Stereocontrolled Total Synthesis of (−)-Kainic Acid. Regio- and Stereoselective Lithiation of Pyrrolidine Ring with the (+)-Sparteine Surrogate

[reaction: see text] A stereocontrolled total synthesis of (-)-kainic acid is described. cis-3,4-Disubstituted pyrrolidine ring was constructed by [3 + 2] cycloaddition of azomethine ylide with chiral butenolide. The crucial introduction of carboxyl group at the C-2 position was executed by regio- and stereoselective lithiation of the pyrrolidine ring in the presence of a (+)-sparteine surrogate followed by trapping with carbon dioxide.