Cobalt-catalyzed arylation of azole heteroarenes via direct C-H bond functionalization

[reaction: see text] We herein report a new cobalt-catalyzed method for arylation of azole heteroarenes, including thiazole, oxazole, imidazole, benzothiazole, benzoxazole, and benzimidazole. The direct arylation of thiazole and oxazole was achieved both with iodo- and bromoarenes as the aryl donors in the presence of cobalt catalyst [Co(OAc)(2)/IMes] and cesium carbonate, while imidazole required the use of zinc oxide as the base. A complete reversal of arylation from C-5 to C-2 was accomplished using the bimetallic Co/Cu/IMes system. A direct comparison of the new cobalt method and the previously developed palladium protocol revealed significant differences, in terms of both chemical yield and selectivity.     

Tris[2‐(1,3‐thiazol‐2‐yl‐κN)‐1H‐benzimidazole‐κN3]zinc(II) dinitrate ethanol hemisolvate monohydrate at 100 K

The Zn^II center in the dicationic complex of the title compound, [Zn(C₁₀H₇N₃S)₃](NO₃)₂·0.5C₂H₅OH·H₂O, is in a distorted octahedral environment with imperfect noncrystallographic C₃ symmetry. Each 2‐(1,3‐thiazol‐2‐yl)‐1H‐benzimidazole ligand coordinates in a bidentate manner, with the Zn—N(imidazole) bond lengths approximately 0.14 Å shorter than the Zn—N(thiazole) bond lengths. Charge‐assisted hydrogen bonds connect cations, anions and water molecules. A lattice void is occupied by an ethanol solvent molecule disordered about a crystallographic inversion center and π‐stacking is observed between one type of symmetry‐related benzene rings.     

Research on heterocyclic compounds. XXIII. Phenyl derivatives of fused imidazole systems

The reaction of various heteroarylamines with ethyl 2-benzoyl-2-bromoacetate was used to obtain some imidazo[1,2-a]pyridines, imidazo[1,2-a]pyrimidines, imidazo[2,1-b]thiazoles and imidazo[2,1-b]benzothiazoles characterized by the presence of a phenyl moiety on the imidazole ring. In the case of thiazole and benzothiazole derivatives, unexpected by-products were isolated and their structures elucidated.     

Color‐Tunable Solid‐State Fluorescence Emission from Carbazole‐Based BODIPYs

Several carbazole‐based boron dipyrromethene (BODIPY) dyes were synthesized by organometallic approaches. Thiazole, benzothiazole, imidazole, benzimidazole, triazole, and indolone substituents were introduced at the 1‐position of the carbazole moiety, and boron complexation of each dipyrrin generated the corresponding compounds 1 , 2 a , and 3 – 6 . The properties of these products were investigated by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X‐ray crystallography, and DFT calculations. These compounds exhibited large Stokes shifts, and compounds 1 , 2 a , and 3 – 5 fluoresced both in solution and in the solid state. Complex 2 a showed the highest fluorescence quantum yield (Φ_F) in the solid state, therefore boron complexes of the carbazole–benzothiazole hybrids 2 b – f , which had several different substituents, were prepared and the effects of the substituents on the photophysical properties of the compounds were examined. The fluorescence properties showed good correlation with the results of crystal‐packing analyses, and the dyes exhibited color‐tunable solid‐state fluorescence.     

Regioselective,Unconventional Pictet–Spengler Cyclization Strategy Toward the Synthesis of Benzimidazole‐Linked Imidazoquinoxalines on a Soluble Polymer Support

