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Volume 12 Issue 3, March 2020

Volume 12 Issue 3

Bigging up aromaticity

Benzene is the archetypal aromatic molecule and it satisfies Hückel's 4n + 2 rule with its 6 π-electrons (n = 1). In a study that explores the limits of aromaticity, Harry Anderson and co-workers have now shown that Hückel's rule holds true for a large wheel-like compound in which 12 zinc porphyrins are linked together with diyne groups. In the 6+ oxidation state, the 162 π-electrons (n = 40) are delocalized around the porphyrin wheel, which is shown on the cover with two template molecules stacked inside it to form a stable 2:1 complex.

See Rickhaus et al

IMAGE: Harry Anderson, University of Oxford. COVER DESIGN: Tulsi Voralia

News & Views

  • News & Views |

    RNA has multiple roles in biology, enabled by its structural diversity. Now, artificially grafted RNA motifs have been encoded in a single RNA strand to form self-assembling nanostructures with controlled geometry and function.

    • Qi Shen
    • Chenxiang Lin
  • News & Views |

    Many current methods to prepare 2-hydroxybiaryls require the prefunctionalization of phenol groups or show limited substrate scope. Now, use of a pentavalent sulfone-bridged bismacycle, formed in situ by telescoped boron-to-bismuth transmetallation and oxidation, allows the direct and regioselective ortho-arylation of unprotected phenols.

    • Adrien Le Roch
    • Alexandre Gagnon
  • News & Views |

    Although the application of force to induce chemical transformations is an active area of research, detailed understanding of these mechanochemical pathways is still lacking. Now, the mechanochemical activation of [4]-ladderane has been studied and found to exhibit unique non-equilibrium dynamic effects.

    • Vincenzo Lordi


  • Perspective |

    The structures of biologically active natural products have long served as inspiration in drug discovery. This Perspective outlines design principles and connectivity patterns for the de novo combination of natural product-derived fragments. The resulting ‘pseudo-natural products’ retain biological relevance yet exhibit structures and bioactivities not found in the natural products and their derivatives.

    • George Karageorgis
    • Daniel J. Foley
    • Herbert Waldmann


  • Article |

    Does aromaticity have a size limit? Evidence is presented for global aromaticity in porphyrin nanorings with circuits of up to 162 π-electrons. The conformation of the nanoring can be altered by changing the template, which in turn controls the aromaticity. Whenever a ring current is observed, its direction is correctly predicted by Hückel’s rule.

    • Michel Rickhaus
    • Michael Jirasek
    • Harry L. Anderson
  • Article |

    A conjugated diradicaloid cage has been synthesized and its aromaticity was investigated. The neutral compound and the dication have dominant monocyclic conjugation pathways and both are aromatic (the former following Hückel’s rule and the latter Baird’s rule). The tetracation ([6n + 4] π-electrons) exhibits global 3D antiaromaticity whereas the hexacation ([6n + 2] π-electrons) exhibits global 3D aromaticity and has high D3 symmetry.

    • Yong Ni
    • Tullimilli Y. Gopalakrishna
    • Jishan Wu
  • Article |

    Homooligomerization systems can be used to construct nanoarchitectures and to aid understanding of natural analogues. But the formation of such artificial systems with structural diversity and complexity comparable to that of biological systems is challenging. Now, an artificial branched kissing-loop motif has been designed, which links tiles folded from a single strand of RNA to give diverse homooligomeric nanostructures.

    • Di Liu
    • Cody W. Geary
    • Yossi Weizmann
  • Article |

    Step-economic access to the biologically relevant 2-hydroxybiaryl motif represents a long-standing challenge in synthetic organic chemistry. Now, a bismuth-mediated oxidative arylation of phenols and naphthols with boronic acids has been developed — supported by experimental mechanistic insight — giving a direct and practical route to this valuable molecular architecture.

    • Mark Jurrat
    • Lorenzo Maggi
    • Liam T. Ball
  • Article |

    Porous liquids promise to combine the advantages of the porosity of solids with those of the fluidity of liquids. Now, a permanently porous ionic-liquid coordination cage has been assembled that encapsulates isomers of butanol and propanol with some size and shape selectivity, as well as three gaseous chlorofluorocarbons with a size-dependent affinity.

    • Lillian Ma
    • Cally J. E. Haynes
    • Jonathan R. Nitschke
  • Article |

    The anti-Markovnikov hydroarylation of unactivated alkenes with unactivated arenes has been achieved with high selectivity by using nickel catalysts bearing large N-heterocyclic carbene ligands. Energy decomposition analysis indicates that the high activity of the catalysts with large carbene ligands arises from stabilizing non-covalent interactions rather than steric effects.

    • Noam I. Saper
    • Akito Ohgi
    • John F. Hartwig
  • Article |

    The deposition of noble metals onto two-dimensional transition metal dichalcogenides is crucial for practical applications, including in catalysis and sensing, yet this process has remained difficult to control. Now, gold and silver have been shown to grow on colloidal transition metal dichalcogenide nanosheets into either atomically thin layers or nanoparticles whose sizes and morphologies depend on the relative strengths of the interfacial noble metal–chalcogen bonds.

    • Yifan Sun
    • Yuanxi Wang
    • Raymond E. Schaak
  • Article |

    Although methods exist for the construction of CF3-containing stereocentres, the utilization of α-trifluoromethyl carbanions remains challenging because of the propensity for fluoride elimination. A strategy has now been developed to stabilize these carbanions through a neighbouring cationic Pd complex and the corresponding Pd-stabilized zwitterions participate in asymmetric cycloadditions with a broad range of acceptors.

    • Barry M. Trost
    • Youliang Wang
    • Chao-I (Joey) Hung
  • Article |

    The mechanochemical activation of [4]-ladderane/ene has been studied and found to exhibit cascade unzipping and a consistent stereochemical distribution of products under various conditions and in different polymer backbones. Ab initio steered molecular dynamics simulations revealed unique non-equilibrium dynamic effects in the mechanochemistry of ladderane, cascade activation and reaction pathway bifurcation.

    • Zhixing Chen
    • Xiaolei Zhu
    • Yan Xia
  • Article |

    Although biaryl rings can be easily formed via cross coupling, their tetrahedral, high-fraction sp3 equivalents cannot. Now the scope, mechanism and biological profile of a general attached-ring synthesis has been probed. This provides direct access to full bridgehead substitution via sp3sp3 coupling and enables rapid entry to natural product space.

    • Benjamin J. Huffman
    • Shuming Chen
    • Ryan A. Shenvi


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