Hydrogen-Bond-Driven Electrophilic Activation for Selectivity Control: Scope and Limitations of Fluorous Alcohol-Promoted Selective Formation of 1,2-Disubstituted Benzimidazoles and Mechanistic Insight for Rationale of Selectivity

Rhodium(I)-Catalyzed Cascade Annulation of 1,n-Diynyl Nitrones to 3,4-Fused Fully Substituted Furans

A method for the assembly of fully substituted furans containing a 3,4-fused 5-8-membered carbocycle, heterocycle, or spirocycle from rhodium(I)-catalyzed and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP)-assisted cascade annulation of 1,n-diynyl nitrones has been developed.

Syntheses and exploration of the catalytic activities of organotin(IV) compounds

Six organotin(IV) compounds (1-6) have been synthesized by reaction of the polydentate pro-ligands H3L and H2L, respectively, with the corresponding diorganotin chlorides. All of the compounds were characterized by FT-IR spectroscopy, 1H, 13C{1H}, and 119Sn (1H) NMR spectroscopy, HRMS spectrometry, and single-crystal X-ray diffraction. The solid-state structures show that all of the compounds are monomeric (except compound 3) and contain a penta-coordinated tin atom. Compound 3 is a dimer with two hexa-coordinated tin atoms. Compounds 1-3 contain a non-coordinated hydroxymethyl group. All of the compounds have been screened for their catalytic efficacy in the synthesis of 1,2 disubstituted benzimidazoles using o-phenylenediamine and aldehyde derivatives. It has been observed that both the Lewis acidic Sn(IV) centre and the hydroxymethyl group (hydrogen bond donor) catalyse the reactions with a product yield of up to 92%.

Diphenhydramine Hydrochloride-CuCl as a New Catalyst for the Synthesis of Tetrahydrocinnolin-5(1H)-ones

The current study deals with the synthesis and characterization of a novel catalyst made from diphenhydramine hydrochloride and CuCl ([HDPH]Cl-CuCl). The prepared catalyst was thoroughly characterized using various techniques, such as ¹H NMR, Fourier transform-infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis and derivative thermogravimetry. More importantly, the observed hydrogen bond between the components was proven experimentally. The activity of this catalyst was checked in the preparation of some new derivatives of tetrahydrocinnolin-5(1H)-ones via a multicomponent reaction between dimedone, aromatic aldehydes, and aryl/alkyl hydrazines in ethanol as a green solvent. Also, for the first time, this new homogeneous catalytic system was effectively used for the preparation of unsymmetric tetrahydrocinnolin-5(1H)-one derivatives as well as mono- and bis-tetrahydrocinnolin-5(1H)-ones from two different aryl aldehydes and dialdehydes, respectively. The effectiveness of this catalyst was further confirmed by the preparation of compounds containing both tetrahydrocinnolin-5(1H)-one and benzimidazole moieties from dialdehydes. The one-pot operation, mild conditions, rapid reaction, and high atom economy, along with the recyclability and reusability of the catalyst, are other notable features of this approach.

"All-Aqueous" Tandem Boc-Deprotection and Alkylation of N-Bocbenzimidazole Derivatives under Visible Light with Alkyl Aryl Diazoacetates: Application to Site-Selective Insertion of Carbenes into the N-H Bond of Purines

Herein, we have reported a blue LED-induced tandem Boc-deprotection and NH-alkylation of benzimidazole derivatives with methyl aryl diazoacetates. The reactions occur in water at room temperature. The desired products are obtained in good to excellent yields. The putative mechanism of this reaction is discussed based on control experiments and supported by DFT studies. Additionally, the strategy is used to alkylate various purine derivatives via site-selective N¹-alkylation to generate acyclic nucleoside analogues.

Synthesis, Molecular Docking, Dynamics, Quantum-Chemical Computation, and Antimicrobial Activity Studies of Some New Benzimidazole-Thiadiazole Hybrids

