Ionic-liquid tagged prolines as recyclable organocatalysts for enantioselective α-aminoxylations of carbonyl compounds

With the aim of improving catalytic performance and recyclability various ionic-liquid-tagged organocatalysts (ILTOCs) based on (S)-proline as organocatalysts and triazolium or guanidinium salts as ionic liquid tags were applied in the asymmetric α-aminoxylation of ketones and aldehydes with nitrosobenzene in IL as solvents. Amongst such ILTOC’s compounds were found which performed better (ee >99%, yield 97%) than (S)-proline in reported cases. Recycling and reusage of ILTOCs were easily possible and yields higher than 80% and ees higher than 90% were obtained until the fifth cycle. Important information about the crucial role of water in recycling of proline-derived organocatalysts in reactions with carbonyl compounds via enamine activation was found to prevent blockade of the organocatalyst by oxazolidinone formation.