A class of zwitterionic organocatalysts based on an amide anion/iminium cation charge pair has been developed. The zwitterions are easily prepared by reacting aziridines with aminopyridines. They are catalytically applicable to transesterifications and dehydrative esterifications. Mechanistic studies reveal that the amide anion and iminium cation work synergistically in activating the reaction partners, with the iminium cationic moiety interacting with the carbonyl substrates through nonclassical hydrogen bonding. The reaction can be applied to large-scale synthesis of biodiesel under mild conditions.

α,α-Dihalo-N-arylacetamides are commonly used as intermediates in various organic reactions. In the study described here, a catalytic synthesis of α,α-dihalo-N-arylacetamides from β-oxo amides was developed using zwitterionic catalysts and N-halosuccinimides as the halogen sources. The corresponding α,α-dihalo-N-arylacetamides were obtained in good to excellent yields, and no aromatic halogenated side products were detected. The reaction conditions were mild, and no strong base or acid was required.

Fumaric acid diesters are important building blocks for organic synthesis. A class of zwitterionic organocatalysts based on an amide anion/iminium cation charge pair were found to be effective in catalyzing the isomerization of maleic acid diesters to give fumaric acid diesters. Comparison of the performance of different zwitterionic organocatalysts toward the reaction revealed that nonclassical hydrogen bonding was involved in the stabilization of the Michael adduct intermediate.