Synthesis of benzo[4,5]imidazo[1,2-a]indolo[1,2-c]quinazolines from 2-(2-bromoaryl)indoles and 2-methoxybenzimidazoles under recyclable magnetic MOF-199 catalysis

2-(2-Bromoaryl)indoles react with 2-methoxybenzimidazoles in DMF in the presence of a catalytic amount of recyclable Fe₃O₄@SiO₂@MOF-199 along with K₂CO₃ to afford a series of benzo[4,5]imidazo[1,2-a]indolo[1,2-c]quinazolines in good yields. The reaction applies to a broad scope of 2-(2-bromoaryl)indoles containing electron-donating or -withdrawing substituents on bromophenyl and indole moieties, and alkyl substituents at 3-position of indole moiety. A reaction pathway involving a copper-catalyzed Ullmann-type C (sp²)-N coupling and an addition-elimination nucleophilic aromatic substitution via Meisenheimer complex followed by cyclocondensation is proposed for this catalytic process. The Fe₃O₄@SiO₂@MOF-199 catalyst could be recovered and reused several times without any change of catalytic activity.