Polyacrylic Acid Supported L-proline as an Effective Heterogeneous Catalyst for the Direct Asymmetric Aldol Reaction

Abstract

Introduction: L-proline is an efficient chiral small-molecule organocatalyst for the direct asymmetric aldol reaction between unmodified acetone and a variety of aldehydes. background: The direct asymmetric aldol reaction is an effective method to construct C-C bonds in an enantioselective fashion. L-proline, as an efficient chiral small-molecule organocatalyst for the direct asymmetric aldol reaction between unmodified ketone and a variety of aldehydes, is widely used in the synthesis of natural products and drug molecules. However, it is difficult to separate and recover from the reaction medium. Method: However, it is difficult to separate from the reaction medium for reuse. In this work, polyacrylic acid (PAA) supported The acylation reaction between L-hydroxyproline and PAA prepared l-proline (P(AA-co-PA)) catalysts with various catalyst loadings. Fourier characterized them transforms infrared spectroscopy, nuclear magnetic resonance spectrum, gel permeation chromatography and thermogravimetry analysis. objective: The introduction of some hydrophilic groups into the macromolecular chains is to make the supported L-proline catalyst not only insoluble in the organic phase but also capable of enhancing the hydrogen bonding, thus improving the activity and selectivity. Result: These macromolecular catalysts were used to catalyze acetone and benzaldehydes' direct asymmetric aldol reaction. The influence of the catalyst structure on the catalytic performance was studied, and the reaction conditions were optimized. method: Polyacrylic acid (PAA) supported L-proline (P(AA-co-PA)) catalysts with 20% - 80% loadings were prepared by the acylation reaction between L-hydroxyproline and PAA. They were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectrum and gel permeation chromatography. These macromolecular catalysts were used to catalyze the direct asymmetric aldol reaction of acetone and p-nitrobenzaldehyde. Conclusion: The results showed that P(AA-co-PA) with 50 mol% catalyst loading had excellent catalytic performance, much higher than that of L-proline and L-hydroxyproline. Its recovery was achieved by simple filtration. After being reused 7 times, its catalytic performance was still higher than that of L-proline. result: The results showed that P(AA-co-PA) with 50% loading had excellent catalytic performance. At 25 ℃, the yield of β-hydroxyketone reached 88% with high enantiomeric excess value (84%), much higher than that of L-proline and L-hydroxyproline. Moreover, the recovery of the macromolecular catalyst was achieved by simple filtration. After being reused for 7 times, its catalytic performance was still higher than that of L-proline. other: None