Chiral Catalysts

Abstract

This chapter deals with the use of chiral catalysts, such as metal complexes bearing chiral ligands and chiral organocatalysts, for the asymmetric induction through a DKR process. In the last two decades, the widespread application of non-enzymatic chiral catalysts for DKR has known an explosive and impressive growth, gaining popularity within the synthetic community. Indeed, a wide number of novel chiral catalysts combined with novel methodologies have been successfully developed, providing the access to numerous chiral natural products and biologically active compounds. In particular, remarkable results have been reported for enantioselective hydrogenations and transfer hydrogenations of various carbonyl compounds performed with various chiral ruthenium catalysts, with an important participation from the groups of Noyori and Genêt. Moreover, Trost has developed a great number of highly enantioselective dynamic kinetic asymmetric transformations promoted by chiral palladium catalysts, opening the route to a series of important products. It must be noted that the results are generally excellent whatever the nature of the reactions and the catalysts. Even though transition-metal-catalysed enantioselective DKRs will certainly continue to play a central role in synthetic organic chemistry in the future, the last few years have, however, seen an increasing trend in the use of organocatalysts, which present advantages from an economical and environmental point of view. In this context, a number of organocatalysed DKRs have been recently developed with success, by using various chiral organocatalysts, such as cinchona alkaloids or L-proline derivatives among others.