Investigation of Mn(III)-Based Oxidative Free Radical Cyclization Reactions toward the Synthesis of Triptolide: The Effects of Lanthanide Triflates and Substituents on Stereoselectivity
Mn(III)-mediated oxidative free radicalcyclizationreactions are useful for construction of polycyclic compounds. In the total synthesis of triptolide (3) and its related compounds, construction of tricyclic skeletons 4 and 5 was achieved by the Mn(OAc)3-mediated oxidativeradicalcyclization of a series of acyclic precursors 6−9. The addition of a catalytic amount of lanthanidetriflates was found