Highly Enantioselective Hydrogenation of Cyclic Enol Acetates Catalyzed by a Rh-PennPhos Complex

Abstract

The electron-rich and conformationally rigid (R,S,R,S)-Me-PennPhos ligand (shown schematically) appears to chelate rhodium and form well-defined chiral pockets. This allows, for example, efficient differentiation between the two enantiotopic approaches available to a substrate in a hydrogenation reaction. The Rh-Me-PennPhos complex is the first catalyst for the highly enantioselective asymmetric hydrogenation of cyclic enol acetates. For example, 3,4-dihydronaphth-1-yl acetate can be hydrogenated with up to 99% ee.