A simple, efficient, and general multicomponent reaction involving an enolizable ketone, a primary amine, and an N-protected 3-nitroindole was developed for the synthesis of a range of functionalized pyrrolo[3,2-b]indoles. The methodology was efficaciously utilized for the "pyrroloindoliztion" of natural products, the pyrrolization of 3-nitrobenzo[b]thiophene, and the gram-scale synthesis of pyrroloindole. Furthermore, a "one-pot" approach for accessing indolo[3,2-b]indoles was realized.

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.

We have developed a metal-free, mild, and green synthetic route toward benzothieno­[3,2-b]­benzofurans by the annulation of 3-nitrobenzothiophene with phenols. The reaction was found to be general with a range of substituted phenols. In addition, we could extend the methodology for the synthesis of pentacenes and could demonstrate the synthesis in gram-scale. Moreover, we extended the strategy for the synthesis of benzothieno­[2,3-b]­benzofurans by starting from 2-nitrobenzothiophenes.