Asymmetric aza‐Diels–Alder and Cation–olefin Cyclization Sequence: a Concise Way to Fused Chiral Cyclopenta[b]piperidines

An asymmetric aza-Diels–Alder and cation–olefin cyclization sequence has been developed to construct cyclopenta[b]piperidine skeletons with moderate yields and excellent stereoselectivities, by employing 5-enals and N-Ts-1-aza-1,3-butadienes as the starting materials. A designed domino cation–olefin/Friedel–Crafts reaction verified that the cyclization of N-Ts iminium ion underwent a stepwise cationic process.