Steric and Electronic Tuning of Chiral Bis(oxazoline) Ligands with 3,3‘-Bithiophene Backbone

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. Two
pairs of new bis(oxazolines) displaying flexible and atropisomeric 3,3‘-bithiophene backbones were
synthesized and structurally and electronically characterized. 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 purposes, of already known bis(oxazolines). 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 than any consideration of the electronic properties of the chiral
ligands.