New thiophene-pyrrole-derived annulenes containing 6 and 10 heterocyclic units

A series of thiophene-pyrrole-derived annulenes containing either 6 (9a-c) or 10 (14a,b and 17) heterocyclic units and 2 vinylene bridges have been synthesized from the appropriate dialdehydes or tetraaldehydes by the McMurry coupling reaction. All of these annulenes except 17 contain one or two intramolecular aliphatic chains linking the pyrrole units. Spectroscopic properties of these annulenes show no evidence for overall aromaticity or antiaromaticity, although the nature of the aliphatic bridge has a small but definite effect on the UV-visible spectra and electrochemical properties of the compounds.