Enantioselective electrophilic aromatic nitration methodology is needed to advance chirality-assisted synthesis (CAS). Reported here is an enantioselective aromatic nitration strategy operating with chiral diester auxiliaries,and it provides an enantioselective synthesis of aC 3v -symmetric tribenzotriquinacene (TBTQ). These axially-chiral structures are much sought-after building blocks for CAS, but they were not accessible prior to this work in enantioenriched form without resolution of enantiomers.T his nitration strategy controls the stereochemistry of threefold nitration reactions from above the aromatic rings with chiral diester arms.Dicarbonyl-to-arenium chelation rigidifies the reaction systems,s ot hat remote stereocenters position the ester-directing groups selectively over specific atoms of the TBTQ framework. Closely guided by computational design, am ore selective through-space directing arm was first predicted with density functional theory (DFT), and then confirmed in the laboratory,t o outperform the initial structural design. This enantio-and regioselective TBTQ synthesis opens anew pathwaytoaccess building blocks for CAS.Classical electrophilic aromatic nitration reactions are among the best known and most frequently employed aromatic transformations. [1] They readily proceed [2] with unactivated aromatic substrates and provide exquisite control over the number of NO 2 groups introduced, unlike for instance most Friedel-Crafts alkylations and aromatic brominations. [1b-d, 3] Nevertheless,r esolution-free,e nantioselective electrophilic aromatic nitration processes (even with chiral auxiliaries) have yet to be reported. While enantioselective Friedel-Crafts-type reactions [4] and enantioselective aromatic brominations [5] have been studied extensively,o nly the enantioselective nitration of crotylsilanes, [6] but not of aromatic substrates,h as been described.To advance the growing field of chirality-assisted synthesis [7] (CAS), we now describe an enantioselective nitration strategy which makes use of chiral diester auxiliaries with remote stereocenters to induce axial chirality upon trifold nitration. We employ our chiral auxiliaries to achieve the first enantioselective synthesis of a C 3v -symmetric tribenzotriqui-nacene (TBTQ) [8] derivative,w hich is not based on either ak inetic, [9] crystallization-based, [10] or chromatographic [11] resolution. Directing arms with remote stereocenters are positioned at equal distances from the favored and disfavored sites of reactivity to provide for an enantioselective nitration methodology after removal (Figure 1b)ofthe through-space directing groups.T he success of our strategy stems from 1) chelation (Figure 1b)o ft wo ester carbonyl groups to the cationic Wheland intermediates positioned underneath these diester directing arms as well as 2) A 1, 3 strain (Figure 3b), which can be controlled by the size of the alkyl substituents attached to the remote chirality centers of the through-space directing groups.T his combination of A 1,3 strain with ...

Enantioselective electrophilic aromatic nitration methodology is needed to advance chirality‐assisted synthesis (CAS). Reported here is an enantioselective aromatic nitration strategy operating with chiral diester auxiliaries, and it provides an enantioselective synthesis of a C3v‐symmetric tribenzotriquinacene (TBTQ). These axially‐chiral structures are much sought‐after building blocks for CAS, but they were not accessible prior to this work in enantioenriched form without resolution of enantiomers. This nitration strategy controls the stereochemistry of threefold nitration reactions from above the aromatic rings with chiral diester arms. Dicarbonyl‐to‐arenium chelation rigidifies the reaction systems, so that remote stereocenters position the ester‐directing groups selectively over specific atoms of the TBTQ framework. Closely guided by computational design, a more selective through‐space directing arm was first predicted with density functional theory (DFT), and then confirmed in the laboratory, to outperform the initial structural design. This enantio‐ and regioselective TBTQ synthesis opens a new pathway to access building blocks for CAS.

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This work presents the first transition metal-free synthesis of oxygen-linked aromatic polymers by integrating iterative exponential polymer growth (IEG) with nucleophilic aromatic substitution (SNAr) reactions. Our approach applies methyl sulfones as the leaving groups, which eliminate the need for a transition metal catalyst, while also providing flexibility in functionality and configuration of the building blocks used. As indicated by 1) 1H-1H NOESY NMR spectroscopy, 2) single-crystal X-ray crystallography, and 3) density functional theory (DFT) calculations, the unimolecular polymers obtained are folded by nonclassical hydrogen bonds formed between the oxygens of the electron-rich aromatic rings and the positively polarized C–H bonds of the electron-poor pyrimidine functions. Our results not only introduce a transition metal-free synthetic methodology to access precision polymers but also demonstrate how interactions between relatively small, neutral aromatic units in the polymers can be utilized as new supramolecular interaction pairs to control the folding of precision macromolecules.

Molekulare Kranausleger liefern in stereoselektiver Weise Nitroniumionen zu spezifischen Stellen in konkaven polyaromatischen Systemen. S. T. Schneebeli und Mitarbeiter beschreiben in ihrer Zuschrift auf S. 1047, wie die ersten enantioselektiven Nitrierungsreaktionen mithilfe solcher Kranausleger erreicht wurden. Die Ergebnisse stellen einen Durchbruch dar, da sie es ermöglichen, eine der ältesten Reaktionen nun in enantioselektiver Weise durchzuführen.