Microwave-promoted racemization and dynamic kinetic resolution of chiral amines over Pd on alkaline earth supports and lipases

Abstract

Microwave irradiation was applied in the racemization and dynamic kinetic resolution of primary benzylic amines. Racemization reactions catalyzed by 5% Pd/BaSO 4 and 5% Pd/CaCO 3 were faster and more selective when performed under microwave conditions. The use of microwave irradiation stopped the formation of side products, such as secondary amines and ethylbenzene. This was correlated with the selective heating of the metal sites under microwave heating. The influence of the microwave irradiation also was checked in the kinetic resolution; no influence on the activity and enantioselectivity of the immobilized Candida Antarctica Lipase B (Novozym 435) was observed when both conventional and microwave heating were compared. The racemization catalysts were combined in one pot with the biocatalyst Novozym 435 to perform the dynamic kinetic resolution of benzylic amines under microwave irradiation. High yields (up to 88%) of enantiopure amides were obtained in less than 1 h when microwave irradiation was applied.