reaction was performed by using a combined catalyst consisting of a chiral bifunctional primary amine-thiourea 9f and a Brønsted acid with tert-butylammonium trifluoroacetate (t-BuNH2⋅TFA) as additive in dichloromethane at room temperature. The possible mechanism for the reaction has been proposed to explain the origin of the activation and the asymmetric induction.