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1. Detection of interstellar 1-cyanopyrene: A four-ring polycyclic aromatic hydrocarbon

   https://doi.org/10.1126/science.adq6391  

   Wenzel, Gabi; Cooke, Ilsa R; Changala, P Bryan; Bergin, Edwin A; Zhang, Shuo; Burkhardt, Andrew M; Byrne, Alex N; Charnley, Steven B; Cordiner, Martin A; Duffy, Miya; et al (November 2024, Science)

   Polycyclic aromatic hydrocarbons (PAHs) are organic molecules containing adjacent aromatic rings. Infrared emission bands show that PAHs are abundant in space, but only a few specific PAHs have been detected in the interstellar medium. We detected 1-cyanopyrene, a cyano-substituted derivative of the related four-ring PAH pyrene, in radio observations of the dense cloud TMC-1, using the Green Bank Telescope. The measured column density of 1-cyanopyrene is $\sim \text{1}{\text{.52×10}}^{\text{12}}$cm⁻², from which we estimate that pyrene contains up to 0.1% of the carbon in TMC-1. This abundance indicates that interstellar PAH chemistry favors the production of pyrene. We suggest that some of the carbon supplied to young planetary systems is carried by PAHs that originate in cold molecular clouds. 

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2. Synthesis of 2-bromo- and 2-phenyl-neo-confused porphyrins

   https://doi.org/10.1039/d0ob01642j  

   Almejbel, Arwa S.; Lash, Timothy D. (September 2020, Organic & Biomolecular Chemistry)

   null (Ed.)

   Neo-confused porphyrins (neo-CPs), porphyrin isomers with a 1,3-connected pyrrolic subunit, are aromatic structures with a CNNN coordination core. Previously, examples of neo-CPs with fused benzo units or electron-withdrawing ester substituents have been described. In this paper, two new examples of neo-CPs are reported that lack a fused aromatic unit or an ester moiety, but instead have a bromo or phenyl substituent on the neo-confused ring. Acid-catalyzed condensation of suitably substituted 1,2′-dipyrrylmethane dialdehydes with a 2,2′-dipyrrylmethane, followed by oxidation with aqueous ferric chloride solutions, afforded the neo-CPs in 40–45% yield. These porphyrin analogues had slightly reduced diatropic ring currents and slowly decomposed in solution. The related palladium( ii ) and nickel( ii ) complexes proved to be very unstable, even though the diatropicity of the macrocycle was enhanced. This study shows that stabilizing substituents are necessary for investigations into this class of porphyrinoids. Attempts to prepare imidazole versions of neo-CPs were unsuccessful. 

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3. Synthesis of n ‐alkyl methacrylate polymers with pendant carbazole moieties and their derivatives

   https://doi.org/10.1002/pola.29285  

   Bandera, Yuriy; McFarlane, Tucker M.; Burdette, Mary K.; Jurca, Marek; Klep, Oleksandr; Foulger, Stephen H. (December 2018, Journal of Polymer Science Part A: Polymer Chemistry)

   ABSTRACT New methacrylate monomers with carbazole moieties as pendant groups were synthesized by multistep syntheses starting from carbazoles with biphenyl substituents in the aromatic ring. The corresponding polymers were prepared using a free‐radical polymerization. The novel polymers containN‐alkylated carbazoles mono‐ or bi‐substituted with biphenyl groups in the aromatic ring.N‐alkyl chains in polymers vary by length and structure. All new polymers were synthesized to evaluate the structural changes in terms of their effect on the energy profile, thermal, dielectric, and photophysical properties when compared to the parent polymer poly(2‐(9H‐carbazol‐9‐yl)ethyl methacrylate). According to the obtained results, these compounds may be well suited for memory resistor devices. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2019, 57, 70–76 

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4. [2]-Ladderanes as isosteres for meta-substituted aromatic rings and rigidified cyclohexanes

   https://doi.org/10.1038/s41467-022-33827-3  

   Epplin, Rachel C.; Paul, Shashwati; Herter, Loïc; Salome, Christophe; Hancock, Erin N.; Larrow, Jay F.; Baum, Erich W.; Dunstan, David R.; Ginsburg-Moraff, Carol; Fessard, Thomas C.; et al (October 2022, Nature Communications)

   Abstract Aromatic ring isosteres and rigidified saturated hydrocarbons are important motifs to enable drug discovery. Herein we disclose [2]-ladderanes as a class ofmeta-substituted aromatic ring isosteres and rigidified cyclohexanes. A straightforward synthesis of the building blocks is presented along with representative derivatization. Preliminary studies reveal that the [2]-ladderanes offer similar metabolic and physicochemical properties thus establishing this class of molecules as interesting motifs. 

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5. The anti-aromatic dianion and aromatic tetraanion of [18]annulene

   https://doi.org/10.1038/s41557-024-01469-1  

   Stawski, Wojciech; Zhu, Yikun; Rončević, Igor; Wei, Zheng; Petrukhina, Marina A; Anderson, Harry L (June 2024, Nature Chemistry)

   Abstract π-Conjugated macrocycles behave differently from analogous linear chains because their electronic wavefunctions resemble a quantum particle on a ring, leading to aromaticity or anti-aromaticity. [18]Annulene, (CH)₁₈, is the archetypal non-benzenoid aromatic hydrocarbon. Molecules with circuits of 4n + 2 π electrons, such as [18]annulene (n = 4), are aromatic, with enhanced stability and diatropic ring currents (magnetic shielding inside the ring), whereas those with 4nπ electrons, such as the dianion of [18]annulene, are expected to be anti-aromatic and exhibit the opposite behaviour. Here we use¹H NMR spectroscopy to re-evaluate the structure of the [18]annulene dianion. We also show that it can be reduced further to an aromatic tetraanion, which has the same shape as the dianion. The crystal structure of the tetraanion lithium salt confirms its geometry and reveals a metallocene-like sandwich, with five Li⁺cations intercalated between two [18]annulene tetraanions. We also report a heteroleptic sandwich, with [18]annulene and corannulene tetraanion decks. 

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