Chiral Proline-Based Ligands for Iridium-Catalyzed Asymmetric Hydrogenation

Multiple pharmaceuticals, herbicides, fragrances and flavors manufactured on an industrial scale are known to involve a transition metal-catalyzed reaction in their synthesis.[1] Among these reactions, the most prominent reaction is the asymmetric hydrogenation catalyzed by a transition metal. The relevance of these products can be noticed by the fact that numerous non-specialists are familiar with their names (e.g. L-DOPA, ibuprofen and vitamin E). The metal-catalyzed hydrogenation is an attractive reaction for asymmetric synthesis, since it combines highly desirable advantages such as perfect atom economy, high conversions, low catalyst loadings and mild reaction conditions.[2] All these characteristics are well appreciated in modern organic synthesis and explain the various applications of metal-catalyzed asymmetric hydrogenation, not only in academic research but also in industrial synthesis. Although this reaction has been explored for many years and an impressive number of enantioselective catalysts have been developed it is still investigated today. The main goals in this field today are to find solutions to render this reaction more universal, meaning applicable to a wider range of substrates, or to discover more generally applicable, effective, inexpensive and readily available catalysts.