Ethynylazulenes - Building blocks for novel oligoazulenes with ethynyl and butadiynyl bridges

The azulenes 3a,b, 6a,b, 9, 12 and 15 ethynylated in the fivemembered 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. ((D Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).