Magnetic MOF-199-Catalyzed Synthesis of Benzo[4,5]imidazo[1,2-f]phenanthridines and Their Analogues by Tandem C(sp²)−C Coupling and Cyclization Followed by Aromatization

Treatment of 2-(2-bromoaryl)- and 2-(2-bromovinyl)benzimidazoles with cyclohexane-1,3-diones in DMF in the presence of reusable Fe₃O₄@SiO₂@MOF-199 along with L-proline and Cs₂CO₃ afforded 2,3-dihydrobenzo[4,5]imidazo[1,2-f]phenanthridin-4(1H)-ones and 2,3-dihydrobenzo[4,5]imidazo[1,2-a]quinolin-4(1H)-ones, respectively, in moderate to good yields. Such C(sp²)−C coupled and cyclized scaffolds were aromatized to benzo[4,5]imidazo[1,2-f]phenanthridines and benzo[4,5]imidazo[1,2-a]quinolines in good yields by a one-pot sequential treatment with NaBH₄, POCl₃/pyridine, and DDQ.