Copper-catalyzed tandem Ullmann type C-N coupling and dehydrative cyclization: synthesis of imidazo[1,2-c]quinazolines

Recent Advances in Metal-Catalyzed Approaches for the Synthesis of Quinazoline Derivatives

Quinazolines are an important class of heterocyclic compounds that have proven their significance, especially in the field of organic synthesis and medicinal chemistry because of their wide range of biological and pharmacological properties. Thus, numerous synthetic methods have been developed for the synthesis of quinazolines and their derivatives. This review article briefly outlines the new synthetic methods for compounds containing the quinazoline scaffold employing transition metal-catalyzed reactions.

Starch mediates and cements densely magnetite-coating of talc, giving an efficient nano-catalyst for three-component synthesis of imidazo[1,2-c]quinazolines

Hot-water-soluble starch (HWSS) was used as a powerful cementing material to produce nano-size conglomerates of talc and magnetite nanoparticles. Coordination of HWSS hydroxyl groups to iron atoms at surface of magnetite leads to grafting and encapsulation of its nanoparticles. The resulting nano-complex showed a higher loading capacity on talc than pristine magnetite nanoparticles. Only a minute amount of HWSS was detected in the fabricated nano-composite Talc\HWSS@Fe3O4. XPS study suggests a considerable interaction between HWSS and Fe3O4 nanoparticles, upon which some of the Fe+3 atoms on surface of Fe3O4 are reduced into Fe+2 atoms. ATR FT-IR spectra of the nano-composite revealed significant delamination of talc sheets on interaction with HWSS-coated Fe3O4 nanoparticles. The nano-composite displayed an efficient catalytic activity in the synthesis of new imidazo[1,2-c]quinazoline derivatives via Grobke-Blackburn-Bienaymé three-component reaction of 4-aminoquinazoline, arylaldehydes and isocyanide. The efficiency of the method was exemplified by synthesizing 7 new products in fairly high yields (68-83%) within short reaction times (24-30 min) using a catalytic amount of the catalyst under solvent-free condition at 120 °C. Clean and fast synthesis of the products and convenient separation of the robust nano-catalyst are the prominent advantages of the present method. The nano-catalyst was properly characterized.

Recyclable Magnetic Cu-MOF-74-Catalyzed C(sp2)-N Coupling and Cyclization under Microwave Irradiation: Synthesis of Imidazo[1,2-c]quinazolines and Their Analogues

Magnetic Cu-MOF-74 (Fe₃O₄@SiO₂@Cu-MOF-74) was synthesized for the first time by grafting MOF-74 (copper as the metal center) on the surface of core-shell magnetic carboxyl-functionalized silica gel (Fe₃O₄@SiO₂-COOH), which was prepared by coating core Fe₃O₄ nanoparticles with hydrolyzed 2-(3-(triethoxysilyl)propyl)succinic anhydride and tetraethyl orthosilicate. The structure of Fe₃O₄@SiO₂@Cu-MOF-74 nanoparticles was characterized by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). The prepared Fe₃O₄@SiO₂@Cu-MOF-74 nanoparticles could be applied as a recyclable catalyst to the synthesis of N-fused hybrid scaffolds. 2-(2-Bromoaryl)imidazoles and 2-(2-bromovinyl)imidazoles were coupled and cyclized with cyanamide in DMF in the presence of a catalytic amount of Fe₃O₄@SiO₂@Cu-MOF-74 along with a base to give imidazo[1,2-c]quinazolines and imidazo[1,2-c]pyrimidines, respectively, in good yields. The Fe₃O₄@SiO₂@Cu-MOF-74 catalyst could be easily recovered by a super magnetic bar and recycled more than four times while almost maintaining catalytic activity.

