Syntheses and Structures of Indolo[6,7-g]indoles, a New Heteroaromatic System

Photolysis of 1,1′-(1,8-naphthylene)-bis(1H-1,2,3-triazole)s (1) in methanol has given new heteroaromatic system compounds, indolo[6,7-g]indoles (2). The spectral properties of these compounds were studied in comparison with those of the corresponding benz[g]indoles (4) obtained from the similar photolysis of 1-(1-naphthyl)-1H-1,2,3-triazoles (3). The 1H NMR and IR spectra of 2 and 4 suggest the existence of a strong intramolecular hydrogen bonding in 2. The X-ray crystallographic analysis of tetraethyl 1H, 10H-indolo[6,7-g]indole-2,3,8,9-tetracarboxy late, 2a, indicates that the molecule has almost twofold rotational symmetry, and the framework is distorted due to the steric overcrowding.