TfOH‐Catalyzed self‐Condensation of β‐Aminoketones for the Synthesis of Tetrahydropyridines

A novel self‐condensation of β‐aminoketones was described. Various multisubstituted 1, 2, 3, 6‐tetrahydropyridine derivatives were synthesized in medium to good yields in the presence of 20 mmol% of TfOH. This transformation probably processed a decomposition of β‐aminoketones (also named retro‐Michael addition), followed by intermolecular Michael addition and intramolecular ring closure. Furthermore, 1, 2, 5, 6‐tetrahydropyridines were obtained in a one‐pot manner through DBU‐promoted isomerization of the in‐situ generated 1, 2, 3, 6‐tetrahydropyridines. The present method exhibited good functional group tolerance, and convenient operation, making it a practical alternative for the construction of multisubstituted tetrahydropyridines.