Counterion-Induced Asymmetric Control in Ring-Opening of Azetidiniums: Facile Access to Chiral Amines.

Counterion-induced stereocontrol is a powerful tool in organic synthesis. However, such enantiocontrol on tetrahedral ammonium cations remains challenging. Described here is the first example of using chiral anion phase-transfer catalysis to achieve intermolecular ring-opening of azetidiniums with excellent enantioselectivity (up to 97 % ee). Precise control over the formation and reaction of the chiral ion pair as well as inhibition of the background reaction by the biphasic system is key to the success of the reaction.