Siliceous mesocellular foam-supported aza(bisoxazoline)copper catalysts

Aza(bisoxazoline) was easily immobilized on siliceous mesocellular foam (MCF) in a systematic approach. It was found that silanol precapping, linker group flexibility, ligand loading, and silanol postcapping were important factors to consider in optimizing silica-supported aza(bisoxazoline) catalysts. The optimized MCF-supported aza(bisoxazoline)-copper catalyst offered the same enantioselectivity as its homogeneous counterpart, and excellent recyclability. The heterogenized catalyst showed a much higher chemoselectivity in a short reaction time. The heterogenized aza(bisoxazoline)-copper(I) catalyst was successfully applied to a circulating flow-type packed bed reactor with excellent productivity and enantioselectivity. The circulating flow-type reactor was found to be very useful for gas-generating catalytic reactions such as cyclopropanation reaction.