Efficient photochemical electron transfer sensitization of homogeneous organic reactions

Photochemical electron transfer induced reactions have become an interesting tool in organic synthesis since transformations can be easily performed which are difficult or impossible with more conventional organic reactions. In this context, electron transfer sensitized reactions are frequently used since the sensitizer can be considered as a catalyst. Various intermediates such as radical ions with a variety of reaction possibilities are involved. Nevertheless, the reactions have been performed with high yields and high selectivities. Particular attention is paid to the stability of the sensitizer. Reaction steps regenerating the sensitizer from different intermediates are discussed. In photochemical electron donor and acceptor sensitized transformations, these steps are often part of the main reaction course. In other cases, co-sensitizers or mediators significantly enhance the efficiency of the transformations although the number of reactive intermediates is increased.