Total synthesis of (-)-(α)-kainic acid via a diastereoselective methylenecyclopropane ring expansion

A concise and enantioselective synthesis of (-)-(alpha)-kainic acid in 13 steps with an overall yield of 15% is reported. The pyrrolidine kainoid precursor with the required C2/C3 trans stereochemistry was prepared with excellent diastereoselectivity (> 20:1) via a MgI2-mediated ring expansion of a tertiary methylenecyclopropyl amide. A selective hydroboration was then employed to set the remaining stereochemistry at the position en route to (-)-(alpha)-kainic acid.