Catalytic Asymmetric Synthesis of Piperidine Derivatives through the [4 + 2] Annulation of Imines with Allenes

Although tertiary phosphines have emerged as remarkably versatile nucleophilic catalysts, there has been only very limited progress in achieving asymmetric catalysis with chiral phosphines. In this report, the first highly enantioselective variant of the Kwon annulation of imines with allenes is described. Thus, C2-symmetric chiral phosphepine 1 serves as an effective catalyst for this powerful process, furnishing an array of functionalized piperidine derivatives with very good stereoselectivity.