Amino−Zinc−Enolate Carbometalation Reactions: Application to Ring Closure of Terminally Substituted Olefin for the Asymmetric Synthesis of <i>cis</i>- and <i>trans</i>-3-Prolinoleucine
The reaction is stereospecific, leading to a trans-3-substituted proline derivative, whereas a cis stereochemistry was observed with the amino-zinc-enolate cyclization of terminally nonsubstituted olefins. Absolute configurations obtained for the 3-prolinoleucine were established by X-ray analysis, NMR, and optical activity comparison of the cis and trans derivatives obtained by an unambiguous pathway