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.