Highly efficient microwave-assisted one-pot synthetic pathways for pyrido2,3-dimidazole derivatives

Herein, we report an efficient microwave-assisted Ni-catalyzed one-pot method for synthesizing functionalized pyrido2,3-dimidazoles, showing broad applicability across various functional groups, including alkyl, alkoxy, hydroxy, halogen, acyl, and amino substituents. This approach enables nucleophilic substitution, nitro group reduction, and imidazole ring formation in a short reaction time, without intermediate isolation, thus saving materials, time, and effort. The desired products were obtained mostly in very good yields, keeping in mind that these were the total yields of 3-step reactions. For challenging nitrille- and thio-functionalized substrates, a Zn-accompanied three-stage pathway is proposed. The protocols‘ versatility is demonstrated with 32 pyridoimidazoles synthesized and confirmed with NMR and HRMS techniques. Many XRD structures of nitro-derived intermediates and the target products are presented, proving the chemical structures of the compounds obtained, and providing insight into their crystal structure. To show practical potential, a scaled-up protocol with reduced reagent and catalyst loadings is also reported. The synthesized compounds have a wide range of potential applications, particularly as precursors for NHC carbene ligands for iridium-based phosphorescent deep blue emitters, suitable for OLED technology. Apart from that, bromine-functionalized compounds, successfully synthesized due to the selectivity of the Ni-based catalytic system, appear to be promising building blocks for further transformations.