Iridium-Catalyzed Asymmetric Hydrogenation of β,γ-Unsaturated γ-Lactams: Scope and Mechanistic Studies

An efficient asymmetric hydrogenation of beta,gamma-unsaturated gamma-lactams using an iridium- phosphoramidite complex is reported. The chiral gamma-lactams were obtained in excellent yields and enantioselectivities (up to 99% yield and 99% ee). The mechanistic studies indicated that the reduced products were obtained via the hydrogenation of the N-acyliminium cations, generated from beta,gamma-unsaturated gamma-lactams, which was verified by H-1 NMR analysis. The reaction was carried out at a reduced catalyst loading of 0.1 mol %, and the reduced products can be transformed to two potential bioactive compounds. A new route is provided for the synthesis of chiral gamma-lactams.