Exploiting supramolecular interactions for asymmetric catalysis.

Supramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi-pi interactions and electrostatic effects. The aim of this thesis is the use of this type of interactions, in particular hydrogen bonding, for the development of new catalytic systems. In the first part of the work the synthesis of a new class of supramolecular bis(oxazolines) named SupraBox using urea moiety as self-assembly inducer is reported. A library of 16 ligands, with different degree of structural diversity, were prepared by a 3-step modular synthesis starting from readily available starting materials. Palladium- and Copper-complexes were characterized by NMR spectroscopy, UV spectroscopy and mass spectrometry to investigate their structures and properties and used as catalysts in kinetic resolutions of racemic diols and in the desymmetrization of meso diols with good results. In the second part, a new class of peptidomimetic organocatalysts starting from two bifunctional diketopiperazines was investigated. Four different organocatalysts were prepared and tested in the conjugate addition reaction of several aldehydes to beta-nitrostyrene and (E)-2-(furan-2-yl)nitroethene with good to excellent diastereo- and enantioselectivities. A rationale for the mechanism is also proposed: a Monte Carlo/Energy Minimization (MC/EM) conformational search by molecular mechanics methods was undertaken on the four catalysts proving the importance of hydrogen bonding between catalyst and substrate.