Organocatalytic Asymmetric Synthesis of trans-γ-Lactams.

An N-heterocyclic carbene (NHC)-catalyzed highly diastereo- and enantioselective formal [3+2] reaction of o-hydroxy aromatic aldimines and cinnamaldehydes for the preparation of enantioenriched trans-gamma-lactams was developed. An internal hydrogen bond between the o-hydroxy and the imine function was crucial for the reactivity and chemical selectivity. Trans-gamma-lactam 3d was easily oxidized to multifunctional 1,4-benzoquinone 8, which could further be transformed to biaryl 9 in the presence of a phosphoric acid. Finally, preliminary results for a kinetic resolution of (+/-)-trans-gamma-lactam 3d under asymmetric NHC catalysis are reported.