis of benzimidazoles from diamines and carboxylic acids was developed under microwave irradiation condition, which provided a practical and efficient method for high-throughput synthesis of this important class of heterocyclic compounds.     

Cp2ZrCl2-catalyzed synthesis of 2-aminovinyl benzimidazoles under microwave conditions

A microwave-assisted general method for the synthesis of 2-aminovinyl benzimidazoles has been developed.Treatment of the 1,2-phenylenediamines and N-arylated/N,N-dialkylated 3-aminoacroleins with bis(cyclopentadienyl)zirconium(IV) dichloride(Cp2Zr Cl2) as the catalyst under microwave irradiation for 3–5 min followed by in situ Mn O2 oxidation afforded thirteen 2-aminovinyl benzimidazoles in good yields.     

以水作溶剂微波法合成1,4-二氢苯并咪唑并[1,2-a]嘧啶类衍生物

以芳香醛、2-氨基苯并咪唑和丙二腈为原料,用传统法和微波辐射法三组分一锅煮法合成1,4-二氢苯并咪唑并[1,2-a]嘧啶类化合物。反应均在无催化剂条件下以水作反应溶剂进行。结果表明,采用微波辐射优于常规方法,三组分摩尔比n(2-氨基苯并咪唑)∶n(丙二腈)∶n(取代苯甲醛)=1∶1.1∶1,辐射功率400 W,时间为6～8 min时,1,4-二氢苯并咪唑并[1,2-a]嘧啶的收率在85%以上,反应速率比常规加热条件下提高70倍。通过荧光发射光谱研究证实,该系列化合物具有明显的荧光性质,其荧光发射峰位于480～550 nm。     

芳香基苯并咪唑衍生物的合成、表征及抑菌活性研究

在微波辐射下,通过二茂铁磺酰氯和相应的苯并咪唑合成了4种芳香基苯并咪唑衍生物。经^1H NMR、MS及元素分析确证产物结构。通过X线衍射测定了化合物4a的晶体结构。用琼脂稀释法测定化合物抑菌活性,并与对照药剂50%多菌灵可湿性粉剂比较,结果表明化合物4a～4d对番茄早疫病菌、烟草赤星病菌和小麦赤霉病菌有与对照药剂近似的抑菌活性。     

SYNTHESIS,NMR AND MOLECULAR MODELING STUDY OF 4,9a-DIARYL-9,9a-DIHYDRO 1H-[1,4]THIAZINO[4,3-a][1,3]BENZIMIDAZOLES

A series of substituted 4,9a-diaryl-9,9a-dihydro-1H-[1,4]thiazino[4,3-a][1,3]benzimidazoles was prepared in good yields from the reaction of bis(aroylmethyl) sulfides with ortho-phenylenediamine in glacial acetic acid under reflux and under microwave irradiation. Microwave irradiation is found to accelerate the reaction, besides giving better yield in the case of the thiazinobenzimidazoles with electron-withdrawing groups in the aryl rings than the thermal reaction.     

Synthesis of 2-substituted benzimidazoles and bis-benzimidazoles by microwave in the presence of alumina-methanesulfonic acid

A microwave-assisted method for the synthesis of 2-substituted benzimidazoles in the presence of alumina-methanesulfonic acid (AMA) is reported. In addition, by this method some new bis-benzimidazoles from the direct reaction of phenylenediamine and dicarboxylic acid under microwave irradiation in good to excellent yields are described.     

Microwave-assisted parallel synthesis of fused heterocycles in a novel parallel multimode reactor

New rotor types using disposable glass vials for small-scale parallel synthesis in multimode microwave reactors are introduced. One rotor comprises 16 groups of four vials, whereas the second uses four silicon carbide plates with a 6 x 4 matrix to process the vials. Both rotors achieve utmost temperature homogeneity upon microwave irradiation and can be used for microwave-mediated reactions at temperatures of up to 200 degrees C and pressures of 20 bar. The generation of three different heterocycle libraries furnishing thiophenes, oxindoles, and benzimidazoles using the new rotor types is described.     

Aerobic photooxidative synthesis of benzimidazoles from aromatic aldehydes and diamines using catalytic amounts of magnesium iodide

This Letter proposes a safe, mild, and environmentally benign method for the synthesis of benzimidazoles from aromatic aldehydes and diamines by aerobic photooxidation using irradiation with visible light, a catalytic amount of magnesium iodide, which serves as both a Lewis acid and an oxidant, and molecular oxygen as the terminal oxidant.