Neue Phosphor-Pyridin-Liganden für die Iridium-katalysierte enantioselektive Hydrierung

We herein report the synthesis and application of novel P,N-ligands derived form pyridine.
The modularity of the new ligands is reflected in their synthesis. Both ring size and
substitution pattern of the pyridine moiety are easily varied. The electronic properties of the
ligands are tunable in the phosphorus introduction step, by using either an aryl- or an
alkylphosphine (Figure 1).
In using this new ligand type in catalytic hydrogenation for a range of unfunctionalized
olefins, we observed excellent conversions and enantioselectivities. The results are
comparable, and in some cases even better, than those induced by chiral phosphinooxazolines
(Figure 2).
The scope of this catalyst type was extended to include the reduction of substituted furans and
benzofurans. For the first time, tetrahydrofuran- and dihydrobenzofuran-derivatives were
synthesized by an enantioselective hydrogenation reaction with selectivities of over 90% ee
(Figure 3).