Recyclable Magnetic MOF-Catalyzed Synthesis of 1-Aminoisoquinolines and 6-Aminophenanthridines from 5-(2-Bromoaryl)tetrazoles and 1,3-Diketones under Microwave Irradiation

In this study, 5-(2-bromoaryl)tetrazoles were reacted with 1,3-diketones in DMF in the presence of a catalytic amount of magnetic Cu-MOF-74 (Fe₃O₄@SiO₂@Cu-MOF-74) and a base under microwave irradiation to yield the corresponding 1-aminoisoquinolines. The Fe₃O₄@SiO₂@Cu-MOF-74 catalyst could be easily recovered from the reaction mixture and reused four times without any significant loss of catalytic activity. An initial copper-catalyzed C(sp²)-C(sp³) bond formation accompanied by <i>retro</i>-Claisen deacylative cyclocondensation (for acyclic 1,3-diketones) and direct cyclocondensation (for cyclohexane-1,3-diones) is proposed as a key reaction pathway for this process. Cyclohexanone-fused 1-aminoisoquinolines produced from the reaction between 5-(2-bromoaryl)tetrazoles and cyclohexane-1,3-diones could be aromatized into 6-aminophenanthridines via a one-pot sequential process involving reduction, dehydration, and oxidation.