Cross double Mannich reaction catalyzed by I2: Synthesis of highly substituted 4-piperidones

Cross double Mannich reaction and tandem cyclization were achieved under iodine catalyzed conditions, yielding a series of highly substituted 4-piperidones. Among the possible diastereomers, only one diastereomer was isolated, which could be ascribed to the chair-like transition state in six-membered ring, in which all of the hindered groups are located in the pseudoequatorial orientation.