Theoretical study on the enantioselective α-amination reaction of 1,3-dicarbonyl compounds catalyzed by a bifunctional-urea

The direct catalytic enantioselective alpha-amination reaction of carbonyl compounds, a powerful approach to asymmetric carbon-nitrogen bond-forming, has been extensively studied, however, our understanding of the mechanism is far from complete. A theoretical study is presented for the a-amination reaction of 2-acetylcyclopentanone with azodicarboxylate catalyzed by a urea-based chiral bifunctional organocatalyst. By performing density functional theory (DFT) calculations, we have identified a detailed mechanism of the reaction and the roles of the amino group and urea in the catalyst. The structures of the catalyst, substrates, intermediates, and transition states involved in the reaction have been located along four possible reaction channels. The rate-determining step is the C-N bond-forming step. The calculations show that the catalyst promotes the reaction by deprotonating 2-acetylcyclopentanone and forming hydrogen bonds with the substrates. The origin of enantioselectivity of the reaction is also discussed. (c) 2007 Published by Elsevier Ltd.