New Synthesis of peri-Fused Tetrahydro[1,3]diazepino[1,2-a]benzimidazoles from 1-Aroylmethyl-2-[(4-hydroxybutyl)amino]benzimidazoles

Abstract

Treatment of 2-[(4-hydroxybutyl)amino]-1H-benzimidazole with ω-bromoacetophenones gave 1-aroylmethyl-substituted derivatives which underwent cyclization to 2-aryl-1-(4-bromobutyl)imidazo[1,2-a]benzimidazole hydrobromides on heating in concentrated hydrobromic acid when Ar = Ph, 4-ClC6H4, 4-BrC6H4, and 4-O2NC6H4. The corresponding bases were readily converted into peri-fused tetrahydro[1,3]diazepino[1,2-a]benzimidazoles via intramolecular alkylation with closure of seven-membered ring. If an electron-donating methoxy group was present in the aryl fragment of the initial ketone, 1-(4-hydroxyphenyl)-2-[2-(pyrrolidin-1-yl)-1H-benzimidazol-1-yl]ethan-1-one was formed in the reaction with HBr.