Verwendung einer neuartigen Ringschlussreaktion zur Totalsynthese von Chlorin-Fulleren- und Chlorin-Chinon-Dyaden als Modellsysteme fuer die Photosynthese

Abstract

The aim of this dissertation was the total synthesis of model compounds for an elementary step of photosynthesis, the light induced charge separation. In contrast to many known model systems in literature, in which porphyrins have been used as electron donors, the donor used in this case was the chromophore of the naturally photosynthetic pigments, a chlorin derivative (dihydroporphyrine). As an electron acceptor a fullerene C60 has been used, which is known to be an excellent electron and energy acceptor since a few years. Another acceptor, which has been used was a quinone, which serves also as an acceptor in the naturally photosynthetic systems. Based on a model synthesis a total synthetic approach to a chlorin derivative with an anellated sulfolene ring could be achieved. This chlorin derivative, which is a precursor for a dimethylene chlorin (heterocyclic o-quinodimethane), could be used for many functionalisations by Diels-Alder reactions. Further a new ring closure method has been developed which has some advantages in preparative use. This new ring closure method involves a thermic cyclization of a carboethoxy-substituted hydrobiline derivative to the corresponding chlorin macrocycle. The cyclization is part of a cascade of reactions during which also the dienophile like fullerene C60 or quinone is covalently linked to the chlorin framework by a Diels-Alder reaction. This led to the desired dyads, in which the luminescence is quenched, which indicates an intramolecular transfer of electrons or energy from the chlorin moiety to the acceptor moiety.