Recyclable silica-supported prolinamide organocatalysts for direct asymmetric Aldol reaction in water

Abstract

Asymmetric organocatalytic materials based on a prolinamide scaffold have been synthesized according to different synthetic routes from a monosilylated precursor: simple or surfactant-assisted co-condensation and grafting on preformed mesostructured silica. The catalytic properties of these materials have been compared for direct asymmetric aldol reactions. The best catalytic material results from a simple co-condensation without structure-directing agent. Simple and green conditions are used for the aldol reaction, the process being performed in water at room temperature, with relatively low amounts of supported organocatalysts and in the absence of an acid co-catalyst. Good recyclabilities are observed without the need for catalyst regeneration, with enantioselectivities (ee up to 92%) higher than that of the parent homogeneous catalysts.