51. A Highly Configurationally Stable [4]Heterohelicenium Cation
    Christelle Herse, Delphine Bas, Frederik C. Krebs, Thomas Bürgi, Jacques Weber, Tomasz Wesolowski, Bo W. Laursen, Jérôme Lacour
    Angew. Chem. Int. Ed. 2003, 42, 3162-3166
    [ supporting info]

A [4](hetero)helicenium cation was resolved using the hexacoordinated phosphorus-containing binphat anion (see picture: N, blue; O, red; C, gray). Its absolute configuration was determined by vibrational circular dichroism spectroscopy. The barrier of interconversion of its enantiomers is higher than that of [6]helicene.

DOI : 10.1002/anie.200351443 

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