Pure Appl. Chem., 2008, Vol. 80, No. 3, pp. 621-637
doi:10.1351/pac200880030621
Expanded radialenes: Modular synthesis and properties of cross-conjugated enyne macrocycles*
Rik R. Tykwinski1, Mojtaba Gholami1, Sara Eisler1, Yuming Zhao2, Frederic Melin3, and Luis Echegoyen3
1Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada; 2Department of Chemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X7, Canada; 3Department of Chemistry, Clemson University, Clemson, SC 29634, USA
Abstract:
During the past two decades, shape-persistent conjugated macrocycles with a broad spectrum of attributes and topologies have been synthesized. This includes macrocycles with remarkable electronic, optical, and supramolecular properties, as well as intriguing frameworks. Expanded radialenes are a class of conjugated shape-persistent macrocycles that arise from the formal insertion of acetylene units into a radialene framework. A related class of macrocycles, the expanded radiaannulenes, contains both endo- and exocyclic vinylene and vinylidene segments, respectively, and accordingly exhibits properties intermediate between radialenes and annulenes. Enyne building blocks have been developed that are suitable for forming a macrocyclic framework through a step-wise sequence of Pd-catalyzed cross-coupling reactions. This "building-block" approach allows us to explore a range of molecular architectures that will ultimately provide for an understanding of π-delocalization in these compounds. The synthesis and structural characterization of the first members of this new class of expanded radialenes and radiaannulenes are described.Abstract: During the past two decades, shape-persistent conjugated macrocycles with a broad spectrum of attributes and topologies have been synthesized. This includes macrocycles with remarkable electronic, optical, and supramolecular properties, as well as intriguing frameworks. Expanded radialenes are a class of conjugated shape-persistent macrocycles that arise from the formal insertion of acetylene units into a radialene framework. A related class of macrocycles, the expanded radiaannulenes, contains both endo- and exocyclic vinylene and vinylidene segments, respectively, and accordingly exhibits properties intermediate between radialenes and annulenes. Enyne building blocks have been developed that are suitable for forming a macrocyclic framework through a step-wise sequence of Pd-catalyzed cross-coupling reactions. This "building-block" approach allows us to explore a range of molecular architectures that will ultimately provide for an understanding of π-delocalization in these compounds. The synthesis and structural characterization of the first members of this new class of expanded radialenes and radiaannulenes are described.
Keywords: cross-conjugation; macrocycles; oligomers; palladium coupling; polydiacetylene.
*Paper based on a presentation at the 12th International Symposium on Novel Aromatic Compounds (ISNA-12), 22-27 July 2007, Awaji Island, Japan. Other presentations are published in this issue, pp. 411-667.