One-Pot MCR-Oxidation Approach toward Indole-Fused Heteroacenes

A straightforward synthetic route toward indole-fused heteroacenes was developed. The strategy is composed of a one-pot process starting with a multicomponent reaction of cyclohexanone, primary amine and N-tosyl-3-nitroindole followed by an oxidation step. The one-pot approach was found to be general, affording both symmetric and nonsymmetric indolo­[3,2-b]­indoles in good yields. The strategy was also utilized for accessing 5-ring fused benzo­[g]­indolo­[3,2-b]­indole. We could extend the methodology for the synthesis of benzothieno­[3,2-b]­indoles starting from 3-nitrobenzothiophene. The importance of the developed method was exemplified by performing the reaction sequence on gram scale and also by the synthetic transformations of indolo­[3,2-b]­indoles. In addition, the change in photophysical properties with extension of conjugation of the synthesized heteroacenes was studied.