In this study, some new compounds, which are 2-aminothiadiazole derivatives linked by a phenyl bridge to the 2-position of the benzimidazole ring, were designed and synthesized as antimicrobial agents. The structures of the compounds were elucidated by ¹H and ¹³C NMR spectroscopy, high-resolution mass spectrometry, and elemental analysis. The antifungal activities of the synthesized compounds were tested on Candida albicans, Candida krusei, Candida glabrata, and Candida parapsilosis. Compound 5f is more active against C. albicans and C. glabrata than standard fluconazole and varicanazole. Compounds were also evaluated for their counteracting activity against Gram-positive Escherichia coli, Serratia marcescens, Klebsiella pneumoniae, and Pseudomonas aeruginosa and Gram-negative Enterococcus faecalis, Bacillus subtilis, and Staphylococcus aureus. Compounds 5c and 5h had minimum inhibitory concentrations against E. faecalis close to that of the standard azithromycin. Molecular docking studies were performed against Candida species' 14-α demethylase enzyme. 5f was the most active compound against Candida species, which gave the highest docking interaction energy. The stabilities of compounds 5c and 5f with CYP51 were tested using 100 ns molecular dynamics simulations. According to the theoretical ADME calculations, the profiles of the compounds are suitable in terms of limiting rules. HOMO-LUMO analysis showed that 5h is chemically more reactive (represented with the lower ΔE = 3.432 eV) than the other molecules, which is compatible with the highest antibacterial activity result.

Design and Syntheses of Ruthenium ENE (E = S, Se) Pincer Complexes: A Versatile System for Catalytic and Biological Applications

This report describes synthesis of two ruthenium(II) ENE pincer complexes (E = S, C1 and E = Se, C2 ) by the reaction of bis(2-(phenylchalcogenyl)ethyl)amine ( L1 , L2 ) with RuCl 2 (PPh 3 ) 3 . The complexes were characterized with the help of 1 H and 13 C{ 1 H} NMR, FTIR, HRMS, cyclic voltammetry and elemental analysis techniques. The structure and bonding mode of ligand with ruthenium in C2 was established with the help of single crystal X-ray diffraction. The complex showed distorted octahedral geometry with two chlorine atoms trans to each other. The Ru-Se bond distances (Å) are 2.4564(3)-2.4630(3), Ru-N distance is 2.181(2), Ru-P distance is 2.2999(6), and Ru-Cl distances are 2.4078(6)-2.4314(6). The complexes showed good to excellent catalytic activity for the N -alkylation of 1,2-phenylenediamine with benzyl alcohol derivatives to synthesize 1,2-disubstituted benzimidazole derivatives. The complexes were also found to be efficient for aerobic oxidation of benzyl alcohols to corresponding aldehydes which are precursors to the bisimines generated in situ during the synthesis of 1,2-disubstituted benzimidazole derivatives. Complex C2 where selenium is coordinated with ruthenium was found to be more efficient as compared to sulfur coordinated ruthenium complex C1 . Since ruthenium complexes are getting increasing attention for developing new anticancer agents, the preliminary studies like binding behavior of both the complexes towards CT-DNA were studied by competitive binding with ethidium bromide (EthBr) using emission spectroscopy. In addition, the interactions of C1-C2 were also studied with bovine serum albumin (BSA) using steady state fluorescence quenching and synchronous fluorescence studies. A good stability of Ru(II) state was observed by cyclic voltammetric studies of C1-C2 . Overall these molecules are good examples of bio-organometallic systems for catalytic and biological applications.

PTSA-catalyzed selective synthesis and antibacterial evaluation of 1,2-disubstituted benzimidazoles

Herein, we developed a convenient and efficient method via protonation of p-toluenesulfonic acid promoted cyclocondensation of o-phenylenediamine and aldehydes for selectively synthesizing 1,2-disubstituted benzimidazoles. This method displayed broad substrate adaptability and afforded the desired products in moderate to excellent yield in short reaction time. The effect of different substituents on the yield was investigated by extending optimum reaction conditions, which was further confirmed by theoretical calculations. It suggested that the surface electrostatic potential of oxygen atom and nitrogen atom on the substrates played important role in the synthesis of 1,2-disubstituted benzimidazoles. Besides, the crystal structure of compound 2t in the orthorhombic space group P2(1)/c was presented. Also, the anti-mycolicibacterium smegmatis (MC2155) activity was evaluated using rifampicin as a positive control. The products (2a, 2b, 2c, 2i, 2j, 2k, 2m) showed good antibacterial activities which were comparable to rifampicin.

An Isoindoline Bridged [M(η6-arene)2]+ (M = Re, 99mTc) ansa-Arenophane and its Dinuclear Macrocycles with Axial Chirality

This work presents a straightforward method for the preparation of an isoindoline bridged [M(arene)2]+ (M = Re, 99mTc) ansa-[3]arenophane. This intramolecular formation of an ansa-complex is accompanied by the intermolecular...

