Highly Enantioselective Amido Iridium Catalysts for the Hydrogenation of Simple Ketones

摘要

In the production of chiral compounds chemocatalysis competes with other techniques such as, for example, the resolution of racemates, the "chiral pool" approach, and biocatalysis. Highly enantioselective chemocatalysts based on simple and inexpensive ligands could drastically increase the importance of chemocatalysis. We report here on highly enantioselective phosphorus-free catalysts with a novel structure for the hydrogenation of simple ketones. The chiral ligands can be synthesized in a one-pot reaction starting from inexpensive chemicals. The modular nature of this synthesis ensures the introduction of a broad variety of substitution patterns. The catalyst synthesis starts with air- and moisture-stable substrates. Until now, chemocatalysts based on the phosphane-ruthenium-diamine complexes developed by Noyori, catalysts related to this structural type, and more complex chelate systems have been the most successful catalysts for the asymmetric hydrogenation of ketones. In contrast, phosphorus-free (iridium) catalyst systems are drastically less efficient and/or enantioselective in this asymmetric hydrogenation.