Enantioselective Organocatalytic Reduction of beta-Trifluoromethyl Nitroalkenes: An Efficient Strategy for the Synthesis of Chiral beta-Trifluoromethyl Amines

An efficient organocatalytic stereoselective reduction of -trifluoromethyl-substituted nitroalkenes, mediated by 3,5-dicarboxylic ester-dihydropyridines (Hantzsch ester type), has been successfully developed. A multifunctional thiourea-based (S)-valine derivative was found to be the catalyst of choice, promoting the reaction in up to 97%ee. The methodology has been applied to a wide variety of substrates, leading to the formation of differently substituted precursors of enantiomerically enriched -trifluoromethyl amines. The mechanism of the reaction and the mode of action of the metal-free catalytic species were computationally investigated; on the basis of DFT transition-state (TS) analysis, a model of stereoselection was also proposed.