Cleavage and Reassembly of the C═O Bond of 2-Alkynylbenzaldehydes: A Metal-Free Access to Inden-1-ones

A metal-free approach to inden-1-ones from 2-alkynylbenzaldehydes mediated by pyrrolidine has been developed. The reaction proceeds under mild conditions in a step- and atom-economy process by cleaving the C═O bond and constructing new C-C as well as C═O bonds. Oxygen-18 and deuterium labeling experiments revealed an aza-Petasis-Ferrier rearrangement of an intermediate 1-amino-3-methylene-dihydroisobenzofuran.

Visible light promoted tandem dehydrogenation-deaminative cyclocondensation under aerobic conditions for the synthesis of 2-aryl benzimidazoles/quinoxalines from ortho-phenylenediamines and arylmethyl/ethyl amines

Visible light promoted tandem dehydrogenation-deaminative cyclocondensation of arylmethyl/ethyl amines with ortho-phenylenediamines under aerobic conditions is reported for the synthesis of 2-aryl benzimidazoles/quinoxalines.

The synthesis and structure of an amazing and stable carbonized material Cu-PC@OFM and its catalytic applications in water with mechanism explorations

An amazing and stable carbonized octahedral frame material Cu-PC@OFM was synthesized and characterized through HRTEM, SEM, XRD, XPS, and Raman spectroscopy and nitrogen adsorption/desorption analysis.

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

Heterocycles have been found to be of much importance as several nitrogen- and oxygen-containing heterocycle compounds exist amongst the various USFDA-approved drugs. Because of the advancement of nanotechnology, nanocatalysis has found abundant applications in the synthesis of heterocyclic compounds. Numerous nanoparticles (NPs) have been utilized for several organic transformations, which led us to make dedicated efforts for the complete coverage of applications of metal nanoparticles (MNPs) in the synthesis of heterocyclic scaffolds reported from 2010 to 2019. Our emphasize during the coverage of catalyzed reactions of the various MNPs such as Ag, Au, Co, Cu, Fe, Ni, Pd, Pt, Rh, Ru, Si, Ti, and Zn has not only been on nanoparticles catalyzed synthetic transformations for the synthesis of heterocyclic scaffolds, but also provide an inherent framework for the reader to select a suitable catalytic system of interest for the synthesis of desired heterocyclic scaffold.

Natural dolomitic limestone-catalyzed synthesis of benzimidazoles, dihydropyrimidinones, and highly substituted pyridines under ultrasound irradiation

Natural dolomitic limestone (NDL) is employed as a heterogeneous green catalyst for the synthesis of medicinally valuable benzimidazoles, dihydropyrimidinones, and highly functionalized pyridines via C–N, C–C, and C–S bond formations in a mixture of ethanol and H₂O under ultrasound irradiation. The catalyst is characterized by XRD, FTIR, Raman spectroscopy, SEM, and EDAX analysis. The main advantages of this methodology include the wide substrate scope, cleaner reaction profile, short reaction times, and excellent isolated yields. The products do not require chromatographic purification, and the catalyst can be reused seven times. Therefore, the catalyst is a greener alternative for the synthesis of the above N-heterocycles compared to the existing reported catalysts.

Iron-Catalyzed Acceptorless Dehydrogenative Coupling of Alcohols With Aromatic Diamines: Selective Synthesis of 1,2-Disubstituted Benzimidazoles

Benzimidazoles are important N-heteroaromatic compounds with various biological activities and pharmacological applications. Herein, we present the first iron-catalyzed selective synthesis of 1,2-disubstituted benzimidazoles via acceptorless dehydrogenative coupling of primary alcohols with aromatic diamines. The tricarbonyl (η4-cyclopentadienone) iron complex catalyzed dehydrogenative cyclization, releasing water and hydrogen gas as by-products. The earth abundance and low toxicity of iron metal enable the provision of an eco-friendly and efficient catalytic method for the synthesis of benzimidazoles.

(Z)-Selective anti-Markovnikov or Markovnikov thiol-yne-click reactions of an internal alkyne by amide hydrogen bond control

Herein, we show exclusive control of stereo and regioselective thiol-yne click (TYC) reactions of internal alkynes via amide hydrogen bond control. By exploiting appropriate hydrogen bonding interactions like N-HS, N-HN and C-HO, either (Z)-selective anti-Markovnikov or Markovnikov products could be obtained for an internal alkyne, exclusively.

