Enantioselective Addition of Vinylzinc Reagents to 3,4-Dihydroisoquinoline <i>N</i>-Oxide

Ligand <b>2a</b> promotes the enantioselective addition of vinylzinc reagents to 3,4-dihydroisoquinoline <i>N</i>-oxide to yield chiral allylic hydroxylamines. With 0.1 equiv of the ligand, the product is obtained in up to 84% ee, whereas with 1.2 equiv of the ligand, the ee is increased to the 90−95% range with a variety of aliphatic, cyclic, and aromatic vinylzinc reagents. This method was used to synthesize the protected unnatural amino acid <i>N</i>-Cbz-d-1,2,3,4-tetrahydroisoquinoline-1-carboxylic acid in three steps from the allylic hydroxylamine.