Mechanistic details of amino acid catalyzed two-component Mannich reaction: experimental study backed by density functional calculations

The role of pH-dependent ionic structures of L-amino acids in catalysis has been investigated for the two-component Mannich reactions between dimethyl malonate (DMM)/ethyl acetoacetate (EAA) and imines. As catalysts, L-amino acids performed well, even better than corresponding base catalysts and provided the β-amino carbonyl compounds in very high yields. Density functional calculations were used to gain the mechanistic insight of the reaction. High catalytic efficiency of amino acids was attributed to the facile formation of carbanion intermediate through barrierless transition state TS1 (- 19.43 kcal/mol) and then its stabilization owing to carbanion interaction with protonated amino acid.