Chiral Zirconium-Catalyzed Asymmetric Mannich-Type Reactions Using Acylhydrazones as Imine Equivalents

In the presence of a catalytic amount of a new zirconium catalyst, prepared from zirconium(IV) t-butoxide and (R)-3,3′-dibromo-1,1′-bi-2-naphthol, 4-trifluoromethylbenzoylhydrazones reacted with silyl enolates to afford the corresponding adducts, β-N′-acylhydrazinocarbonyl compounds, in good yields with high enantiomeric excesses. Reductive cleavage of the nitrogen-nitrogen bond of the hydrazino compound using samarium diiodide gave a chiral β-aminocarbonyl compound. In addition, the hydrazino compound was also successfully converted to chiral β-lactam and pyrazolidinone derivatives.