Bisguanidinium-Catalyzed Epoxidation of Allylic and Homoallylic Amines under Phase Transfer Conditions
Kek Foo Chin, Xinyi Ye, Yongxin Li, Richmond Lee, Adil Kabylda, Dasheng Leow, Xin Zhang, Esther Cai Xia Ang, Choon‐Hong Tan
Abstract
A highly enantioselective epoxidation reaction of allylic and homoallylic amines has been disclosed using an ion pair catalyst, which consists of chiral cationic bisguanidinium [BG]2+ and an achiral tetraperoxyditungstate anion [W2O2(μ-O)(O2)4]2–. The terminal oxidant is a stoichiometric amount of aqueous hydrogen peroxide, an environmentally benign reagent. Up to 96% enantiomeric excess and 99% yields 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(μ-O)(O2)4]2– is nudged nicely into the central cavity of the chiral dication. The ion pair catalyst was also characterized using infrared (IR) and Raman spectroscopies. The synthesis of (−)-venlafaxine was achieved via this reported methodology to demonstrate its usefulness.