1,2-Disubstituted Benzimidazoles by the Iron Catalyzed Cross-Dehydrogenative Coupling of Isomeric o-Phenylenediamine Substrates

Benzimidazoles are common in nature, medicines, and materials. Numerous strategies for preparing 2-arylbenzimidazoles exist. In this work, 1,2-disubstituted benzimidazoles were prepared from various mono- and disubstituted ortho-phenylenediamines (OPD) by iron-catalyzed oxidative coupling. Specifically, O₂ and FeCl₃·6H₂O catalyzed the cross-dehydrogenative coupling and aromatization of diarylmethyl and dialkyl benzimidazole precursors. N,N'-Disubstituted-OPD substrates were significantly more reactive than their N,N-disubstituted isomers, which appears to be relative to their propensity for complexation and charge transfer with Fe³⁺. The reaction also converted N-monosubstituted OPD substrates to 2-substituted benzimidazoles; however, electron-poor substrates produce 1,2-disubstituted benzimidazoles by intermolecular imino-transfer. Kinetic, reagent, and spectroscopic (UV-vis and EPR) studies suggest a mechanism involving metal-substrate complexation, charge transfer, and aerobic turnover, involving high-valent Fe(IV) intermediates. Overall, comparative strategies for the relatively sustainable and efficient synthesis of 1,2-disubstituted benzimidazoles are demonstrated.

Synthesis and cytotoxic evaluation of novel quinozalinone derivatives with substituted benzimidazole in position 3

Quinazolinone and benzimidazole are both fused heterocyclic compounds which have shown valuable biological properties including cytotoxic, antibacterial, and antifungal activities. In this study, a series of novel quinazolinone derivatives substituted with benzimidazole were synthesized in two parts. In the first part 2 - phenyl - 1H - benzimidazol - 6 - amine (4) was synthesized from the reaction of 4-nitro-o-phenylenediamine and benzoic acid. In the second part, new 3-(2-phenyl-1H benzoimidazol-5-yl)- 3H-quinazolin-4-one derivatives (8a-8f) were also prepared. Finally compound 4 was reacted with the different benzoxazinone derivatives (8a-8f) to give the target compounds. The structures of the synthesized compounds were confirmed by IR and ¹HNMR. Cytotoxic activities of the final compounds were assessed at 100, 200, 300, 400, and 500 μM against MCF-7 and HeLa cell lines using the MTT colorimetric assay. Almost all compounds exhibited good cytotoxic activity against both cell lines. Compound 9d demonstrated the highest cytotoxic activity against MCF7 and Hela cell lines with IC₅₀ 70 μM and 50 μM, respectively.

Complexes of (η5-Cp*)Ir(iii) with 1-benzyl-3-phenylthio/selenomethyl-1,3-dihydrobenzoimidazole-2-thione/selenone: catalyst for oxidation and 1,2-substituted benzimidazole synthesis

The treatment of 1-benzyl-3-phenylthio/selenomethyl-1,3-dihydrobenzoimidazole-2-thione/selenone [L1-L4] with [(η⁵-Cp*)IrCl(μ-Cl)]₂ at 25 °C followed by NH₄PF₆ results in [(η⁵-Cp*)Ir(L)Cl][PF₆] (1-4 for L = L1 to L4), authenticated with high-resolution mass spectrometry (HR-MS) and multi-nuclei nuclear magnetic resonance (NMR) imaging (¹H, ¹³C{¹H} and ⁷⁷Se{¹H}). The structures of 1-4, established with single-crystal X-ray diffraction, reveal a "piano-stool" geometry around the Ir. The Ir-thio/selenoether (Ir-S/Ir-Se) bond distances (Å) are 2.347(18)-2.355(4)/2.4663(12)-2.4663(13) and Ir-thione/selenone (Ir-S/Ir-Se) distances are 2.4146(19)-2.417(2)/2.5141(16)-2.5159(12). The reaction of 1,2-phenylenediamine with benzylic alcohols and furfuryl alcohol under mild and ambient conditions, catalyzed efficiently with complexes 1-4, generates bisimine in situ. Cyclization and rearrangement via 1,3-hydride shift triggered by its electrophilic activation with Ir(iii) species finally results in 1,2-disubstituted benzimidazole. The yield of the heterocycles in this one-pot synthesis is excellent to good. The aldehydes generated in situ by aerial oxidation of alcohols in the presence of 1-4 as catalysts are precursors to the bisimine as the protocols of this heterocycle synthesis carried out in the absence of 1,2-phenylenediamine give them in excellent-to-good yield. The oxidation of alcohols by hydrogen transfer to acetone was catalyzed efficiently with complexes 1-4 and resulted in aldehyde/ketone in excellent-to-good yield. Each catalytic process is marginally more efficient with 1 than its counterparts.

