Silyl-substituted tetrathia[7]helicenes: synthesis, x-ray characterization and reactivity

We describe the synthesis of trialkylsilyl-substituted trans-1,2-bis(thieno[3,2-e]benzothiophene-2-yl)ethenes as suitable soluble precursors for the preparation of the corresponding silylated tetrathia[7]helicenes, which, in turn, can be desilylated or transformed into dihalogen-substituted derivatives through electrophilic substitution of silyl substituents. X-ray structural studies showed that the presence of the two triisopropylsilyl groups on the terminal thiophene rings accounts for the high solubility of the alkene and for the very large dihedral angle in the helicene.