A new immobilization scheme for enantioselective catalysts was developed by using a combination of ionic liquids and compressed CO2. Under continuous flow conditions, stable conversion and asymmetric induction was achieved over more than 60 h in the enantioselective Ni‐catalyzed hydrovinylation of styrene. While the ionic liquid dissolves and activates the organometallic catalyst in a tuneable manner, the presence of compressed CO2 greatly facilitates mass transfer and gives easy access to continuous processes (see the schematic representation).

A new and environmentally benign protocol for enzymatic reactions in ionic liquids is described using supercritical CO2 as the mobile phase; the products are obtained in solvent-free form and the enzyme/ionic liquid mixture can be recycled in batchwise or continuous flow operations.

Abstract:The combination of kinetic resolution in ionic liquids (IL) and selective extraction with supercritical carbon dioxide (scCO 2 ) provides a new approach for the separation of enantiomers as exemplified by the lipase-catalyzed esterification of chiral secondary alcohols. Excellent enantioselectivities are achieved upon conversion of alcohols 1a ± e to the corresponding acetates 4a ± e or laureates 5a ± e using various modifications of the lipase from Candida antarctica (CaL-B) in imidazolium-based ionic liquids. The anion of the ionic liquid has a significant influence on the performance of the bio-catalyst with bis(trifluoromethanesulfonamide) [BTA] giving the best results. The acetates 4a ± e can be extracted from the reaction mixture preferentially over the alcohols 1a ± e with scCO 2 under certain conditions, but preparatively useful selectivities would require advanced multi-step extraction procedures. In contrast, efficient separation is possible with relatively simple equipment if alcohols 1a ± e are extracted preferentially from their corresponding laureates 5a ± e. A ™green∫ continuous process for the resolution of racemic alcohols without the use of organic solvents was devised on the basis of these findings.