Highly diastereo- and enantioselective reactions of enecarbamates with an aldehyde

Catalytic asymmetric addition reactions of enecarbamates with ethyl glyoxylate have been developed using CuClO4·4CH3CN and a diimine ligand as the catalyst. Highly diastereo- and enantioselective addition reactions of α-mono-substituted enecarbamates have been also achieved. These reactions afforded the corresponding adducts with high selectivity; that is, syn adducts from Z-enecarbamates and anti adducts from E-enecarbamates. The proposed reaction mechanism is an aza-ene type pathway, where the proton of an enecarbamateʹs N–H group plays an important role, not only for accelerating the reaction but also for providing a transition state suitable for the highly selective chiral induction.