Photochemical deracemization catalyzed by chiral triplet sensitizers with a lactam binding motif

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A deracemization is a process in which a racemic mixture is selectively and ideally quantitatively converted into a specific enantiomer. Due to the fact that enantiomers have identical standard enthalpies of formation a deracemization is impossible in a thermal equilibrium mediated by a chiral catalyst. However, deracemization reactions can be performed photochemically with a chiral triplet sensitizer that displays a hydrogen bonding motif (lactam) and acts as catalyst. Possible substrates for this transformation include allenes, cycloalkanes, sulfoxides, and 1,1'-biaryls. Experimentally, the most relevant parameters are to be identified which are responsible for a high enantioselectivity. To this end, it is also planned to modify the chromphore of the sensitizer, a thioxanthone or xanthone, by appropriate substitution and to adapt its triplet energy to the individual substrates. The major focus is on method development but the work will be accompanied by photophysical studies and will be directed towards synthetic applications.