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Towards Stapling of Helical Alleno-Acetylene Oligomers - Synthesis of an Enantiopure Bis(ethynylvinylidene)-Substituted Cyclohexadeca-1,3,9,11-tetrayne

2014-02-01
MUELLER, I. -E. Sophie
BERNET, Bruno
Dengiz, Çağatay
SCHWEIZER, W. Bernd
DIEDERICH, Francois
We are interested in developing strategies to bridge (staple) enantiomerically pure acyclic alleno-acetylenic oligomers to enhance their conformational preferences for helical secondary structures, which are postulated to be at the origin of their exceptional chiroptical properties. We found that ring-closing metathesis (RCM), which has been used for the stapling of peptide helices, failed with an acyclic alleno-acetylene dimer decorated with lateral olefinic side chains. Instead, enyne RCM to an enantiomerically pure dienyne occurred. We switched to the introduction of diacetylene-containing bridges and report here the 15-step synthesis of a moderately strained, enantiomerically pure cyclohexa-1,3,9,11-tetrayne with an oxidative acetylenic coupling in the key step. The chiroptical properties of the new compounds are discussed.