An acenaphthylene-fused cyclopyrrole was synthesized by using an oxidative coupling reaction of the corresponding 2,2'-bipyrrole. Two conformational isomers 1 a and 1 b were isolated, and their molecular structures were elucidated by X-ray crystallographic studies. The less-polar and lower-symmetry 1 b isomer can be converted into the 1 a isomer through a thermal ring flip. Application of the perimeter model developed by Michl to magnetic circular dichroism spectroscopic data and theoretical calculations demonstrate that there is a marked redshift of the near-IR absorption maxima relative to cycloisoindole because there is a significant stabilization of the LUMO due to the differing effects of a fused ring expansion with acenaphthylene and benzene moieties on the frontier π molecular orbitals. Fused ring expansion: An oxidative coupling reaction of the corresponding 2,2'-bipyrrole leads to the synthesis of an acenaphthylene-fused cyclopyrrole. Application of Michl's perimeter model to magnetic circular dichroism spectral data and the results of theoretical calculations demonstrate that there is a marked redshift of the near-IR absorption maxima (see figure).
ASJC Scopus subject areas
- Organic Chemistry