Enantiomerically Pure Alleno-Acetylenic Macrocycles: Synthesis, Solid-State Structures, Chiroptical Properties, and Electron Localization Function Analysis

Abstract

New enantiomerically pure alleno-acetylenic macrocycles were prepd. by oxidative homocoupling of optically active 1,3-diethynylallenes. Enantiomer sepn. resulted from a combined strategy of synthesis and chiral HPLC techniques. Two other achiral stereoisomers were also isolated and fully characterized. In addn., the X-ray structures of the chiral D4- and C2-sym. macrocycles are reported. The chiroptical properties of these macrocycles are discussed on the basis of quantum chem. calcns., by using the CAM-B3LYP functional. Studies were carried out to investigate the vibronic fine structure obsd. exptl. 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 topol. of the MOs involved, thus relating electronic properties to structural features. Further anal. of the canonical MOs and the electron localization function (ELF) shows that these macrocycles belong to a relatively rare class of highly stable and formally anti-arom. Hueckel compds.