Bisguanidinium-Catalyzed Epoxidation of Allylic and Homoallylic Amines Under Phase Transfer Conditions

A highly enantioselective epoxidation reaction of allylic and homoallylic amines has been disclosed using an ion pair catalyst, which consists of a chiral cationic bisguanidinium [BG]2+and achiral tetraperoxyditungstate anion [W2O2(u-O)(O2)4]2-. The terminal oxidant is stoichiometric amount of aqueous hydrogen peroxide, an environmentally benign reagent. Excellent enantiomeric excess (up to 96%) and yields (up to 99%) were achieved for 1,1’- disubstituted and 1,2-disubstituted allylic protected amines and 1,2-disubstituted homoallylic protected amines. The identity of the ion pair catalyst was uncovered using X-ray crystallography and revealed that the achiral tetraperoxyditungstate anion species [W2O2(u-O)(O2)4]2- is nudged nicely into the central cavity of the chiral dication. The ion pair catalyst was also characterized using IR and Raman spectroscopies. The synthesis of (-)-Venlafaxine was achieved via this new methodology to demonstrate its usefulness.