Cross-Coupling Reactions DOI: 10.1002/ange.200703978 Synthesis and Characterization of Expanded Radialenes, Bisradialenes, and Radiaannulenes** Mojtaba Gholami, Frederic Melin, Robert McDonald, Michael J. Ferguson, Luis Echegoyen, and Rik R. Tykwinski* Shape-persistent, conjugated macrocycles have been designed to exhibit a broad spectrum of interesting attributes and topologies. [1] Over the past two decades amazing progress has been made towards the synthesis of these macrocycles, which have remarkable electronic, optical, nonlinear optical, and supramolecular properties. [2–4] A subset of this general class of molecules are the radialenes (1) and expanded radialenes (2 and 3 ; see Scheme 1), which arise from the formal insertion of acetylene units into the framework of a radialene molecule. [5] A related class of macrocycles, radiaannulenes (4, Scheme 1), contain both endo- and exocyclic vinyl segments within the conjugated core. [6] Both the expanded radialenes and the radiaannulenes are cross-conjugated macrocycles, [3,4] and their rigid two-dimensional structure provides a useful frame- work for the development of fundamentally interesting p-rich molecules. The study of expanded radialenes was initiated by Diederich and co-workers, [7] who explored the rich chemistry of butadiynyl-based radialenes 3 and radiaannulenes 4. These studies, and others, used a combination of functional group variation and extensive analysis of their physical properties, and have suggested that molecules such as 3 and 4 can be generated with intriguing optical and electronic properties. [3,4] Radialenes 2 would be expected to share many of the attractive electronic characteristics of their larger cousins 3. Furthermore, a recent computational study has suggested that upon a single-electron reduction, a trimeric derivative of 2 (n = 0) should become antiaromatic. [8] To date, however, the synthesis of radialenes 2 has proved challenging, and only a single example has been reported (2, n = 3, R = alkyl). [9] Herein, we report a general protocol for the synthesis of expanded radialenes 5–8 from acyclic oligomers 9–12 and vinyl bromide 13 (Scheme 2). Also described are our initial efforts to extend this method through coupling with tetra- bromoethane (14) to generate the first examples of enyne bisradialenes, namely 15 and 18, and radiaannulenes, namely 16 and 17. Finally, the structural (X-ray crystallography), electronic (cyclic voltammetry), and optical (absorbance and emission) properties of the isolated macrocycles 5–7, 15/16, and 17 are described. The new expanded radialenes were synthesized from enyne oligomers 9–12, [10] which were desilylated and then reacted with 13 under Pd-catalyzed Sonogashira conditions (Scheme 2). [11] For example, dimer 9 was desilylated with tetra-n-butylammonium fluoride (TBAF) in wet THF to give the terminal diyne. Following workup, the diyne was then reacted with 13 in the presence of [Pd(PPh 3 ) 4 ], CuI, and iPr 2 NH in THF at reflux to give the highly strained expanded [3]radialene 5 in a reasonable yield of 32%. The successful ring closure to give 5 provides a noteworthy achievement of Scheme 1. Structures of radialenes, expanded radialenes, and radiaan- nulenes. [*] M. Gholami, Prof. Dr. R. R. Tykwinski Department of Chemistry University of Alberta Edmonton, AB, T6G 2G2 (Canada) Fax: (+ 1) 780-492-8231 E-mail: rik.tykwinski@ualberta.ca Dr. F. Melin, Prof. Dr. L. Echegoyen Department of Chemistry Clemson University Clemson, South Carolina, 29634 (USA) E-mail: luis@clemson.edu Dr. R. McDonald, Dr. M. J. Ferguson X-ray Crystallography Laboratory Department of Chemistry University of Alberta Edmonton, Alberta, T6G 2G2 (Canada) [**] The financial support provided by the University of Alberta, the Natural Sciences and Engineering Research Council of Canada (NSERC), and the National Science Foundation (grant number CHE-0509989) is greatly appreciated. This material is based on work supported by the National Science Foundation while L.E. was working here. All opinions, findings, conclusions, and recommen- dations expressed herein are those of the authors and do not necessarily reflect the views of the National Science Foundation. Supporting information for this article is available on the WWW under http://www.angewandte.org or from the author. Angewandte Chemie 9239 Angew. Chem. 2007, 119, 9239–9243 # 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& &&&&&&&&&&&&&&&&&&&&&&&&&&&& Nutzen Sie die blauen Literaturverknüpfungen &&&&&&&&&&&&&&&&&&&&&&&&&&&& &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&