Bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pair-catalyzed enantioselective sulfoxidation

Catalytic use of peroxomolybdate for asymmetric transformations has attracted increasing attention due to its catalytic properties and application in catalysis. Herein, we report chiral bisguanidinium dinuclear oxodiperoxomolybdosulfate [ BG ] 2+ [(μ-SO 4 )Mo 2 O 2 (μ-O 2 ) 2 (O 2 ) 2 ] 2− ion pair, as a catalyst for enantioselective sulfoxidation using aqueous H 2 O 2 as the terminal oxidant. The ion pair catalyst is isolatable, stable and useful for the oxidation of a range of dialkyl sulfides. The practical utility was illustrated using a gram-scale synthesis of armodafinil, a commercial drug, with the catalyst generated in situ from 0.25 mol% of bisguanidinium and 2.5 mol% of Na 2 MoO 4 ·2H 2 O. Structural characterization of this ion pair catalyst has been successfully achieved using single-crystal X-ray crystallography.