The asymmetric reduction of β-keto esters to their corresponding hydroxy alcohols can be performed by employing homogeneous and heterogeneous chemo- and bio-catalysis. This review covers the scope and limitations of ...The asymmetric reduction of β-keto esters to their corresponding hydroxy alcohols can be performed by employing homogeneous and heterogeneous chemo- and bio-catalysis. This review covers the scope and limitations of different catalysts and methodologies that were employed for the reaction and compare between them on the basis of catalytic performance, product separation and catalyst recycling procedure. In general, heterogeneous catalytic systems are advantageous from industrial point of views as they can be easily separated by filtration and re-used. Nickel modified with tartaric acid and sodium bromide was found to be suitable heterogeneous catalyst for the enantioselective hydrogenation, yet its performance is lower than this of homogeneous chiral metal catalysts such as Ru-BINAP. Heterogenization of the chiral complex via immobilization or entrapment using organic and inorganic supports was thus tested. However, though the resulted heterogeneous analogues were highly enantioselective and could be re-used, the activity of the system is often very low compared to homogeneous system due to mass transfer limitations. Alternatively, performing liquid phase hydrogenation under homogeneous conditions, using Ru-BINAP soluble derivatives, yielded high activit5＇ and enantioselectivity. Product separation and catalysts recycling were facilitated by either extraction of the product with solvent that does not dissolve the complex or by selective filtration of the product. Alternatively, precipitation of the complex at the end of the reaction was also reported.展开更多
文摘The asymmetric reduction of β-keto esters to their corresponding hydroxy alcohols can be performed by employing homogeneous and heterogeneous chemo- and bio-catalysis. This review covers the scope and limitations of different catalysts and methodologies that were employed for the reaction and compare between them on the basis of catalytic performance, product separation and catalyst recycling procedure. In general, heterogeneous catalytic systems are advantageous from industrial point of views as they can be easily separated by filtration and re-used. Nickel modified with tartaric acid and sodium bromide was found to be suitable heterogeneous catalyst for the enantioselective hydrogenation, yet its performance is lower than this of homogeneous chiral metal catalysts such as Ru-BINAP. Heterogenization of the chiral complex via immobilization or entrapment using organic and inorganic supports was thus tested. However, though the resulted heterogeneous analogues were highly enantioselective and could be re-used, the activity of the system is often very low compared to homogeneous system due to mass transfer limitations. Alternatively, performing liquid phase hydrogenation under homogeneous conditions, using Ru-BINAP soluble derivatives, yielded high activit5＇ and enantioselectivity. Product separation and catalysts recycling were facilitated by either extraction of the product with solvent that does not dissolve the complex or by selective filtration of the product. Alternatively, precipitation of the complex at the end of the reaction was also reported.