A novel strategy for an unconventional Pictet–Spengler reaction has been developed for the regioselective cyclization of the imidazole ring system at the C2 position. The developed strategy was utilized to develop a diversity‐oriented parallel synthesis for bis(heterocyclic) skeletal novel analogs of benzimidazole‐linked imidazoquinoxalines on a soluble polymer support under microwave conditions. Condensation of polymer‐immobilized o‐phenylenediamines with 4‐fluoro‐3‐nitrobenzoic acid followed by nucleophilic aromatic substitution with an imidazole motif affords bis(heterocyclic) skeletal precursors for the Pictet–Spengler reaction. The unconventional Pictet–Spengler cyclization with various aldehydes was achieved regioselectively at the C2 position of the imidazole ring to furnish rare imidazole‐fused quinoxaline skeletons. During the Pictet–Spengler cyclization, aldehydes bearing electron‐donating groups afford 4,5‐dihydro‐imidazoquinoxalines, which then auto‐aromatize into benzimidazole‐linked imidazo[1,2‐a]quinoxalines. However, interestingly, aldehydes bearing electron‐withdrawing groups directly provide aromatized imidazo[1,2‐a]quinoxalines, which unexpectedly afford novel benzimidazole‐linked 4‐methoxy‐4,5‐dihydro‐imidazo[1,2‐a]quinoxalines after polymer cleavage.     

Nickel(II) and copper(II) complexes of 2,2’‐bibenzo[d]thiazole: Synthesis,characterisation and biological studies

Benzothiazole moiety has gained a lot of attention because of its importance as essential pharmacophore in the development of metal based drugs. Nickel(II) and copper(II) complexes of a benzothiazole based ligand, 2,2’‐bibenzo[d]thiazole (L¹), synthesized by the reaction of benzothiazole‐2‐carbonylchloride and o‐aminothiophenol, is reported. The compounds were characterised by elemental and percentage metal analyses, spectroscopic (FTIR and UV–vis), ¹H and ¹³C NMR, Mass spectra, thermal, magnetic moment and molar conductance analyses. The mass spectra, elemental and percentage metal composition of the metal complexes gave a 2:1 ligand to metal stoichiometric mole ratio. The spectral data showed that the ligand was coordinated to the metal ions through the nitrogen atoms of the benzothiazole moiety. The electronic spectra and magnetic susceptibility measurements showed that the nickel and copper complexes adopted square planar geometries. The ligand and its metal(II) complexes were screened against some drug resistant microbes and were found to exhibit varied degree of antimicrobial activities. The nickel complex was more active compared to ciprofloxacin against Staphylococcus aureus and Bacillus cereus. Similarly, the antioxidant potential of the ligand was evaluated. The ligand is a better ferrous ion chelating agent compared to 1,10‐phenanthroline and 2,2‐bipyridine. The ligand and its complexes exhibited good antimicrobial and Fe²⁺ chelating properties making them probable compounds of interest in antibiotic and antioxidant drug researches.     

Synthesis, structural and crystallographic study of some carbamates derived from 9-methyl-9-azabicyclo[3.3.1]nonan-3α-ol

A series of benzimidazole, thiazole and benzothiazole carbamates derived from 9-methyl-9-azabicyclo[3.3.1]nonan-3α-ol was synthesized and studied by ¹H, ¹³C, 2D NMR and IR spectroscopy. To assist in the interpretation of the spectroscopic data, the crystal structure of 3 (9-methyl-9-azabicyclo[3.3.1]nonan-3α-yl 2-amino-1H-benzimidazole-1-carboxilate) was determined by X-ray diffraction. It has been found that 1-carbamates and 2-carbamates can be obtained in the case of the benzimidazole derivatives. The benzimidazole-1-carbamates are obtained in higher yields (41, 38%) than the benzimidazole-2-carbamates (3, 9%). The compounds studied displayed in CDCl₃ solution a preferred chair–boat conformation with the substituted ring in a distorted boat form and the N–CH₃ substituent in an axial position with respect to the chair piperidine ring. This conformation is similar to that determined by X-Ray diffraction for compound 3.     

Synthesis and nuclear magnetic resonance spectra of fused pyrimidines

Ethy phenylpropiolate reacted with 2-aminobenzothiazoles, benzimidazoles, thiazoline and thiazole to give the corresponding fused 2-oxopyrimidines. 2-Mercaptobenzimidazole reacted with ethyl phenylpropiolate to give 4-phenyl-2H-1-thiapyrimido(1,2-a ]benzimidazol-2-one in very good yield. The thiones, methylthio iodides and the hydrobromides of some of the products were prepared. Analysis of the nmr spectra of the benzothiazole and benzimidazole products and their 3-deuterio analogs showed that the proton at position 6 is shielded and absorbs together with the proton at position 3 near δ 6.0 ppm. The nmr and ir spectral data of all the products are tabulated and discussed.     

