Steric and electronic tuning of chiral bis(oxazoline) ligands with 3,3'-bithiophene backbone

Some examples of a new class of bis(oxazolines), displaying flexible and atropisomeric 3,3’-bithiophene backbones were synthesized and structurally and electronically characterized.[1] For the first time, the electrochemical oxidative potential was used as a reliable index of the electronic density on the nitrogen atom of the chelating groups of new and, for comparative purpose, of already known bis(oxazolines). The role played by the electronic properties and the steric features of bis(oxazoline) ligands in the Cu(I)-catalyzed cyclopropanation of styrene effected with ethyl diazoacetate was investigated. The Cu(I)-complexes of the new ligands were prepared and their enantioselection ability and catalytic efficiency were tested. This investigation suggests that steric factors and catalyst geometrical features are clearly more important that any consideration on the electronic properties of the chiral ligands.