Synthesis of cyclic chlorophyll oligomers

As a new model of photosynthetic light-harvesting antennas, cyclic dimer, trimer, and tetramer of chlorophyllous moieties were prepared by intermolecular transesterification of a hydroxy-methoxycarbonyl-chlorin using 1,3-dichlorotetrabutyl distannoxane as a catalyst. ¹H NMR and UV-vis spectra showed that the cyclic oligomers tended to form stacked conformers through intramolecular π-π interactions of the chlorin macrocycles. It was demonstrated that the cyclic trimer could form a complex with fullerenes in CDCl₃.