Synthesis and Properties of Partially Saturated Fluorenyl-Derived [n]helicenes Featuring an Overcrowded Alkene
Résumé
The straightforward, multigram-scale synthesis of the partially saturated H -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 -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.
Domaines
Chimie
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Pallova et al-2021-Synthesis and Properties of Partially Saturated Fluorenyl-Derived [n]helicenes.pdf (1.5 Mo)
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