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Synthesis and Properties of Partially Saturated Fluorenyl‐Derived [ n ]Helicenes Featuring an Overcrowded Alkene
Author(s) -
Pallova Lenka,
Gauthier Etienne S.,
Abella Laura,
Jean Marion,
Vanthuyne Nicolas,
Dorcet Vincent,
Vendier Laure,
Autschbach Jochen,
Crassous Jeanne,
Bastin Stéphanie,
César Vincent
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202100150
Subject(s) - enantiopure drug , alkene , diastereomer , enantiomer , circular dichroism , intramolecular force , chemistry , helicene , stereochemistry , molecule , organic chemistry , enantioselective synthesis , catalysis
The straightforward, multigram‐scale synthesis of the partially saturated H 6 ‐fluoreno[ n ]helicenes ( n =5 or 7) featuring a central, overcrowded alkene is described. The key cyclization step was based on an intramolecular McMurry reaction from the corresponding 1,5‐diketones. Chiral stationary phase HPLC analysis and isomer separation indicate that each helicenic compound is constituted of three diastereoisomers at room temperature, i. e. the configurationally stable ( R,R,P )/( S,S,M ) pair of enantiomers and an apparently achiral compound resulting from the rapid interconversion between the ( R,S,P ) and ( S,R,M ) enantiomers. The partially saturated H 6 ‐fluoreno[ n ]helicenes are oxidatively aromatized to give an efficient access to the corresponding fluoreno[ n ]helicenes. The chiroptical properties (vibrational and electronic circular dichroism) of the chiral, enantiopure compounds have been measured and analyzed by quantum‐chemical calculations, confirming their helicoidal nature.