Ionic‐Liquid‐Supported Organocatalyst: Efficient and Recyclable Ionic‐Liquid‐Anchored Proline for Asymmetric Aldol Reaction

Abstract

Ionic-liquid-anchored (2S,4R)-4-hydroxyproline 12 catalyzes direct asymmetric aldol reactions with comparable enantioselectivities in DMSO, and with superior enantioselectivities in neat acetone or 2-butanone, than (S)-proline (8) (up to 28 % ee difference) itself. Furthermore, the supported catalyst 12 can be easily recycled and reused for at least four times without significant loss of yields and enantioselectivity.

Application of Chiral Ionic Liquids for Asymmetric Induction in Catalysis

“…Enantiomeric excess could not be determined in some cases, while in other cases, it was above 80%. It was also tested the reaction of cyclohexanone with nitrostyrene catalyzed by both CILs (45,46). In this case, these organocatalysts result in high yields (up to 99%), good enantioselectivities (up to 85%), and high diastereoselectivities (syn/anti ratio up to 97:3).…”

“…In 2006, Chan and coworkers have described the syntheses of new proline-based CILs (52, 53) and the application of these ILs in asymmetric aldol reaction between ketones and aldehydes under mild conditions (Scheme 13) [45]. In particular for the reaction of 4-cyanobenzaldehyde and acetone, the CIL 52 gave better results in yield (59%) and ee (72%) in contrast to those obtained with CIL 53 (10% yield and 11% ee).…”

A Snapshot of Ionic-Liquid-Tagged Proline-Based Organocatalysts

“…From a mechanistic standpoint, Zlotin has stated that 'they [IL-tagged organocatalysts] create the hydrophobic environment of the enamine-type transition state, which resembles a hydrophobic pocket of aldolases, which is essential for efficient reaction stereocontrol'. [15] The first report of an IL-tagged organocatalyst based on the proline scaffold was by Miao and Chan in May 2006, [16] although there was a near concurrent report of a pyrrolidinebased organocatalyst reported by Luo et al [17] in April of the same year. The catalyst design adopted by Chan (1, Fig.…”

Synthesis of D-pantolactone via Combined a Novel Organocatalyst Catalyzed Asymmetric Aldol Reaction and Hydrogenation Catalyzed by Cu-/SiO<sub>2</sub>

“…In nature, small organic molecules, in particular amino acids [11][12][13] and their derivatives [14][15][16][17], are rich chiral sources, which are used as the catalysts, but with recycling problems, such as extensive work-up procedures with the corresponding waste generation or more time to recover the catalyst between two cycles [18][19][20]. However ionic liquids (ILs) have been widely used as environmentally benign solvents to replace common organic media [21] with advantages of reusable, strong design ability, low pollution, low toxicity, and excellent miscibility with organic compounds [22][23][24]. Because of the above-mentioned highly tunable characteristics (broad cation/anion combinations) and the enhancement of reaction efficiency by using ILs as solvents [25][26], ILs have gained wide recognition in specific engineering, especially as catalysts to catalyze aldol reactions [27][28].…”