Asymmetric Michael addition of carbonyl compounds to N-substituted maleimides is an
important method for obtaining optically pure succinimides, which are important chiral
fine chemical intermediates. Environmentally friendly and sustainable procedures require
the use of a heterogeneous, recyclable catalyst obtained from natural chirality sources
and cheap auxiliaries. Here we report the application of in situ formed chiral inorganic-organic
hybrid catalysts using amino acids such as l-phenylalanine and clay minerals or alumina,
which were highly active and provided excellent enantioselectivities, up to 99%, in
the addition of aldehydes to a large variety of N-substituted maleimides. Examinations
indicated the occurrence of the asymmetric reaction on the surface of the recyclable
solid hybrid materials. The catalytic materials were examined by thermogravimetry,
XRD, FT-IR and Raman spectroscopy, SEM and adsorption experiments. Results of these
methods showed that the amino acid is deposited as surface crystallites or intercalated
in the layered cation exchangers, which both function as a supply of the chirality
source, whereas the reactions are catalysed by the chiral compounds adsorbed on the
surface. This catalytic system was used to conveniently prepare chiral succinimides
at the gram scale, easily purified by crystallization. Accordingly, these chiral hybrid
materials are convenient heterogeneous catalysts for obtaining valuable compounds
in high optical purities using natural chirality sources, inorganic solids and ethyl
acetate, a green organic solvent.