Synthesis of novel tetra- and pentacyclic benzimidazole derivatives

Treatment of 7,12-dihydro[5,6][1,3]thiazepino[3,2-a]benzimidazole 6,6-dioxide (1) with NaH (1.2 equiv.) for 30 min in THF at room temperature under nitrogen atmosphere, followed by addition of alkyl propiolate (4 equiv.) gave tetracyclic benzimidazole derivatives (7). Subsequent reactions of 7 with Na in p-xylene at reflux, followed by addition of HOAc at room temperature gave pentacyclic benzimidazole derivative (8) in good to excellent yields.