Ionic liquid-supported proline as catalyst in direct asymmetric aldol reaction

An Efficient and Recyclable Ionic Liquid-Supported Proline Catalyzed Knoevenagel Condensation

“…Ionic liquid-supported proline IV ([Promim]CF 3 COO) was synthesized following a similar route reported previously (Scheme 1) [17]. The [Promim]CF 3 COO (IV) was used to catalyze the Knoevenagel condensation of malononitrile with varying aldehydes and carbonyl derivatives (Scheme 2).…”

“…Ionic liquid-supported proline, 1-Methyl-3-{2-[(2S)-pyrrolidine-2-carbonyloxy]-ethyl}-1H-imidazol-3-ium trifluoroacetate (IV), was prepared and indicated according to the literature [17]. …”

“…The implementation of task specific ionic liquids further enhances the versatility of classical ionic liquids where both reagent and medium are coupled [16]. In our previous study, ionic liquid-supported proline was used to catalyze direct asymmetric aldol reaction [17]. Further, we investigated the catalytic activity of ionic liquid-supported proline for Knoevenagel condensation reactions and the regenerability.…”

The direct catalytic asymmetric aldol reaction

“…As these approaches have been reviewed previously, 10–24 the goal of this review will be to highlight and compare the reactivity, scope and selectivity of a wide range of catalysts, rather than catalogue every example of their use. This review will not focus on design parameters such as catalyst immobilization, 25–35 attaching hydrophobic groups to the catalyst, 30, 36–38 reactions in micelles, 39, 40 host-guest catalytic systems, 41, 42 or the use of ionic liquids 43–54 or surfactants, 55–60 which can be found elsewhere. 12, 13 Instead, this review will highlight what is currently possible synthetically and what challenges remain unmet for enamine-based catalysts.…”

An Ionic Liquid Containing L‐Proline Moiety as Highly Efficient and Recyclable Chiral Organocatalyst for Michael Addition

“…The reactions catalyzed by recovered catalysts showed no decrease in both yield and enantioselectivity. Although the excellent yields and stereoselectivities could be obtained by using this series of ionic liquid‐supported catalysts, the weak ester bonds for linking between the ionic liquid and proline or pyrrolidine can be easily hydrolyzed under the strong external conditions, resulting in the difficulties of the recovery of the catalysts. Lombardo's group used more stable amide bond instead of ester bond to improve the linking between ionic liquid and proline, and the obtained ion‐tagged 4‐hydroxy‐proline was then used successfully as a robust and efficient catalyst to the asymmetric Aldol reaction .…”