Abstract
The combination of an asymmetric organocatalytic aldol reaction with a subsequent hydrogenation for the synthesis of D-pantolactone is demonstrated. This process consists of an initial aldol reaction catalyzed by a novel chiral L- histidine-modified-ionic-liquid- [EMIm] [His], which has been designed and synthesized as an efficient recoverable catalyst for the asymmetric aldol reaction with superior enantioselectivity in CH<sub>2</sub>Cl<sub>2</sub>, than L-histidine itself. [EMIm] [His] retains its activity and enantioselectivity over at least five reaction cycles, and its universal applicability has been demonstrated. Moreover optimum process of Cu-/SiO<sub>2</sub>-catalysed hydrogenation of condensation product- (D) -3- formyl -2- hydroxy -3- ethyl butyrate to obtain D-pantolactone has been established allowing the synthesis of D-pantolactone in >99% purity, 93% yield and 93% enantiomeric excesse (ee). The results show that CuO-CeO<sub>2</sub>/SiO<sub>2</sub> exhibits better catalytic activity than CuO/SiO<sub>2</sub> for better dispersion and larger surface area, and the best reaction conditions are as follows: 120°C, <i>n</i> (H<sub>2</sub>): <i>n</i> (isobutylaldehyde) =80:1, P (H<sub>2</sub>) =8.0 MPa, liquid airspeed: 0.6 h<sup>-1</sup>.
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