Intramolecular Cyclization of Ene-Imine Using Dibutylzirconocene

The reaction of ene-imine with Cp₂ZrBu₂ was carried out. When a crude imine, which was prepared from ene-aldehyde and primary amine in the presence of MgSO₄, was treated with Cp₂ZrBu₂ at room temperature overnight, cyclopentane derivative having trans-substituents was obtained in high yield along with a small amount of cyclopentane derivative having cis-substituents. Presumably, cis-zirconacycle is a thermodynamic product. Reactions using various ene-imines were carried out. In the case of ene-imine prepared from ene-aldehyde and ^tBuNH₂, only cyclopentane having cis-substituents was produced. In this reaction, chiral amine was used, and diastereoselective cyclization of ene-imine was carried out. As a result, cyclopentane derivative having cis-substituents was obtained in an optically active form after hydrogenolysis of the cyclized compound.