Preparation of 2-aryl and 2-aryloxymethyl imidazo[1,2-a]pyridines and related compounds

A series of substituted 2-aryl imidazo[1,2-a]pyridines has been prepared in which a variety of substituents are introduced on the 4′-position of the phenyl ring and on the 3, 5 , 6 or 7 position of the heterocyclic ring. Most examples have acetamido, bromo, cyano, or formyl substituents at the 4′-position. Analogous imidazo-[2,1-b]fhiazoles and imidazo[1,2-a]pyrimidines have also been prepared. Another series of compounds consisting of 4′-formylphenoxymethyl derivatives of imidazole, the three positional isomers of pyridine, thiazole, benzimidazole and ring-substituted imidazo[1,2-a]pyridines has been prepared. 2-(4′-Formylphenylethenyl) derivatives of imidazole and imidazo[1,2-a]pyridine were also prepared.     

Feasible Approach to Tricyclic and Tetracyclic cyclododecanone

2‐Bromocyclododecanone was utilized as precursor to synthesize polyfused heterocyclic cyclododecane ring systems. Transformation of 2‐bromocyclododecanone ( 5 ) with 1H‐benzimidazole‐2‐thiole ( 6 ), benzo[d]thiazole‐2‐thiol ( 9 ), 2‐naphthol ( 12 ), and thiophenol ( 15 ) afforded thiazolo[2,3‐b]benzimidazole ( 8 ), thiazolo[2,3‐b]benzothaizole derivative ( 11 ) naphtho[1,2‐d]furan derivative ( 14 ) and 2‐(phenylthio)cyclododecanone ( 16 ), respectively.     

Palladium-catalyzed C-H bond direct alkynylation of 5-membered heteroarenes: a well-defined synthetic route to azole derivatives containing two different alkynyl groups

A widely applicable oxidative coupling of 5-membered heteroarenes and terminal alkynes that uses a combination of palladium and silver salts was developed. Under suitable conditions, imidazole and benzimidazole, which are sluggish under similar previously reported oxidative coupling conditions, as well as imidazo[1,5-a]pyridines, oxazole, benzoxazole, thiazole, and benzothiazole could be alkynylated. In addition, the bromine atom on the substrates was intact under the reaction conditions, and conventional Sonogashira coupling did not occur at all. With these reactivities in hand, a well-defined synthetic route to imidazo[1,5-a]pyridines and thiazole containing two different alkynyl groups was achieved in a simple manner. In addition, linear correlations were observed between the fluorescence wavelength and the Hammett substituent constants of aryl groups, not only on the C1- but also on the C3-alkynyl group of the obtained 1,3-bis(arylethynyl)imidazo [1,5-a]pyridines.     

Crystal structures and Hirshfeld surface analysis of transition‐metal complexes of 1,3‐azolecarboxylic acids

The crystal structures of five new transition‐metal complexes synthesized using thiazole‐2‐carboxylic acid (2‐Htza), imidazole‐2‐carboxylic acid (2‐H₂ima) or 1,3‐oxazole‐4‐carboxylic acid (4‐Hoxa), namely diaquabis(thiazole‐2‐carboxylato‐κ²N,O)cobalt(II), [Co(C₄H₂NO₂S)₂(H₂O)₂], 1 , diaquabis(thiazole‐2‐carboxylato‐κ²N,O)nickel(II), [Ni(C₄H₂NO₂S)₂(H₂O)₂], 2 , diaquabis(thiazole‐2‐carboxylato‐κ²N,O)cadmium(II), [Cd(C₄H₂NO₂S)₂(H₂O)₂], 3 , diaquabis(1H‐imidazole‐2‐carboxylato‐κ²N³,O)cobalt(II), [Co(C₄H₂N₂O₂)₂(H₂O)₂], 4 , and diaquabis(1,3‐oxazole‐4‐carboxylato‐κ²N,O⁴)cobalt(II), [Co(C₄H₂NO₃)₂(H₂O)₂], 5 , are reported. The influence of the nature of the heteroatom and the position of the carboxyl group in relation to the heteroatom on the self‐assembly process are discussed based upon Hirshfeld surface analysis and used to explain the observed differences in the single‐crystal structures and the supramolecular frameworks and topologies of complexes 1 – 5 .     