Small molecule piperazinyl-benzimidazole antagonists of the gonadotropin-releasing hormone (GnRH) receptor

In this communication, we report the synthesis and characterization of a library of small molecule antagonists of the human gonadotropin releasing hormone receptor based upon the 2-(4-tert-butylphenyl)-4-piperazinyl-benzimidazole scaffold via Cu-catalysed azide alkyne cycloaddition. Our main purpose was to find a more soluble compound based on the WAY207024 lead with nanomolar potency to inhibit the GnRH receptor. A late stage diversification by the use of click chemistry was, furthermore developed to allow for expansion of the library in future optimisations. All compounds were tested in a functional assay to determine the individual potency of inhibiting stimulation of the receptor by the endogenous agonist GnRH. In conclusion, we found that compound 8a showed improved solubility compared to WAY207024 and nanomolar affinity to GnRH receptor.

Synthesis and characterization of a novel long-alkyl-chain ester-substituted benzimidazole gelator and its octan-1-ol solvate

The synthesis of a novel benzimidazole derivative with a long-chain-ester substituent, namely methyl 8-[4-(1H-benzimidazol-2-yl)phenoxy]octanoate, (3), is reported. Ester (3) shows evidence of aggregation in solution and weak gelation ability with toluene. The octan-1-ol solvate, methyl 8-[4-(1H-benzimidazol-2-yl)phenoxy]octanoate octan-1-ol monosolvate, C₂₂H₂₆N₂O₃·C₈H₁₈O, (4), exhibits a four-molecule hydrogen-bonded motif in the solid state, with N-H...O hydrogen bonds between benzimidazole molecules and O-H...N hydrogen bonds between the octan-1-ol solvent molecules and the benzimidazole unit. The alkyl chains of the ester and the octan-1-ol molecules are in unfolded conformations. The phenylene ring is canted by 10.27 (6)° from the plane of the benzimidazole ring system. H...C contacts make up 20.7% of the Hirshfeld surface coverage. Weak C-H...π interactions involving the benzimidazole alkyl chain and three aromatic rings are observed.

Selective and eco-friendly procedures for the synthesis of benzimidazole derivatives. The role of the Er(OTf)3 catalyst in the reaction selectivity

An improved and greener protocol for the synthesis of benzimidazole derivatives, starting from o-phenylenediamine, with different aldehydes is reported. Double-condensation products were selectively obtained when Er(OTf)₃ was used as the catalyst in the presence of electron-rich aldehydes. Conversely, the formation of mono-condensation products was the preferred path in absence of this catalyst. One of the major advantages of these reactions was the formation of a single product, avoiding extensive isolation and purification of products, which is frequently associated with these reactions.

Theoretical calculations helped to understand the different reactivity established for these reactions. Thus, we found that the charge density on the oxygen of the carbonyl group has a significant impact on the reaction pathway. For instance, electron-rich aldehydes better coordinate to the catalyst, which favours the addition of the amine group to the carbonyl group, therefore facilitating the formation of double-condensation products.

Reactions with aliphatic or aromatic aldehydes were possible, without using organic solvents and in a one-pot procedure with short reaction time (2–5 min), affording single products in excellent yields (75–99%). This convenient and eco-friendly methodology offers numerous benefits with respect to other protocols reported for similar compounds.

An Efficient Synthesis of 2-Substituted Benzimidazoles via Photocatalytic Condensation of o-Phenylenediamines and Aldehydes

A photocatalytic method has been developed for the efficient synthesis of functionalized benzimidazoles. This protocol involves photocatalytic condensation of o-phenylenediamines with various aldehydes using the Rose Bengal as photocatalyst. The method was found to be general and was successfully employed for accessing pharmaceutically important benzimidazoles by the condensation of aromatic, heteroaromatic and aliphatic aldehydes with o-phenylenediamines, in good-to-excellent yields. Notably, the method was found to be effective for the condensation of less reactive heterocyclic aldehydes with o-phenylenediamines.