Synthesis of 2-Aminoquinazoline- and 2-Aminopyrimidine-Fused Hybrid Scaffolds by Copper-Catalyzed C(sp 2 )-N Coupling and Cyclization Followed by Oxidation

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.

Synthesis of Imidazo[1,2-f]phenanthridines by Recyclable Magnetic MOF-Catalyzed Coupling and Cyclization of 2-(2-Bromoaryl)imidazoles with Cyclohexane-1,3-diones Followed by Aromatization

2-(2-Bromoaryl)imidazoles react with cyclohexane-1,3-diones in the presence of a catalytic amount of recyclable Fe₃O₄@SiO₂@MOF-199 and a base to give the corresponding C-C coupled and cyclized products 6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-ones in high yields. The magnetic MOF catalyst could be easily recovered and reused four times without any significant loss of catalytic activity. The coupled and cyclized scaffolds were aromatized to imidazo[1,2-f]phenanthridines in high yields by a one-pot sequential procedure including reduction, dehydration, and oxidation. The present protocol could be applied to the synthesis of Zephycandidine A, which is known to exhibit anti-tumor activity.

Microwave-assisted green construction of imidazole-fused hybrid scaffolds using 2-aminobenzimidazoles as building blocks

A class of trinuclear imidazole-fused hybrid scaffolds was constructed by the reaction of 2-(2-bromoaryl)- and 2-(2-bromovinyl)imidazoles with 2-aminobenzimidazoles as building blocks in the presence of a base under microwave irradiation. A nucleophilic aromatic substitution followed by cyclization is proposed as a reaction pathway of this green process.

A green synthesis of trinuclear imidazole-fused hybrid scaffolds has been developed by transition metal-free double C(sp²)–N coupling and cyclization of 2-(2-bromoaryl)- and 2-(2-bromovinyl)imidazoles with 2-aminobenzimidazoles as building blocks under microwave irradiation.

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.

Copper-Catalyzed Lactamization of (E)-2-(2-Bromophenyl)-3-arylacrylamides for the Synthesis of (E)-3-Arylideneindolin-2-ones

A copper-catalyzed, ligand-free intramolecular C-N coupling of (E)-2-(2-bromophenyl)-3-arylacrylamides has been developed. This protocol provides an efficient and practical synthetic route for the biologically important (E)-3-arylideneindolin-2-ones from o-bromophenylacetic acids and aromatic or conjugated alkenyl aldehydes. Readily available starting materials, mild and noble metal-free conditions, high efficiency, and good tolerability for phenolic hydroxyl groups make this approach attractive and applicable.

Construction of Binuclear Benzimidazole-Fused Quinazolinones and Pyrimidinones Using Aryl Isocyanates as Building Blocks by Transition-Metal-Free C(sp2)-N Coupling

A class of binuclear N-fused hybrid scaffolds was constructed by the reaction of 2-(2-bromoaryl)- and 2-(2-bromovinyl)benzimidazoles with aryl isocyanates as building blocks in the presence of a base under microwave irradiation. A nucleophilic addition followed by an unprecedented transition-metal-free C(sp²)-N coupling is proposed as a reaction pathway of this green process.