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.
One-Pot MCR-Oxidation Approach toward Indole-Fused Heteroacenes
P. V. Santhini, Akhil Krishnan R., Sheba Ann Babu, Betna Shamlin Simethy, Gourab Das, Vakayil K. Praveen, Sunil Varughese, and Jubi John*
J. Org. Chem. 2017, 82, 10537–10548.
Full Text Link: http://dx.doi.org/10.1021/acs.joc.7b02039