ORGN 234 |
Formation and properties of cyclo[6]pyrrole and cyclo[7]pyrrole
| Thomas Köhler1, Daniel Seidel1, Vincent Lynch1, Forrest O. Arp1, Zhongping Ou2, Karl M. Kadish2, and Jonathan L. Sessler1. (1) Department of Chemistry and Biochemistry, Institute for Cellular and Molecular Biology, The University of Texas at Austin, 1 University Station – A5300, Austin, TX 78712-0165, (2) Department of Chemistry, The University of Houston, Houston, TX 77204-5003 |
We recently reported that 3,3´,4,4´-tetraalkylbipyrroles (e.g., 1) may be coupled under biphasic oxidative conditions (FeCl3; dichloromethane - 1 M aqueous sulfuric acid) to produce cyclo[8]pyrroles [30]octaphyrins(0.0.0.0.0.0.0.0), such as 2. However, much to our surprise, the synthesis of 3 and 4 was made possible by replacing the sulfuric acid by HCl in the FeIII–mediated cyclization of 1. Specifically, under these conditions, we found that two other meso-carbon-free macrocycles, namely cyclo[6]pyrrole 3 (HCl salt of [22]hexaphyrin(0.0.0.0.0.0)) and cyclo[7]pyrrole 4 (HCl salt of [26]heptaphyrin(0.0.0.0.0.0.0.0)), were obtained in isolated yields of 15% and 5%, respectively, as well as the expected cyclo[8]pyrrole 2 (obtained in 25% yield). This “matched set” of heteroannulenes was analyzed by spectroscopic, electrochemical, and X-ray diffraction methods.  |
| |
|
|