Heteroannulation of 3‑Nitroindoles and 3‑Nitrobenzo[<i>b</i>]thiophenes: A Multicomponent Approach toward Pyrrole-Fused Heterocycles

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-<i>b</i>]­indoles. The methodology was efficaciously utilized for the “pyrroloindoliztion” of natural products, the pyrrolization of 3-nitrobenzo­[<i>b</i>]­thiophene, and the gram-scale synthesis of pyrroloindole. Furthermore, a “one-pot” approach for accessing indolo­[3,2-<i>b</i>]­indoles was realized

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 <i>N</i>-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-<i>b</i>]­indoles in good yields. The strategy was also utilized for accessing 5-ring fused benzo­[g]­indolo­[3,2-<i>b</i>]­indole. We could extend the methodology for the synthesis of benzothieno­[3,2-<i>b</i>]­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-<i>b</i>]­indoles. In addition, the change in photophysical properties with extension of conjugation of the synthesized heteroacenes was studied