Design of Photosensitive Cobalt Complex Intermediates and Their Application in the Green Syntheses of Molecules Containing the Quinazolin-4(3H)-imine Scaffold

Cobalt/photoredox cooperative catalysis is a well-explored technology for visible-light photoredox catalysis. Recently, the photosensitivity of Co(II) complexes in homogeneous catalysis has aroused the interest of scientists. In this study, photosensitive Co(II) complex intermediates were designed to develop new synthetic methods. These intermediates, consisting of Co(II) and two substrate molecules, bind to O₂ and absorb visible light over a wide spectral range, triggering in situ oxidative decarboxylation to produce molecules containing the quinazolin-4(3H)-imine scaffold. These reactions employed glyoxylic acid and ketoacids as new building blocks, and good to excellent yields of the corresponding products were obtained under mild reaction conditions using green and inexpensive reagents and solvents. These results are of importance since the design of Co-based photosensitive intermediates will aid in establishing novel methods for harnessing visible light and hence lead to innovation in organic syntheses.

Cp*CoIII-catalyzed formal [4 + 2] cycloaddition of 2-phenyl-1H-imidazoles to afford imidazo[1,2-c]quinazoline derivatives

A synthetic protocol based on Cp*Co^III-catalyzed C-H amidation/annulation of 2-aryl-1H-imidazoles with 1,4,2-dioxazol-5-ones was developed to give imidazo[1,2-c]quinazoline derivatives with broad substrate scope in moderate to good yields. The method has good prospects of application in the synthesis of imidazo[1,2-c]quinazoline drugs.

Halogen hydrogen-bonded organic framework (XHOF) constructed by singlet open-shell diradical for efficient photoreduction of U(VI)

Synthesis of framework materials possessing specific spatial structures or containing functional ligands has attracted tremendous attention. Herein, a halogen hydrogen-bonded organic framework (XHOF) is fabricated by using Cl- ions as central connection nodes to connect organic ligands, 7,7,8,8-tetraaminoquinodimethane (TAQ), by forming a Cl-···H3 hydrogen bond structure. Unlike metallic node-linked MOFs, covalent bond-linked COFs, and intermolecular hydrogen bond-linked HOFs, XHOFs represent a different kind of crystalline framework. The electron-withdrawing effect of Cl- combined with the electron-rich property of the organic ligand TAQ strengthens the hydrogen bonds and endows XHOF-TAQ with high stability. Due to the production of excited electrons by TAQ under light irradiation, XHOF-TAQ can efficiently catalyze the reduction of soluble U(VI) to insoluble U(IV) with a capacity of 1708 mg-U g-1-material. This study fabricates a material for uranium immobilization for the sustainability of the environment and opens up a new direction for synthesizing crystalline framework materials.

Recent Advances in the Tandem Copper-Catalyzed Ullmann-Goldberg N-Arylation–Cyclization Strategies

N‒Aryl bond formation under copper catalysis has been playing a pivotal role and has been extensively used as a key step in the total syntheses of several therapeutic molecules. The...

Dual Role of Glyoxal in Metal-Free Dicarbonylation Reaction: Synthesis of Symmetrical and Unsymmetrical Dicarbonyl Imidazoheterocycles

A practical and efficient method has been developed for the dicarbonylation of imidazoheterocycles using glyoxals as dicarbonyl precursors under metal-free conditions in acetic acid. A series of symmetrical and unsymmetrical dicarbonyl imidazoheterocycles was synthesized in good yields. Aryl and alkyl glyoxals also demonstrated excellent reactivity under similar reaction conditions and delivered corresponding dicarbonyl imidazoheterocycles in high yields. It is believed that the glyoxal plays a dual role both as a dicarbonyl source and as an oxidant in this transformation. A probable mechanistic pathway has been proposed based on control experiments and electrospray ionization high-resolution mass spectrometry analysis.

A straightforward TBHP-mediated synthesis of 2-amidobenzoic acids from 2-arylindoles and their antimicrobial activity

Synthesis of 2-amidobenzoic acids has been achieved through TBHP-mediated oxidative ring opening of 2-arylindoles. The synthesized compounds have been evaluated for their antimicrobial activity.

