Theoretical elucidation on the functional role of pyrrolidine‐type ionic liquids in inducing stereoselectivity of the Michael addition of cyclohexanone with trans‐β‐nitrostyrene

Abstract

Density functional theory calculations have been carried out to elucidate the stereoselectivity of the Michael addition of cyclohexanone with trans-β-nitrostyrene, induced by a chiral ionic liquid (CIL) pyrrolidine-imidazolium bromide. By comparison of the C-C bond forming processes in the absence and presence of Br(-) anion, we found that intermolecular H-bonds between the imidazolium cation and the nitro group of trans-β-nitrostyrene and the steric hindrance of the imidazolium cation moiety on the Si-face of enamine dominate the stereoselectivity of the Michael addition. The presence of Br(-) anion obviously reduces the barrier by increasing the polarity of the C4=C5 bond of enamine. The theoretical results rationalize well the early experimental finding, and reveal a valuable clue for the further CIL design with high catalytic efficiency.