65. Resolution of [4]Heterohelicenium Dyes via Unprecedented Pummerer-like Chemistry
    Benoît Laleu, Pierre Mobian, Christelle Herse, Bo W. Laursen, Gérard Hopfgartner, Gérald Bernardinelli, Jérôme Lacour
    Angew. Chem. Int. Ed. 2005, 44, 1879-1883

Addition of an enantiopure sulfoxide auxiliary is the key to the resolution of highly stable [4]helicenium dyes. This transformation allows a facile chromatographic separation of the diastereomers (the structure of one such diastereomer is shown; S yellow, O red, N blue). Then an unprecedented Pummerer-like CC bond fragmentation takes place to release the enantiopure cations.

DOI : 10.1002/anie.200462321 

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