The instability of carbamate-protected alkyl imines has greatly hampered the development of catalytic asymmetric Mannich reactions suitable for the synthesis of optically active carbamate-protected chiral alkyl amines. A highly enantioselective Mannich reaction with in situ generation of carbamate-protected imines from stable α-amido sulfones catalyzed by an organic catalyst has been developed. This reaction provides a concise and highly enantioselective route converting aromatic and aliphatic aldehydes into optically active aryl and alkyl β-amino acids.