New Bis(oxazoline) Ligands with Secondary Binding Sites for the Asymmetric Cyclopropanation of Furans

The diastereo- and enantioselective cyclopropanation of furans was achieved in up to 91% ee using a new set of chiral bis(oxazoline) ligands that are able to use secondary binding sites to enhance selectivity. In contrast, with substrates such as styrene and N-Boc-pyrrole, with which no secondary interactions with the ligands can occur, only moderate selectivities (