A novel (S)-proline-modified task-specific chiral ionic liquid—an amphiphilic recoverable catalyst for direct asymmetric aldol reactions in water

Ionic Liquid Immobilized Organocatalysts for Asymmetric Reactions in Aqueous Media

“…Under aqueous conditions, catalyst 3, 6c and 8 with long alkyl chains on the imidazolium cations gave poor yields owing to the polymerization of nitrostyrene (Scheme 1). In 2008, Zlotin et al [54] designed and synthesized a new type of IL immobilized proline catalysts, 9a and 9b, which contain a long-chain hydrocarbon group (Scheme 2). Owing to the amphiphilic character of the two catalysts, excellent diastereoselectivities (anti/syn ratio up to 97:3) and enantioselectivities (up to 99% ee) of the aldol reaction between cyclic ketones and aromatic aldehydes in water were obtained.…”

Application of Chiral Ionic Liquids for Asymmetric Induction in Catalysis

“…In a previous work by Zlotin and co-workers, similar proline based CILs also displayed a good efficiency to promote asymmetric aldol reaction (Scheme 15, Table 11) [47].…”

Pursuing Chemical Efficiency by Using Supported Organocatalysts for Asymmetric Reactions under Aqueous Conditions

“…Better results were observed using ionic liquid-functionalized 4-trans-hydroxy-L-proline derivatives 39 (Figure 11), although a higher catalyst loading (30 mol%) was necessary to afford the corresponding aldol products (20-95%, 71-94% de, 80-99% ee) in water as solvent. The catalyst was recovered from the reaction by extraction and reused up to five times without detrimental on the achieved results [103]. A higher recyclability, up to 8 cycles, was displayed using compound 40 (15 mol%, Figure 11) as catalyst in the aldol reaction between an array of cyclic ketones and aromatic aldehydes in water at 25 ºC, giving good yields (38-97%) and excellent diastereo-and enantioselectivities (60-94% de, 92-99% ee) [104].…”