Highly enantioselective construction of fused pyrrolidine systems that contain a quaternary stereocenter: Concise formal synthesis of (+)-conessine

No protecting groups were required in a concise and atom-economical synthesis of the optically active tetracyclic pyrrolidine 3 under mild conditions. A highly diastereoselective Pauson-Khand reaction (1→2) was used to construct the compact tetracycle with its quaternary stereocenter. The stereoselectivity of the cycloaddition was affected by the substituent on the propargylic moiety.