Synthesis of chiral ionic liquids

The interest in using room temperature ionic liquids (RTILs) as potential replacement solvents for organic synthesis, extraction, electrochemistry, and materials science has increased tremendously in the recent years. Among them, chiral ionic liquids are particularly attractive due to their potential for chiral discrimination, asymmetric synthesis, optical resolution of racemates, stereoselective polymerization, gas chromatography, NMR shift reagents and liquid crystals. Even though the difficult syntheses of chiral ionic liquids and their high cost often precluded their use, the possibility to use chiral ionic liquids as inducers for asymmetric reactions has greatly prompted researchers to continuely synthesize new chiral solvents. The chiral ionic liquids are designed either from the chiral pool (aminoacids, amines, aminoalcohols, and alkaloids) or by asymmetric synthesis; they can bear central, axial or planar chirality. This review deals mainly with recent advances in synthesis of chiral ionic liquids. Based on the species of cation or anion, they are classified into imidazolium-based, pyridinium-based, ammonium-based, and thiazolinium-based etc. In addtion, some new synthesis techniques are also introduced.