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.