On the Origin of Opposite Stereoselection in the Asymmetric Hydrogenation of Phenyl- and tert-Burtyl-Substituted Enamides Asymmetric Hydrogenation of Enamides with Rh-BisP and Rh-MiniPHOS Catalysts: Scope, Limitations, and Mechanism

摘要

Imamoto et al. have provided a clue to rationalize the factors that control the stereoselection induced in the catalytic hydrogenation of both aryl- and alkyl α-substituted enamides by P-chirogenic diphosphine Rh precatalysts. Aryl-substituted enamides have been found to afford the corresponding hydrogenated compounds with good to excellent ee's with the exclusion of ortho-substituted systems, which gave optically active amines with moderate enatioselectivities. t-Bu or 1-adamantyl-substituted enamides were reduced to the corresponding amines in excellent ee's with an opposite stereochemical configuration at the α-position. Valuable information on reaction mechanisms has been obtained by deuterium isotope-labeling and molecular modeling studies.