Proline‐Catalyzed Highly Enantioselective and anti‐Selective Mannich Reaction of Unactivated Ketones: Synthesis of Chiral α‐Amino Acids

Universal L-proline: The title reaction complements well-known syn-selective Mannich reactions. The Mannich products can be converted readily into the free amino acids by hydrogenolytic deprotection under mild conditions (see scheme). DMSO=dimethyl sulfoxide; R1=alkyl, OH; R2=alkyl.