Stereoselective conjugate addition of lactams to nitroalkenes and formal total synthesis of indolizidine 167B

Optically active 5-substituted pyrrolidin-2-ones underwent conjugate addition to nitroalkenes to give the corresponding adducts in a diastereoselective manner. The presence of 18-crown-6 was crucial to achieve good stereoselective addition. Addition of 6-substituted piperidin-2-ones also gave the corresponding adduct in a stereoselective manner. The adduct was readily converted into a bicyclic lactam through intramolecular nitroaldol reaction, and the formal synthesis of indolizidine 167B was achieved.