The diastereoselectively switchable enantioselective trapping of protic carbamate ammonium ylides with imines is reported. The intriguing Rh(2)(OAc)(4) and chiral Bronsted acid cocatalyzed three-component Mannich-type reaction of a diazo compound, a carbamate, and an imine provides rapid and efficient access to both syn- and anti-alpha-substituted alpha,beta-diamino acid derivatives with a high level control of chemo-, diastereo-, and enantioselectivity.