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1. Site-selective [2 + 2 + n ] cycloadditions for rapid, scalable access to alkynylated polycyclic aromatic hydrocarbons

   https://doi.org/10.1039/C9SC06102A  

   Kiel, Gavin R.; Bergman, Harrison M.; Tilley, T. Don (March 2020, Chemical Science)

   null (Ed.)

   Polycyclic aromatic hydrocarbons (PAHs) are attractive synthetic building blocks for more complex conjugated nanocarbons, but their use for this purpose requires appreciable quantities of a PAH with reactive functional groups. Despite tremendous recent advances, most synthetic methods cannot satisfy these demands. Here we present a general and scalable [2 + 2 + n ] ( n = 1 or 2) cycloaddition strategy to access PAHs that are decorated with synthetically versatile alkynyl groups and its application to seven structurally diverse PAH ring systems (thirteen new alkynylated PAHs in total). The critical discovery is the site-selectivity of an Ir-catalyzed [2 + 2 + 2] cycloaddition, which preferentially cyclizes tethered diyne units with preservation of other (peripheral) alkynyl groups . The potential for generalization of the site-selectivity to other [2 + 2 + n ] reactions is demonstrated by identification of a Cp 2 Zr-mediated [2 + 2 + 1]/metallacycle transfer sequence for synthesis of an alkynylated, selenophene-annulated PAH. The new PAHs are excellent synthons for macrocyclic conjugated nanocarbons. As a proof of concept, four were subjected to alkyne metathesis catalysis to afford large, PAH-containing arylene ethylene macrocycles, which possess a range of cavity sizes reaching well into the nanometer regime. Notably, these high-yielding macrocyclizations establish that synthetically convenient pentynyl groups can be effective for metathesis since the 4-octyne byproduct is sequestered by 5 Å MS. Most importantly, this work is a demonstration of how site-selective reactions can be harnessed to rapidly build up structural complexity in a practical, scalable fashion. 

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2. Gold‐Catalyzed Diyne‐Ene Annulation for the Synthesis of Polysubstituted Benzenes through Formal [3+3] Approach with Amide as the Critical Co‐Catalyst

   https://doi.org/10.1002/anie.202407360  

   Wei, Jingwen; Pham, Thong; Attah, Emmanuel Ifeanyi; Liu, Mengjia; Yaroshuk, Timothy; Chen, Hao; Wojtas, Lukasz; Shi, Xiaodong (July 2024, Angewandte Chemie International Edition)

   The one‐step synthesis of tetra‐substituted benzenes was accomplished via gold‐catalyzed diyne‐ene annulation. Distinguished from prior modification methods, this novel strategy undergoes formal [3+3] cyclization, producing polysubstituted benzenes with exceptional efficiency.  The critical factor enabling this transformation was the introduction of amides, which were reported for the first time in gold catalysis as covalent nucleophilic co‐catalysts.  This interesting protocol not only offers a new strategy to achieve functional benzenes with high efficiency, but also enlightens potential new reaction pathways within gold‐catalyzed alkyne activation processes. 

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3. Synthesis of oxaboranes via nickel-catalyzed dearylative cyclocondensation

   https://doi.org/10.1039/d2sc01840c  

   Koeritz, Mason T.; Banovetz, Haley K.; Prell, Sean A.; Stanley, Levi M. (July 2022, Chemical Science)

   We report Ni-catalyzed dearylative cyclocondensation of aldehydes, alkynes, and triphenylborane. The reaction is initiated by oxidative cyclization of the aldehyde and alkyne coupling partners to generate an oxanickelacyclopentene which reacts with triphenylborane to form oxaboranes. This formal dearylative cyclocondensation reaction generates oxaboranes in moderate-to-high yields (47–99%) with high regioselectivities under mild reaction conditions. This approach represents a direct and modular synthesis of oxaboranes which are difficult to access using current methods. These oxaboranes are readily transformed into valuable building blocks for organic synthesis and an additional class of boron heterocycles. Selective homocoupling forms oxaboroles, oxidation generates aldol products, and reduction and arylation form substituted allylic alcohols. 

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4. Functionalized [2.2]Paracyclophanedienes as Monomers for Poly( p -phenylenevinylene)s

   https://doi.org/10.1021/acsmacrolett.3c00714  

   Mann, Arielle; Wang, Chengyuan; Dumlao, Bianca L.; Weck, Marcus (January 2024, ACS Macro Letters)

   Poly(p-phenylenevinylene)s (PPVs) featuring complex side-chains, to date, have only been synthesized by non-living polymerization methods which have no control over PPVs molecular weights, dispersities, or end groups. [2.2]Paracyclophane-1,9-diene (pCpd) have gained attention as a monomer for its ability to be ring-opened to PPV in a living fashion. pCpd, an organic cyclic scaffold with planar chirality, has seen minimal structural diversity due to the harsh reaction conditions required to afford the highly strained compound. Herein, we introduce a general method to overcome this by targeting the synthesis of a monohydroxy-pCpd via mono-demethylation of a dialkoxy-pCpd. The monohydroxy-pCpd can then be functionalized easily which we demonstrate using three distinct side-chains with four moieties commonly incorporated in conjugated polymers: an alkyl bromide, an oligo(ethylene glycol) chain, an enantiomerically pure side-chain, and a Boc-protected amine. These monofunctionalized-pCpds were investigated as monomers in the ring-opening me-tathesis polymerizations (ROMP) to afford functionalized PPVs in a living manner. The functional group-containing PPVs are synthe-sized with full control over their end groups, repeat units, and dispersities. The feasibility of post-polymerization modifications to incor-porate any desired moiety to PPV fabricated by this method was demonstrated using an azide-alkyne click reaction. All PPVs synthesized were soluble in organic solvents and display the same fluorescent emission indicating their conjugated backbones are unaltered. 

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5. Is Phenylnitrene a Missing Link in the Formation of Polycyclic Aromatic Nitrogen Heterocycles?

   https://doi.org/10.1002/anie.202503940  

   Arns, Rahel; McClish, Rory; Hemberger, Patrick; Bodi, Andras; Bouwman, Jordy; Kasper, Tina; Schleier, Domenik (May 2025, Angewandte Chemie International Edition)

   The incorporation of heteroatoms into the framework of polycyclic aromatic hydrocarbons (PAHs), in particular of nitrogen to yield polycyclic aromatic nitrogen heterocycles (PANHs), has been proposed for both astronomical and combustion environments, but no suitable precursors and pathways have been found. Analogous pathways to PAH formation are kinetically or energetically inhibited in the presence of a nitrogen heteroatom. We report on the reaction of phenylnitrene (3PhN, c‐C6H5N) with resonance‐stabilized propargyl radicals (C3H3) and find that the association reaction bifurcates depending on the orientation of the attacking propargyl radical and yields multiple isomeric products. Among them, we identify the condensed‐ring quinoline and conclude that nitrenes are viable candidates to drive the formation of PANHs. 

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