An efficient synthesis of benzo[b]benzofurano[2,3-e]-[1,6]naphthyridine-8-ones

An efficient method for the synthesis of benzob]benzofurano2,3-e]1,6]naphthyridine-8-one derivatives has been developed via Pictet-Spengler reaction of 4-(3-aminobenzofuran-2-yl)quinoline- 2-ones, which could be obtained from alkylation of 4-bromomethylquinoline-2-ones with salicylonitrile and subsequent Thorpe-Ziegler isomerization, with aromatic aldehydes under p-TsOH as catalyst in good yields.