Condensed heterotricycles: novel transformation of dibenz[b,e][I,4]diazepinones to benzimidazole derivatives under Vilsmeier-Haack reaction conditions

Abstract

Condensation of methyl 2-chloro-5-nitrobenzoate with o-phenylenediamine in DMSO in the presence of triethylamine affords 2-nitrodibenz[b,e][l,4]diazepin-ll(10H)-one (I) in 37% yield. Reaction of I with DMF-POCl₃ leads to its novel transformation to l-(2-dimethylcarbamoyl-4-nitrophenyl)benzimidazole (IV) in high yield. Dibenz[b,e][l,4]diazepin-ll(10H)-one (II) and its 8-chloro derivative (III) afford analogous products VI and VII respectively. The structure of IV is proved by acid hydrolysis to l-(2-carboxy-4-nitrophenyl)benzimidazole (VIII), identical with a sample synthesized from benzimidazole and 2-chloro-5-nitrobenzoic acid. N-Formyl-morpholine and I undergo reaction in the presence of POCI₃ to give the morpholide analogue V of IV. 2-Nitro-5-acetyldibenz[b,e][l,4]diazepin-ll(10H)-one (XII) is formed in the reaction of I with dimethylacetamide-POCl₃. XII is reduced to the amine XIII, which upon diazotization and treatment with hypophosphorus acid yields known 5-acetyldibenz[b,c][l,4]diazepin-ll(I0H)-one (XIV). The present study constitutes the first example of ring contraction among dibenz[6,e]-diazepine derivative.