Catalytic Asymmetric Addition of Dialkylzinc to 3,4-Dihydroisoquinoline N-Oxides Utilizing Tartaric Acid Ester as a Chiral Auxiliary

The catalytic asymmetric addition of dialkylzinc to a carbon-nitrogen double bond in 3,4-dihydroisoquinoline N-oxides was achieved by utilizing a catalytic amount of 2-magnesium 3-zinc salt of dicyclopentyl (R,R)-tartrate to afford (S)-1-alkyl-2-hydroxy-1,2,3,4-tetrahydroisoquinolines. In order to realize higher enantioselectivity, it was crucial to add the nitrones slowly into dialkylzinc in the presence of a catalytic amount of the 2-magnesium 3-zinc salt of (R,R)-tartrate.