New Macrocyclic Frameworks from Indoles and Benzofurans

During the last few years macrocyclic frameworks from heterocycles such as indoles and benzofurans have recieved a great deal of chemical attention not only because of the widespread appearance of these heterocycles in biological systems and medical agents for photodynamic therapy but also because of their potential to act as catalysts and to build cone shaped cavities for anions or even neutral molecules. The primary aim of this project is to synthesise planar and non- planar methylene or ethenyl-linked cyclic trimers or tetramers of activated indoles and/or benzofurans which could exhibit the above-mentioned properties in forming metal complexes. These compounds may look very similar to porphyrins or cyclic annulenes made from furans, but without any doubt the additional condensed benzene rings would change the reactivity and the electronic properties of the chromophores, as well as the steric demands of the heterocycles, resulting in non-planar cone shaped or flattened partial cone shaped cycles, to a large extent. Useful synthetic strategies on the way to these so-called calixindoles, calixbenzofurans and mixed calixindole-benzofurans respectively include electrophilic substitutions on the activated heterocycles, Vilsmeier reactions to introduce formyl groups on the C2 and/or C7 positions and Wittig and McMurry reactions to generate ethenyl links. Metal complexes will be generated and their properties carefully investigated regarding the size and type of the metal. Especially the newly synthesised indolephosphonium salts will be subject of intensive research with respect to their activity in Wittig reactions as well as their ability to lose the phosphonium group in an acidic environment and to generate a carbocation essential for forming cyclic frameworks. Other aims of this project deal with the synthesis of even larger rings (calix[5]indoles etc.) and the examination of their properties and crystal structures, as well as with investigations to generate calixindoles from basic environments, which would allow for template reactions on metals. This would generate a major further development of calixindoles.