New β-aminoalcohol-based nanostructured magnetic catalyst and its application on enantioselective Henry reaction

The Henry reaction, also named nitroaldolic, is one of the most important ways to form a C-C bond and it is promising due to its economy and high versatility of the nitro group,[1] which can be transformed in several functional groups through the Nef reaction.[2] Therefore many high efficient catalytic systems have been developed to perform the asymmetric version of this reaction, and few of them are based on a chiral β-aminoalcohol- CuII complex.[3] Catalyst L1, developed in a previous work by our research group, has provided good results in the asymmetric addition of nitromethane to aromatic aldehydes (Scheme 1). However homogeneous asymmetric catalysis has the disadvantage of poor recovery of the catalyst from reaction mixture, so nowadays many efforts have been carried out on heterogeneous catalysis using nanomaterials as supports for chiral ligands.[4] The aim of this work is to present a highly efficient nanostructured catalytic system (L2), obtainable through a Copper-Catalyzed Azide Alkyne Cycloaddition (CuAAC) on azido functionalized silica coated magnetite nanoparticles. Initially we also synthetized ligand L3, an analogous of L2, to verify its homogeneous phase catalytic activity in the addition of nitromethane to aromatic aldehydes, in the presence of Cu(OAc)2. In this communication we report on the employment of catalysts L2 and L3 in the addition of nitromethane to aromatic aldehydes. Specifically, we confirmed the retained catalytic activity of L3 by testing it on a variety of aldehydes; moreover, the preliminary results obtained with the magnetically recoverable and reusable nanocatalyst L2 appeared totally comparable both in terms of yield and ee to those in homogeneous phase tests. Further attempts with different substrates are currently ongoing