Synthesis and Some Reactions of 2-(2-Aminoanilino)cyclohepta[b]pyrroles: Leading to 5H-Cyclohepta[1′,2′: 4,5]pyrrolo[2,3-b][1,5]benzodiazepine, a Novel 20π Antiaromatic System, and Cydohepta[1′,2′: 4,5] pyrrolo[1,2-a]benzimidazoles

Abstract 2-Chlorocyclohepta[b]pyrroles reacted with o-phenylenediamine to give 2-(2-aminoanilino)cyclohepta[b]pyrroles (2a,b) in good yields. Treatment of 2a and 2b with polyphosphoric acid afforded cyclohepta[1′,2′: 4,5]pyrrolo[1,2-a]benzimidazole (4a) in good yields. Treatment of 2b with acids gave 6-(ethoxycarbonyl) derivatives (4b) of 4a and 12H-5,13-dihydrocyclohepta[1′,2′: 4,5]pyrrolo[2,3-b][1,5]benzodiazepin-12-one (5). Compound 5 was methylated with methyl iodide in the presence of DBU to give 5H-12-methoxycyclohepta[1′,2′: 4,5]pyrrolo[2,3-b][1,5]benzodiazepine, a novel 20π antiaromatic system. Treatment of 2b with sodium ethoxide gave 4b and 2H-1-(cyclohepta[b]pyrrol-2-yl)-1,3-dihydrobenzimidazol-2-one (7a). Compound 5 rearranged to 7a in the refluxing sodium ethoxide-ethanol solution. Reactions of 2a and 2b with triethyl orthoformate gave corresponding 1-(cyclohepta[b]pyrrol-2-yl)benzimidazoles. Reactions of 2a and 2b with acetic anhydride are also mentioned.