N‐Heterocyclic Carbene‐Catalyzed Annulation of α‐Chloroaldehydes with γ‐/δ‐Amino‐α,β‐Unsaturated Ketones: Enantioselective Synthesis of Pyrrolidones and Piperidones

The N‐heterocyclic carbene‐catalyzed [2+3] and [2+4] annulations of α‐chloroaldehydes with γ‐/δ‐amino‐α,β‐unsaturated ketones were developed, giving the corresponding pyrrolidones and piperidones in good yields with exclusive trans‐selectivities and excellent enantioselectivities. Pyrrolidones and piperidones: The N‐heterocyclic carbene‐catalyzed [2+3] and [2+4] annulations of α‐chloroaldehydes with γ‐ or δ‐amino‐α,β‐unsaturated ketones were developed to give 3,4‐disubstituted pyrrolidones and piperidones in good yields with exclusive trans‐selectivities and excellent enantioselectivities.