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.

A Combined Experimental–Computational Investigation to Uncover the Puzzling (Chiro‐)optical Response of Pyridocyclophanes: One‐ and Two‐Photon Spectra

“…UV/Vis and ECD spectra were recorded with aJ asco J-815 spectropolarimeter. 1 Ha nd 13 CNMR spectra were recorded with Bruker 600 MHz or 400 MHz spectrometers at 298 K with residual solvent peaks as internal reference. The chemical shifts are reported in d (ppm) and the coupling constants J are given in Hz.…”

“…The chiroptical responses of related allenoacetylenic macrocycles have been studied by analyzing the molecular orbitals involved in the main transitions 12. 13 In this respect, TD‐DFT theory permits us to directly simulate the chiroptical response, even for molecular systems like the AACs here studied.…”

Chiroptical Detection of Nonchromophoric, Achiral Guests by Enantiopure Alleno‐Acetylenic Helicages

“…Rigidification of the backbones resulted in further enhancement of these properties. [11] We therefore became interested in transferring the molecular properties of alleno-acetylenes to supramolecular assemblies.…”

Chiroptische Detektion achiraler Gäste ohne Chromophor durch enantiomerenreine alleno‐acetylenische helicale Käfige

“…Kürzlich entwickelte unsere Gruppe das enantiomerenreine 1,3‐Diethinylallen 1 8 (Schema ) als optisch und thermisch stabilen Baustein für die Synthese alleno‐acetylenischer Oligomere9 und Makrocyclen10 mit herausragenden chiroptischen Eigenschaften. Diese konnten durch Rückgratversteifung weiter verstärkt werden,11 was uns anspornte, sie auf supramolekulare Aggregate zu übertragen.…”