Angewandte Chemie International Edition
© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Cover Picture: Angew. Chem. Int. Ed. 8/2002
The cover picture shows the simple, one-step synthesis of cyclopyrroles, a new class of aromatic heteroannulene. Using a newly developed biphasic oxidative coupling procedure that employs aqueous FeCl3 as the oxidant, these novel porphyrin-like systems may be obtained in yields exceeding 70% starting from well-known bipyrrolic precursors. While formally derived from porphyrin as the result of substituting a pyrrole for each of the original bridging meso-carbon atoms, the cyclopyrroles differ from these quintessential tetrapyrrolic macroycles by virtue of Q-like absorption bands that are red-shifted into the near IR. Cyclopyrroles also show a propensity for protonation and anion binding that is underscored by the X-ray structure of the sulfate salt that makes up the background for this illustration. More on these exciting new molecules can be found in the communication by J. L. Sessler et al. on pp. 1422–1425.