Tartaric Acid Derived Chiral Guanidine-Catalyzed Asymmetric Epoxidation Of N-Sulfonyl Imines

Asymmetric organocatalysis began in2000, and achieved rapid development in the past ten years. Chiral organocatalysts in many cases, are inexpensive, robust, and readily available, so they have many applications in asymmetric catalysis.A series of tartaric acid derived chiral guanidines were synthesised using diethyl L-tartrate as starting materials through a straightforward seven-step sequence, and were used to catalyze the reaction of asymmetric epoxidation of N-sulfonyl imines. The reaction parameters such as catalyst, solvent, temperature and oxidant were studied, and the optimized reaction conditions were established. Under the optimal conditions, we explored the substrate scope of the N-sulfonyl imines and eighteen oxaziridines were synthesized with excellent yields (up to98%) and good enantioselectivities (up to88%ee). The products obtained were identified by1H NMR,13C NMR and HRMS.Optically active oxaziridines as oxidizing agents have been widely applied in asymmetric syntheses, such as enantioselective hydroxylation of enolates, asymmetric epoxidation of olefins, and enantioselective oxidation of sulfides. Synthesis of a series of chiral oxaziridines for asymmetric oxidation of organic compounds has great significance.