title: Outstanding chiroptical properties: a signature of enantiomerically pure alleno-acetylenic macrocycles and monodisperse acyclic oligomers.
abstract: A second series of shape-persistent alleno-acetylenic macrocycles and monodisperse acyclic oligomers with conformationally less flexible backbones were synthesized in enantiomerically pure form by short, high-yielding routes starting from optically active 1,3-diethynylallenes. All seven stereoisomers-two pairs of enantiomers and three achiral stereoisomers-in the macrocyclic series were separated and configurationally assigned. The electronic circular dichroism (ECD) spectra of the D2 -symmetric, (P,P,P,P)- and (M,M,M,M)-configured macrocycles display remarkably intense chiroptical responses. A strong amplification of chirality is observed in the acyclic oligomeric series. Their preference for helical secondary structures of one handedness was supported by X-ray analysis and computational studies. This new set of data provides proof that outstanding ECD responses are a hallmark of alleno-acetylenic macrocyclic and acyclic oligomeric chromophores.
authors.affiliation: Laboratorium für Organische Chemie, ETH Zurich, Vladimir-Prelog-Weg 3, 8093 Zurich (Switzerland), Fax: (+41) 44-632-1109.
authors.forename: Etienne J
authors.initials: EJ
authors.lastname: Donckele
authors.forename: Ori
authors.initials: O
authors.lastname: Gidron
authors.forename: Nils
authors.initials: N
authors.lastname: Trapp
authors.forename: Francois
authors.initials: F
authors.lastname: Diederich
keywords: acetylene; allenes; chiroptical properties; circular dichroism; macrocycles