Synthesis towards complex bridged alkaloids derived from diketopiperazines: a cationic cascade approach to stephacidins, paraherquamides and related systems

Regioselective enolate formation, followed by stereoselective electrophilic quenching of unsymmetrical proline-derived diketopiperazines (DKPs), enabled the synthesis of variously substituted DKPs, including one substrate which could be further substituted and cyclised to give the bicyclo[2.2.2]diazaoctane core structure present in paraherquamide and stephacidin natural products.