Enantio- and Regioselective Iridium-Catalyzed Hydrogenation of Olefins : From Development to Total Synthesis

The work presented in this thesis concerns the iridium-catalyzed asymmetric hydrogenation of cyclic olefins and allylic alcohols for the preparation of useful chiral intermediates with various substitution patterns. The strategy provides stereocontrol for both non-functionalized as well as functionalized substrates and aims to be implemented in the stereoselective preparation of chiral building blocks having more than one stereocenter. The first part (Chapter 2) is focused on the asymmetric hydrogenation of 1,4-cyclohexadienes bearing a number of different functionalities. The development of a novel set of imidazole-based Ir-N,P catalyst enabled the efficient and enantioselective hydrogenation of prochiral substrates. In addition, the challenging regioselective mono-hydrogenation of only one of the two trisubstituted double bonds of the diene was accomplished. The sequential preparation of chiral cyclic allylsilanes by means of iridium-catalyzed asymmetric hydrogenation and their employment in the Hosomi-Sakurai reaction was also studied (Chapter 3). Several patterns of alkyl substitution on the prochiral olefins were evaluated and the hydrogenation afforded the allylsilanes in high conversions and excellent enantiomeric excesses. These chiral silanes were then used in the TiCl4-promoted allylation of aldehydes, which took place with high diastereoselectivity. In Chapter 4, the kinetic resolution of allylic alcohols via asymmetric hydrogenation is described. High selectivity was observed for a broad range of substrates using a combination of an Ir-N,P catalyst and K2CO3 under mild reaction conditions. This highly efficient process is complementary to our previously reported asymmetric hydrogenation/DKR protocol. The final part (Chapter 5) covers the application of Ir-catalyzed hydrogenations as key steps in total synthesis. A sequential strategy involving enantio- and regioselective hydrogenations was successfully employed in the synthesis of the natural sesquiterpene (-)-Juvabione. In the following project, two allylic alcohols were hydrogenated to prepare chiral intermediates for a convergent formal synthesis of the renin inhibitor Aliskiren. At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.