Ethynylazulenes — Building Blocks for Novel Oligoazulenes with Ethynyl and Butadiynyl Bridges

The azulenes 3a , b , 6a , b , 9 , 12 and 15 ethynylated in the five‐membered ring were prepared by Pd‐catalysed cross‐coupling of the corresponding iodoazulenes 1a , b , 4a , b , 7 , 10 and 13 , respectively, with trimethylsilylacetylene and subsequent desilylation. The synthesis of some acyclic oligomers 23 – 30 , 32 – 36 and 38 – 40 from these ethynylazulenes could be accomplished by oxidative Eglinton coupling as well as Pd/Cu‐catalysed cross‐coupling reactions with the appropriate iodoazulenes 1a , b , 4b , 31 and 34 . The UV/Vis spectra of the novel oligomers 32 , 35 and 36 allow an estimation of the bandgap ( E g ) of poly(1,3‐azulenylethynylene)s lower than 2 eV. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)