Enantioselective Addition of Vinylzinc Reagents to a Cyclic Nitrone

Significance

This method provides an alternative to the more often studied Pictet-Spengler reaction. The nitrone group is more reactive than most imine analogues and the resulting hydroxylamine 2 is readily reduced to the amine using zinc metal. N-Oxide 1 was prepared with the Na₂WO₄ catalyst in presence of H₂O₂. The method was illustrated by the synthesis of the enantiopure protected amino acid D-Tiq (3), which represents a significant improvement over the previous reports (resolution of the racemic salt).