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

Abstract

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.

Indolo[3,2-b]indole donor-based D–π–A dyes for DSCs: investigating the role of π-spacers towards recombination

“…38,[42][43][44][45][46][47][48] Very recently, we introduced a facile route involving a sequential MCR-oxidation approach to the synthesis of these fused indole heteroacenes. 49,50 The present methodology involves an initial MCR of an enolizable ketone (cyclohexanone), a 11 amine, and N-tosyl-3-nitroindole furnishing the intermediate pyrrolo [3,2-b]indole, which on further oxidation with chloranil affords indolo [3,2-b]indole moieties in good yields. The advantage of our method as compared existing methods was clearly demonstrated by the generation of symmetrical and unsymmetrical indolo[3,2-b]indoles, which are highly relevant for material applications.…”

“…The advantage of our method as compared existing methods was clearly demonstrated by the generation of symmetrical and unsymmetrical indolo[3,2-b]indoles, which are highly relevant for material applications. 49,50 The strategically synthesized indolo [3,2-b]indole dyes (IID series) were found to offer many promising features, considering the functionalities that are required for a stable and efficient DSC dye, which include (1) extended p-conjugation that enhances the intermolecular interaction; (2) a symmetric conjugated structure leading to a more rigid backbone; (3) properly placed alkyl groups for increased solubility, to prevent the approach of triiodide in getting closer to TiO 2 and also to prevent aggregation. These interesting skeletal characteristics make indolo [3,2-b]indole a potential building block for use in DSC.…”

Diastereoselective Total Synthesis of (+)-Raputindole A: An Iridium- Catalyzed Cyclization Approach

“…The use of KOH and CTAB in THF-H2O under transfer phase catalysis made the deprotection possible, but an inseparable mixture of raputindole A (1) and its monotosyl derivative was obtained. [26][27][28][29][30] Inspection of the 1 H-NMR spectrum of the crude mixture, revealed the formation of a multiplet at d 6.5-6.53 ppm which correlates with the one observed in 6-iodo-indole 9 and is suggestive of the southern indole moiety. This conclusion was also corroborated by NOESY analysis of the crude mixture.…”

Pd(0)‐guanidine@MCM‐41: a very effective catalyst for rapid production of bis (pyrazolyl)methanes

“…In this technique, more than two starting materials react together in a one‐pot reaction to form a product wherein all or most of the reactants atoms contribute . That is important from the atom economic standpoint . Environmental friendly operation via reducing the number of synthetic steps and work up, the energy consumption, reaction time, waste production, and eliminating the isolation of unstable intermediates are among the advantages of MCRs .…”