Microwave assisted one pot synthesis of 2-ethylamino benzimidazole,benzoxazole and benzothiazole derivatives

A rapid and efficient one-pot method for the synthesis of 2-ethylamino benzimidazole, benzoxazole, and benzothiazole derivatives has been described. The reaction of o-phenylenediamines or o-aminophenols or 2-mercaptoanilines with EDC.HCl under microwave irradiation afforded the corresponding 2-ethylamino benzimidazole, benzoxazole and benzothiazole derivatives in excellent yields.     

2‐(4‐methylpyridin‐2‐yl)‐1H‐benzimidazole derivatives. Part II,lH nmr characterization

A selected series of 2‐(4‐methylpyridin‐2‐yl)‐1H‐benzimidazole derivatives, bases and cyclic mono‐ and bis‐salts, were synthesized. Complete ^'1H nmr characterization is reported. Ambiguous assignments were solved using ¹H‐¹H NOESY analysis. Significant ir and ¹H nmr data are presented concerning: i) tautomeric equilibrium of imidazole hydrogen; ii) hydrogen bonds; iii) conformational inversion of partially saturated rings.     

Synthesis and Antimicrobial Activities of Novel 2‐[substituted‐1H‐pyrazol‐4‐yl] Benzothiazoles,Benzoxazoles, and Benzimidazoles

In an endeavor to find a new class of antimicrobial agents, a series of novel substituted benzimidazole, benzoxazole, and benzothiazole derivatives 6 containing pyrazole moiety have been synthesized by reaction of 3‐aryl‐4‐formyl pyrazole 4 with substituted phenylenediamine or o‐aminophenol or o‐aminothiophenol 5 . Reaction of phenyl hydrazine or 2‐hydrazinopyridine 1 with substituted acetophenones 2 gave the corresponding hydrazones 3 , which on Vilsmeier–Haack reaction with POCl₃–DMF gave substituted 3‐aryl‐4‐formyl pyrazoles 4 . All final compounds 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j , 6k were evaluated for in vitro antibacterial activities against Escherichia coli and Staphylococcus aureus strains and in vitro antifungal activity against Candida albicans and Aspergillus niger strains by using serial dilution method. The antimicrobial activities were expressed as the minimum inhibitory concentration in µg/mL. The compound containing benzimidazole and benzoxazole moiety gave better antibacterial and antifungal activities than benzothiazole compounds.     

DFT Studied Hetero‐Diels–Alder Cycloaddition for the Domino Synthesis of Spiroheterocycles Fused to Benzothiazole and Chromene/Pyrimidine Rings in Aqueous Media

Structurally diverse spiroheterocycles; spiro[pyrimido[2,1‐b ]benzothiazole‐3,3′‐chromene]‐2′,4′‐dione, spiro[pyrimido[2,1‐b ]benzothiazole‐3,5′‐pyrimidine]‐2′,4′,6′‐trione, and spiro[pyrimido[2,1‐b ]benz‐thiazole‐3,2′‐cyclohexane]‐1′,3′‐dione have been synthesized by an environmentally benign, efficient, and facile one‐pot pseudo‐four component reaction of 2‐aminobenzothiazoles with aromatic aldehydes and cyclic β‐diketones in aqueous medium. The process involves hetero‐Diels–Alder cycloaddition and provides facile access to spiroheterocycles fused with potentially interesting biologically active scaffolds. The configuration of hetero‐Diels–Alder cycloadduct has been ascertained through density functional theory calculations.     

