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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Alkaline ion-solvating membranes derived from a tetrazole functionalized poly(arylene alkylene) are prepared, characterized and evaluated as electrode separators in alkaline water electrolysis. The base polymer, poly[[1,1'-biphenyl]-4,4'-diyl(1,1,1-trifluoropropan-2-yl)], is synthesized by superacid catalyzed polyhydroxyalkylation and subsequently functionalized with tetrazole pendants. After equilibration in aqueous KOH, the relatively acidic tetrazole pendants are deprotonated to form the corresponding potassium tetrazolides. The room temperature ion conductivity is found to peak at 19 mS cm -1 in 5 wt. % KOH, and slightly declines with increasing KOH concentration to 13 mS cm -1 in 30 wt. % KOH. Based on an overall assessment of the mechanical properties, conductivity and electrode activity, 30 wt. % KOH is applied for alkaline electrolysis cell tests. Current densities of up to 1000 mA cm -2 were reached with uncatalyzed Ni-foam electrodes at a cell voltage of less than 2.6 V, with improved gas barrier characteristics compared to that of the several times thicker Zirfon separator., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

We synthesized some of the longest unimolecular oligo( p -phenylene ethynylenes) (OPEs), which are fully substituted with electron-withdrawing ester groups. An iterative convergent/divergent (a.k.a. iterative exponential growth - IEG) strategy based on Sonogashira couplings was utilized to access these sequence-defined macromolecules with up to 16 repeating units and 32 ester substituents. The carbonyl groups of the ester substituents interact with the triple bonds of the OPEs, leading to (i) unusual, angled triple bonds with increased rotational barrier, (ii) enhanced conformational disorder, and (iii) associated broadening of the UV/Vis absorption spectrum. Our results demonstrate that fully air-stable, unimolecular OPEs with ester groups can readily be accessed with IEG chemistry, providing new macromolecular backbones with unique geometrical, conformational, and photophysical properties.

Crystal-packing forces can have a significant impact on the relative stabilities of different molecules and their conformations. The magnitude of such effects is, however, not yet well understood. Herein we show, that crystal packing can completely overrule the relative stabilities of different stereoisomers in solution. Heating of atropoisomers (i.e. "frozen-out" conformational isomers) in solution leads to complex mixtures. In contrast, solid-state heating selectively amplifies minor (<25 mole %) components of these solution-phase mixtures. We show that this heating strategy is successful for compounds with up to four rotationally hindered σ bonds, for which a single stereoisomer out of seven can be amplified selectively. Our results demonstrate that common supramolecular interactions-for example, [methyl⋅⋅⋅π] coordination and [C-H⋅⋅⋅O] hydrogen bonding-can readily invert the relative thermodynamic stabilities of different molecular conformations. These findings open up potential new avenues to control the folding of macromolecules., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)