An Efficient Copper‐Catalyzed Regioselective One‐Pot Synthesis of Pyrido[1,2‐a]benzimidazole and Its Derivatives

Abstract

A facile and effectual regioselective one‐pot synthesis protocol has been developed for the construction of pyrido[1,2‐a]benzimidazole and its derivatives using Copper(I) bromide as the catalyst, 1,10‐phenanthroline as ligand, and K3PO4 (Tripotassium phosphate) as the base in Dimethyl sulfoxide as solvent at 110 °C for 12 h. The reaction conditions were optimized by screening various copper catalysts, ligands, solvents, and bases. The substrate scope of the reaction was also carried out with electron‐withdrawing and donating functional groups to prepare novel functionalized regioselective benzimidazole compounds in good to excellent yields. All the isolated compounds were characterized by 1H, 13C, and 19F NMR.

Three Polyoxometalate-Based Ag–Organic Compounds as Heterogeneous Catalysts for the Synthesis of Benzimidazoles

“…Polyoxometalates (POMs), as an excellent inorganic functional material with unique diversity structures and physical–chemical properties, exhibited outstanding performance in catalysis. − Regrettably, bulk POMs with high solubility in polar media make it difficult to recover and recycle the catalysts, which limits their applications as heterogeneous catalysts. − Notably, due to their oxygen-rich surface, high anionic charge, and diverse size, POMs can serve as inorganic building subunits to assemble with organic ligands and metal cations to achieve controlled assembly of POM-based compounds with fascinating structures and special properties. − This provides an effective approach for the development of heterogeneous catalysts based on POMs. Benefiting from their facile preparation and relative stability, the well-known Keggin-type POMs, [PMo 12 O 40 ] 3– /[PW 12 O 40 ] 3– , have been extensively used as building subunits for the assembly of various POM-based compounds. − On the other hand, as a d 10 metal cation, Ag + is easy to coordinate with N and O and has a variety of coordination modes, making it a good metal connector to construct POM-based compounds. − For example, Wang’s group synthesized three POM-based metal–organic complexes using H 3 PMo 12 O 40 (K 6 P 2 W 18 O 62 ·15H 2 O), Ag + , and bis­(pyridyl-tetrazole) ligands and studied their fluorescence properties, electrochemical behaviors, and photocatalytic activities .…”