The oxidative aromatization of Hantzsch 1,4-dihydropyridines by molecular oxygen using surface functionalized silica supported cobalt catalysts

Cobalt complexes were covalently anchored onto the surface of silica by the complexation of organically modified silicas with Co(OAc)2 and CoCl2 and investigated for the oxidative aromatization of Hantzsch 1,4-dihydropyridines using molecular oxygen. The catalyst obtained by the complexation of Co(OAc)2 with organically modified 3-aminopropyl silica (Cat 1) was found to be most effective and stable under the reaction conditions. It can be easily recovered and recycled. The work-up procedure is simple and the corresponding pyridines were obtained in good to excellent yields.

Graphical abstractThe oxidative aromatization of Hantzsch 1,4-dihydropyridines to the corresponding pyridines with molecular oxygen as oxidant is catalyzed by covalently anchored cobalt complexes onto the surface of silica gel. Cat 1 was found to be the most effective and stable under the reaction conditions. It can be easily recovered and recycled. Figure optionsDownload full-size imageDownload as PowerPoint slide