Corroles programmed for regioselective cycloaddition chemistry - synthesis of a bisadduct with C60-fullerene

A symmetrical beta,beta'-tetrasulfoleno-corrole is described here as an excellent and selective precursor to highly reactive corrole-beta,beta'-dienes, opening a selective route to specific beta,beta'-functionalized corroles via cycloaddition chemistry. The beta,beta'-tetrasulfoleno-corrole was prepared by acid catalyzed condensation of tolylaldehyde and a beta,beta'-disulfoleno-dipyrromethane, which was obtained by standard procedures. Crystalline deep green beta,beta'-tetrasulfoleno-corrole was isolated in 8-10% yield. Thermolysis of the corrole at 140 degrees C and in presence of an excess of C-60-fullerene gave a difullereno-corrole selectively (> 80% yield). The spectroscopic data indicated attachment of the two fullerene units at the "western," directly connected pyrrole rings. The tetrasulfoleno-corrole thus showed a remarkable preference for loss of sulphur dioxide and subsequent cycloaddition at the two "western" rings. In the difullereno-adduct, two sulfolene groups in the remaining "eastern" beta,beta ''-disulfoleno-pyrroles still are available as "caged dienes" for further thermal diene formation, and attachment of additional groups via [4 + 2]-cycloaddition reactions.