Novel Synthetic Investigation in the Field of Indolo[2,3-B]quinoxaline Ring Containing Tetracyclic and Pentacyclic Heterocycles

A series of seven new indolo[2,3-b]quinoxaline ring containing compounds were efficiently synthesized in three different pathways. In the first case, the relevant pentacyclic systems (3,4) were received by the condensation reaction between 7-acetyl-1,5,6,7-tetrahydropyrrolo[3,2-f]indole-2,3-dione and o-phenylenediamine in glacial acetic acid. In the second case, tetracyclic indolo[2,3-b]qui-no¬xa¬li¬ne derivatives (7, 8a-d) were synthesised by a one-pot approach using Pd-catalyzed Sonogashira-hagihara C-C cross-coupling reaction between various terminal acetylenes and 9-iodo-6H-indo¬lo¬[2,3-b]quinoxaline in presence of various Pd catalysts. The third pathway is based on the Cu-catalyzed modified Ullmann protocol. The appropriate indolo-quinoxaline derivative (9) was successfully syn¬the¬sized by arylamination, using benzylamine (as a nucleophile) and 6-benzyl-9-iodo-6H-indolo[2,3-b]qui¬no¬xaline as an aryl halide. The reaction was performed in DMF in the presence of CuI.