Design and Synthesis of Imidazo/Benzimidazo[1,2-c]quinazoline Derivatives and Evaluation of Their Antimicrobial Activity

A new class of fused quinazolines has been designed and synthesized via copper-catalyzed Ullmann type C-N coupling followed by intramolecular cross-dehydrogenative coupling reaction in moderate to good yields. The synthesized compounds were tested for in vitro antibacterial activity against three Gram negative (Escherichia coli, Pseudomonas putida, and Salmonella typhi) and two Gram positive (Bacillus subtilis, and Staphylococcus aureus) bacteria. Among all tested compounds, 8ga, 8gc, and 8gd exhibited promising minimum inhibitory concentration (MIC) values (4-8 μg/mL) for all bacterial strains tested as compared to the positive control ciprofloxacin. The synthesized compounds were also evaluated for their in vitro antifungal activity against Aspergillus niger and Candida albicans and compounds 8ga, 8gc, and 8gd having potential antibacterial activity also showed pronounced antifungal activity (MIC values 8-16 μg/mL) against both strains. The bactericidal assay by propidium iodide and live-dead bacterial cell screening using a mixture of acridine orange/ethidium bromide (AO/Et·Br) showed considerable changes in the bacterial cell membrane, which might be the cause or consequence of cell death. Moreover, the hemolytic activity for most potent compounds (8ga, 8gc, and 8gd) showed their safety profile toward human blood cells.

One-Pot Tandem Amidation, Knoevenagel Condensation, and Palladium-Catalyzed Wacker Type Oxidation/C-O Coupling: Synthesis of Chromeno-Annulated Imidazopyridines

A direct one-pot synthesis of chromeno-annulated imidazo[1,2- a]pyridines is achieved by the reaction of 2-amino-1-(2-ethoxy-2-oxoethyl)pyridinium salts with 2-bromoarylaldehydes using Pd(TFA)₂ as a catalyst and Cu(OAc)₂ as an oxidant. The overall strategy involves tandem base-mediated amidation and Knoevenagel condensation, followed by palladium-catalyzed Wacker type oxidation and intramolecular C-O coupling reaction. The method is simple, tolerates different functional groups, and gives moderate to good yields of chromeno[2',3':4,5]imidazo[1,2- a]pyridin-12-one derivatives. The developed tandem reaction was also successfully applied for the synthesis of pyrano-fused imidazo[1,2- a]pyridines by using 3-bromo-3-arylacrylaldehydes.

Synthesis of N-Fused Benzimidazole-4,7-diones via Sequential Copper-Catalyzed C-N Coupling/Cyclization and Oxidation

2-(2-Bromovinyl)- and 2-(2-bromoaryl)-benzimidazoles, including their 4,7-dimethoxy analogs, react with primary amides by microwave irradiation (or usual heating) in dimethylformamide in the presence of a catalytic amount of CuI along with a base to give the corresponding benzo[4,5]imidazo[1,2-c]-pyrimidines and -quinazolines in good yields. Treatment of benzo[4,5]imidazo[1,2-c]-pyrimidines and -quinazolines having methoxy group on benzimidazole moiety with aqueous ceric ammonium nitrate affords unprecedented N-fused hybrid scaffolds, benzo[4,5]imidazo[1,2-c]-pyrimidin-6,9-diones and -quinazoline-8,11-diones, respectively, in high yields.

Synthesis of Benzo[4,5]imidazo[1,2-c]pyrimidin-1-amines and Their Analogs via Copper-Catalyzed C-N Coupling and Cyclization

2-(2-Bromovinyl)benzimidazoles and 2-(2-bromophenyl)benzimidazoles react with cyanamide by microwave irradiation in dimethylformamide in the presence of a catalytic amount of CuI along with a base to give the corresponding benzo[4,5]imidazo[1,2-c]pyrimidin-1-amines and benzo[4,5]imidazo[1,2-c]quinazolin-6-amines, respectively, in moderate to good yields. 2-(2-Bromophenyl)indoles also react with cyanamide under similar conditions to afford indolo[1,2-c]quinazolin-6-amines. The reaction pathway seems to proceed via a sequence such as intermolecular C-N coupling, C-N formative cyclization, and tautomerization.

One-pot strategy of copper-catalyzed synthesis of 1,2-disubstituted benzimidazoles

A simple, one-pot and copper-catalyzed coupling reaction for the construction of 1,2-disubstituted benzimidazole derivatives is described. A low-cost copper salt and a weak base, K₃PO₄, were utilized in this reaction. A variety of 1,2-disubstituted benzimidazoles were obtained in moderate to excellent yields.