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

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 2Cl 2, 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 2-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 2/SiO 2 exhibits better catalytic activity than CuO/SiO 2 for better dispersion and larger surface area, and the best reaction conditions are as follows: 120°C, n (H 2): n (isobutylaldehyde) =80:1, P (H 2) =8.0 MPa, liquid airspeed: 0.6 h -1.