Asymmetric FeII-Catalyzed Thia-Michael Addition Reaction to α,β-Unsaturated Oxazolidin-2-one Derivatives

A highly enantioselective Fe-II-catalyzed thia-Michael addition to alpha,beta-unsaturated carbonyl derivatives was developed. The scope of the reaction was demonstrated with a selection of aromatic, heterocyclic and aliphatic thiols, and various Michael acceptors. The corresponding beta-thioethers were obtained in good to excellent yields (up to 98%) and moderate to excellent enantioselectivities (up to 96:4 er). Unusual hepta-coordination of the metal and chelation to alpha,beta-unsaturated oxazolidin-2-one derivatives allowed the construction of a coherent model rationalizing the enantios elective event. DFT calculations support the proposed model for observed stereoselectivities.