Entropy‐Induced Selectivity Switch in Gold Catalysis: Fast Access to Indolo[1,2‐a]quinolines

Abstract

New N-heterocyclic compounds for organic functional materials and their efficient syntheses are highly demanded. A surprising entropy-induced selectivity switch in the gold-catalyzed intramolecular hydroarylation of 2-ethynyl N-aryl indoles was found and its exploitation led to straightforward syntheses of indolo[1,2-a]quinolines. Experimental and computational mechanistic investigations gave insight into this uncommon selectivity phenomenon and into the special reactivity of the indolo[1,2-a]quinolines. The high functional group tolerance of this methodology enabled access to a diverse scope with high yields. In addition, bidirectional approaches, post-functionalization reactions, and π-extension of the core structure were feasible. An indepth study of the photophysical properties explored the structure-effect relationship for different derivatives and revealed a high potential of these compounds for future applications as functional materials.

Gold‐Catalyzed Bidirectional Access to Planar Heptacyclic Benzobispyrido[1,2‐a]indoles and Benzobispyrrolo[1,2‐a]Quinolines for Materials Science

“…This provides an explanation for the high instability against oxygen for BBPQ‐1 , where the combination of a high lying HOMO and a non‐blocked pyrrole carbon results in a high reactivity of this position towards oxygen leading to decomposition. This aspect correlates with observations in our preceding work, where related molecules show a similar reactivity on the unprotected pyrrole carbon, when the HOMO is relatively high in comparison to more stable molecules [5] . Although BBPI‐1 has an unprotected pyrrole carbon similar to BBPQ‐1 , the HOMO energy is calculated to be 0.36 eV lower.…”

“…In this work we exclusively used CD 2 Cl 2 in order to prevent overlapping of the product signals with the residual signal of undeuterated solvent. In preceding work [5] we demonstrated that the related monodirectionally prepared compounds tend to be protonated very easily when using non‐purified CDCl 3 which contains traces of acid; a small shift in some 1 H NMR signals could be observed, which was not the case when using CDCl 3 filtered through aluminum oxide.…”

“…Recently, we developed an efficient and versatile method to access indolo[1,2‐ a ]quinolines with high functional group tolerance enabled by the gold‐catalyzed hydroarylation of alkynylindoles (Scheme 1a) [5,6] . In this work, we already presented the synthesis of symmetric dimers linked via the C5 or C7 carbon.…”

Versatile access to nitrogen-rich π-extended indolocarbazolesviaa Pictet–Spengler approach

“…Until recently, appropriate starting materials necessary for the bidirectional PSR were difficult or impossible to synthesize. Fortunately, we lately developed a versatile gold-catalyzed [51][52][53][54][55][56][57][58][59] method for the building of benzodipyrroles and therein showed the example of bis(2-aminophenyl)-substituted benzodipyrrole 1 (Scheme 2). 60 This substrate is accessible starting from 1,4-diiodo-2,5-dimethoxybenzene in a straightforward four step synthesis and should be suitable for the synthesis of BBPQs via the PSR.…”

Cascade Oxidative Trifluoromethylthiolation and Cyclization of 3-Alkyl-1-(2-(alkynyl)phenyl)indoles

“…In particular, 6-alkyl-12-formyl-5,6-dihydroindolo­[2,1- a ]­isoquinolines, the 3-formylindole derivatives, were also shown to possess inhibitory activity toward human mammary carcinoma cells (Figure b) . In addition, indolo­[1,2- a ]­quinolines bearing combined scaffolds of indoles and quinolines were demonstrated to exhibit applications in organic materials such as organic semiconductors and solar cell photosensitizers (Figure c). − Though having been reported, synthetic approaches to construct indolo­[1,2- a ]­quinolines are rather limited . A Pd-catalyzed annulation of strained alkenes followed by a retro-Diels–Alder reaction was developed by Lautens and co-workers to prepare the indolo­[1,2- a ]­quinoline framework (Scheme a).…”