Enantioselective Hydrogenation of Enones with a Hydroformylation Catalyst

Use of a typical rhodium precatalyst for hydroformylation results in the enantioselective hydrogenation of cyclic enones with up to 90% ee. Extensive screening of chiral ligands reveals the simple ligand Chiraphos as the best ligand, so far. The hydrogenation shows high chemoselectivity. Exclusive formation of saturated, chiral P-branched ketones is observed. It is proposed that the catalyst follows a frustrated hydroformylation pathway (monohydride-based mechanism) and differs by that from the classical cationic Schrock-Osborn type rhodium precatalysts (dihydride-based mechanism) for enantioselective hydrogenation. The catalyst operates under neat conditions and is easily recyclable by simply distilling off the reaction mixture and treatment with syn gas prior to hydrogenation.