Synthesis of Enantioenriched ß-Hydroxy-γ-Acetal Enamides by Rhodium-Catalyzed Asymmetric Transfer Hydrogenation.

The asymmetric reduction of ß-keto-γ-acetal enamides has been investigated. A wide range of enantioenriched ß-hydroxy-γ-acetal enamides were obtained through asymmetric transfer hydrogenation catalyzed by a tethered Rh(III)-DPEN complex with yields up to quantitative and enantioselectivities up to 99%. The reaction proved to be highly chemoselective toward the reduction of the carbonyl group over the C═C bond.