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

An efficient asymmetric hydrogenation of β,γ-unsaturated γ-lactams using an iridium–phosphoramidite complex is reported. The chiral γ-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 β,γ-unsaturated γ-lactams, which was verified by ¹H 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 γ-lactams.