title: Enantiomerically pure alleno-acetylenic macrocycles: synthesis, solid-state structures, chiroptical properties, and electron localization function analysis.
abstract: New enantiomerically pure alleno-acetylenic macrocycles were prepared by oxidative homocoupling of optically active 1,3-diethynylallenes. Enantiomer separation resulted from a combined strategy of synthesis and chiral HPLC techniques. Two other achiral stereoisomers were also isolated and fully characterized. In addition, the X-ray structures of the chiral D(4)- and C(2)-symmetric macrocycles are reported. The chiroptical properties of these macrocycles are discussed on the basis of quantum chemical calculations, by using the CAM-B3LYP functional. Studies were carried out to investigate the vibronic fine structure observed experimentally in the UV/Vis and CD spectra. The origin of the intense chiroptical response of the chiral alleno-acetylenic macrocycles is explained by considering the topology of the molecular orbitals involved, thus relating electronic properties to structural features. Further analysis of the canonical molecular orbitals and the electron localization function (ELF) shows that these macrocycles belong to a relatively rare class of highly stable and formally anti-aromatic Hückel compounds.
authors.affiliation: Laboratorium für Organische Chemie, ETH Zürich, Hönggerberg, HCI, 8093 Zürich, Switzerland.
authors.forename: Pablo
authors.initials: P
authors.lastname: Rivera-Fuentes
authors.forename: José Lorenzo
authors.initials: JL
authors.lastname: Alonso-Gómez
authors.forename: Ana G
authors.initials: AG
authors.lastname: Petrovic
authors.forename: Paul
authors.initials: P
authors.lastname: Seiler
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Santoro
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Harada
authors.forename: Nina
authors.initials: N
authors.lastname: Berova
authors.forename: Henry S
authors.initials: HS
authors.lastname: Rzepa
authors.forename: François
authors.initials: F
authors.lastname: Diederich