Synthesis of Imidazo[1,2-f]phenanthridines by Recyclable Magnetic MOF-Catalyzed Coupling and Cyclization of 2-(2-Bromoaryl)imidazoles with Cyclohexane-1,3-diones Followed by Aromatization.

Abstract

2-(2-Bromoaryl)imidazoles react with cyclohexane-1,3-diones in the presence of a catalytic amount of recyclable Fe3O4@SiO2@MOF-199 and a base to give the corresponding C–C coupled and cyclized products 6,7-dihydroimidazo[1,2-f]phenanthridin-8(5H)-ones in high yields. The magnetic MOF catalyst could be easily recovered and reused four times without any significant loss of catalytic activity. The coupled and cyclized scaffolds were aromatized to imidazo[1,2-f]phenanthridines in high yields by a one-pot sequential procedure including reduction, dehydration, and oxidation. The present protocol could be applied to the synthesis of Zephycandidine A, which is known to exhibit anti-tumor activity.