Rhodium-Catalyzed and Zinc(II)-Triflate-Promoted Asymmetric Hydrogenation of Tetrasubstituted α,β-Unsaturated Ketones

The asymmetric hydrogenation of tetrasubstituted α,β-unsaturated ketones has been accomplished using an in situ formed rhodium-Josiphos catalyst. The reaction is enhanced by addition of catalytic zinc(II) triflate, which significantly improves turnover frequency while suppressing epimerization of the products.