Metal‐to‐Ligand Alkyl Migration Inducing Carbon–Sulfur Bond Cleavage in Dialkyl Yttrium Complexes Supported by Thiazole‐Containing Amidopyridinate Ligands: Synthesis,Characterization, and Catalytic Activity in the Intramolecular Hydroamination Reaction

Neutral Y^III dialkyl complexes supported by tridentate N^?,N,N monoanionic methylthiazole– or benzothiazole–amidopyridinate ligands have been prepared and completely characterized. Studies on their stability in solution revealed progressive rearrangement of the coordination sphere in the benzothiazole‐containing system through an unprecedented metal‐to‐ligand alkyl migration and subsequent thiazole ring opening. Attempts to synthesize hydrido species from the dialkyl precursor led to the generation of a dimeric yttrium species stabilized by a trianionic N^?,N,N^?,S^? ligand as the result of metal‐to‐ligand hydride migration with chemoselective thiazole ring opening and subsequent dimerization through intermolecular addition of the residual Y?H group to the imino fragment of a second equivalent of the ring‐opened intermediate. DFT calculations were used to elucidate the thermodynamics and kinetics of the process, in support of the experimental evidence. Finally, all isolated yttrium complexes, especially their cationic forms prepared by activation with the Lewis acid Ph₃C⁺[B(C₆F₅)₄]^?, were found to be good candidate catalysts for intramolecular hydroamination/cyclization reactions. Their catalytic performance with a number of primary and secondary amino alkenes was assessed.     

Synthesis and Antibacterial Activity of Sulfur‐linked Bis and Tris Heterocycles

The bis and tris heterocycles‐benzoxazolyl/benzothiazolyl/benzimidazolyl quinazolines linked by sulfur and/or nitrogen were prepared from 2,4‐dichloroquinazoline and benzazolyl‐2‐thiol/benzazolyl‐2‐amine and studied their antibacterial activity. The nitro‐substituted sulfur‐linked bisbenzothiazolylquinazoline (12f) , bisbenzimidazolylquinazoline ( 13f ), and nitro‐substituted sulfur and nitrogen‐linked bisbenzothiazolylquinazoline ( 15f ) were found to be potential antibacterial agents against Staphylococcus aureus .      

Complex hydrogen bonded cations-IV further symmetric ions

Solutions containing the complex hydrogen bonded cations (NMe imidazole)₂ H⁺; (thiazole)₂H⁺ and (benzothiazole)₂H⁺ have been prepared. The spectra display a pronounced double maximum in the v_s infrared band, which is replaced by a single band in the D-bridged analogues. The activity of the far infrared v_s band, the frequency of the NH bending mode, and the observation of internal modes characteristic of both donor and acceptor all indicate that the hydrogen bonding proton is not located at the mid point of the NβN bridge.Salts of the complex (benzothiazole)₂H⁺ cation have been obtained in the solid state, and have a similar infrared spectrum to the complex in solution.     

Structure électronique et stabilité thermique d'heterocycles appartenant à la serie de l'imidazole et du thiazole

Résumé La structure électronique de l'imidazole, du benzimidazole, du thiazole et du benzothiazole a été calculée par une méthode de champ self-consistant simplifiée tenant compte des électrons et . L'énergie d'arrachement d'un atome d'hydrogène fixé sur le noyau hétérocyclique a été évaluée de faÇon approximative, en vue d'interpréter la variation de stabilité observée dans les expériences de pyrolyse.

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The electronic structure of imidazole, benzimidazole, thiazole and benzothiazole has been calculated by a simplified LCAO-SCF method taking into account and electrons. Breacking energy for an hydrogen atom bounded to the heterocyclic ring is estimated by an approximated way and used for explaining changes of stability observed in pyrolysis experiments.

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Zusammenfassung Die Elektronenstruktur von Imidazol, Benzimidazol, Thiazol und Benzthiazol wurde mittels eines vereinfachten LCAO-SCF-Verfahrens unter Einschlu\ von - und -Elektronen berechnet. Dann wurde die Trennungsenergie für ein am Heteroring gebundenes H-Atom abgeschÄtzt und zur Interpretation der relativen StabilitÄt, wie sie bei Pyrolysen beobachtet wird, verwendet.