Homogeneous asymmetric Diels-Alder reaction using copper(II) porphyrin-DNA complexes as asymmetric catalysts in ionic liquid solutions

Abstract

Taking advantage of the excellent dissolution ability of ionic liquids, which can also dissolve DNA and hydrophobic compounds, we investigated the homogeneous asymmetric Diels-Alder reaction using DNA, a natural chiral source, and porphyrin copper(II) complexes as asymmetric catalysts in ionic liquid solutions. In [N₄₄₄₄][Gly], the reaction substrates were phase-separated, and the reaction mixture gelled or solidified at low temperatures, resulting in ineffective asymmetric catalysis. However, the reaction proceeded in a homogeneous system in 75 % [N₁₂₂₃][N(CN)₂], which is not possible in water alone, and high yield, diastereoselectivity, and enantioselectivity were obtained at -20 °C. The utilization of ionic liquids as solvents would not only enable homogeneous reactions, but also reactions at low temperatures, and would be a powerful tool for high stereoselectivity in DNA-organometallic-catalyzed asymmetric reactions.