The Use of N,P-Iridium and N,P-Palladium Complexes in Asymmetric Synthesis

Abstract: The work presented in this thesis concerns asymmetric catalysis using chiral N,P-ligands and iridium or palladium transition metals. The first part  (Chapters 2 and 3) highlights the N,P-iridium catalyzed asymmetric hydrogenation of 1,4-cyclohexadienes having functionalized or unfunctionalized substituents, including allylsilane side chains. A series of N,P-iridium catalysts were synthesized and screened on a number of cyclohexadienes. The developed N,P-iridium catalysts have provided excellent chemo-, regio- and enantioselectivity for most of the products obtained. For substrates having an allylsilane sidechain, the chiral cyclic allylsilane products were used to induce stereocontrol in a subsequent Hosomi-Sakurai reaction using TiCl4 as Lewis acid and aldehydes as electrophiles. The corresponding homoallylic alcohols were obtained in good to excellent diastereoselectivity. The second part (Chapter 4) describes the N,P-iridium catalyzed asymmetric hydrogenation of various vinyl fluorides. A number of tri- and tetrasubstituted vinyl fluorides were synthesized and evaluated for the asymmetric hydrogenation. The corresponding saturated chiral fluoro compounds were obtained in very high enantioselectivity (up to 99% ee). The defluorination, usually known to occur under the catalytic hydrogenation conditions, were not observed for the majority of the substrates. Finally, Chapter 5 describes the application of N,P-ligands in the asymmetric cycloisomerization of 1,6-enynes using a palladium precatalyst. The enantioselectivities for the products were found to depend both on the substrate as well as the hydrogen source. These developed catalytic reactions provide attractive methods to create multiple stereogenic centers in a molecule in relatively few steps from readily available starting materials.