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 alpha-chloroaldehydes with gamma-/delta-amino-alpha,beta-unsaturated ketones were developed, giving the corresponding pyrrolidones and piperidones in good yields with exclusive trans-selectivities and excellent enantioselectivities.